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Linda K. McLoon, Christy L. Willoughby, Stephen P. Christiansen, Vallabh E. Das, Michael J. Mustari; Sustained IGF-I Treatment Improves Eye Alignment in Adult Strabismic Monkeys. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6341.
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© ARVO (1962-2015); The Authors (2016-present)
To test the potential efficacy of sustained release insulin-like growth factor-I on eye alignment in adult strabismic monkeys.
Two adult strabismic monkeys with sensory induced exotropia [monkey GL -13degrees (OD) and 20 degrees (OS); monkey SJ 25degrees bilaterally] caused by alternating monocular occlusion treatment in infancy, were treated with a single sustained release pellet of insulin-like growth factor-I (IGF-I). The pellets were implanted in the connective sheath around a single medial rectus muscle (MR), and they released a dose of 1 microgram per day for up to 90 days. Eye position and smooth pursuit was assessed in each monkey before and during the course of IGF-I treatment. One monkey was euthanized at the end of 3 months to examine the extraocular muscles for morphometric and/or innervation density changes.
Both monkeys showed an improvement in their eye position after 3 months of sustained IGF-I treatment. Monkey SJ had a reduction in his exotropia from 25 degrees to 19 degrees (OD) and 15 degrees (OS). Monkey GL had a reduction in his exotropia from 20 to 17 degrees (OD) and 13 to 10 degrees (OS). The basis for the difference in effectiveness between the two treated monkeys is unclear. The treated MR muscles had increased mean myofiber cross-sectional areas compared to untreated control monkeys. Both the treated MR and the contralateral MR had 4-6 fold increase in density of nerve bundles compared to untreated control adult monkey MR.
This is the first demonstration of improved eye misalignment after sustained IGF-I treatment in adult strabismic primates. It is very interesting that sustained IGF-I release reduced the angle of deviation in the adult monkeys, despite the prolonged presence of the strabismus. Future studies will focus on increasing IGF-I dosing and duration of treatment to determine if we can further reduce misalignment as well as maintain the improved eye position after treatment has ended.
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