Longitudinal Evaluation of Eye Misalignment and Eye Movements Following Surgical Correction of Strabismus in Monkeys.
OBJECTIVE
Strabismus correction surgery is well documented in both the literature and practice with varying levels of success and permanence. Our goal was to characterize longitudinal changes in eye alignment and eye movements following strabismus correction surgery in a monkey model for developmental strabismus.


METHODS
We studied two juvenile rhesus monkeys with exotropia previously induced via an optical prism-rearing paradigm in infancy. Eye misalignment was corrected via a resection-recession surgery of the horizontal rectus muscles of one eye. Binocular search coils were used to collect eye movement data during smooth-pursuit, saccades, and fixation tasks before surgical treatment, immediately after surgery, and through 6 months after treatment.


RESULTS
Both animals showed an immediate ∼70% reduction in misalignment as a consequence of surgery that regressed to a 20%-40% improvement by 6 months after treatment. Significant changes were observed in saccade and smooth-pursuit gain of the nonviewing eye after surgery, which also reverted to presurgical values by 6 months. A temporary improvement in fixation stability of the nonviewing eye was observed after surgery; naso-temporal (N/T) asymmetry of monocular smooth-pursuit remained unchanged.


CONCLUSIONS
Surgical realignment is followed by plastic changes that often lead to reversal of surgery effects. Immediate improvement in misalignment and changes in eye movement gains are likely a result of contractility changes at the level of the extraocular muscle, whereas longer-term effects are likely a combination of neural and muscle adaptation.
College of Optometry, University of Houston, Houston, Texas, United States.
Mythri
M
Pullela
College of Optometry, University of Houston, Houston, Texas, United States.
Brittany A
BA
Degler
Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, United States.
David K
DK
Coats
College of Optometry, University of Houston, Houston, Texas, United States.
Vallabh E
VE
Das
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D004195:Disease Models, Animal; D005133:Eye Movements / Q000502:physiology*; D005500:Follow-Up Studies; D008253:Macaca mulatta; D009801:Oculomotor Muscles / Q000503:physiopathology* / Q000601:surgery; D013508:Ophthalmologic Surgical Procedures / Q000379:methods*; D011184:Postoperative Period; D013285:Strabismus / Q000503:physiopathology* / Q000601:surgery; D013997:Time Factors