document_title: Retina

question_text: where does information from the right retina show up in the cortex

text: Retina

text: Structure[edit]

text: Inverted versus non-inverted retina[edit]

text: The vertebrate retina is inverted in the sense that the light sensing cells are in back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the rods and cones. In contrast, in the cephalopod retina the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot.

text: The overlying neural fibre layer does not degrade vision in the inverted retina. The neurons are transparent and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors.[4][5] In any case, the fovea centralis, the part of the retina with the highest resolution, does not have a layer of blood vessels and nerve cells over it, so there is no possibility of image degradation here.

text: The cephalopods have a non-inverted retina which is comparable in resolving power to the eyes of many vertebrates. Squid eyes do not have an analog of the vertebrate retinal pigment epithelium (RPE). Although their photoreceptors contain a protein, retinochrome, that recycles retinal and replicates one of the functions of the vertebrate RPE, one could argue that cephalopod photoreceptors are not maintained as well as in vertebrates and that, as a result, the useful lifetime of photoreceptors in invertebrates is much shorter than in vertebrates.[6] Having easily replaced stalk-eyes (some lobsters) or retinae (some spiders, such as Deinopis[7]) rarely occurs.

text: The cephalopod retina does not originate as an outgrowth of the brain, as the vertebrate one does. It is arguable that this difference shows that vertebrate and cephalopod eyes are not homologous but have evolved separately. From an evolutionary perspective, a more complex structure such as the inverted retina can generally come about as a consequence of two alternate processes: (a) an advantageous "good" compromise between competing functional limitations, or (b) as a historical maladaptive relic of the convoluted path of organ evolution and transformation. Vision is an important adaptation in higher vertebrates.

text: A third view of the "inverted" vertebrate eye is that it combines two benefits: the maintenance of the photoreceptors mentioned above, and the reduction in light intensity necessary to avoid blinding the photoreceptors, which are based on the extremely sensitive eyes of the ancestors of modern hagfishes (a fish that lives in very deep, dark water).[8]

text: Retinal layers[edit]

text: The vertebrate retina has ten distinct layers.[10] From closest to farthest from the vitreous body:

text:
Inner limiting membrane – basement membrane elaborated by Müller cells.
Nerve fibre layer – axons of the ganglion cell nuclei (note that a thin layer of Müller cell footplates exists between this layer and the inner limiting membrane).
Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres for messages and some displaced amacrine cells.[2]
Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells.[2]
Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the amacrine cells, bipolar cells, and horizontal cells.[2]
Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively. These make synapses with dendrites of bipolar cells.[2] In the macular region, this is known as the Fiber layer of Henle.
Outer nuclear layer – cell bodies of rods and cones.
External limiting membrane – layer that separates the inner segment portions of the photoreceptors from their cell nucleus.
Layer of rods and cones – layer of rod cells and cone cells.
Retinal pigment epithelium – single layer of cuboidal cells (with extrusions not shown in diagram). This is closest to the choroid.

text: These layers can be grouped into 4 main processing stages: photoreception; transmission to bipolar cells; transmission to ganglion cells, which also contain photoreceptors, the photosensitive ganglion cells; and transmission along the optic nerve. At each synaptic stage there are also laterally connecting horizontal and amacrine cells.

text: The optic nerve is a central tract of many axons of ganglion cells connecting primarily to the lateral geniculate body, a visual relay station in the diencephalon (the rear of the forebrain). It also projects to the superior colliculus, the suprachiasmatic nucleus, and the nucleus of the optic tract. It passes through the other layers, creating the optic disc in primates.[11]

text: Additional structures, not directly associated with vision, are found as outgrowths of the retina in some vertebrate groups. In birds, the pecten is a vascular structure of complex shape that projects from the retina into the vitreous humour; it supplies oxygen and nutrients to the eye, and may also aid in vision. Reptiles have a similar, but much simpler, structure.[12]

text: In adult humans, the entire retina is approximately 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods. The optic disc, a part of the retina sometimes called "the blind spot" because it lacks photoreceptors, is located at the optic papilla, where the optic-nerve fibres leave the eye. It appears as an oval white area of 3 mm². Temporal (in the direction of the temples) to this disc is the macula, at whose centre is the fovea, a pit that is responsible for our sharp central vision but is actually less sensitive to light because of its lack of rods. Human and non-human primates possess one fovea, as opposed to certain bird species, such as hawks, who are bifoviate, and dogs and cats, who possess no fovea but a central band known as the visual streak.[citation needed] Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The farthest edge of the retina is defined by the ora serrata. The distance from one ora to the other (or macula), the most sensitive area along the horizontal meridian is about 32 mm.[clarification needed]

text: In section, the retina is no more than 0.5 mm thick. It has three layers of nerve cells and two of synapses, including the unique ribbon synapse. The optic nerve carries the ganglion cell axons to the brain, and the blood vessels that supply the retina. The ganglion cells lie innermost in the eye while the photoreceptive cells lie beyond. Because of this counter-intuitive arrangement, light must first pass through and around the ganglion cells and through the thickness of the retina, (including its capillary vessels, not shown) before reaching the rods and cones. Light is absorbed by the retinal pigment epithelium or the choroid (both of which are opaque).

text: The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon).

text: Between the ganglion cell layer and the rods and cones there are two layers of neuropils where synaptic contacts are made. The neuropil layers are the outer plexiform layer and the inner plexiform layer. In the outer neuropil layer, the rods and cones connect to the vertically running bipolar cells, and the horizontally oriented horizontal cells connect to ganglion cells.

text: The central retina predominantly contains cones, while the peripheral retina predominantly contains rods. In total, there are about seven million cones and a hundred million rods. At the centre of the macula is the foveal pit where the cones are narrow and long, and, arranged in a hexagonal mosaic, the most dense. At the foveal pit the other retinal layers are displaced, before building up along the foveal slope until the rim of the fovea, or parafovea, is reached, which is the thickest portion of the retina. The macula has a yellow pigmentation, from screening pigments, and is known as the macula lutea. The area directly surrounding the fovea has the highest density of rods converging on single bipolar cells. Since its cones have a much lesser convergence of signals, the fovea allows for the sharpest vision the eye can attain.[2]

text: Though the rod and cones are a mosaic of sorts, transmission from receptors, to bipolars, to ganglion cells is not direct. Since there are about 150 million receptors and only 1 million optic nerve fibres, there must be convergence and thus mixing of signals. Moreover, the horizontal action of the horizontal and amacrine cells can allow one area of the retina to control another (e.g. one stimulus inhibiting another). This inhibition is key to lessening the sum of messages sent to the higher regions of the brain. In some lower vertebrates (e.g. the pigeon), there is a "centrifugal" control of messages – that is, one layer can control another, or higher regions of the brain can drive the retinal nerve cells, but in primates this does not occur.[2]

text: Layers imagable with Optical Coherence Tomography (OCT)[edit]

text: On OCT there are 18 layers that can be identified in the retina. The layers and anatomical correlation are as follows:[13][14][15]

text: From innermost to outermost, the layers identifiable by OCT are as follows:

text:
#
OCT Layer / Conventional Label
Anatomical Correlate

Reflectivity
on OCT

Specific
anatomical
boundaries?

Additional
references

1

Posterior cortical vitreous

Posterior cortical vitreous

Hyper-reflective

Yes

[14]

2

Preretinal space

In eyes where the vitreous has fully or partially detached from the retina, this is the space created between the posterior cortical vitreous face and the internal limiting membrane of the retina.

Hypo-reflective

[14]

3
Internal limiting membrane (ILM)
Formed by Müller cell endfeet
(unclear if it can be observed on OCT)

Hyper-reflective

No

[14]

Nerve fiber layer (NFL)

Ganglion cell axons travelling towards the optic nerve

4
Ganglion cell layer (GCL)
Ganglion cell bodies (and some displaced amacrine cells)

Hypo-reflective

[14]

5
Inner plexiform layer (IPL)
Synapses between bipolar, amacrine and ganglion cells

Hyper-reflective

[14]

6
Inner nuclear layer (INL)
a) Horizontal, bipolar and amacrine cell bodies
b) Müller cell nuclei

Hypo-reflective

[14]

7
Outer plexiform layer (OPL)
Synapses between photoreceptor, bipolar and horizontal cells

Hyper-reflective

[14]

8
(Inner half)  Henle’s nerve fiber layer (HL)

Photoreceptor axons
(obliquely orientated fibres; not present in mid-peripheral or peripheral retina)

Hypo-reflective

No

[14]

(Outer half)  Outer nuclear layer (ONL)

The photoreceptor cell bodies

9
External limiting membrane (ELM)

Made of zonulae adherens between Müller cells and photoreceptor inner segments

Hyper-reflective

[14]

10
Myoid zone (MZ)
The innermost portion of the photoreceptor inner segment (IS) containing:
Smooth and rough endoplasmic reticulum
Ribosomes
Golgi bodies
Microtubules
(rarely: mitochondria)

Hypo-reflective

No

[16][17]

11
Ellipsoid zone (EZ)
The outermost portion of the photoreceptor inner segment (IS) packed with mitochondria

Very Hyper-reflective

No

[13][18][16][14][19][20]

IS/OS junction or Photoreceptor integrity line (PIL)

The photoreceptor connecting cilia which bridge the inner and outer segments of the photoreceptor cells.

12
Photoreceptor outer segments (OS)
The photoreceptor outer segments (OS)  which contain disks filled with opsin, the molecule that absorbs photons.

