Saccades in the absence of binocular vision

The mechanism of suppression in strabismus is unclear and contribution of the suppressing eye to the generation of eye movements has received little attention. A
series of nine experiments tested how the strabismic eye contributes to saccade generation in the presence of suppression and also considered the effect of the strabismic eye in the presence of abnormal retinal correspondence (ARC). These data were compared with data from subjects with normal binocular single vision (BSV).
Chapters 2 and 3 describe the equipment,
laboratory set-up and testing of the equipment
used
in the thesis
for measuring eye movements, Skalar IRIS 6500 infrared limbal
tracker, and presenting stimuli
to each eye separately. The design of a novel method
for
dissociation of the eyes using
four liquid
crystal polymer shutters
is presented.
Chapter 4 compares
the characteristics of saccades made by subjects with normal BSV
(n=5) and strabismus
(n=8). The effect of distractors on saccades
is explored
in Chapter
5 in
subjects with normal BSV (n=5). The experiment documents the distractor
effect
produced
in the described laboratory set-up, and compares
it with that previously
reported
by Walker et al
(1997). This is investigated further by comparing the effect of
distractor presentations
to the dominant eye, non-dominant eye or both
eyes. There was
no difference in the effect on saccade
latency or gain with distractors
presented to the
dominant or non-dominant eye. The effect of binocular distractors on saccade gain was
greater
than monocular presentations.
Chapter 6
repeats
the experiment of Chapter 5 in
subjects with constant strabismus and
suppression
(n=6) and constant strabismus with ARC (n=2) and
found that distractors in
the strabismic eye did affect saccades however the
response differed from normal BSV.
This was
true even
though
it was shown that the distractor was not perceived by the
strabismic eye.
Chapter 7 investigates the influence of the central
fixation
target in the strabismic eye
on saccade generation by inducing disconjugate
saccade adaptation
in
subjects with
normal BSV (n=8) and constant strabismus and suppression
(n=6). The findings were
that
in the presence of suppression, disconjugate adaptation similar
to that in normal
BSV was possible.
The conclusion of
this thesis
is to suggest that information from the suppressed eye
is
available
to the saccadic system by either a sub-cortical pathway or processed cortically
without conscious awareness.