A Guide to Laser Vision Correction
Dr. Robert Maloney believes that a well-informed patient is key to successful vision correction surgery. He wants to be sure that you fully understand what you can expect from your procedure you choose.
He wants to help you care for and preserve your eyesight in the best way possible. Here, you can find the information that you need to help you make informed choices about health care for your eyes.
The Human Eye and How Vision Works
Anatomy of the Eye
Sclera and Cornea
The outer layer surrounding the eyeball is made up of two parts: the sclera and the cornea. The sclera-the white, opaque part of the eye-makes up the back five-sixths of the eye's outer layer and provides protection for the eyeball. The cornea, about the size of a dime and as thick as a credit card, makes up the remaining sixth of the eye's outer layer. It is the transparent dome, similar to the crystal of a wrist watch, at the front of the eyeball. The cornea provides most of the eye's focusing power, so small changes in its curvature can make an enormous difference in how clearly you see objects.
The cornea has three main layers. The epithe lium is the thin outer protective layer of cells; it is made up of the same kind of tissue that covers most of your body, and is continually regenerating, or renewing itself. The stroma is the strong, fibrous layer that makes up 90 percent of the cornea's thickness and provides the cor nea with its structure and shape. The endothelium is the single cell layer that lines the inside of the cornea and helps regulate the cornea's fluid content.
The iris, which determines one's eye color, is located behind the cor nea. It is composed of connective tissue and smooth muscle fibers. The muscles of the iris control how much light passes through to the retina.
The Pupil appears as a black circle in the middle of the iris. The pupil can be likened to the aperture, or shutter, of a camera. When it is very bright, as on a sunny day, the iris muscles make the pupil constrict , or be come small, so only a small amount of light will pass into the eye. In darkness the opposite happens, and the pupil dilates, or enlarges, to let in more light.
The lens is a circular structure located directly behind the pupil and held in place by slender, strong ligaments. Although most of the bend ing of light is accomplished by the cornea, the curved lens fine-tunes the angle of light passing through it, focusing the light onto the retina. When the ligaments tighten, the lens becomes flatter, or less convex, allowing you to see objects at a distance. When the ligaments relax, the elastic lens becomes rounder, or more convex, like a magnifying glass, so you can see objects that are close. This ability of the lens to refine the focus through flexing is called accommodation.
The visual acuity is the jellylike substance, about 99 percent water, that fills the space be tween the lens and the retina on the inner back wall of the eye. Light passes through the visual acuity before striking the retina.
The retina is a complex layer of nerve tissue that lines the inside back wall of the eyeball. Similar to film in a camera, the retina "captures" the image through an electrochemical reaction to light. Electrical impulses are then transmitted through the optic nerve to the brain, which inter prets, or "develops," the image.
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