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Andrew David Pucker, Ashley R Jackson, Kirk M McHugh, Donald O Mutti; Morphological Ciliary Muscle Changes Associated with Form Deprivation Myopia in the Guinea Pig. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4436.
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Myopic subjects are known to have larger posterior ciliary muscle than non-myopic subjects, though the field currently lacks an animal model for studying this relationship. The purpose of this study was to investigate whether form deprivation-induced myopia in guinea pigs results in morphological changes in the ciliary muscle similar to the thickening seen in human myopia.
Nineteen guinea pigs were bred from in house progenitors obtained from Cincinnati Children’s Hospital (unknown strain) and the United States Army (Strain 13). At 2-3 days of age the right eyes of animals were treated with translucent occluders for 7 days while the left eyes served as controls. Refractive error and vitreous chamber depth (VCD) measurements were determined with retinoscopy and A-scan ultrasonography, respectively. Ciliary muscle dimensions were determined histologically by fluorescently labeling smooth muscle cells (anti-α-smooth muscle actin conjugated with FITC) and cell nuclei (Draq5) and quantitatively analyzing ciliary muscle characteristics with Stereo Investigator (MBF Bioscience). Animals were considered responsive to treatment if they had anisometropia > -2.00 D and VCD differences > 0.1 mm.
Eight responsive animals (4 of each strain) were obtained and analyzed. On average responsive animals had (mean ± SD of right minus left eyes; 95% confidence interval) ciliary muscle lengths (720.24 ± 98.92 μm vs. 753.61 ± 91.37 μm; 47.30, -114.04), cross-sectional areas (0.045 ± 0.01 mm2 vs. 0.052 ± 0.02 mm2; 0.001, -0.016), cell numbers (185.63 ± 43.05 cells vs. 213.41 ± 77.60 cells; 16.05, -71.61), and cell sizes (244.02 ± 22.83 μm2/cell vs. 250.23 ± 23.77 μm2/cell; 17.95, -30.36) that were smaller in the treated eyes compared to the control eyes. The unresponsive animals had no clear growth trends for any ciliary muscle measurement (all confidence intervals included zero).
This study found no evidence that form deprivation-induced myopia resulted in ciliary muscle hypertrophy even though form deprivation resulted in longer, myopic eyes. While additional animals are needed to fully investigate if a relationship truly exists, the results of this study suggest that induced myopia does not promote, and may actually inhibit, ciliary muscle growth, opposite in direction to that seen in human juvenile myopia.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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