Hypo-reflective

[21][14]

13
Interdigitation zone (IZ)
Apices of the RPE cells which encase part of the cone OSs.
Poorly distinguishable from RPE. Previously: "cone outer segment tips line" (COST)

Hyper-reflective

No

14

RPE/Bruch’s complex

RPE phagosome zone

Very Hyper-reflective

No

[13][14]

RPE melanosome zone

Hypo-reflective

RPE mitochondria zone + Junction between the RPE & Bruch's membrane

Very Hyper-reflective

15

Choriocapillaris

Thin layer of moderate reflectivity in inner choroid

No

[14]

16

Sattler’s layer

Thick layer of round or ovalshaped hyperreflective profiles, with hyporeflective cores in mid-choroid

[14]

17

Haller’s layer

Thick layer of oval-shaped hyperreflective profiles, with hyporeflective cores in outer choroid

[14]

18

Choroidal-scleral juncture

Zone at the outer choroid with a marked change in texture, in which large circular or ovoid profiles abut a
homogenous region of variable reflectivity

[14]

text: Development[edit]

text: Retinal development begins with the establishment of the eye fields mediated by the SHH and SIX3 proteins, with subsequent development of the optic vesicles regulated by the PAX6 and LHX2 proteins.[22] The role of Pax6 in eye development was elegantly demonstrated by Walter Gehring and colleagues, who showed that ectopic expression of Pax6 can lead to eye formation on Drosophila antennae, wings, and legs.[23] The optic vesicle gives rise to three structures: the neural retina, the retinal pigmented epithelium, and the optic stalk. The neural retina contains the retinal progenitor cells (RPCs) that give rise to the seven cell types of the retina. Differentiation begins with the retinal ganglion cells and concludes with production of the Muller glia. Although each cell type differentiates from the RPCs in a sequential order, there is considerable overlap in the timing of when individual cell types differentiate.[22] The cues that determine a RPC daughter cell fate are coded by multiple transcription factor families including the bHLH and homeodomain factors.[24]

text: In addition to guiding cell fate determination, cues exist in the retina to determine the dorsal-ventral (D-V) and nasal-temporal (N-T) axes. The D-V axis is established by a ventral to dorsal gradient of VAX2, whereas the N-T axis is coordinated by expression of the forkhead transcription factors FOXD1 and FOXG1. Additional gradients are formed within the retina that aid in proper targeting of RGC axons that function to establish the retinotopic map.[22]

text: Blood supply[edit]

text:
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text: The retina is stratified into distinct layers, each containing specific cell types or cellular compartments[25] that have metabolisms with different nutritional requirements.[26] To satisfy these requirements, the  ophthalmic artery bifurcates and supplies the retina via two distinct vascular networks: the choroidal network, which supplies the choroid and the outer retina, and the retinal network, which supplies the retina's inner layer.[27]

text: Circulatory mechanisms[edit]

text: At first glance, one may think that the vertebrate retina is "wired wrongly" or "badly designed"; but in fact, the retina could not function if it were not inverted. The photoreceptor layer must be embedded in the retinal pigment epithelium (RPE), which performs at least seven vital functions,[28] one of the most obvious being to supply oxygen and other necessary nutrients needed for the photoreceptors to function. These nutrients include glucose, fatty acids, and retinal. The mammalian photoreceptor amplification process uses large quantities energy for vision in photopic conditions (requiring less under scotopic conditions) and, thus, requires the large supply nutrients supplied by the blood vessels in the choroid, which lies beyond the RPE. The choroid supplies about 75% of these nutrients to the retina and the retinal vasculature only 25%.[29]

text: When light strikes 11-cis-retinal (in the disks in the rods and cones), 11-cis-retinal changes to all-trans-retinal which then triggers changes in the opsins. Now, the outer segments do not regenerate the retinal back into the cis- form once it has been changed by light. Instead the retinal is pumped out to the surrounding RPE where it is regenerated and transported back into the outer segments of the photoreceptors. This recycling function of the RPE protects the photoreceptors against photo-oxidative damage[30][31] and allows the photoreceptor cells to have decades-long useful lives.

text: In birds[edit]

text: The bird retina is devoid of blood vessels, perhaps to give unobscured passage of light for forming images, thus giving better resolution. It is, therefore, a considered view that the bird retina depends for nutrition and oxygen supply on a specialized organ, called the "pecten" or pecten oculi, located on the blind spot or optic disk. This organ is extremely rich in blood vessels and is thought to supply nutrition and oxygen to the bird retina by diffusion through the vitreous body. The pecten is highly rich in alkaline phosphatase activity and polarized cells in its bridge portion – both befitting its secretory role.[32] Pecten cells are packed with dark melanin granules, which have been theorized to keep this organ warm with the absorption of stray light falling on the pecten. This is considered to enhance metabolic rate of the pecten, thereby exporting more nutritive molecules to meet the stringent energy requirements of the retina during long periods of exposure to light.[33]

text: Biometric identification and diagnosis of disease[edit]

text: The bifurcations and other physical characteristics of the inner retinal vascular network are known to vary among individuals,[34] and these individual variances have been used for biometric identification and for early detection of the onset of disease. The mapping of vascular bifurcations is one of the basic steps in biometric identification.[35] Results of such analyses of retinal blood vessel structure can be evaluated against the ground truth data[36] of vascular bifurcations of retinal fundus images that are obtained from the DRIVE dataset.[37] In addition, the classes of vessels of the DRIVE dataset have also been identified,[38] and an automated method for accurate extraction of these bifurcations is also available.[39] Changes in retinal blood circulation are seen with aging[40] and exposure to air pollution,[41] and may indicate cardiovascular diseases such as hypertension and atherosclerosis.[42][43][44] Determining the equivalent width of arterioles and venules near the optic disc is also a widely used technique to identify cardiovascular risks.[45]

text: Function[edit]

text: The retina translates an optical image into neural impulses by the patterned excitation of the colour-sensitive pigments of its rods and cones, the retina's photoreceptor cells. The excitation is processed by the neural system and various parts of the brain working in parallel to form a representation of the external environment in the brain.

text: The cones respond to bright light and mediate high-resolution colour vision during daylight illumination (also called photopic vision). The rods are saturated at daylight levels and don't contribute to pattern vision. However, rods do respond to dim light and mediate lower-resolution, monochromatic vision under very low levels of illumination (called scotopic vision). The illumination in most office settings falls between these two levels and is called mesopic vision. At mesopic light levels, both the rods and cones are actively contributing pattern information. What contribution the rod information makes to pattern vision under these circumstances is unclear.

text: The response of cones to various wavelengths of light is called their spectral sensitivity. In normal human vision, the spectral sensitivity of a cone falls into one of three subtypes, often called blue, green, or red but more accurately known as short, medium, or long wavelength-sensitive cone subtypes. It is a lack of one or more of the cone subtypes that causes individuals to have deficiencies in colour vision or various kinds of colour blindness. These individuals are not blind to objects of a particular colour but are unable to distinguish between colours that can be distinguished by people with normal vision. Humans have this trichromatic vision, while most other mammals lack cones with red sensitive pigment and therefore have poorer dichromatic colour vision. However, some animals have four spectral subtypes, e.g. the trout adds an ultraviolet subgroup to short, medium, and long subtypes that are similar to humans. Some fish are sensitive to the polarization of light as well.

text: In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment. Inside the cell the normal levels of cyclic guanosine monophosphate (cGMP) keep the Na+ channel open, and thus in the resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal. This causes the receptor to activate multiple G-proteins. This in turn causes the Ga-subunit of the protein to activate a phosphodiesterase (PDE6), which degrades cGMP, resulting in the closing of Na+ cyclic nucleotide-gated ion channels (CNGs). Thus the cell is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity.

text: When thus excited by light, the photoceptor sends a proportional response synaptically to bipolar cells which in turn signal the retinal ganglion cells. The photoreceptors are also cross-linked by horizontal cells and amacrine cells, which modify the synaptic signal before it reaches the ganglion cells, the neural signals being intermixed and combined. Of the retina's nerve cells, only the retinal ganglion cells and few amacrine cells create action potentials.

text: In the retinal ganglion cells there are two types of response, depending on the receptive field of the cell. The receptive fields of retinal ganglion cells comprise a central, approximately circular area, where light has one effect on the firing of the cell, and an annular surround, where light has the opposite effect. In ON cells, an increment in light intensity in the centre of the receptive field causes the firing rate to increase. In OFF cells, it makes it decrease. In a linear model, this response profile is well described by a difference of Gaussians and is the basis for edge detection algorithms. Beyond this simple difference, ganglion cells are also differentiated by chromatic sensitivity and the type of spatial summation. Cells showing linear spatial summation are termed X cells (also called parvocellular, P, or midget ganglion cells), and those showing non-linear summation are Y cells (also called magnocellular, M, or parasol retinal ganglion cells), although the correspondence between X and Y cells (in the cat retina) and P and M cells (in the primate retina) is not as simple as it once seemed.

text: In the transfer of visual signals to the brain, the visual pathway, the retina is vertically divided in two, a temporal (nearer to the temple) half and a nasal (nearer to the nose) half. The axons from the nasal half cross the brain at the optic chiasma to join with axons from the temporal half of the other eye before passing into the lateral geniculate body.

text: Although there are more than 130 million retinal receptors, there are only approximately 1.2 million fibres (axons) in the optic nerve. So, a large amount of pre-processing is performed within the retina. The fovea produces the most accurate information. Despite occupying about 0.01% of the visual field (less than 2° of visual angle), about 10% of axons in the optic nerve are devoted to the fovea. The resolution limit of the fovea has been determined to be around 10,000 points.[clarification needed] The information capacity is estimated at 500,000 bits per second (for more information on bits, see information theory) without colour or around 600,000 bits per second including colour.[citation needed]

text: Spatial encoding[edit]

text: When the retina sends neural impulses representing an image to the brain, it spatially encodes (compresses) those impulses to fit the limited capacity of the optic nerve. Compression is necessary because there are 100 times more photoreceptor cells than ganglion cells. This is done by "decorrelation", which is carried out by the "centre–surround structures", which are implemented by the bipolar and ganglion cells.

text: There are two types of centre–surround structures in the retina – on-centres and off-centres. On-centres have a positively weighted centre and a negatively weighted surround. Off-centres are just the opposite. Positive weighting is more commonly known as excitatory, and negative weighting as inhibitory.

text: These centre–surround structures are not physical apparent, in the sense that one cannot see them by staining samples of tissue and examining the retina's anatomy. The centre–surround structures are logical (i.e., mathematically abstract) in the sense that they depend on the connection strengths between bipolar and ganglion cells. It is believed that the connection strengths between cells is caused by the number and types of ion channels embedded in the synapses between the bipolar and ganglion cells.

