Improvement of Eye Alignment in Adult Strabismic Monkeys by Sustained IGF-1 Treatment.
OBJECTIVE
The goal of this study was to determine if continuous application of insulin-like growth factor-1 (IGF-1) could improve eye alignment of adult strabismic nonhuman primates and to assess possible mechanisms of effect.


METHODS
A continuous release pellet of IGF-1 was placed on one medial rectus muscle in two adult nonhuman primates (M1, M2) rendered exotropic by the alternating monocular occlusion method during the first months of life. Eye alignment and eye movements were recorded for 3 months, after which M1 was euthanized, and the lateral and medial rectus muscles were removed for morphometric analysis of fiber size, nerve, and neuromuscular density.


RESULTS
Monkey 1 showed a 40% reduction in strabismus angle, a reduction of exotropia of approximately 11° to 14° after 3 months. Monkey 2 showed a 15% improvement, with a reduction of its exotropia by approximately 3°. The treated medial rectus muscle of M1 showed increased mean myofiber cross-sectional areas. Increases in myofiber size also were seen in the contralateral medial rectus and lateral rectus muscles. Similarly, nerve density increased in the contralateral medial rectus and yoked lateral rectus.


CONCLUSIONS
This study demonstrates that in adult nonhuman primates with a sensory-induced exotropia in infancy, continuous IGF-1 treatment improves eye alignment, resulting in muscle fiber enlargement and altered innervational density that includes the untreated muscles. This supports the view that there is sufficient plasticity in the adult ocular motor system to allow continuous IGF-1 treatment over months to produce improvement in eye alignment in early-onset strabismus.
Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States 2Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States.
Linda K
LK
McLoon
Departments of Ophthalmology and Pediatrics, Boston University School of Medicine, Boston, Massachusetts, United States.
Stephen P
SP
Christiansen
Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States.
Geoffrey M
GM
Ghose
College of Optometry, University of Houston, Houston, Texas, United States.
Vallabh E
VE
Das
Washington National Primate Center and Department of Ophthalmology, University of Washington, Seattle, Washington, United States.
Michael J
MJ
Mustari
D000818:Animals; D003692:Delayed-Action Preparations; D004195:Disease Models, Animal; D005133:Eye Movements / Q000187:drug effects*; D005500:Follow-Up Studies; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008253:Macaca mulatta; D009801:Oculomotor Muscles / Q000187:drug effects / Q000503:physiopathology*; D013285:Strabismus / Q000188:drug therapy* / Q000503:physiopathology; D016896:Treatment Outcome; D015348:Vision, Binocular / Q000502:physiology*
D003692:Delayed-Action Preparations; D007334:Insulin-Like Growth Factor I