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17 Jun 2002
Thin photosensitive ceramic films could replace damaged photoreceptors in the human eye.
Scientists at the University of Houston's Space Vacuum Epitaxy Center (SVEC), US, have developed ceramic photocells that, when implanted into the human eye, could restore lost vision. These photocells respond to light in much the same way as rods and cones, the natural photoreceptors in the eye.
Alex Ignatiev, who directs the SVEC, explained: "There are some diseases where the sensors in the eye, the rods and cones, have deteriorated but all the wiring is still in place. In such cases, thin-film ceramic sensors could serve as substitutes for bad rods and cones."
Previous attempts to build artificial rods and cones have been unsuccessful. Most of these earlier efforts however have involved silicon-based photodetectors, the problem being that silicon is toxic to the human body and reacts badly with the fluids in the eye. Ignatiev and colleagues believe their ceramic microdetectors will not share this problem.
The individual detectors are grown in a hexagonal array pattern that mimics the arrangement of the rods and cones they are designed to replace. An added advantage of this structure is that nutrients in the eye can flow through and around them, which was not the case in the silicon implant.
Each individual microdetector is 5 µm wide, the size of a human cone cell, and works on a similar principle to standard solar cells. They also have optical activity throughout the visible spectrum implying that full color vision could be restored.
The overall structure, which is only 1 µm thick, consists of approximately 100 000 tiny ceramic detectors. The researchers mount this fragile structure on a 200 micron thick polymer layer before implanting it into the eye. The polymer layer dissolves in about two weeks, leaving the microdetector array intact on the retina.
After 60 successful implantations into rabbits, Ignatiev and colleagues noted no adverse reactions to the animals or within the microdetector array. Human trials based at the University of Texas Health Science Center are expected to begin this year.
Author
Jacqueline Hewett is news reporter on optics.org and Opto & Laser Europe magazine.
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