text: The centre–surround structures are mathematically equivalent to the edge detection algorithms used by computer programmers to extract or enhance the edges in a digital photograph. Thus, the retina performs operations on the image-representing impulses to enhance the edges of objects within its visual field. For example, in a picture of a dog, a cat and a car, it is the edges of these objects that contain the most information. In order for higher functions in the brain (or in a computer for that matter) to extract and classify objects such as a dog and a cat, the retina is the first step to separating out the various objects within the scene.

text: As an example, the following matrix is at the heart of the computer algorithm that implements edge detection. This matrix is the computer equivalent to the centre–surround structure. In this example, each box (element) within this matrix would be connected to one photoreceptor. The photoreceptor in the centre is the current receptor being processed. The centre photoreceptor is multiplied by the +1 weight factor. The surrounding photoreceptors are the "nearest neighbors" to the centre and are multiplied by the -1/8 value. The sum of all nine of these elements is finally calculated. This summation is repeated for every photoreceptor in the image by shifting left to the end of a row and then down to the next line.

text:
-1/8
-1/8
-1/8

-1/8
+1
-1/8

-1/8
-1/8
-1/8

text: The total sum of this matrix is zero, if all the inputs from the nine photoreceptors are of the same value. The zero result indicates the image was uniform (non-changing) within this small patch. Negative or positive sums mean the image was varying (changing) within this small patch of nine photoreceptors.

text: The above matrix is only an approximation to what really happens inside the retina. The differences are:

text:
The above example is called "balanced". The term balanced means that the sum of the negative weights is equal to the sum of the positive weights so that they cancel out perfectly. Retinal ganglion cells are almost never perfectly balanced.
The table is square while the centre–surround structures in the retina are circular.
Neurons operate on spike trains traveling down nerve cell axons. Computers operate on a single floating point number that is essentially constant from each input pixel. (The computer pixel is basically the equivalent of a biological photoreceptor.)
The retina performs all these calculations in parallel while the computer operates on each pixel one at a time. The retina performs no repeated summations and shifting as would a computer.
Finally, the horizontal and amacrine cells play a significant role in this process, but that is not represented here.

text: Here is an example of an input image and how edge detection would modify it.

text: Once the image is spatially encoded by the centre–surround structures, the signal is sent out along the optic nerve (via the axons of the ganglion cells) through the optic chiasm to the LGN (lateral geniculate nucleus). The exact function of the LGN is unknown at this time. The output of the LGN is then sent to the back of the brain. Specifically, the output of the LGN "radiates" out to the V1 primary visual cortex.

text: Simplified signal flow: Photoreceptors → Bipolar → Ganglion → Chiasm → LGN → V1 cortex

text: Clinical significance[edit]

text: There are many inherited and acquired diseases or disorders that may affect the retina. Some of them include:

text:
Retinitis pigmentosa is a group of genetic diseases that affect the retina and cause the loss of night vision and peripheral vision.
Macular degeneration describes a group of diseases characterized by loss of central vision because of death or impairment of the cells in the macula.
Cone-rod dystrophy (CORD) describes a number of diseases where vision loss is caused by deterioration of the cones and/or rods in the retina.
In retinal separation, the retina detaches from the back of the eyeball. Ignipuncture is an outdated treatment method. The term retinal detachment is used to describe a separation of the neurosensory retina from the retinal pigment epithelium.[46] There are several modern treatment methods for fixing a retinal detachment: pneumatic retinopexy, scleral buckle, cryotherapy, laser photocoagulation and pars plana vitrectomy.
Both hypertension and diabetes mellitus can cause damage to the tiny blood vessels that supply the retina, leading to hypertensive retinopathy and diabetic retinopathy.
Retinoblastoma is a cancer of the retina.
Retinal diseases in dogs include retinal dysplasia, progressive retinal atrophy, and sudden acquired retinal degeneration.
Lipemia retinalis is a white appearance of the retina, and can occur by lipid deposition in lipoprotein lipase deficiency.

text: Diagnosis[edit]

text: A number of different instruments are available for the diagnosis of diseases and disorders affecting the retina. Ophthalmoscopy and fundus photography have long been used to examine the retina. Recently, adaptive optics has been used to image individual rods and cones in the living human retina, and a company based in Scotland has engineered technology that allows physicians to observe the complete retina without any discomfort to patients.[47]

text: The electroretinogram is used to non-invasively measure the retina's electrical activity, which is affected by certain diseases. A relatively new technology, now becoming widely available, is optical coherence tomography (OCT). This non-invasive technique allows one to obtain a 3D volumetric or high resolution cross-sectional tomogram of the fine structures of the retina, with histologic quality.

text: Treatment[edit]

text: Treatment depends upon the nature of the disease or disorder.

text: Common treatment modalities[edit]

text: The following are commonly modalities of management for retinal disease:

text:
Intravitreal medication, such as anti-VEGF or corticosteroid agents
Vitreoretinal surgery
Use of nutritional supplements
Modification of systemic risk factors for retinal disease

text: Uncommon treatment modalities[edit]

text:
showRare or uncommon methods of treatment for retinal disease

Retinal gene therapy

Main article: Adeno associated virus and gene therapy of the human retina
Gene therapy holds promise as a potential avenue to cure a wide range of retinal diseases. This involves using a non-infectious virus to shuttle a gene into a part of the retina. Recombinant adeno-associated virus (rAAV) vectors possess a number of features that render them ideally suited for retinal gene therapy, including a lack of pathogenicity, minimal immunogenicity, and the ability to transduce postmitotic cells in a stable and efficient manner.[48] rAAV vectors are increasingly utilized for their ability to mediate efficient transduction of retinal pigment epithelium (RPE), photoreceptor cells and retinal ganglion cells. Each cell type can be specifically targeted by choosing the appropriate combination of AAV serotype, promoter, and intraocular injection site.
Several clinical trials have already reported positive results using rAAV to treat Leber's congenital amaurosis, showing that the therapy was both safe and effective.[49][50] There were no serious adverse events, and patients in all three studies showed improvement in their visual function as measured by a number of methods. The methods used varied among the three trials, but included both functional methods such as visual acuity[50][51][52] and functional mobility[51][52][53] as well as objective measures that are less susceptible to bias, such as the pupil's ability to respond to light[49][54] and improvements on functional MRI.[55] Improvements were sustained over the long-term, with patients continuing to do well after more than 1.5 years.[49][50]
The unique architecture of the retina and its relatively immune-privileged environment help this process.[56] Tight junctions that form the blood retinal barrier separate the subretinal space from the blood supply, thus protecting it from microbes and most immune-mediated damage, and enhancing its potential to respond to vector-mediated therapies. The highly compartmentalized anatomy of the eye facilitates accurate delivery of therapeutic vector suspensions to specific tissues under direct visualization using microsurgical techniques.[57] In the sheltered environment of the retina, AAV vectors are able to maintain high levels of transgene expression in the retinal pigmented epithelium (RPE), photoreceptors, or ganglion cells for long periods of time after a single treatment. In addition, the eye and the visual system can be routinely and easily monitored for visual function and retinal structural changes after injections with noninvasive advanced technology, such as visual acuities, contrast sensitivity, fundus auto-fluorescence (FAF), dark-adapted visual thresholds, vascular diameters, pupillometry, electroretinography (ERG), multifocal ERG and optical coherence tomography (OCT).[58]
This strategy is effective against a number of retinal diseases that have been studied, including neovascular diseases that are features of age-related macular degeneration, diabetic retinopathy and retinopathy of prematurity. Since the regulation of vascularization in the mature retina involves a balance between endogenous positive growth factors, such as vascular endothelial growth factor (VEGF) and inhibitors of angiogenesis, such as pigment epithelium-derived factor (PEDF), rAAV-mediated expression of PEDF, angiostatin, and the soluble VEGF receptor sFlt-1, which are all antiangiogenic proteins, have been shown to reduce aberrant vessel formation in animal models.[59] Since specific gene therapies cannot readily be used to treat a significant fraction of patients with retinal dystrophy, there is a major interest in developing a more generally applicable survival factor therapy. Neurotrophic factors have the ability to modulate neuronal growth during development to maintain existing cells and to allow recovery of injured neuronal populations in the eye. AAV encoding neurotrophic factors such as fibroblast growth factor (FGF) family members and GDNF either protected photoreceptors from apoptosis or slowed down cell death.[59]
Organ transplantation
Transplantation of retinas has been attempted, but without much success. At MIT, The University of Southern California, RWTH Aachen University, and the University of New South Wales, an "artificial retina" is under development: an implant which will bypass the photoreceptors of the retina and stimulate the attached nerve cells directly, with signals from a digital camera.

text: Notable researchers and discoveries[edit]

text: In 1894, Santiago Ramón y Cajal published the first major characterization of retinal neurons in Retina der Wirbelthiere (The Retina of Vertebrates).[60]

text: George Wald, Haldan Keffer Hartline, and Ragnar Granit won the 1967 Nobel Prize in Physiology or Medicine for their scientific research on the retina.[61]

text: A recent University of Pennsylvania study calculated that the approximate bandwidth of human retinas is 8.75 megabits per second, whereas a guinea pig's retinal transfer rate is 875 kilobits per second.[62]

text: MacLaren & Pearson and colleagues at University College London and Moorfields Eye Hospital in London, in 2006, showed that photoreceptor cells could be transplanted successfully in the mouse retina if donor cells were at a critical developmental stage.[63] Recently Ader and colleagues in Dublin showed, using the electron microscope, that transplanted photoreceptors formed synaptic connections.[64]

text: In 2012, Sebastian Seung and his laboratory at MIT have launched EyeWire, an online Citizen science game where players trace neurons in the retina.[65] The goals of the EyeWire project are to identify specific cell types within the known broad classes of retinal cells, and to map the connections between neurons in the retina, which will help to determine how vision works.[66][67]

text: Additional images[edit]

text:
The structures of the eye labeled

Another view of the eye and the structures of the eye labeled

Illustration of image as 'seen' by the retina independent of optic nerve and striate cortex processing.


