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Merck Manual

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Introduction to Corneal Disorders


Melvin I. Roat

, MD, FACS, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision May 2020| Content last modified May 2020
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The cornea is the clear layer in front of the iris and pupil. It protects the iris and lens and helps focus light on the retina. It is composed of cells, protein, and fluid. The cornea looks fragile but is almost as stiff as a fingernail. However, it is very sensitive to touch.

An Inside Look at the Eye

An Inside Look at the Eye

Corneal disorders include the following:

Corneal disease or damage can cause pain, tearing, and decreased sharpness of vision (visual acuity).

A slit lamp, which is an instrument that enables a doctor to examine the eye under high magnification, is usually used to examine the cornea. During the examination, the doctor may apply eye drops that contain a yellow-green dye called fluorescein. The fluorescein temporarily stains damaged areas of the cornea, making it possible to see damaged areas that are not otherwise visible.

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