The human eye is a complex organ that consists of three layers of tissue. The outer layer, known as the sclerotic coat, is the tough layer that creates the white of the eye and the cornea. The middle layer, called the choroid coat, is pigmented and forms the iris of the eye. The retina, the third and inner layer, is the membrane found in the back of the eye. There are a variety of diseases and disorders that can affect parts of the eye and cause blindness.
Cone-Rod Dystrophy
The retina is the portion of the eye that is light-sensitive, meaning it receives the light signals and sends them through the optic nerve to the brain where the vision is processed. The retina consists of rods and cones which are photoreceptors that absorb light. When the rods and cones are not functioning properly vision is affected.
Cone-rod dystrophy is a progressive disease in which the rods and cones deteriorate over time. This inherited disease decreases visual acuity, affects peripheral vision and eventually lead to blindness. Although there is no cure for cone-rod dystrophy, according to Muscular Dystrophy Support, protecting the retinas from bright light may help to slow down the progression of the disease.
Diabetic Retinopathy
Diabetic retinopathy is an eye disease that results from the long-term effects of diabetes. Diabetes is a disease that occurs when there is either not enough insulin---a hormone necessary to move sugar from the blood into the cells---or the insulin is not functional. The result is too much sugar, or glucose, in the blood. The excessive sugar in the blood can cause damage throughout the body including blood vessels.
When the blood vessels in the retina are damaged, vision is impaired. If left untreated, diabetic retinopathy can lead to blindness. Approximately 40 to 45 percent of all Americans with diabetes exhibit some level of diabetic retinopathy, according to the National Eye Institute.
Glaucoma
Glaucoma is the name of a group of eye diseases that are characterized by an increase in internal eye pressure. This increase in pressure damages the optic nerve which leads to blindness. Those with the early stages of glaucoma often do not have any symptoms. The Glaucoma Research Foundation reports that about half of all those affected by glaucoma do not know they have the disease. This makes glaucoma a dangerous disease because the loss of vision can occur without warning.
Stargardt's Disease
Stargardt's disease is an inherited disease that affects the macula of the eye. The macula is the middle portion of the retina necessary for daily activities such as reading, driving and recognizing colors. In Stargardt's disease, the macula slowly degenerates causing symptoms such as difficulty reading in children. Loss of vision slowly progresses until 20/40 is reached. From that point, the American Macular Degeneration Foundation reports that vision it rapidly deteriorates to 20/200 which is legal blindness.