document_title: MacBook Air

question_text: when was the last time macbook air was updated

root

text: MacBook Air

text: History[edit]

text: Steve Jobs introduced the first MacBook Air during a speech at his keynote at the 2008 Macworld conference on January 15, 2008.[6] The first-generation MacBook Air was a 13.3"-only model, initially promoted as the world's thinnest notebook.[7] It featured a custom[8] Intel Merom CPU and Intel GMA graphics. In late 2008, the CPU was updated to a faster, non-custom Penryn CPU and integrated Nvidia GeForce graphics while the hard drive capacity was increased and the micro-DVI video port was replaced by the Mini DisplayPort.[9] A mid-2009 refresh, introduced alongside the MacBook Pro family, featured a slightly higher-capacity battery, and a faster Penryn CPU.[10]

tag: p

text: On October 20, 2010, Apple released a redesigned 13.69" model, with improved enclosure, screen resolution, battery, and flash storage instead of a hard drive. In addition, a new 11.6" model was introduced, offering reduced cost, weight, battery life, and performance relative to the 13.3" model, but better performance than typical netbooks of the time.[11][12][13][14]

text: On July 20, 2011, Apple released updates to the 11.6" and 13.3" models of the MacBook Air, which also became Apple's entry-level laptops due to lowered prices and the discontinuation of the white MacBook around the same time.[5] The mid-2011 MacBook Airs were powered by the new Sandy Bridge 1.6 or 1.7 GHz dual-core Intel Core i5, or 1.8 GHz dual-core Intel Core i7 processors, that came with an Intel HD Graphics 3000 processor, and with a backlit keyboard, two USB 2.0 ports, FaceTime camera, a standard of 2 GB of RAM (configurable up to 4 GB), Thunderbolt which shares function with Mini DisplayPort and Bluetooth was upgraded to v4.0.[15][16] Maximum SSD flash memory storage options were increased up to 256 GB. Both 11" and 13" models had an analog audio output/headphone minijack (that also supports an iPhone/iPod touch headset with microphone), but only the 13" model had an integrated SDXC-capable SD Card slot. These models use a less expensive "Eagle Ridge" Thunderbolt controller that provides two Thunderbolt channels (2 × 10 Gbit/s bidirectional), compared to the MacBook Pro which uses a "Light Ridge" controller that provides four Thunderbolt channels (4 × 10 Gbit/s bidirectional). A USB ethernet adapter was immediately available upon release and a Thunderbolt-to-Firewire 800 adapter became available in mid-year 2012.

text: On June 11, 2012, Apple released an updated model in the same form factor as the prior model. The new model is powered by the new Ivy Bridge dual-core Intel Core i5 and i7 processors, doubles the RAM and SSD speeds, has the new USB 3 ports (with USB 2 capability) in place of the USB 2 ports and the new MagSafe 2 charging port.[17] The camera was upgraded to 720p FaceTime HD.

text: On June 10, 2013, Apple released another update in the same form factor as the 2012 model during the company's Worldwide Developer Conference (WWDC). The 11" and 13" models have a minimum standard 4 GB RAM, with a maximum configuration of 8 GB. Both models are powered by the Haswell ULT 1.3 GHz dual-core Intel Core i5 processors, with Turbo Boost up to 2.6 GHz, while a 1.7 GHz Dual-Core i7, with Turbo Boost up to 3.3 GHz, option is also available. Each model's storage standard is 128 GB SSD, upgradeable to 256 GB and 512 GB SSD. Due to Haswell CPUs, battery life has considerably improved from the previous generation, and the mid-2013 models are capable of 9 hours on the 11" model and 12 hours on the 13" model; a team of reviewers exceeded expected battery life ratings during their test.[18]

text: While Apple's MacBook lines have been affected towards consumer trend to smartphones,[19] they still managed to ship 2.8M Macs in Q2 2012, notably Air, compared to 500K total Ultrabooks,[20][21] despite there being dozens of Ultrabooks from various manufacturers on the market while Apple only offered 11" and 13" models of it.[22] Through July 1, 2013, the MacBook Air took in 56% of all Ultrabook sales in the United States, despite being one of the higher-priced competitors. [23]

text: Design[edit]

text: The MacBook Air features an anti-glare LED backlit display and a full-size keyboard, as well as a large trackpad that responds to multi-touch gestures such as pinching, swiping, and rotating.[24] Since the release of Snow Leopard, the Air's trackpad has supported handwriting recognition of Chinese characters.[25]

text: On the 11" Air, the left side of the computer has a MagSafe power connector, a USB port, a headphone jack, and a microphone.[24] The right side of the computer has a USB port and a Mini DisplayPort, now sharing Thunderbolt function beginning with the 2011 model. On top of the screen bezel there is a webcam, first dubbed iSight and now the FaceTime camera.

text: The MacBook Air was the first subcompact laptop offered by Apple since the full-featured 12" PowerBook G4 was discontinued in 2006. It was also Apple's first computer with an optional solid-state drive.[26] ArsTechnica found "moderate" performance improvements of the 64GB[note 1] solid-state drive of the first-generation Air over the standard 80 GB hard drive in tests. On October 14, 2008, new models were announced with improved capacities of 128 GB SSD and 120 GB hard drive. For the late-2010 MacBook Air and later models, only flash storage is available, with the standard options currently being 128 GB and 256 GB.[27]

text: The CPU in the first-generation MacBook Air was a custom Intel Core 2 Duo Merom that was 40% of the size of the standard chip package.[28] For models of late 2008, the CPU was replaced with a low-voltage Penryn chip with 6MB of cache, running on a 1066 MHz bus.[29]

text: MacBook Air components are officially non-user-replaceable, though third-parties do sell upgrade kits for the SSDs. The flash memory and battery are enclosed within the casing, with RAM soldered onto the motherboard. The flash memory, difficult to access, has a 128MB cache[30] and a mSATA connection (updated to a proprietary PCIe interface) to the motherboard.[31]

text: Apple incorporated several features in the design of the MacBook Air, such as the reduction of lead to make it more environmentally friendly. The MacBook Air contains no BFRs and PVC wiring, meets Energy Star 5.0 requirements, has a recyclable enclosure, and is rated EPEAT Gold. Its display is made from arsenic-free glass, and contains no mercury.[7][32] To reduce the computer's size and weight, several features were sacrificed. It was Apple's first notebook since the PowerBook 2400c without a built-in removable media drive.[33] It also omits a FireWire port, Ethernet port, line-in, media card slots (except the 13" 2010 through 2015 models, which have an SD card slot), and a Kensington Security Slot.[34]

text: To gain optical drive features, users could either purchase an external USB SuperDrive or other brand, or the bundled Remote Disc software, only for browsing or software installation to access the drive of another computer wirelessly[35] that has the program installed.[36][37] It can also be used to reinstall the system software from the included installation DVD. Remote Disc supports NetBooting, so the Air can boot from its installation DVD in another computer's drive, which requires Remote Install Mac OS X to be running on that computer. The software does not allow playback or information of DVDs, CDs or installing Windows.[35] For these features, an external USB drive is required.[35] More recent versions of OS X replaced the installation DVD with a USB flash drive containing the software, eliminating remote installation.

text: The 2010 models include two speakers for stereo sound while earlier versions have one speaker located under the keyboard. The 2011 model replaces DisplayPort with a Thunderbolt 1 port, and also has a 1280×720 FaceTime HD Camera, replacing the previous 640×480 iSight camera. The 2012 model replaces USB 2 with USB 3, and uses the MagSafe 2 instead of the MagSafe connector for charging. The 2015 model updated the Thunderbolt port to Thunderbolt 2.

text: Specifications[edit]

text:
Discontinued

Current

tag: table

text:
[hide]Table of models

Model
Early 2008
(February)[38]

Late 2008
(October)[9]

Mid 2009
(June)[39]

Late 2010
(October)[40][41]

Mid 2011
(July)[42][43]

Mid 2012
(June)[44][45]

Mid 2013
(June)[46][47]

Early 2014
(April)[48]

Early 2015
(March)[49]

Mid 2017
(June)[50]

Model identifier
MacBookAir1,1
MacBookAir2,1
MacBookAir3,1 (11"), MacBookAir3,2 (13")
MacBookAir4,1 (11"), MacBookAir4,2 (13")
MacBookAir5,1 (11"), MacBookAir5,2 (13")
MacBookAir6,1 (11"), MacBookAir6,2 (13")
MacBookAir7,1 (11"), MacBookAir7,2 (13")
MacBookAir7,2

Model number (on underside)
A1237
A1304
A1370 (11"), A1369 (13")
A1465 (11"), A1466 (13")
A1466

Part number (Order number)
MB003LL/A
MB543LL/A, MB940LL/A
MC233LL/A, MC234LL/A
MC504LL/A, MC505LL/A, MC506LL/A, MC503LL/A
MC968LL/A, MC969LL/A, MC965LL/A, MC966LL/A
MD223LL/A, MD224LL/A, MD231LL/A, MD232LL/A
MD711LL/A, MD712LL/A, MD760LL/A, MD761LL/A
MD711LL/B, MD712LL/B, MD760LL/B, MD761LL/B
MJVM2LL/A, MJVP2LL/A, MJVE2LL/A, MJVG2LL/A, MMGF2LL/A (2016, 8 GB, 128 GB SSD), MMGG2LL/A (2016, 8 GB, 256 GB SSD)
MQD32LL/A (128 GB SSD), MQD42LL/A (256 GB SSD)

Display
(glossy)
N/A
11.6", native 1366 × 768 (16:9). Lower resolutions supported
N/A

13.3", native 1280 × 800 pixels (16:10). Lower resolutions supported
13.3", native 1440 × 900 (16:10). Lower resolutions supported

Graphics
(Shared with system memory)
Intel GMA X3100 using 144 MB of DDR2 SDRAM with Micro-DVI output
Nvidia GeForce 9400M using 256 MB of DDR3 SDRAM with Mini DisplayPort output
Nvidia GeForce 320M using 256 MB of DDR3 SDRAM with Mini DisplayPort output
Intel HD Graphics 3000 processor using 256 MB (11" base model) or 384 MB (all other models) of DDR3 SDRAM
Intel HD Graphics 4000 processor with up to 1 GB DDR3 SDRAM shared from main memory
Intel HD Graphics 5000 processor with up to 1.5 GB LPDDR3 SDRAM shared from main memory
Intel HD Graphics 6000 processor with up to 1.5 GB LPDDR3 SDRAM shared from main memory

