Dear Dr. Gott: My mother-in-law is 70 years old. She never had a need to see an eye doctor until last week, when she scratched her eye. She found a local ophthalmologist who told her that she has Fuchs' disease, something she had never heard of before.

As a coincidence, I decided since I turned 50 recently that it was time for me to have my eyes checked. Lo and behold, and hundreds of dollars later, I had an exam and was told that I needed glasses. When I asked my eye doctor about Fuchs', he told me briefly about the condition. Can you tell me more?

Dear Reader: The outermost layer of the eye is known as the cornea. It doesn't contain any blood vessels to nourish or protect it, but it gets its nourishment from the aqueous humor behind the eyes and from tears. Its purpose is to protect the eye from debris, dust and germs. In order for a person to see well, all five layers of the cornea must be free of any cloudy areas. Visual disorders are quite common, affecting about 120 million people in the United States, causing them to wear glasses or contact lenses. The disorders to which I refer are known as refractive errors. They affect the cornea and include myopia (nearsightedness), hyperopia (farsightedness) and astigmatism (uneven curvature of the cornea).

Some of the more common disorders of the cornea include allergies that may be the result of a prescribed medication, animal hair, eye makeup, mascara, pollen and more; pinkeye (conjunctivitis), which can be caused by a viral or bacterial infection; irritants in the environment; eyedrops and ointments; infection of the cornea brought on by bacteria or fungi from contact lenses that have not been cleaned properly; dry eyes, which can result from antihistamines, nasal decongestants, antidepressants and tranquilisers; herpes zoster (shingles) produced by the varicella-zoster virus; and ocular herpes, a recurrent viral infection caused by the herpes-simplex virus.

A less common disorder is known as Fuchs' dystrophy, a slowly progressing disease that ordinarily affects both eyes. The condition is slightly more common in women than in men and can be detected in its earliest stages when a person is in his or her mid-30s; however, the disease rarely affects a person's vision until the age of 50 or older.

Fuchs' occurs when the cells that line the inside of the blood vessels deteriorate for no apparent reason. With the continuation of the loss of cells, the endothelium cannot function efficiently enough to pump fluid out of the connective tissue. The cornea swells, and vision becomes distorted. Over time, the epithelium will take on fluid that will result in visual impairment, pain and a visual haze.

In the early stages, a person may awaken with blurred vision that will clear as the day progresses. This occurs because the cornea is thicker in the morning as it retains fluids during sleep that evaporate during the day. With progression of the disease, the swelling will remain constant and vision will be reduced throughout waking hours.

Treatment will begin by reducing the swelling with the help of drops, ointments or soft contact lenses. When the disease affects quality of life by interfering with normal daily activities, a corneal transplant might be in order. At this stage, the success rate for this surgery is good; however, long-term survival of the new cornea might be a problem that will have to be addressed. Fuchs' generally affects both eyes equally, progresses gradually over time, occurs in otherwise healthy people, and is usually inherited.

Dr. Peter H. Gott is a retired physician and the author of several books, including "Live Longer, Live Better," "Dr. Gott's No Flour, No Sugar Diet" and "Dr. Gott's No Flour, No Sugar Cookbook," which are available at most bookstores or online. His website is www.AskDrGottMD.com.