File:Eyeball.jpg

Summary

A black-looking aperture, the pupil, that allows light to enter the eye (it appears dark because of the absorbing pigments in the retina).

A colored circular muscle, the iris, which is beautifully pigmented and gives us our eye color (the central aperture of the iris is the pupil). This circular muscle controls the size of the pupil so that more or less light, depending on conditions, is allowed to enter the eye. Eye color, or more correctly, iris color, is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More eumelanin is found in brown-eyed people, and more pheomelanin is found in blue- and green-eyed people. The melanocortin-1 receptor (MC1R) gene is a regulator of eumelanin production and is located on chromosome 16q24.3. Point mutations in the MC1R gene affect melanogenesis. The presence of point mutations in the MC1R gene alleles is a common feature in light-skinned and blue- and green-eyed people (1, 2).

A transparent external surface, the cornea, that covers both the pupil and the iris. This is the first and most powerful lens of the optical system of the eye and allows, together with the crystalline lens, the production of a sharp image at the retinal photoreceptor level.

The "white of the eye", the sclera, which forms part of the supporting wall of the eyeball. The sclera is continuous with the cornea. Furthermore, this external covering of the eye is in continuity with the dura of the central nervous system

Copyright status:

This image is public domain and published through a government website

Source:

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=webvision&part=A5