Front side bus/DMI
800 MHz
1066 MHz
800 MHz (11"), 1066 MHz (13")
Intel Direct Media Interface
2.5 GT/s
Intel Direct Media Interface
5.0 GT/s

Processor
1.6 GHz (L7500) or 1.8 GHz (L7700) Intel Core 2 Duo with 4 MB on-chip L2 cache
1.6 GHz (SL9300) or 1.86 GHz (SL9400) Intel Core 2 Duo with 6 MB on-chip L2 cache
1.86 GHz (SL9400) or 2.13 GHz (SL9600) Intel Core 2 Duo with 6 MB on-chip L2 cache
(11") 1.4 GHz (SU9400) Intel Core 2 Duo with 3 MB on-chip L2 cache
Optional 1.6 GHz (SU9600) Intel Core 2 Duo with 3 MB on-chip L2 cache
(13")1.86 GHz (SL9400) Intel Core 2 Duo with 6 MB on-chip L2 cache
Optional 2.13 GHz (SL9600) Intel Core 2 Duo with 6 MB on-chip L2 cache
(11") 1.6 GHz (i5-2467M) dual-core Intel Core i5 with 3 MB shared L3 cache
(13") 1.7 GHz (i5-2557M) dual-core Intel Core i5 with 3 MB shared L3 cache
(Higher-End 11" & 13") Optional 1.8 GHz (i7-2677M) dual-core Intel Core i7 with 4 MB shared L3 cache
(11") 1.7 GHz (i5-3317U) dual-core Intel Core i5 with 3 MB shared L3 cache
(13") 1.8 GHz (i5-3427U) dual-core Intel Core i5 with 3 MB shared L3 cache
(Higher-End 11" & 13") Optional 2.0 GHz (i7-3667U) dual-core Intel Core i7 with 4 MB shared L3 cache
1.3 GHz (i5-4250U) dual-core Intel Core i5 with 3 MB shared L3 cache
Optional 1.7 GHz (i7-4650U) dual-core Intel Core i7 with 4 MB shared L3 cache
1.4 GHz (i5-4260U) dual-core Intel Core i5 with 3 MB shared L3 cache
Optional 1.7 GHz (i7-4650U) dual-core Intel Core i7 with 4 MB shared L3 cache
1.6 GHz (i5-5250U) dual-core Intel Core i5 with 3 MB shared L3 cache
Optional 2.2 GHz (i7-5650U) dual-core Intel Core i7 with 4 MB shared L3 cache
1.8 GHz (i5-5350U) dual core Intel Core i5 with 3 MB shared L3 cache
Optional 2.2 GHz (i7-5650U) dual-core Intel Core i7 with 4 MB shared L3 cache

Memory
2 GB of 667 MHz DDR2 SDRAM
2 GB[note 2] of 1066 MHz DDR3 SDRAM
2 GB of 1066 MHz DDR3 SDRAM
Optional 4 GB
2 GB (11" base model; Optional 4 GB) or 4 GB of 1333 MHz DDR3 SDRAM (all other models)
4 GB of 1600 MHz DDR3L SDRAM Optional 8 GB
4 GB of 1600 MHz LPDDR3 SDRAM Optional 8 GB (8 GB standard for the 13" version since April 19, 2016)
8 GB of 1600 MHz LPDDR3 SDRAM

Storage
80 GB 4200-rpm 1.8-inch PATA HDD or 64 GB SSD
120 GB 4200-rpm 1.8-inch SATA HDD or 128 GB SSD
64 (MC505LL/A) or 128 GB (MC506LL/A) (11"), 128 (MC503LL/A) or 256 GB (MC504LL/A) (13") SSD
64 GB (11") SSD
128 GB (11") SSD Optional 256 GB upgrade128 or 256 GB (13") SSD
64 GB or 128 GB SSD (11") Optional 256 GB or 512 GB upgrade
128 or 256 GB SSD (13") Optional 512 GB upgrade
128 GB or 256 GB PCIe-based SSD Optional 512 GB upgrade

Video Camera
iSight (640 × 480)
FaceTime HD (720p)

Power Connector
MagSafe
MagSafe 2

Connectivity
Internal 802.11 a/b/g and draft-n
Internal 802.11 a/b/g/n (AirPort)
Internal Dual-Band 802.11 a/b/g/n (AirPort, Broadcom BCM43224 300 Mbit/s)
Internal 802.11ac a/b/g/n/ac compatible (AirPort, Broadcom BCM4360-based 867Mbit/s)

Bluetooth 2.1 + EDR
Bluetooth 4.0

Built-in infrared (IR) receiver for Apple Remote
N/A

Optional Apple USB Ethernet Adapter (Year 2008)
Optional Apple USB Ethernet 100 Mbit Adapter
Optional Apple USB Ethernet 100 Mbit Adapter Optional Apple Thunderbolt to Gigabit Ethernet Adapter
Optional Apple Thunderbolt to FireWire 800 Adapter

Latest possible OS X version
Mac OS X 10.7 "Lion"
(Unofficially, can run OS X 10.8 using MacPostFactor)
OS X 10.11 "El Capitan"
(Unofficially, can run macOS 10.12 "Sierra" without wi-fi using Sierra Patcher)
macOS 10.13 "High Sierra"

Battery
(non removable lithium-ion polymer)
N/A
35-watt-hour (11")
38-watt-hour (11")
N/A

37-watt-hour (13")
40-watt-hour (13")
50-watt-hour (13")
54-watt-hour (13")

Battery cycle count [51]
300
500
1000

Unit weight
N/A
2.38 lb (1.08 kg) (11")
N/A

3.0 lb (1.36 kg)
2.96 lb (1.34 kg) (13")

Dimensions
N/A
11.8 in (30 cm) wide × 7.56 in (19.2 cm) deep × 0.11 in (0.3 cm) to 0.68 in (1.7 cm) high (11")
N/A

12.8 in (33 cm) wide × 8.94 in (23 cm) deep × 0.16 in (0.4 cm) to 0.76 in (1.9 cm) high (13")
12.8 in (33 cm) wide × 8.94 in (22.7 cm) deep × 0.11 in (0.3 cm) to 0.68 in (1.7 cm) high (13")

Peripheral connections
1× USB 2.0
2× USB 2.0
2× USB 3.0

1× 3.5 mm headphone jack

Micro-DVI video port
DVI-D/VGA adapter included
1× Mini DisplayPort video port
1× Thunderbolt port
1× Thunderbolt 2 port

N/A
1× SDXC card slot (13" only)

text: Reception[edit]

text: Comparison with iPad and netbooks[edit]

text: Although the 11" Air is only slightly lighter than the 13" Air, the biggest difference is the footprint which gives each model a distinct category; the 13” Air is much closer in size to most other conventional laptops, while the 11” Air is almost small enough to fit in a space that can hold an iPad.[52][53]

text: The 11" MacBook Air carried the desirable essential attributes of a netbook, but without the drawbacks of a slower processor and less capable operating system,[54] albeit at a higher price.[55][56][57][58][59] At the low end, Apple introduced the iPad—a different form factor than the netbook, but with improved computing capabilities and lower production cost. Both of these led to a decline in netbook sales, and most PC manufacturers have consequently discontinued their netbook lines in response.[60] Capitalizing on the success of the MacBook Air,[61] Intel promoted Ultrabook as a new high-mobility standard, which has been hailed by some analysts as succeeding where netbooks failed.[62][63][64]

text: Ultrabook competition[edit]

text: Intel developed a set of specifications for the Ultrabook, a higher-end type of subnotebook produced by various PC manufacturers and usually running Windows. Competing directly with the Air, the Ultrabook is intended to reduce size and weight, and extend battery life without compromising performance.[65][66][67]

text: Through July 1, 2013, the MacBook Air took in 56 percent of all Ultrabook sales in the United States, despite being one of the higher-priced competitors. [23] Apple had previously dominated the premium PC market, in 2009 having a 91 percent market share for PCs priced at more than $1,000, according to NPD, and Ultrabooks were an attempt by other PC manufacturers to move in on Apple's turf.[68] While Apple's MacBook lines were not immune to this consumer trend towards mobile devices,[19] they still managed to ship 2.8 million MacBooks in Q2 2012 (the majority of which were the MacBook Air) compared to 500,000 total Ultrabooks,[20][21] despite there being dozens of Ultrabooks from various manufacturers on the market while Apple only offered 11" and 13" models of the Macbook Air.[22] Forrester Research analyst Frank Gillett attributes Apple's increased success in the enterprise market to the 2010 MacBook Air and the iPad.[69]

text: While several Ultrabooks were able to claim individual distinctions such as being the lightest or thinnest, the MacBook Air was regarded by reviewers as the best all-around Ultrabook in regard to "OS X experience, full keyboard, superior trackpad, Thunderbolt connector and the higher-quality, all-aluminum unibody construction".[70]

text: The Microsoft Surface Pro has a similar size and price to the 11" MacBook Air;[71][72] Apple CEO Tim Cook has criticized the Surface Pro and other Ultrabook hybrids running the touch-based Windows 8, that attempt to combine laptop and tablet functionality in one device, saying that such devices were confusing like trying to "combine a fridge and a toaster".[73][74]

text: When released in October 2010, the 13" model's screen resolution was higher than the average 1366x768 screens of similar sized laptops. However, by mid-2013, with many premium Ultrabooks having high resolution screens (1080p or greater) as standard or upgrades, the MacBook Air has been increasingly criticized for sticking with a low-resolution screen. Many in the tech community had expected Apple to release a MacBook Air with Retina Display by mid-2013, similar to the MacBook Pro Retina which came out in 2012.[75] The October 2013 refresh of the 13" MacBook Pro Retina, with a slimmer chassis and a lower price point, was mentioned as a potential MacBook Air alternative as the battery life is not much shorter while not being considerably bulkier.[4][76] Apple released an entry-level version of the 13" MacBook Pro on October 27, 2016, which was specifically targeted towards MacBook Air users.[77]

text: "Thinnest laptop"[edit]

text: At the launch of the first MacBook Air in January 2008, Apple claimed it to be the thinnest laptop in the world. While this was true of laptops on sale at the time, the 2003 Sharp Actius MM10 Muramasas was thinner at some points than the Macbook Air, being 0.54 inches (14 mm) thick at its minimum.[78] It, like the MacBook Air, was a tapered design, with a maximum height of 0.78 inches (19.8 mm) —slightly thicker than the MacBook Air — shown above as 0.76 inches (19.3 mm).[79] The Sony Vaio X505, released in 2004, had a minimum thickness of 0.38 inches (10 mm) and a maximum of 0.8 inches (20.3 mm).[80]

text: Since the release of the first MacBook Air, other thinner laptops have been released, such as the Dell Adamo,[81] launched in March 2009, which is a constant 0.65 inches (17 mm) thick. Apple subsequently removed "The world's thinnest notebook" from their marketing materials.

