Blindness can occur from damage to any part of the eye or any part of the visual pathway. Commonly, visual impairment is caused by an eye disease or a condition that effects the retina's ability to capture light and send information to the brain to be processed.
In certain causes of retinal blindness, only certain parts of the retina are damaged, namely the light capturing photoreceptor cells. The remaining cells of the retina are spared and can therefore be potentially stimulated in order to generate visual percepts. Two examples of this type of condition affecting photoreceptor cells are age-related macular degeneration (AMD) and retinitis pigmentosa (RP). AMD affects over 10 million Americans and causes loss of central vision due to the loss of photoreceptors (the light-sensing cells).This condition is particularly debilitating in the elderly who may have difficulty walking and remain confined to their homes. RP affects 1.6 million people worldwide and is the leading cause of inherited blindness. RP causes a slow and progressive blindness across the entire visual field.
To date, there are no treatments for either AMD or RP. Cell transplantation and gene therapy may represent viable long-range hope although there are formidable challenges facing these therapeutic approaches. It is also important to keep in mind that even successful cell transplantation and repair of genetic function would only slow or prevent further deterioration rather than restore lost visual function (as would be possible with a prosthesis).
Common Diseases of the Eye
An important note for patients:
It is unlikely that the retinal prosthesis we are developing would be useful for individuals with impaired vision caused by conditions such as glaucoma or diabetic retinopathy. This is due to the fact that in these two diseases, retinal ganglion cells are also damaged and therefore no longer respond effectively to electrical stimulation. Functional retinal ganglion cells are necessary in order for our retinal prosthesis to work. In retinitis pigmentosa and age related macular degeneration, a significant proportion of ganglion cells remain functional and thus can be potentially activated through electrical stimulation.
Useful links regarding eye conditions:
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