Restoring a functional level of vision to people who are blind has been a dream of medicine for centuries. Although we are still far from restoration of high-resolution vision, bionic eye technologies are overcoming crucial bottlenecks and are slowly moving from the laboratory into the clinic and onto the free market.

Causes of Vision Loss

Vision loss can occur in a number of ways. The main focus of retinal prosthetic research is to improve functional vision for people with blindness and/or vision impairment from the result of hereditary diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD).

Disclaimer: The following is for informational purposes only. If you think you are subject to one of the conditions described below, please consult with your care provider.

Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the most common form of inherited blindness that affects 1 in every 3000 – 7000. RP is the result of a change in a gene or genes that would typically lead to functioning photoreceptors, but instead create smaller photoreceptors with a disorderly arrangement. RP develops over a longer period of time compared to other vision diseases, sometimes spanning a person's entire life. Symptoms for RP usually include peripheral vision field loss (also known as "tunnel vision") and night blindness. Currently, there is no known cure for RP.

There are two classifications of RP: syndromic and non-syndromic. Non-syndromic RP is more common than syndromic RP and does not develop with other diseases or disorders. Syndromic RP can occur with other medical conditions or disorders where neurosensory systems other than the eye are affected. People with syndromic RP make up an estimated 20-30% of all RP patients. All RP types are a degradation of the retina caused by genetics, also known as a dystrophy. The rod-cone dystrophy is usually syndromic and involves a loss of cone activation due to relative low rod activation, which present with loss of central vision as well as the usual peripheral vision field loss associated with RP.

RP is associated with a number of different conditions. Usher syndrome, for example, is a combination of RP and deafness and is estimated to contribute to 14% of all RP cases overall. Bardet-Biedl syndrome is a rare genetic disorder that presents with rod-cone dystrophy. Some forms of RP are associated with mitochondrial disorders, such as the Kearns-Sayre syndrome, where the area of the macula is more affected than the periphery.

Devices that may be able to treat RP include Argus II, the suprachoroidal implant, and other retinal implants as well as cortical implants.

Age-Related Macular Degeneration (AMD)

In 2010, there were 2.07 million people with AMD. That number is expected to double to 5.44 million by 2050. As with most health conditions, aging is a significant risk factor for AMD.

The macula is a pigmented circular area located on the back of the eye on the retina. Within the macula is the fovea, an area responsible for processing our central field of view.

There are three factors that are used to characterize the different types of AMD: size of drusen, type of damage caused by progression, and presenting as either “wet” or “dry”. Small yellow deposits of drusen (made of proteins and lipids) can build up in the macula, usually as a sign of Early AMD. Intermediate AMD involves larger size drusen deposits and a change in retinal pigment functioning. While intermediate AMD can cause some vision loss, both early and intermediate AMD are typically present without other symptoms.

Late AMD presents with loss of central vision due to progressive damage to the retina, either as wet AMD or geographic atrophy. Wet AMD, also known as neovascular AMD, is specifically caused by irregular blood vessel growth. These blood vessels can be easily damaged allowing for blood and proteins to spread into the area of the macula. Damage that leads to the degradation of three specific areas of the eye (neighboring photoreceptors, retinal pigment epithelium, and the choriocapillaris) is referred to as geographic atrophy. Further research into how AMD can affect the different layers of the retina is needed to better understand the physiology of geographic atrophy.

Dry AMD includes any type of AMD that is not neovascular or wet. Dry AMD has a significantly higher prevalence of all AMD patients (estimated at 80% or more) compared to Wet AMD.

Devices that may be able to treat AMD include PRIMA as well as other retinal and cortical implants.