text: The 11.6" MacBook Air, introduced in October 2010, is only slightly larger and heavier (when closed) than the iPad 2. The 11.6" Air has been regarded as thin and light compared to other ultraportables, such as the Sony VAIO Z and the 11" Samsung Series 9.[82]

text: As of 2013, several Ultrabooks such as the Sony VAIO Pro have managed smaller dimensions than the MacBook Air by using carbon fiber construction.[83][84][85]

text: Issues[edit]

text: Following its introduction, the MacBook Air was greeted with a mixed reception. The portability of the MacBook Air was praised in reviews, but the compromise in features was criticized.[86][87][88] The full-sized keyboard, weight, thinness, and Multi-Touch trackpad were appreciated in reviews, while the limited configuration options and ports, slow speed (in non-SSD models), non-user-replaceable battery, small hard drive, and price were criticized.[86][87] The flip-down hatch on the side of the original MacBook Air is a tight fit for some headphone plugs and USB devices, requiring users to purchase an extension cable. Apple removed the flip-down hatch on the late 2010 model in favor of open connection ports, as is the case with most other laptops.[89][90]

text: Most of these problems have been dismissed by now, following many revisions and speed enhancements, and with the addition of more portability and ports.[citation needed]

text: Since the release of the first-generation product, some MacBook Air users have complained of CPU lockup caused by overheating. Apple released a software update in early March 2008 to fix the problem with mixed results: the deactivation of one CPU core was corrected; however, the runaway kernel problem remained for some users.[91] The problem is aggravated by system-intensive tasks such as video playback or video chatting.[92]

text: Due to a more mature manufacturing process, the CPUs in the second-generation MacBook Air perform better under load, as the first generation chips ran at a higher temperature—the processor needed to be throttled to avoid overheating and this further degraded performance.[93]

text: On October 17, 2013, Apple announced a replacement program for the 64 GB and 128 GB MacBook Air flash storage drives that are installed in Air systems purchased between June 2012 and June 2013.[94]

text: Timeline of the MacBook family


document_title: List of The Cosby Show characters

question_text: vanessa's fast talking friend on cosby show

question_tokens: vanessa 's fast talking friend on cosby show

text: List of The Cosby Show characters

text: Main characters

text: Cliff Huxtable

text:
Portrayed by
Seasons
No. of episodes

Bill Cosby
All
202 (all)

text: Dr. Heathcliff "Cliff" Huxtable[1] is known for his comical antics, playful admonishments, and relentless teasing humor. He lives in Brooklyn Heights, New York. Cliff had a brother, James Theodore Huxtable, who died of rheumatic fever at the age of 7. In his high school and college years, he was an athlete who wrestled, played football, and ran track. He later served in the Navy before going to medical school. He is an OB/GYN who runs a practice from the office annexed to his home. In the show, most characters outside of family and friends refer to him as "Dr. Huxtable", and he is well-respected in the community.[2][3][4][5][6]

text: Cliff is married to Clair Huxtable. Both Cliff and Clair attended the fictional Hillman College. Together, they have five children: Sondra, Denise, Theodore (Theo), Vanessa, and Rudith (Rudy). Cliff enjoys live jazz, has an extensive collection of albums, and tries to eat junk food whenever he can get away with it.[7]

text: Cliff is very eccentric and silly to most people around him, especially his family, however he is very kind-hearted and an extremely dedicated father with a strong sense of humor. Although he and his wife fostered a tight-knit, loving family, a running gag throughout the series is his thwarted attempts to get the grown children to leave the house.[8]

text: Very playful, Cliff enjoys competition, often making bets with Clair over various things, such as the date a certain jazz song was released, or having a "Smooth Contest" to see which of them looked more elegant for a night on the town, as judged by the children. He also plays a monthly game of pinochle against his father and some friends, which sometimes gets very passionate. Unfortunately, Cliff often finds himself on the losing end of most of his bets and games, as, for example, he has never beaten his father-in-law at chess. However, Cliff eventually broke his losing streak at pinochle against his father and his friend Homer Dobson with the help of Dr. Foster (played by Roscoe Lee Browne), an expert pinochle player who also happened to be his and Clair's literary professor at Hillman College.

text: In the pilot episode, Cosby's character's full name is Clifford, as shown on a sign on the exterior of the house. His full name was subsequently changed to Heathcliff, even though in one episode Clair called him "Heathclifford", and he is commonly called "Cliff" throughout the series.

text: Originally, Cliff was to have worked as a chauffeur, with most of the humor coming from his interactions with customers. However, the show was changed before airing to have Cliff be a medical doctor, and the humor to come from his interactions with his family.

text: Cliff also appears in three episodes of A Different World: the pilot (with Rudy), "Rudy and the Snow Queen" (also with Rudy) and "If Chosen, I May Not Run".

text: He is the only character to appear in every episode.

text: Clair Huxtable

text:
Portrayed by
Seasons
No. of episodes

Phylicia Rashād
All
193

text: Clair Olivia Huxtable (née Hanks) is the elegantly tough, eloquent, and engaging wife of Cliff, who is known for her relaxed confidence and striking emphasis as shown.[4][1] Aside from her deep and decorated self-expression, Clair can also be playful and silly. She is an intelligent, classy, and successful businesswoman. A great debater, Clair rarely if ever loses an argument on the show, a testament to her career as lawyer. She is also highly skilled in areas of recall about facts and dates, which she uses during discussions and debates: in one episode she is shown quoting a passage and even the page number of a book during an appearance at a television roundtable. Clair is bilingual but is only shown speaking Spanish on a couple of occasions. Several episodes also showcased her singing talent. Despite her elegant brand of toughness and strictness, Clair is a very loving mother and wife. The character is loosely based upon Cosby's wife, Camille Olivia Hanks-Cosby.

text: Her age is directly stated only once during the series, and two separate episodes provide contradictory information on the age difference between herself and Cliff. He celebrates his 50th birthday during season three ("Cliff's 50th Birthday"), while she celebrates her 46th during season five ("Birthday Blues," two years later), indicating that she is six years younger. However, in the season four episode "The Locker Room," it is stated that Clair is four years younger.

text: Her character was originally supposed to be a housewife, but when the show finally aired, she became a lawyer. During the series, she becomes a partner in her law firm. As an attorney she helps her family with legal issues, and she successfully represents her eldest daughter, Sondra, in a case over dishonest car repairs. When it came to the Huxtable household, she was in charge, even though she let Cliff think he was in charge (although Cliff was known to lay down the law when he had to). She was the chief disciplinarian of the children, as shown in an episode where Vanessa and her friends sneak off to Baltimore to see a rock concert and Clair delivers a memorable and scathing diatribe to her. Another memorable moment came when the normally composed Clair lost her temper when Sondra announced she wasn't going to law school after paying her tuition to attend Princeton.

text: Clair also appears in four episodes of A Different World: "Clair's Last Stand", "Risky Business" (with Theo and Vanessa), "Forever Hold Your Peace" (with Martin and Olivia) and "Success, Lies and Videotapes".

text: Clair Huxtable has been ranked highly in several lists of the top television mothers. She was voted as television's "Favorite TV Mom" in a poll conducted by the Opinion Research Company in 2004.[9] In 2009, she was included in the Top 5 Classic TV Moms by Film.com.[10] In May 2012, Clair was one of the 12 moms chosen by users of iVillage on their list of "Mommy Dearest: The TV Moms You Love".[11] AOL named her the ninth Most Memorable Female TV Character.[12]

text: Sondra Huxtable Tibideaux

text:
Portrayed by
Seasons
No. of episodes
First appearance

Sabrina LeBeauf
2–8;
recurring in 1
53
"Bonjour Sondra"

text: Sondra Tibideaux (née Huxtable), the eldest daughter of Cliff and Clair, did not appear on screen until mid-way through season one. She did not exist in the pilot episode (Clair: "Why do we have four children?" Cliff: "Because we did not want five.") In her first appearance, she is a sophomore in college, and Cliff notes her to be 20 years old (episode 10), making her birth year 1964. She earned a degree from Princeton University and had intentions of pursuing a career as a lawyer, like her mother. She married her boyfriend, Elvin Tibideaux, in season four, and later gave birth to twins—a boy and a girl—named after Nelson and Winnie Mandela. More serious, earnest and responsible than the other children, Sondra fits many of the characteristics of the first born from a large family. Though she had her moments of bizarre thinking (e.g. dropping out of law school to open up a wilderness store with Elvin), she'd usually snap out of them relatively quickly. Because of her intelligence level and overachieving nature, she is looked upon by her parents proudly, but also is held to a higher standard than the rest of the children. Sondra appeared sporadically in early seasons of the series due to the character being off at college at the time.

text: Sondra was created when Bill Cosby wanted the show to express the accomplishment of successfully raising a child (e.g. a college graduate). Whitney Houston was considered for the role of Sondra Huxtable. Sabrina LeBeauf almost missed out on the role because she is only 10 years younger (b. 1958) than Phylicia Rashad (b. 1948).

text: The character is loosely based upon Cosby's eldest daughter, Erika, who was approximately the same age as Sondra.

