Fovea

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Fovea centralis

 

The fovea centralis is a small, central pit composed of closely packed cones in the eye.

 

It is located in the center of the macula lutea of the retina.

 

It is responsible for sharp central vision necessary  for activities for which visual detail is of primary importance, such as reading and driving.

 

The parafovea is the intermediate belt, where visual acuity is below the optimum.

 

The parafovea extends to a radius of 1.25 mm from the central fovea.

 

The perifovea contains a more diminished density of cones, having 12 per 100 micrometres versus 50 per 100 micrometres in the most central fovea.

 

The perifovea is found at a 2.75 mm radius from the fovea centralis.

 

Approximately half of the nerve fibers in the optic nerve carry information from the fovea..

 

The  remaining half of optic nerve givers carry information from the rest of the retina.

 

The fovea is a depression in the inner retinal surface.

 

The fovea is about 1.5 mm wide.

 

Its photoreceptor layer is composed entirely of cones and which is specialized for maximum visual acuity.

 

Within the fovea is a region of 0.5mm diameter called the foveal avascular zone.

 

The fovea avascular zone has no blood vessels, and is responsible for the depression in the center of the fovea.

 

 

This allows the light to be sensed without any dispersion or loss.

 

The foveal pit is surrounded by the foveal rim that contains the neurons displaced, and is the thickest part of the retina.

 

The fovea receives most of its oxygen from the vessels in the choroid,

 

The high density of cones along with the absence of blood vessels at the fovea accounts for the high visual acuity capability at the fovea.

 

The center of the fovea is the foveola.

 

The foveola is about 0.35 mm in diameter where only cone photoreceptors are present and there are virtually no rods.

 

The central fovea consists of very compact cones.

 

It is the only area in the retina where 20/20 vision is attainable, and is the area where fine detail and colour can be distinguished.

 

The center of the fovea holds very few blue-sensitive cones.

 

The ratios of ganglion cells to photoreceptors is about 2.5; almost every ganglion cell receives data from a single cone, and each cone feeds onto between 1 and 3 ganglion cells.

 

The acuity of foveal vision is limited only by the density of the cones.

 

The fovea is the area of the eye with the highest sensitivity to fine details.

 

The cones in the central fovea express pigments that are sensitive to green and red light.

 

The fovea comprises less than 1% of retinal, but accounts for  50% of the visual cortex in the brain.

 

It sees only the central two degrees of the visual field, so the eyes must constantly shift their gaze to subsequently bring different portions of the image into the fovea.

 

This shifting is seen with reading.

 

The fovea does not have rods, and is not sensitive to dim lighting.

 

To observe dim lighting, looking out of the side of their eyes where the density of rods is greater, and hence dim objects are more easily visible.

 

There are high concentration of the yellow carotenoid pigments lutein and zeaxanthin in the fovea.

 

Carotenoid pigments lutein and zeaxanthin play a protective role against the effects of high intensities of blue light which can damage the sensitive cones.

 

The  arotenoid pigments lutein and zeaxanthin enhance the acuity of the fovea by reducing the sensitivity of the fovea to short wavelengths and counteracting the effect of chromatic ab2242ation.

 

The maximum density of blue cones occurs in a ring about the fovea, so the maximum acuity for blue light is lower than that of other colors and occurs approximately 1° off center.

 

Each  square millimeter of the fovea contains approximately 147,000 cone cells, or 383 cones per millimeter.

 

The  distance between the lens and fovea, the focal length is 17.1 mm.

 

The combined effects of the macular pigment and the distribution of short wavelength cones results in the fovea having a lower sensitivity to blue light.

 

Only under certain patterns of blue light illumination, a dark spot is visible at the point of focus.

 

In binocular vision, the two eyes converge to enable bifoveal fixation, need to achieve high stereoacuity.

 

 

 

 

 

 

 

 

 

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