Also known as retinal prostheses, retinal implants are a type of technology meant to help restore sight for patients suffering from partial vision loss or blindness caused by retinal degeneration. Developments and clinical trials are still ongoing for this method, and it still has a long way to go before the public can consider it as a foolproof solution to blindness.
Nevertheless, the latest generation of retinal implants has revealed remarkable promise in tests involving a handful of blind patients. The surgical procedure involves implanting microchip electrodes and microelectronics that will help restore the function of damaged photoreceptors or the light-activated cells in the retina. It helps patients recognize objects and obstacles. Researchers also aim at treating degenerative diseases such as age-related macular degeneration and retinitis pigmentosa using this procedure.
Types Of Retinal Implants
There are two main types of retinal implants by placement. Subretinal implants are installed between the retinal pigment epithelium and the outer retinal layer. While epiretinal implants are placed inside the surface of the retina.
- Subretinal implants – The core of a subretinal implant is a microchip about 0.1 mm in thickness and 3mm by 3 mm in size. It contains around 1,500 light-sensitive photodiodes, electrodes, and amplifiers that generate pixels. An external power supply is connected to the microchip through a line that is implanted subdermally. This energy source amplifies electrical signals produced by the light on the implant, providing enough stimulation for retinal neurons.
In one clinical testing, patients with subretinal implants were able to distinguish horizontal from vertical objects and were able to use normal eye movements as they shifted their gaze. Overall, the subjects were happy that they could see light again and regarded the experiment as an encouraging experience.
- Epiretinal implants – Unlike the device we mentioned earlier, epiretinal implants directly stimulate the retinal ganglion cells, bypassing all other retinal layers. In principle, these could provide better visual perception even if all other retinal layers are damaged.
The disadvantage is that they rely on an external camera to capture visual information. Therefore, patients will not be able to move their eyes naturally and are supposed to scan the visual field with their head. In one clinical trial by ARGUS, a company producing epiretinal implants, patients were reported to gain a perception of light and improve visual perception over time.
Candidates
The best candidates for these devices are those with retinal diseases that cause blindness. Patients must have an intact ganglion cell layer to pass as a subject. The assessment procedure is typically non-invasive, with the use of optical coherence tomography imaging. Other factors to consider are the overall health, residual vision, and family commitment to the rehabilitation of the patient.
In the last two decades, we’ve seen several advancements in visual prostheses that provided encouraging results. Retinal implants, particularly, are showing great potential in stimulating neurons to restore sight. In the next couple of years, we can look forward to something that could potentially give all blind people a second lease on sight.