text: Denise Huxtable Kendall

text:
Portrayed by
Seasons
No. of episodes
Final appearance

Lisa Bonet
1–3, 6–7;
recurring in 4&5
119
"Cliff and Jake"

text: Denise Kendall (née Huxtable) is the second daughter of Cliff and Clair Huxtable.[13] At the beginning of the series, she is sixteen years old, putting her year of birth in 1968. She loves fashion and music, but did not want to attend school to pursue either interest. She is noted as being an individual who usually wishes to march to the beat of her own drum, and often learns lessons up front for herself rather than based off the experiences of others. A two-year stint at Hillman College ends with Denise wishing to see what she can accomplish on her own, which leads her to Africa as a photographer's assistant. While there, she meets and marries Navy Lt. Martin Kendall, and also becomes stepmother to Martin's three-year-old daughter Olivia, his child from a previous marriage. Denise eventually decides to become a special education teacher and makes arrangements to attend Medgar Evers College to this effect, but that idea does not work out as Denise eventually leaves New York again when Martin is posted to Singapore on a long-term assignment. It is revealed in the series finale that she is pregnant.

text: During the first two seasons, Denise was portrayed as a very popular high-schooler, with many friends, who seemingly had a different boyfriend every episode. Along with her constantly fluctuating love life, were her various hairstyles and choices of clothing, which were occasionally made fun of by Cliff. In later seasons, however, she exhibited a more flighty nature, often expressing ideas that left Cliff and Clair greatly puzzled.

text: In season three, Denise left home to attend Hillman College, a fictional, historically African-American college, of which her mother, father and grandfather were all alumni. The Cosby Show's producers created a spin-off series, entitled A Different World, which initially dealt with the life of Denise at college. Denise was written out of the series following its inaugural season (which aired concurrently with season four of The Cosby Show), after actress Lisa Bonet became pregnant. Shortly after the start of season five, Denise traveled to Africa for a year, and there she fell in love with and married Martin. In the season six premiere, she returned home, shocking her parents with the news of her surprise marriage to a divorced single father. However, Cliff and Clair accepted the couple when they met Olivia, who immediately won their hearts and was welcomed into the family. She appears regularly during the first three seasons, and is in only four episodes each of seasons four and five (a picture of her can be seen in the opening credits of season four), she appears regularly in season six, but only appears in a handful of episodes during season seven.

text: The character is loosely based upon Cosby's daughter, Erinn, who was approximately the same age as Denise. Additionally, Denise attended Hillman College, whereas Erinn attended Spelman College, the university that Hillman is believed to be modeled after.

text: Theo Huxtable

text:
Portrayed by
Seasons
No. of episodes

Malcolm-Jamal Warner
All
176

text: Theodore Aloysius "Theo" Huxtable is the middle child and only son of Cliff and Clair Huxtable, and is athletic and obsessed with impressing girls, and obtaining a sports car or motorcycle. He is fourteen years old when the series begins, making his birth year 1970. In the pilot episode, he is lectured by his father for not applying himself at school ("I brought you in this world, and I'll take you out"). Also in the early seasons, he was somewhat of a troublemaker, as illustrated through incidents both alluded to and explicitly portrayed in the series, such as letting his best friend's younger sister pierce his ear, resulting in an infected earlobe, but his behavior had improved by the time he left high school.

text: A running theme of the early seasons revolved around Theo's academic struggles, especially in his sophomore-year geometry class, taught by Mrs. Westlake (Sonia Braga). As the seasons progressed, Theo gradually evolved from being an under-achiever to a successful high school—and college—student (in interviews, Cosby noted a similar change in his real-life son, Ennis). While Theo was a student at NYU, it was revealed that he suffered from dyslexia, a learning disability that inspired him to work harder, and as a result overcame it. By the final season, Theo was a student teacher, helping other children with dyslexia at a local education center. In the show's final episode, he graduated from NYU with a degree in psychology.

text: In the pilot, and once more in season one (the episode "Bad Dreams"), he is referred to by Vanessa as "Teddy", instead of "Theo."

text: Theo has a long-running, but on-and-off relationship with a girl named Justine, who is mentioned many times throughout the series, but appears in only nine episodes. During his high school years, Theo's best friend was Walter Bradley (Carl Anthony Payne II), better known as "Cockroach", who was more of a scholastic underachiever than Theo. The two of them would occasionally compose rap songs for various school assignments. When Theo got tickets to "Dance Mania" (a "Soul Train"-like television dance show), and only one of them was allowed into the studio, Theo let Cockroach have the spot, but did not feel good about it when he saw Cockroach on TV, and as the center of their friends' attention the next day at school. This episode marked the final appearance of the character, and Cockroach was rarely mentioned in subsequent episodes. Theo appears in the series the most out of the Huxtable children.

text: The character is loosely based upon Cosby's only son Ennis, who was approximately the same age as Theo (and was also dyslexic).

text: Theo also appears in two episodes of A Different World: "My Dinner With Theo" (with Rudy) and "Risky Business" (with Clair and Vanessa).

text: Vanessa Huxtable

text:
Portrayed by
Seasons
No. of episodes

Tempestt Bledsoe
All
157

text: Vanessa Huxtable is the fourth child and third daughter of Cliff and Clair. In season one, she is eleven years old, making her birth year 1973. As Vanessa grew up, she faced typical teenage problems and heartbreaks, such as wearing make-up before her 15th birthday in violation of her parents' rules and spending a lot of time talking on the phone with her friends. Unlike her older brother, she was an excellent student and seemed to enjoy school; at the beginning of season seven, she went off to college one year early. She became engaged in the final season to Dabnis Brickey, a man in his late twenties. Dabnis was the head of maintenance at Lincoln University in Pennsylvania, where Vanessa was enrolled. However, Vanessa realized that she was not ready to get married, and they broke off the engagement. They maintained they were "just friends" by the end of the season.

text: In the early seasons, Vanessa is usually considered to be nosy, as she usually—sneakily—tries to find out what goes on in the Huxtable house, especially when it involves someone (usually Theo) in trouble with their parents. But, in a later episode, the tables are turned, as Theo catches Vanessa's friends smoking cigarettes in her room, although Vanessa herself did not take part, and even tried to dissuade her friends from doing so.

text: She often fought with her younger sister, Rudy, over typical childish issues. At one point, their fighting caused damage to both their bedrooms and the kitchen ceiling, driving Cliff to declare their rooms off limits because of "World War Five" and exile them to the basement until repairs were finished. But, on one occasion, Vanessa got into a physical tussle with Denise over a sweater that Vanessa stole from Denise's closet after Denise did not allow her to borrow it.

text: One of Vanessa's best friends in high school was a girl named Kara (played by Elizabeth Narvaez), who could ramble on about nothing in particular at high speed. Whenever Cliff—who once referred to Kara as "Turbo Tongue"—was on the receiving end of her babbling, he would always reply with a bewildered "Thank you." Vanessa appeared sporadically in the final two seasons of the series due to the character being away at college.

text: The character is loosely based upon Cosby's daughter, Ensa, who was approximately the same age as Vanessa.

text: Vanessa also appears in the A Different World episode "Risky Business" (with Clair and Theo).

text: Rudy Huxtable

text:
Portrayed by
Seasons
No. of episodes

Keshia Knight Pulliam
All
177[14]

text: Rudith Lillian "Rudy" Huxtable is the youngest of the Huxtable children.[15] She is only five years old at the beginning of the series, making her birth year 1979. She comes of age during the course of the show.[16]

text: A number of Rudy's friends appear in episodes as the series progresses. Among the best known are the taciturn Peter Chiara who repeatedly ran out the Huxtables' front door when frightened; and the chauvinist, blues-loving Kenny, whom she nicknames "Bud", and who always gets advice from his (unseen) older brother about basically everything. This unfortunately gives him the wrong conception about certain things and gets him in trouble, although he seemed to grow out of it as the series reached its end.

text: Keshia Knight Pulliam was nominated for an Emmy for her performance in season two, becoming the youngest nominee ever.[17] One of her fellow nominees that year was Phylicia Rashad. Neither won.

text: The Huxtable family was originally going to be two boys and two girls. The youngest child, Rudy, was initially supposed to be a boy, but the character was re-written for a girl (Keshia Knight Pulliam) when no boys auditioned. Jaleel White, later known for his role as Steve Urkel on Family Matters, revealed in a 2011 interview with Vanity Fair that he had auditioned for the role of Rudy.[18]

text: The character is loosely based upon Cosby's youngest daughter, Evin, who was approximately the same age as Rudy.[19]

text: Rudy also appears in three episodes of A Different World: the pilot (with Cliff), "Rudy and the Snow Queen" (also with Cliff) and "My Dinner with Theo" (with Theo).

text: Elvin Tibideaux

text:
Portrayed by
Seasons
No. of episodes
First appearance

Geoffrey Owens
4–8;
recurring in 2&3
44
"Cliff in Love"

text: Elvin Tibideaux is Sondra's boyfriend, and later, husband. They met at Princeton, where they both earned degrees. The two constantly bickered during early episodes, until his interactions with the Huxtables, particularly Clair, challenged him to confront his "male-chauvinist" attitudes.

text: When they return from their honeymoon, they shock Cliff and Clair by announcing their intentions to forego medical school and law school, and start a wilderness supply store in Brooklyn. When his children are born, Elvin then announces that he will re-apply to medical school. This decision later convinces Sondra to resume her studies at law school.

text: Elvin was a wrestler in high school and for one year at Princeton, but had to quit after injuring his hip. During season three, he helped Theo with some strategy and moves.

text: Martin Kendall

text:
Portrayed by
Seasons
No. of episodes
First appearance

Joseph C. Phillips
6 and 7,
recurring in 8
21
"Denise: The Saga Continues"

text: Lt. Martin Kendall is a Navy officer, husband of Denise Huxtable, and father of Olivia. Phillips' role as Martin Kendall came about when Denise unexpectedly married him in Africa, unbeknownst to her parents and family. When the newlyweds arrive back home, Martin learns that Denise's family not only does not know about their marriage, they do not know about him at all, so he wants to introduce himself to the Huxtables now that he has married into their family and to show his intentions of marrying his daughter were honorable. This does not go over smoothly at first, as Clair and Cliff are uneasy with the whirlwind marriage of Martin, however in due time they become accustomed to this blended family. Kendall also had an ex-wife, named Paula (played by Victoria Rowell of The Young and the Restless). In the finale, it is revealed that he and Denise are expecting a baby together.

