Retinal implants restore useful vision

Retinal implants represent considerable progress in the treatment of inherited blindness. At present, several research groups around the world are working towards restoring sight to blind patients. One encouraging approach comes from German-based company Retina Implant, whose first clinical trial of a batterypowered subretinal implant has shown that previously blind patients can recognise objects and even read letters to form words for the first time in decades. Retinitis pigmentosa (RP) is one of the most common forms of inherited retinal degeneration. First appearing in childhood, RP damages the patient’s photoreceptor cells, causing their sight to worsen gradually over time. At present, there is no accepted treatment to cure or even slow the effects of this disease. However, retinal implants now offer hope for improvement in this condition.

Prevalence of retinitis pigmentosa

Retinitis pigmentosa is a hereditary degenerative condition that affects around one person in every 3,000-4,000 in the Western world. It is one of the leading causes of progressive sight loss, with symptoms appearing in early childhood and increasing in severity over time. At first a patient may notice the deterioration of peripheral and night vision, with most becoming legally blind by the age of 40. In an undamaged eye, the fundus is made up of millions of rods and cones through which light passes. The light is converted through several stages into electronic signals, which then pass to the ganglion cells and communicate with the optic nerve. This information is passed to the visual cortex of the brain where the image is constructed. A distinguishable characteristic of diseases such as RP is that the function of the eye remains intact – it is the rods and cones that are affected. Currently, the pharmaceutical industry is investigating various approaches to slow progression of the disease, but all require years of further clinical study. Furthermore, none are expected to restore vision to late-stage RP patients. The most recent and promising advance in sight restoration for RP patients involves the use of retinal implants. Currently, there are two main approaches: subretinal and epiretinal.