Researchers face numerous
challenges in developing retinal prosthetic devices that are effective,
safe, and durable enough to last for the lifetime of the individual.
The device must be
biocompatible with delicate eye tissue, yet tough enough to withstand
the corrosive effect of the salty environment. Moreover, it should
remain stably tacked to a precise area of the retina and not overly
compress or pull at the tissue, whose resilience can be compared
to that of a wet Kleenex®. The apparatus also needs to be
powered at a high enough level to stimulate electrodes, yet not
generate enough heat to damage the remaining functional retina.
Additionally, image processing needs to be performed in real time
so there is no delay in interpreting an object in view. Development
of effective surgical approaches are also critically important
to ensure a successful implant.
Three Artificial Retina
Project devices are now in testing or development. Engineering
goals include enhancing the resolution
(increasing the number of electrodes and thus the number of dots
produced) and decreasing the size of the device and complexity
of the surgical procedure.
Model 1
(Argus I)
The Model 1 device
[developed by Second Sight Medical Products, Inc. (SSMP)] was
implanted in six patients between 2002 and 2004, whose ages ranged
from 56 to 77 at time of implant and all of whom have retinitis
pigmentosa. The device consists of a 16-electrode array in a one-inch
package that allows the implanted electronics to wirelessly communicate
with a camera mounted on a pair of glasses. It is powered by a
battery pack worn on a belt. This implant now enables patients
to detect when lights are on or off, describe an object’s
motion, count individual items, and locate objects in their environ-ment.
To evaluate the long-term effects of the retinal implant, five
devices have been approved for home use.
Model 2 (Argus
II)
The smaller, more
compact Model 2 retinal prosthesis (developed by SSMP with DOE
contributions) is currently undergoing clinical
trials to evaluate its safety and utility. This model is much
smaller, contains 60 electrodes, and surgical implant time has
been reduced from the 6 hours required for Model 1 to 2 hours.
Model 3
The Model 3 device,
which will have more than 200 electrodes, is undergoing design
and fabrication studies at the DOE national laboratories. This
device will use more advanced materials than those in the two
previous models. A special coating, only a few microns thick,
will replace the bulky sealed package used in the other models.
Additionally, the new model will be constructed of flexible materials
that conform to the shape of the inner eye and will be many times
smaller than earlier models.
The ultimate goal
for the prosthetic device is to create a lasting device that will
enable facial recognition and the ability to read large print.