Fovea, also known as fovea centralis is an important part of the eye. It is located in the middle of the macula area of the retina and is responsible to provide sharp and clear vision. It is only in the fovea that the retina is spread to allow light to fall directly on the cones. These cells therefore give a sharp and clear image and are known as central fovea.
The belt that surrounds the fovea is known as the parafovea while the outer region is called the perifovea. The parafovea belt is an area where the ganglion cell layers exist. These consist of more than five rows of cells and also have a very high density of cones. Therefore this is where the visual sharpness is below the optimum level.
The perifovea has diminished density of cones that have 12 per 100 micrometres than 50 per 100 micrometres in the central fovea. The perifovea is surrounded by a large portion of peripheral area that provides high information of low resolution which is compressed. The fovea delivers about 50% of the information to the nerve fibers in the optic nerve and the rest of the 50% transfer the information to the rest of the retina. The parafovea stretches to about 1 ¼ mm from the central fovea while the perifovea stretches 2 ¾ mm a little away from the fovea centralis.
The fovea which is very important for the human eye helps in reading, driving, watching television or any other activity that involves vision. The fovea is less than 1% of the retinal size. It dominates about 50% of the visual cortex in the brain.
The forveal pit is about 4 to 8 degrees temporal to the optical axis. The fovea is twice the width of a human’s thumbnail at arm’s length. The foveal rim surrounds the foveal pit and this is where the neurons are displaced from the pit. This is that part of the retina which is the thickest. The fovea is not sensitive to dim light as it doesn’t have rods.
The fovea is surrounded with a yellow pigment known as xanthophylls along with the lutein and the carotenoids in the cone. This pigment absorbs the blue light and helps to prevent the problem of chromatic aberration.
Other than humans, even reptiles, birds and fish have fovea which is a small pit in the surface of the retina. It is found only in simian primates in mamals. The retinal fovea is different in different animals.
In most humans, the photo-receptors in the fovea are of three kinds. Blue, red and green help humans to see all the colors that a person has to see. In some organisms there are four independent channels for color information. They have four different cone cells in the eye. This characteristic is known as tetrachromacy. The rods are in the fovea periphery and helps for a sharp vision in the dark.