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Emory University, Atlanta, GA

MICHAEL J. MUSTARI - Primate Testing - 2007

Horizontal Saccade Disconjugacy in Strabismic Monkeys

LaiNgor Fu,1,2   Ronald J. Tusa,1,3  Michael J. Mustari,1,3  and  Vallabh E. Das1,3

1 From the Division of Sensory-Motor Systems, Yerkes National Primate Research Center, and the 3Department of Neurology, Emory University, Atlanta, Georgia; and the 2Retina Foundation of the Southwest, Dallas, Texas.

Subjects and Rearing Paradigms
Behavioral data were collected from four strabismic (AMO1 to AMO4) juvenile rhesus monkeys (Macaca mulatta) and 1 monkey without strabismus. Monkeys with strabismus were born and reared at the Yerkes National Primate Research Center according to an alternate monocular occlusion (AMO) method for the first few months of life designed to induce ocular misalignment but not to affect visual acuity.9,10 In the AMO rearing procedure, soon after birth (within the first 24 hours), an occluding patch (either dark opaque goggle lenses or dark opaque contact lenses) is placed in front of one eye for a period of 24 hours and then switched to the fellow eye for the next 24 hours. The patch is alternated daily for a period of 4 to 6 months. In this method, binocular vision is severely disrupted during the first few months of life, the critical period during which the monkey brain normally develops proper eye alignment, stereovision, and binocular sensitivity.3,11,12 During AMO rearing, contact lens wear was monitored every 2 hours during the day to verify compliance with the rearing protocol.

Surgical Procedures and Eye Movement Measurements
After AMO rearing, the animals were allowed to grow normally until they were approximately 2 to 3 years of age, and then behavioral experiments were begun. Sterile surgical procedures carried out under aseptic conditions with isoflurane anesthesia (1.25%-2.5%) were used to stereotaxically implant a head stabilization post. During the same surgical procedure, a scleral search coil was implanted in one eye according to the technique of Judge et al.17 Later, during second surgery, a second scleral search coil was implanted in the other eye. All procedures were performed in strict compliance with National Institutes of Health guidelines and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research, and the protocols were reviewed and approved by the Institutional Animal Care and Use Committee at Emory University.

PURPOSE. Previous studies have shown that binocular coordination during saccadic eye movement is affected in humans with large strabismus. The purpose of this study was to examine the conjugacy of saccadic eye movements in monkeys with sensory strabismus.

METHODS. The authors recorded binocular eye movements in four strabismic monkeys and one unaffected monkey. Strabismus was induced by first occluding one eye for 24 hours, switching the occluder to the fellow eye for the next 24 hours, and repeating this pattern of daily alternating monocular occlusion for the first 4 to 6 months of life. Horizontal saccades were measured during monocular viewing when the animals were 2 to 3 years of age.

RESULTS. Horizontal saccade testing during monocular viewing showed that the amplitude of saccades in the nonviewing eye was usually different from that in the viewing eye (saccade disconjugacy). The amount of saccade disconjugacy varied among animals as a function of the degree of ocular misalignment as measured in primary gaze. Saccade disconjugacy also increased with eccentric orbital positions of the nonviewing eye. If the saccade disconjugacy was large, there was an immediate postsaccadic drift for less than 200 ms. The control animal showed none of these effects.

CONCLUSIONS. As do humans with large strabismus, strabismic monkey display disconjugate saccadic eye movements. Saccade disconjugacy varies with orbital position and increases as a function of ocular misalignment as measured in primary gaze. This type of sensory-induced strabismus serves as a useful animal model to investigate the neural or mechanical factors responsible for saccade disconjugacy observed in humans with strabismus

Please email:  MICHAEL J. MUSTARI, mjmustar@rmy.emory.edu to protest the inhumane use of animals in this experiment. We would also love to know about your efforts with this cause: saen@saenonline.org

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Rats, mice, birds, amphibians and other animals have been excluded from coverage by the Animal Welfare Act. Therefore research facility reports do not include these animals. As a result of this situation, a blank report, or one with few animals listed, does not mean that a facility has not performed experiments on non-reportable animals. A blank form does mean that the facility in question has not used covered animals (primates, dogs, cats, rabbits, guinea pigs, hamsters, pigs, sheep, goats, etc.). Rats and mice alone are believed to comprise over 90% of the animals used in experimentation. Therefore the majority of animals used at research facilities are not even counted.

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