The clarity or clearness of the vision, a measure of how well a person sees. The ability to distinguish details and shapes of objects; also called central vision.

Unable to see. Without part or all of the sense of sight.

A clouding of the lens of the eye. The normally clear aspirin-sized lens of the eye starts to become cloudy. The result is much like smearing grease over the lens of a camera. It impairs normal vision. There are many causes of cataracts including cortisone medication, trauma, diabetes, many other diseases and simply aging. Cataracts will affect almost all people if they are fortunate enough to live long enough. The symptoms of cataracts include double or blurred vision and unusual sensitivity to light and glare. Cataracts can be diagnosed when the doctor examines the eyes with a viewing instrument. The ideal treatment for cataracts is surgical implantation of a new lens. Wearing sunglasses can help prevent cataracts.

A common complication of diabetes affecting the blood vessels in the retina.  If untreated, it may lead to blindness.  If diagnosed and treated promptly, blindness is usually preventable.

A common eye condition in which the fluid pressure inside the eyes rises because of slowed fluid drainage from the eye. If untreated, it may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness.

The elderly, African-Americans, and people with family histories of the disease are at greatest risk. There are no symptoms in the early stage of glaucoma. Glaucoma is often called "the sneak thief of sight." Often, by the time the patient notices vision loss, glaucoma can only be halted, not reversed.

The criteria used to determine eligibility for government disability benefits and which do not necessarily indicate a person's ability to function.  In the US, the criteria for legal blindness are: Visual acuity of 20/200 or worse in the better eye with corrective lenses (20/200 means that a person at 20 feet from an eye chart can see what a person with normal vision can see at 200 feet); or Visual field restriction to 20 degrees diameter or less (tunnel vision) in the better eye.

A visual impairment, not corrected by standard glasses, contact lenses, medicine, or surgery, that interferes with the ability to perform everyday activities. Most people develop low vision because of eye diseases such as cataracts, glaucoma, diabetic retinopathy or age-related macular degeneration (AME). Low vision primarily affects people over age 65. High risk populations include Hispanics and African Americans, who are likely to develop low vision at an earlier age. While lost vision usually cannot be restored, many people can learn to make the most of the vision that remains.

 A disease that progressively destroys the macula, the central portion of the retina, impairing central vision. Macular degeneration rarely causes blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision.

The macula is in the center of the retina at the back of the eye. As we read, light is focused onto the macula where millions of cells change the light into nerve signals that travel to the brain and tell it what we are seeing. This is our central vision. With normal central vision, we are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision.

Any one of a large group of inherited disorders in which abnormalities of the photoreceptors (the rods and cones) in the retina lead to progressive visual loss. People with retinitis pigmentosa (RP) first experience defective dark adaptation ("night blindness"), then constriction of the visual field ("tunnel vision") and eventually loss of central vision.

RP may be inherited in a number of different ways: as an autosomal dominant, autosomal recessive, or X-linked recessive trait or as a mitochondrial disorder. More than 30 different genes are known to cause RP.

RP can occur alone or be part of a syndrome involving abnormalities outside the retina. For example, Usher syndrome (of RP and deafness) is a relatively common form of syndromic RP.