MORE THOUGHTS ABOUT EFFORTS TO DEVELOP RETINAL IMPLANTS/PROSTHESES TO AID THE BLIND

I have previously written on this subject (simply search the site using appropriate terms). My thoughts today after reading an article in the New York Times of October 25 “Plugging Into the Eye, With a New Design” by Anne Eisenberg. I have two thoughts  – one on the topic of how these developments are presented in the popular press and the second technical.

First, it pains me that the piece leaves the sight impaired with the hope that the concept of a retinal implants will ultimately restore their sight. The beautiful figure  of an artificial eyeball shown in the piece certainly gives this impression. The fact is, however, that the best that these devices can do, in the  actuial words of the piece, “Most retinal prostheses seem to function to let people detect light and dark”. This is really what I might expect to result when one inserts something near or behind the retina – something happens! When one considers the problem of coupling of such crude imaging devices to the optic nerve…… a nerve bundle that contains some eight million individual fibers……?

I really do not want to be overly negative about these developmental efforts that are being carried out in many parts of the world. This work is only in the very early stages and, again from the piece, “The eye adapts” may prove to be the operative thought and some improvement in vision may ultimately result.

But……..

The point that I have continually made, that forms the fundamental teaching of this work, is that the eye does not function as a camera, i.e., making the assumption that the retina is located at the intensity-only-sensitive “film” plane of the eye. Coming closer to the pixilated solid state devices that are being developed, the assumption is made that the eye behaves as a digital camera. As far as I can determine this is the principle that underlies all of the retinal prosthesis developments that I have seen.

But this is not the case as I explain. Following from Osterberg’s classic retinal morphology measurements, the retina is seen to be a diffractive surface (implying that it forms the Fourier of focal plane of the eye). Now…we do not currently know how to fabricate the retinal light detection elements (i.e., sensitive to light intensity and phase) but, again from this work, we do now know (exactly!) where light wavelengths interact on the retinal surface. Read to the body of this work, but I refer to the finding that the central fovea is solely sensitive to long wavelength (“red”), 550 nm mid band at 8-9 degrees of retinal eccentricity etc.

Again, we do not yet know how to replicate the light detection devices of the retina, but, it would seem to me that application of this knowledge could lead to prostheses that at least begin to mimic the actual process of vision.

And….I believe that technology is available to actually fabricate in silicon the actual light interactive properties of the retina from the fovea to 20 degrees of retinal eccentricity.

I would, as proposed in the past, like to collaborate with any group in this endeavor.

GCH

Ojai, CA