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S. A. McFadden, M. Coassin, M. S. Mattson, M. H. Howlett, J. A. Kornfield, D. M. Schwartz; Scleral Strengthening Inhibits Ocular Elongation and Induces an Alternative Response to Form Deprivation Myopia. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1192.
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Scleral biomechanical changes due to extracellular matrix reorganization are thought to be involved in the pathogenesis of progressive myopia. Collagen cross-linking agents can strengthen the sclera but involve UV light which can induce severe toxicity to the retina1. We have developed a non-toxic cross-linking method effective in vitro2 and studied its effect on form-deprivation (FD) myopia in guinea pig eyes.
The sclera of the right eye was treated in 27 guinea pigs at 4-5 days of age with sub-conjunctival injections of Eosin Y in PBS followed by irradiation with green light (2 mW/cm2) for 5 mins. 12 days after surgery, myopia was induced in the right eye with FD for 14 days. Control animals were also given FD, but without any prior surgical treatment. Ocular parameters were measured repeatedly before, during and after the FD period using established methods3. Treated retinas were examined histologically.
Prior to FD, EY treatment and irradiation caused the eye to elongate, primarily due to expansion in the anterior chamber, which was counteracted by an expanding choroid, and therefore very little change in refractive error occurred. Eosin Y treated eyes developed myopia from FD and recovered from this myopia exactly the same as untreated animals. However, surgically-treated eyes achieved these changes in refractive error by unusual means, and inhibited their ocular elongation in response to FD instead of accelerating it, and their vitreous chambers actually shrank. Unable to elongate posteriorly, the EY-treated eyes adopted an alternative response to FD, and instead changed the optics of the eye to support FD myopia and recovery from FD. The retinas of the treated eyes appeared normal in cell type and density.
Treatment of the sclera with Eosin Y and irradiation severely inhibited the excessive ocular elongation characteristic of myopia. Since preliminary findings show no toxic effects on the retina, this method may provide a treatment for severe cases of ocular elongation. When the eye cannot elongate by remodeling of the sclera, it adopts an alternative means to develop and recover from form-deprivation induced myopia.1Wollensak G et al. 2005. Acta Ophthalmol Scand. 83:477-82.2Mattson M. 2008. PhD Thesis. CALTECH, USA.3Howlett MH, McFadden SA. 2005. Vision Res. 46:267-83.
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