Pre-
and post-operative characterization of visual function after the removal of
bilateral congenital cataracts in adulthood.
I.
Fine1, .H.S.
Smallman1,2, .P.G. Doyle3, G.M.B. Boynton4*,
D.I.A. MacLeod1
1Psychology,
University of California, San Diego,
La Jolla, CA, USA
2Pacific
Science and Engineering Group, San Diego, CA, USA
3Mathematics,
Dartmouth College, Hanover, NH, USA
4The
Salk Institute for Biological Studies, La Jolla, CA, USA
Key
words: PSYCHOPHYSICS, LEARNING**, PHOTORECEPTOR, CONTRAST
We report the case study of one of the
authors, PD, who had bilateral congenital
cataracts removed at age 43. Pre-operatively PD used atropine to dilate his
pupils, allowing him to see through cataract-free regions at the edge of his pupils.
Unlike previous similar cases,
we were able
psychophysically characterize PD's visual functioning pre-operatively as well
as post-operatively. Pre-operatively, PD's optics severely attenuated spatial
frequencies above 5 cycles/degree, and he experienced
monocular diplopia with high
contrast stimuli. We have documented
several adaptations to a lifetime with limited visual input, and have also found evidence for
post-operative neural plasticity at various stages of visual processing. (1) PD
showed a post-operative shift in his
Stiles-Crawford effect; the alignment of his photoreceptors reoriented phototropically towards the
newly-bright centers of his pupils. (2) Diplopic images in each eye were
suppressed neurally. (3) Pre-operatively,
despite strong attenuation of high spatial
frequencies, PD
showed contrast constancy, or neural "sharpening" of his blurred visual input. As a result, post-operatively PD showed contrast overconstancy, an
"over-sharpening" of his visual input that decreased over time. (4) PD showed crowding effects for identifying Snellen letters (similar to those found in amblyopes)
which did not improve post-operatively.
We compare these and other observations to visual perception in normal adults.
Supported by: NIH-01711 Visual adaptation before and after
the removal of bilateral congenital cataracts in adulthood: contrast constancy
and border perception
Contrast constancy
and edge perception after the removal of congenital cataracts as an adult
((I. Fine1, H.S.
Smallman1,2, D.I.A. MacLeod1))
Dept. of Psychology, University of
California, San Diego, CA, 920931;
Pacific Science and Engineering
Group, San Diego, CA 921222.
((I.
Fine1, H.S. Smallman2,
D.I.A. MacLeod1))
Dept. of Psychology, University of California, San Diego, CA, 920931;
Pacific Science and Engineering Group, 6310 Greenwich Drive, San Diego, CA
92122.
Purpose: We have spent the a last
year studying PD, an observer who had severe bilateral congenital bilateral
cataracts from infancy. We have examined many aspects of
PDs visual processing. Here we
describe the changes in his CSFs, and
their apparent effect on his supra-threshold contrast matching and border perception. Pre-operatively,
PDs poor optics attenuated high spatial
frequencies. After the first surgery, PD noted new Mach-band-like brightness perturbations near high contrast borders
through his newly operated left eye, suggesting that he was over-sharpening the improved retinal image. We tracked his contrast-constancy and his perception of borders post-operatively to see how well
he compensated for his improved optics. We
measured his contrast sensitivity function (CSF) before and after these
cataracts were removed. Before surgery, spatial frequencies above 5 cpd were
strongly attenuated. Postoperatively this attenuation was much less severe. We
have examined many aspects of PDs visual processing - the effects of the
change in his CSF on contrast matching and edge detection will be described
here. Methods: We compared PD and
to normals observers
using two tasks. In the
contrast matching, task
observers were asked to adjusted the contrast of
sinusoidal test gratings varying
in spatial frequency betweenfrom 0.4 tand
o 12 cpd until
their contrast appeared to matched that of
standard gratings at of 20% contrast
with spatial frequencies of 0.47 or 2.36 cpd. In the square wave task, observers were
asked to adjusted the
a randomly-modulated square waveform of
a square wave with aof fundamental
frequency of 1.15 cpd until bright and dark
regions appeared uniform i.e. make a perfect square wave. Results: In the contrast
matching task normal observers showed contrast constancy
their contrast settings did not vary
systematically withwere independent of spatial
frequency. PD did not show contrast constancy - with
gratings with spatial frequencies higher
than 4 cpd he strongly underestimated the contrast of gratings higher in frequency than 4 cpd needed to match
the contrast of the low spatial frequency
standards. In the square wave task PD
underestimated the contrast needed in higher spatial frequency components far
more than normal observers (a blurred square wave seemed perfectly square to
him, a real square
wave had Mach bands). Conclusions:
Post-operatively PD over-estimated the contrast of high spatial frequencies in
both tasks, consistent with failing to fully adapt to his post-operative
optics. We modeled PDs performance, and
found we could roughly model that
his performance on both taskscontrast
constancy and square wave tasks were mutually consistent, and were solely fairly
consistent with the change in his CSF. It appears that PD had developed a mechanism to sharpen his blurry
pre-operative retinal images.
None. Supported by NIH-01711.