A Non-Invasive Approach to the Bionic Eye

Abstract

According to the World Health Organisation definition for blindness, that is, visual acuity bellow 3/60 for the best eye on the Snellen scale, there are thought to be 38 million blind people worldwide (Delbeke et al., 2004). This figure is expected to double over the next 25 years due to combination of an increasing population and aging worldwide. There are additionally 110 million people who have severely impaired vision and are high risk of becoming blind. The most common causes of blindness are: cataract, trachoma, glaucoma, diabetic retinopathy, age related macular degeneration (AMD) and retinitis pigmentosa (RP). In the west countries, cataract and glaucoma make up only 11% of the total causes of blindness. In these regions AMD and RP are prevalent eye diseases. AMD increases dramatically with age, so that (with about 2million cases in the USA) it is the leading cause of blindness among Americans of European descent (Friedman et al., 2004). The AMD and RP result in the loss of photosensitivity primarily due to destruction of the rod and cone photoreceptors. Medical intervention to date has been disappointing. There is no known mechanism by which the eye can self-repair. Anti-angiogenesis drugs can significantly slow down the progression of wet type AMD, but in most cases there is very little treatment. Even more significantly, none of the drugs are capable of restoring lost vision. The idea of using stem cells in therapies is still complex and may be many decades away from potential treatment. Prosthetic implants are therefore the only method at present by which we can offer a return of some of the lost vision. Here we present a special type of vision restoration based on the optical stimulation of retinal ganglion cells (RGCs), which remain operational.

Key Terms in this Chapter

ChannelRhodopsin/Melanopsin: proteins that can make cells light sensitive.

Photoreceptor cells: retina cells that convert light into a change of cell membrane potential.

Retina: a very thin, multilayer network of neural cells at the back of the eyeball of vertebrates.

LED: Light Emitting Diode.

Implant: device made to replace or act as a missing biological structure.

Retinal Ganglion cells: neural cells in the retina which receive the signals from the bipolar and amacrine cells (the cells that process the visual information passed by the photoreceptors) and send action potentials to the brain down axons, which form the optic nerve.

Photosensitization: making neurons light sensitive.