All ETDs from UAB

Advisory Committee Chair

Claudio Busettini

Advisory Committee Members

Mark O Bevensee

Paul D Gamlin

Paul J May

Thomas T Norton

Document Type

Dissertation

Date of Award

2010

Degree Name by School

Doctor of Philosophy (PhD) School of Optometry

Abstract

Disconjugate movements of the two eyes can either be the result of unequal left-eye and right-eye commands or the sum of binocular conjugate and vergence commands, which symmetrically affect the two eyes in equal and opposite directions, respectively. Of particular relevance is the nature of the intra-saccadic vergence acceleration observed during combined vergence-saccade responses. This effect may be the result of asymmetric left-eye and right-eye saccades or a saccadic-driven acceleration of the vergence signal. The latter is consistent with the OPN Multiply model, in which the saccadic pause of the omnipause neurons (OPNs) elicits the vergence enhancement. We verified, in macaque monkeys, that OPNs also pause for blinks. Surprisingly, the OPNs pause too late to play a trigger role for blinks analogous to their role for saccades. We recorded motoneurons of the orbicularis oculi muscle, which drive blinks, to confirm this. The onset of the transient eye movements that occur with blinks is not saccadic, but the effect of the OPN pause offset on their profiles implies that they have a later saccadic component. This pause quantification was then used to test the influence of the OPNs on vergence by eliciting reflex blinks at different times during the vergence eye movement. The resulting eye movement perturbation was unspecific for convergence vs. divergence, invalidating the OPN Multiply model. The nature of asymmetric saccades was then tested more directly by using the double-step saccadic paradigm, in which visual targets are moved during the saccades to them, producing systematic landing errors. Identical 20% errors presented to both eyes elicited a rapid conjugate change in saccadic gain completed well inside a recording session. Contrary to the monocular view, however, equivalent target jumps applied to only one eye's target, with the other eye's target remaining stationary, produced very little adaptation during a session. Additionally, this adaptation affected both eyes rather than just the eye to which the error was presented. The weak monocular saccadic adaptation appears to be driven by the vergence system. However, this vergence adaptation does not follow any present model, as it never begins prior to the latter half of the saccade.

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