Sensitivity deficits consistent with aberrant crossed visual pathways in human al-binos

Surv Ophthalmol

290

26(5) March-April

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OPHTHALMOLOGY

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study. STEVEN G. KRAMER

Sensitivity Deficits Consistent With Aberrant Crossed Visual Pathways in Human Albinos, by R. St. John and B. Timney. Invest Ophthalmol Es Sci 21:873-877, 1981 An abnormal ism.

Instead

organization

of the neuroanatomical

of remaining

ipsilateral,

decussate at the optic chiasm and project tation of decussating fibers is accompanied abnormalities

within

the visual

connections

a proportion

to the contralatcral by disruptions

cortex.

There

of the visual

of ganglion-cell

is both

axons

pathways

that

is associated

originate

Measurements fields,

were made

for the central, but there

their contrast higher from

anatomical

however,

showed

depression region

fields

in all subjects.

temporal

retinas.

and

clcctrophysiological

no differences

between

to classify central,

for the temporal

to the aberrant

subjects,

contrast

was a wide variation

to the origin

it was possible

in sensitivity

corresponding

For seven

There

for a loss corresponding

functions,

sensitivity,

a marked

the retinal

and

was no evidence

sensitivity

overall

showed

of visual

nasal,

albinretina

lateral gcniculate nucleus (LGN). The overreprcscnof the laminar structure of the LGN and by functional cvidcncc

albinos have abnormally crossed visual pathways. The present study examined some perceptual such pathways on the visual abilities of 12 oculocutancous albinos and one ocular albino. obtained

with

in the temporal

pathway

of the aberrant

nasal,

and

projections.

temporal that

(Abstract

of wcrc

of the visual On the basis

One group,

retina.

in some

human

functions

into two groups.

indicating

is degraded.

sensitivity

in the dimensions

the albinos

retina,

that

consequcnccs

The

other

albinos,

of

with group

information

by C. Hoyt)

Comment Albino

mammals

ganglion

cell axons

disruption

of its normal

Himalayan

rabbits,

electrophysiologic Data

have cross

from

laminar

hamsters and

work

scrambled

visual

in the chiasm structure.

in Siamese

cats

show

stimulated

cortical

in which

in man that

input

a proportion

in the contralateral studies

cats have revealed

evidence

principal ways. In one group ofsiamese a reordering of geniculostriate output monocularly

Anatomic

and Siamese

anatomic

pathways

to terminate

in albino similar

demonstrates from

such

of normally

lateral ferrets,

geniculate

mice,

aberrantly-crossing

similar aberrant

uncrossed nucleus,

rats, guinea visual

temporal producing

pigs, mink, pathways.

a

tigers,

Previous

findings. pathways

cats, the disordered input is suppressed, at the cortical level. In either case,

can be handled

in one of two

while in the second group, there is the result is a prcpondcrance of

cells.

St. John and Timney’s paper provides pathway in human albinos is functionally,

further psychophysical as well as anatomically,

evidence to support abnormal. Though

the proposition they properly

that the visual caution against

extending their conclusions too far, it would seem that human albinos may handle disordered geniculate input in a fashion similar to the two major groupings defined in Siamese cats. One group of their patients showed a decrease in contrast sensitivity in the nasal field, suggesting partial suppression ofthe temporal retina output. A corresponding field defect was not found, though one wonders what static pcrimctry would show. The data in human albinos suggests a practical application. Given the evidence for a congenitally aberrant visual pathway with its resultant lack of binocularly stimulated cortical cells, we would cxpcct poor fusional capacity in strabismic albinos after surgical correction. W. T. SC:HL’t.TS