CPS Seminar Speaker David Williams SEA 4.244

Contact Name: 
Jenna Whitney
Date: 
Apr 14, 2008 12:00pm - 1:00pm

Speaker/Affiliation: David R. Williams Ph.D. Pro

fessor Brain & Cognitive Sciences Optics Ophthalmology & Biomedical Eng

ineering Director Center for Visual Science University of Rochester
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br>When/Location: 4/14/2008 12:00 PM SEA 4.244

Host: Mary Hayhoe
Title of Talk: ''Imaging Retinal Mosaics in the Living Eye''

R

eception with Refreshments at 11:30 AM

Abstract: The ability to imag

e the human retina in vivo at a microscopic spatial scale allows the non-in

vasive investigation of the organization of retinal neurons in subjects who

se visual performance can be measured with psychophysical methods. The chal

lenges of imaging mosaics of cells in the living retina include the require

ment to irradiate the retina with safe levels of light and the fact that th

e light signal returning from even the most reflective mosaic of cells the
cones is roughly 10 000 times less than the retinal illumination. These l

imitations are exacerbated by the high magnification required to resolve si

ngle cells and encourage the use of long exposures to harvest every photon

trickling back out of the eye. Eye movements complicate this strategy caus

ing motion blur in images taken with exposures longer than a few millisecon

ds. Finally large aberrations in the cornea and lens of the normal eye usu

ally preclude imaging cellular features with conventional imaging methods.

This talk will describe a combination of technologies that can overcome the

se formidable limitations. The development of adaptive optics for the eye m

akes it possible to correct essentially all of the eye%92s monochromatic ab

errations providing diffraction-limited images of retinal mosaics in vivo.
Adaptive optics has spurred the development of methods to track retinal po

sition with sub-cellular accuracy allowing the integration of long light e

xposures despite fixational eye movements. The initial application of adapt

ive optics focused on imaging the cone mosaic providing the first images o

f all three cone classes responsible for human color vision as well as the

direct observation of the consequences for the cone mosaic of a host of gen

etic mutations. It is now possible to image the mosaic of retinal pigment e

pithelial (RPE) cells that lies behind the photoreceptors and is critically
important in the regeneration of the photopigment upon which vision depend

s. RPE cells also service photoreceptors by sequestering lipofuscin a toxi

c material that would otherwise kill photoreceptors. An adaptive optics sca

nning laser ophthalmoscope designed to image lipofuscin autofluorescence ca

n resolve the mosaic of RPE cells which may help track the progression of

age-related macular degeneration as well as the efficacy of therapy for thi

s increasingly prevalent disease. More superficial layers in the retina th

an the cones have been more difficult to image due to their obligate transp

arency. Nonetheless fluorescent labeling methods including the retrograde

transport of rhodamine dextran injected into the LGN and intravitreal injec

tions of AAV designed to cause retinal cells to express GFP now make it pos

sible to imaging individual ganglion cells in living monkey eyes including
subcellular structures such as axons and dendrites. These methods may have
important applications in the study of glaucoma which causes ganglion cel

l death. They may also eventually lead to the ability to optically monitor

or control the neural responses of hundreds of retinal neurons simultaneous

ly which could clarify the roles of dozens of morphologically distinct ret

inal neurons whose function is currently unknown.