Summarize how the structures of the eye direct light onto the fovea centralis

The cornea refracts light coming into the eye. The fovea has the highest acuity because of the composition of photoreceptors. It is dominated by cones which provide the acuity. This is the first level of processing the incoming information. The processing at this level involves the three layers of cells at the retina, i.e. cones and rods, bipolar cells, and ganglion cells with the aid of the interneurons: horizontal cells and amacrine cells.

The fovea centralis, also commonly known as the fovea, is the section of the eye’s retina with the highest focus. It has the highest concentration of cone photoreceptors, which are the cells in the eye that perceive color, and this high level of cones is what allows for such a sharpened focus in this part of the eye. The fovea is also what allows for color vision in humans because color perception is greatest in this region. Foveal vision, which is focused, centered vision involved in driving, sports, and reading, is made possible by the fovea centralis.

When focusing on an object, the fovea centralis allows an area of focus that is about 1 inch (2.54 cm) in diameter at a distance that is about arm’s length. This area represents a range contained between the central 2° of vision. As a result of this small range of focus, the eye must roam around larger objects to be able to focus on them, a principle that is most noticeable when observing someone reading. The gaze-contingency paradigm arose from this phenomenon as a method for measuring movements of the eye.

The average diameter of the human fovea centralis is about 0.04 inches (1 mm), which is less than 1% of the total surface area of the retina. Despite this small size, the fovea centralis contributes to about 50% of the nerve fibers in the optic nerve, and about 50% of the brain volume in the visual cortex area of the brain. This high level of specificity is created by the structure of the cone cells and retinal ganglion cells, or visual neurons, in the region. Each retinal ganglion cell is dependent upon a single cone cell for visual information, and each cone cell sends visual information to up to three three retinal ganglion cells. This is much more specific when compared with the rest of the retina, which means that the fovea centralis region enables a much higher level of visual detail than the other areas of the retina.

This region is located in the macula, a central area of the retina that is yellow-toned and a natural sunscreen for the retina, as it absorbs high-energy blue and ultraviolet light. The macula, however, does not contain a direct blood supply, so the fovea centralis derives oxygen from a nearby region called the choroid. Under conditions of bright light, the fovea cannot get enough oxygen and hypoxia, or oxygen deprivation, occurs.