A Brief Eye Anatomy Class
O.K., so you want to know how your eye works and how to decipher the rest of the disease sections. Let's start with the structure and functions of your most important organ (well, we're ophthalmologists!). Your eye can be thought of as a camera. In fact, the original cameras were designed after the functions of the eye, and modern cameras work in a similar fashion.
The front cover of the lens of the camera is analogous to the cornea of the eye, which is the clear part you see when looking at someone's eye. The iris of the eye (the colored part) is analogous to the iris of a camera, and opens and closes depending upon the light. If there is low light, the iris opens wide to allow more light to enter. If there is a lot of light, the iris closes to decrease the amount of light entering the eye. Similarly, a camera adjusts its iris when you take a picture to avoid over exposure or under exposure of the film. The lens of the eye is similar to the lens of the camera, in that it focuses the image on the back of the eye. The vitreous cavity in the eye is analogous to the body of the camera, the "box" of the eye itself and is filled with a clear tissue "gel" called vitreous. The retina, the most important part of the eye from a retinal surgeon’s point of view (!) is analogous to the film in the camera. The retina has to be functioning properly to send a message to your brain to "take the picture."
The retina is much like the inner tube in a tire, or the bladder of a basketball. It begins just posterior to the iris, just behind the area called the pars plana, and lines the inner wall of the eye. It has blood vessels that enter and exit at the optic nerve head (arteries enter carrying oxygenated blood, veins exit carrying blood back to the heart and lungs). The central portion of the retina, where you focus the image, is the macula. It is roughly the area inside of the arcade vessels, which extend from the optic nerve around the center part of vision. The true focal point of the eye is the foveal avascular zone (FAZ), which is only 400 microns wide (0.4mm). It is this small area that allows you to read, discriminate objects, etc. If damage is inflicted on this very small portion of the retina, then reading vision and focusing is lost.
|
Normal macula and fovea The macula is the center of vision (and retina) and the fovea (FAZ) is the focal point approximately only 0.4mm in diameter. Reading, driving, etc. is all performed here. |
The retina, if you look at it in cross section, consists of the retina itself, which is the inner most portion of the eye wall, and is actually very sensitive nervous tissue which sends messages via the optic nerve to the brain (sending the "picture" for you to see). Just outside the retina is a single layer of cells called the retinal pigment epithelium (RPE). The RPE is very important, in that it provides nutrients to the photoreceptors and cleans them as they do their job of seeing. Below the RPE is a multi-layered membrane called Bruch's’ membrane, which separates the RPE and retina from the choroid. The choroid is a vascular layer which provides most of the oxygen to the photoreceptors and RPE so that they can do their job of sight. The choroid is much like a sponge of blood vessels, and becomes very important in the development of subretinal membranes and other disorders. Finally, the sclera is the outermost portion of the eye itself, and is the white portion of the eye that is the true "wall" of the eye.
Disclaimer Stuff: The opinions expressed in this website are those of RVT. Diagnosis and therapy should be based on a thorough examination by and recommendations of a qualified eye provider.