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Neural
Prostheses: Vision |
The most basic form of visual prosthesis is a pair of glasses: a machine which makes up for degradation or malformation of the eye. Ophthalmic technology evolution has transformed glasses into machines which, when used, feel more natural. Contact lenses enable the visually-impaired to look and feel like they have perfect vision without a cumbersome frame balancing on their ears and noses. This simulation of perfect vision is almost seamless, except when it is time to go to sleep, and the lenses must be taken out and cleaned, and them put back in the morning.
The next step
in this technological evolution was the creation and implementation of
fully implantable lenses, which actually replace (or in some cases merely
enhance) the old, dysfunctional lenses. The lenses are very small (as seen
compared to a penny) and are put into the eye by a clever surgical procedure.
Take, for example, a patient with cataracts. This means that
there has been a clouding of the lenses (Cataract is a Greek word meaning
"white water falling." Early Greeks thought the blurred vision of a cataract
was like looking through a waterfall). A small opening is made in the sac 
which
holds the eye's diseased natural lens (Figure 1). A chemical is injected
into the opening which dissolves the lens and the remains are vacuumed
out. A special "folding lens" (Figure 2) is put into a needle like tube,
and is injected into the now emptied sac (Figure 3). Within a short amount
of time, vision is restored to the patient, and vision is rendered almost
perfect (glasses may be necessary for reading).
Perhaps the most interesting work in visual prostheses
is in the restoration of vision to the completely blind. This is a procedure
which has not been successfully carried out, but there have been many attempts
to do so, and much research is currently being conducted to tackle this
problem. One researcher, William Dobelle, has worked for many years on
a solution. In Dobelle's version of a artificial eye (Dobelle,
1994), information from sensors in a pair of glasses (light and ultrasonic)
is processed by an on-board computer which is worn on the belt of the user.
Leads from this computer extend along the back and enter the body through
a "pedestal" which perforates the scalp. 
From
the pedestal, wires travel underneath the scalp and end in stimulating
electrodes which penetrate the surface of the visual cortex of the brain.
When the computer sends an electrical impulse to one of these electrodes,
the visual cortex of the brain is stimulated, and the result is the sensation
of a bright light, called a phosphene, which appears somewhere in the blind
eye's normally blackened visual field. If a grid of these electrodes is
strategically implanted and then each electrode is controlled by the computer,
patterns of these phosphenes can convey visual information to the user,
in the same way Light Brights can create visual displays on a black background
(minus the color - at this point anyway!). The patterns are generated according
to what the head-mounted camera "sees", and could be used not to give a
blind person natural eyesight, but to provide low-resolution images which
would help navigate and get around objects such as chairs and other furniture
in unfamiliar territories.
Dobelle points out that this work is the result of twenty years of work, and of the collaboration of hundreds of researchers. At this point, he and his colleagues have actually permanently implanted multiple volunteers with this system. Although Dobelle admits that the technology is not yet good enough, he stresses the value of perseverance as he endeavors to provide artificial vision for the blind.
