Corneal opacity occurs when the cornea becomes scarred by injury or infection. Scarring prevents light being able to pass through the cornea where it would normally be bent and focused through the iris onto the retina, causing vision degradation and loss. Corneal disorders like corneal opacity affect both humans and animals, most notably cattle.

The cornea is the thin transparent tissue that covers the surface of the eye. It has two jobs: to protect the eye from dirt, debris, and germs, and to let in and bend light. It actually is responsible for more than half the eye's ability to focus. Though the cornea is very thin, it has five layers. Damage any of the layers can cause corneal clouding.

One of the most common symptoms of corneal opacity is decreased vision or vision loss. A person may feel like there is something in his eye, even after flushing the eye and having someone look in it. He may also suffer light sensitivity and unexplained eye redness, as well as have an area on the eye that looks cloudy or milky.

There are several factors that increase the likelihood of developing corneal opacity. These include a vitamin A deficiency, measles, and viral infections including ocular or eye herpes, herpes zoster or shingles, and conjunctivitis or pink eye. Having an eye injury from a chemical or from something poking or hitting the eye, or wearing contact lenses too long or during the night can also increase a person's chances.

When corneal opacity is suspected, a physician will use a slit lamp, which focuses very bright light into a slit, to examine the numerous structures of the eye. Using a magnifying lens and eye drops that dilate the pupils and numb the eye, the doctor is able to check for foreign bodies, and corneal scarring. In most cases, corneal opacity can be treated by a doctor with oral medications or steroid and antibiotic eye drops. For more serious scarring, laser surgery is used to remove the scarring from the corneal surface. In the most severe cases, a cornea transplant may be needed.

To decrease the risk of corneal opacity, contact lens wearers should follow the guidelines established for use and care of their lenses. Individuals should wear eye protection whenever there is any risk of eye injury. All eye infections should receive immediate attention, and a doctor should be consulted any time anyone suffers an eye injury.