text: Joseph C. Phillips played Sondra's date in a season two episode, before coming back as a new character, and playing the husband of Denise. Martin appears frequently in the sixth season but is only seen in a handful episodes of the seventh season, Joseph C. Phillips's final season as a regular. Martin makes his final appearance in an episode of season eight, "Olivia Comes Out of the Closet."

text: Martin also appears in the Different World episode "Forever Hold Your Peace" (with Clair and Olivia).

text: Olivia Kendall

text:
Portrayed by
Seasons
No. of episodes
First appearance

Raven-Symoné
6–8
63
"Denise: The Saga Continues"

text: Olivia Kendall is Denise Huxtable's precocious stepdaughter, who is three years old when she first appears in the series. Olivia is the only child of Martin and Paula Kendall. After a few years of marriage, her parents divorced, and her mother, Paula, gave Martin full custody, as she felt overwhelmed by marriage and motherhood. Olivia was then raised by her grandparents and father.

text: When Olivia was almost four years old, her father Martin married Denise Huxtable, whom he met in Africa. The new family moved in with Denise's parents, Clair and Cliff Huxtable, who are now Olivia's step-grandparents. Martin, as a Naval officer, is required to travel a lot, so for a while, Olivia was unable to spend time with him. During his absences, her stepmother, Denise, raised her. Olivia continued to live with her step-grandparents while her parents were in Singapore during the final season.

text: The character was named after Bill Cosby's wife, Camille Olivia Hanks-Cosby.

text: Olivia also appears in the Different World episode "Forever Hold Your Peace" (with Clair and Martin).

text: Pam Tucker

text:
Portrayed by
Seasons
No. of episodes
First appearance

Erika Alexander[20]
7–8
21
"Period of Adjustment"

text: Pam Tucker is Clair Huxtable's distant cousin.[21] The daughter of a single mother, Pam comes to live with the Huxtables after her mother moved to California to take care of Pam's grandmother.[22] Upon moving in, Pam is a high school junior—younger than Vanessa, but older than Rudy. At first, she is not used to the Huxtables' upper-middle-class lifestyle or close-knit family relationships.[23] Eventually, she fits in, and becomes just another one of the Huxtable clan. Pam makes her first appearance in the fourth episode, "A Period of Adjustment," Tin season seven.

text: Frequently, Pam is shown interacting with her best friend, Charmaine Brown (Karen Malina White), and Charmaine's boyfriend, Lance Rodman (Allen Payne).

text: The character had a mixed reception.[24][25][26]

text: Recurring characters

text:
Russell and Anna Huxtable (Earle Hyman and Clarice Taylor): Cliff's parents (seasons 1–8)
Kenny, aka "Bud" (Deon Richmond): Rudy's longtime friend (32 episodes)
Charmaine Brown (Karen Malina White): Pam's best friend (13 episodes) (later became a regular on the final season of A Different World)
Winnie Tibideaux (Domonique & Monique Reynolds, Jalese & Jenelle Grays, Jessica Ann Vaughn) daughter of Sondra and Elvin (18 episodes)
Peter Chiara (Peter Costa) Rudy's friend (13 episodes)
Walter Bradley, aka "Cockroach" (Carl Anthony Payne II) Theo's best friend in high school (12 episodes)
Nelson Tibideaux (Christopher & Clayton Griggs, Darrian & Donovan Bryant, Gary LeRoi Gray) son of Sondra and Elvin (7 episodes)
Denny (Troy Winbush) Theo's high school, college friend (11 episodes)
Lance Rodman (Allen Payne) Charmaine's boyfriend (11 episodes)
Janet Meiser (Pam Potillo) Vanessa's friend (10 episodes)
Howard (Reno Wilson Theo's college friend (10 episodes)
Justine Phillips (Michelle Thomas) Theo's longtime girlfriend (8 episodes)
Kara (Elizabeth Narvaez) Vanessa's friend (8 episodes)
Stanley (Merlin Santana) Rudy's boyfriend (7 episodes)
Kim Ogawa (Naoka Nakagawa) Rudy's friend (7 episodes)
Carrie Hanks (Ethel Ayler) Clair's mother (6 episodes)
Robert Foreman (Dondre T. Whitfield) Vanessa's boyfriend (6 episodes)
Lou Hernandez (Alex Ruiz) Theo's college friend (6 episodes)
Dabnis Brickey (William Thomas Jr.) Vanessa's fiance (6 episodes)
Jeffry Engels (Wallace Shawn) the Huxtables' neighbor (5 episodes)
Smitty (Adam Sandler) Theo's high school friend (4 episodes)
Arthur Bartell a.k.a. "Slide" (Mushond Lee) Pam's ex-boyfriend (4 episodes)
Al Hanks (Joe Williams) Clair's father (4 episodes)
Aaron Dexter (Seth Gilliam) Pam's boyfriend (3 episodes)
Mrs. McGee (Elaine Stritch) Rudy's teacher (3 episodes)
Jade (Vanessa A. Williams) Theo's friend (2 episodes, season 5)
Cheryl (Vanessa A. Williams) Theo's friend (2 episodes, season 7)
Eunice Chantilly (unseen character) Cliff's former girlfriend (She is mentioned in several episodes as a foil device but never seen)

tag: ul

text: Notable guest stars

text:
Debbie Allen as Emma ("If the Dress Fits, Wear It", season 5)
John Amos as Dr. Herbert ("The Physical", season 5)
Tichina Arnold as Delores ("Theo's Women", season 5)
Angela Bassett as Mrs. Mitchell ("Mr. Quiet", season 1), and Paula ("Bookworm", season 4)
Norman Beaton as Carleton ("There's Still No Joy in Mudville" season 7)
U.S. Senator Bill Bradley as Cliff's teammate #1 ("The Boys of Winter", season 5)
Sônia Braga as Anna Maria Westlake ("Mrs. Westlake" and "An Early Spring", season 2)
Valerie Brisco-Hooks as herself ("Off to the Races", season 2)
Roscoe Lee Browne as Dr. Foster ("Shakespeare", season 4)
Red Buttons as Jake, owner of Jake's Appliances ("Cliff and Jake", season 7)
Naomi Campbell as Julia ("The Birth" and "Cyranoise de Bergington", season 5)
Betty Carter as Amanda Woods ("How Do You Get to Carnegie Hall", season 5)
Robert Culp as Scott Kelly ("Bald and Beautiful", season 3)
Sammy Davis, Jr. as Ray Palomino ("No Way, Baby", season 5)
Dave DeBusschere as Cliff's teammate #2 ("The Boys of Winter", season 5)
Plácido Domingo as Alberto Santiago ("Birthday Blues", season 5)
Teresa Edwards as Opponent #2 ("The Boys of Winter", season 5)
Yvonne Irvin as Clair's Sister ("Clair's Sister", season 2)
Al Freeman, Jr. as Ernie Scott ("Back to the Track, Jack", season 1)
Minnie Gentry as Gramtee ("The Storyteller", season 6)
Dizzy Gillespie as Mr. Hampton ("Play It Again Vanessa", season 1)
Erica Gimpel as Jennifer ("Waterworks", season 4)
Robin Givens as Susanne ("Theo and the Older Woman", season 2)
Pam Grier as Samantha ("Planning Parenthood", season 3)
Moses Gunn as Joe Kendall ("Grampy and NuNu Visit the Huxtables", season 6)
Walt Hazzard as Cliff's teammate #3 ("The Boys of Winter", season 5)
Lena Horne as herself ("Cliff's Birthday", season 1)
Iman as Mrs. Montgomery ("Theo and the Joint", season 1)
Danny Kaye as Dr. Burns ("The Dentist", season 2), in one of his last TV appearances
Alicia Keys as Maria ("Slumber Party", season 1)
B.B. King as Riley Jackson ("Not Everybody Loves the Blues", season 6)
LaChanze as Sylvia ("The Prom", season 4)
Audrey Landers as Cookie Bennett ("Cliff and Jake", season 7)
Sheldon Leonard as Dr. Wexler ("Physician of the Year," season 1)
Nancy Lieberman as Opponent #1 ("The Boys of Winter", season 5)
Miriam Makeba as herself ("Olivia Comes Out of the Closet", season 8)
S. Epatha Merkerson as Book Club Member 5 ("Bookworm", season 4)
Melba Moore as Patricia Abbott ("Twinkle, Twinkle Little Star", season 4)
Rita Moreno as Mrs. Granger ("You Only Hurt the One You Love", season 3)
Lou Myers as Mr. Davis ("You Only Hurt the One You Love", & "Andalusian Flu", season 3)
Tony Orlando as Tony Castillo ("Mr. Quiet", season 1)
Tito Puente as timbal player ("Play It Again, Russell", season 2)
Christopher Plummer as Professor Jonathan Lawrence ("Shakespeare", season 4)
Patricia Richardson as Mrs. Schrader ("Calling Doctor Huxtable", season 3)
John Ritter as Ray Evans ("Total Control", season 7)
Frank Robinson as Frank Potter ("There's Still No Joy in Mudville", season 7)
Victoria Rowell as Paula Kendall ("Cliff's Wet Adventure", season 6)
Howard "Sandman" Sims as himself ("Mr. Sandman", season 6)
Special Ed as J.T. Freeze ("Warning: A Double-Lit Candle Can Cause a Meltdown", season 8)
Bern Nadette Stanis as Carolyn Thompson ("Adventures in Babysitting", season 7)
Leslie Uggams as Kris Temple ("The Return of the Clairettes", season 7)
Blair Underwood as Denise's boyfriend (uncredited) ("Jitterbug Break", season 1), and Mark ("Theo and the Older Woman", season 2)
Mario Van Peebles as Garvin ("Clair's Sister", season 2)
Jim Valvano as John Velarde ("The Getaway", season 8)
Dick Vitale as Dan Vicente ("The Getaway", season 8)
Malinda Williams as Althea Logan ("Calling Doctor Huxtable", season 3) and Shana ("Denise Kendall: Singles Counselor", season 6)
Nancy Wilson as Lorraine Kendall ("Grampy and NuNu Visit the Huxtables", season 6)
Stevie Wonder as himself ("A Touch of Wonder", season 2)
Amy Yasbeck as Alicia Evans ("Total Control", season 7)