Wednesday September 10, 2003
Researchers at the University of Newcastle are at the forefront of international research into ways that new technology can be applied to restore sight to the blind.
By using a tiny electronic circuit to deliver controlled, electronic stimulation to the surviving nerve cells of the retina in patients suffering from degenerative blindness, the team hope to replace some of the physiological events that take place on a normal, healthy retina.
In many cases of degenerative diseases of the retina such age-related macular degeneration and retinitis pigmentosa, not all of the nerve cells on the retina are destroyed despite the retina as a whole becoming dysfunctional. In a normal, functional eye, a spot of light hitting the retina triggers a cascade of physiological events, but in an eye affected by diseases such as these, this train of events is interrupted and the electrochemical signal to the brain is not initiated. Despite this the pathway and mechanism for delivering the electrochemical signal remains in tact according to Gregg Suaning from the University of Newcastle - "The electrochemical signal is capable of being initiated through artificial (electronic) stimulation. By delivering a controlled, localised, electronic pulse to the appropriate nerve cells, the electrochemical signal described above can be "kick started", thus replacing the 'cascade of physiological events' that initiates the signal in a normal eye."
The brain is likely to interpret this signal as if it were a spot of light on the retina because the signal is the same irrespective of the way in which it is initiated.
Work on the "100 Channel Vision Prosthesis Circuit" began in 1997 and the team have designed all of the electronics necessary to build and test the device including a complex chip capable of delivering highly controlled electronic impulses to 100 individual sites on the retina.
The wireless radio transmission system that transfers power and data across the eye tissue and the external electronics are all in place, and tests in sheep have shown that the device is able to create brain activity that is consistent with vision. The next step is to implant the device in a human patient who can then provide the best kind of feedback by telling the researchers what they see. This procedure is currently in planning and approval from regulatory panels is being sought but there is no definite answer as to when the technology may be ready for use.
The implant itself will constructed of a form of ceramic so that the electronic circuits are protected in the corrosive, salty environment of the eye and further research is being undertaken on the "best" method of interfacing the stimulator to the surviving nerve cells.
As the most complex of our senses, the human vision system cannot be replicated using a 100 channel implant but even an approximation of normal sight can bring enormous benefits - night and day can be differentiated so that the body clock may be synchronised to the 24 hour day, detection of movement and obstacles is enhanced to aide in mobility and recent studies have shown that reading speeds of up to 70 words per minute may be achieved by viewing in a 10x10 grid format.
A similar project in the US has seen Sandia National Laboratories release a prototype "eye-chip" that receives data from a tiny camera lodged in the frame of the patient's glasses. The device aims to produce 1000 points of light (compared with millions in the biological eye) delivering a yellowish image that is slow to form but nonetheless a vast improvement on complete blindness.
Part of an ambitious project involving several US national labs and Universities, this project also targets blindness caused by degenerative diseases where neural paths to the brain are left intact.Share
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