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Medical Author:

Andrew A. Dahl, MD, FACS

Andrew A. Dahl, MD, FACS

Andrew A. Dahl, MD, is a board-certified ophthalmologist. Dr. Dahl's educational background includes a BA with Honors and Distinction from Wesleyan University, Middletown, CT, and an MD from Cornell University, where he was selected for Alpha Omega Alpha, the national medical honor society. He had an internal medical internship at the New York Hospital/Cornell Medical Center.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• What is blindness?
• What are the different types of blindness?
• What causes blindness?
• What are symptoms and signs of blindness?
• How is blindness diagnosed?
• What are treatments for blindness?
• What is the prognosis for blindness?
• When is someone considered legally blind?
• Is blindness preventable?
• Find a local Eye Doctor in your town
• Blindness Index

Blindness is diagnosed by visual acuity testing in each eye individually and by measuring the visual field or peripheral vision. People may have blindness in one (unilateral blindness) or both eyes (bilateral blindness). Historical information regarding the blindness can be helpful in diagnosing the cause of blindness. Poor vision that is sudden in onset differs in potential causes than blindness that is progressive or chronic. Temporary blindness differs in cause from permanent blindness. The cause of blindness is made by examination of all parts of the eye by an ophthalmologist.

The treatment of blindness depends on the cause of blindness. In third-world nations where there are many people who have poor vision as a result of a refractive error, merely prescribing and giving glasses will alleviate the problem. Nutritional causes of blindness can be addressed by dietary changes. There are hundreds of thousands of people who are blind from cataracts. In these patients, cataract surgery would, in most cases, restore their sight. Inflammatory and infectious causes of blindness can be treated with medication in the form of drops or pills.

The prognosis for blindness again is dependent on its cause. In patients with blindness due to optic-nerve damage or a stroke of indeterminate age, visual acuity can usually not be restored. Patients with long-standing retinal detachment in general cannot be improved with surgical repair of their detachment. Patients who have corneal scarring or cataract have a good prognosis if they are able to access surgical care of their condition.