Sunday 9 February 2014

Retinal Prosthesis Argus® II

 Image provided by Dr. Wentai Liu 
 What Argus® II is?

A retinal prosthesis is a biomedical implant intended to partially restore useful vision to people who have lost their sight 

due to a degenerative retinal disease such as retinitis pigmentosa (RP) that severely damages the photoreceptors in the eye. 

The sourse of picture

How does it work?

Argus II bypasses the damaged photoreceptors altogether. A miniature video camera housed in the patient’s glasses captures a scene. The video is sent to a small patient-worn  computer (i.e., the video processing unit – VPU) where it is processed and transformed into instructions that are sent back to the glasses via a cable. These instructions are transmitted wirelessly to an antenna in the implant. The signals are then sent to the electrode array, which emits small pulses of electricity. These pulses bypass the damaged photoreceptors and stimulate the retina’s remaining cells, which transmit the visual information along the optic nerve to the brain, creating the perception of patterns of light. Patients learn to interpret these visual patterns.

What kind of sight loss for?

Argus II currently provides some useful vision to patients with severe to profound vision loss due to outer retinal degeneration, such as retinitis pigmentosa (RP) .

What patient can see?

Argus II provides “somewhat pixelized” vision composed of spots of light which, in an ideal case, cover the central 20° visual field. This can be compared to a 30 cm ruler held out at arm’s length.
Some patients are able to easily discern forms, identify large written characters, and locate light sources, while others are not able to interpret spatial information about the visual scene with their system. In the study, patients were consistently better at performing orientation and mobility tasks using Argus II. 

As of March 2014 in commercial use and clinical trials, the Argus II system has been implanted into over 80 people (Fernandes RA et al). The best result achieved by the device was a visual acuity of 20/1260. Just to compare, the blindness is defined as greater than 20/500 by the World Health Organization.

Where is it approved?

Argus II is approved for use in the European Economic Area (CE Mark) in 2011. Since February 2013 also is approved in USA by FDA: statement 

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