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Liqin Jiang, Christine Frances Wildsoet; Choroidal Structure and Relation to Responses to Imposed Defocus in Young Guinea Pigs. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1107.
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© ARVO (1962-2015); The Authors (2016-present)
We previously reported on two strains of guinea pigs, Elm Hill (EH) and New Zealand (NZ), which vary in their sensitivity to myopia-inducing stimuli and their choroidal responses to +5 and - 5 D defocusing lenses. Curiously, only EH animals, which were shown to be less sensitive to myopiagenic stimuli (Garcia et al. 2015 ARVO), showed bidirectional choroidal responses after four days of lens wear (Jiang et al. 2016 ARVO). To further explore these strain-dependent differences, we tested lower lens powers in much younger guinea pigs and also examined choroidal structures in more detail.
Eleven day-old pigmented guinea pigs were used (NZ strain, n=8 and EH strain, n=12). Choroidal thickness and refractions were measured using high frequency A-scan ultrasonography and retinoscopy without cycloplegia respectively, both under anesthesia, both at baseline and 1 and 5 days after left eyes were fitted with -2 or +2 D lenses; right eyes wore plano lenses as controls. Choroidal structures were also evaluated using posterior segment SD-OCT (Bioptigen) in age-matched adult guinea pigs.
Young EH guinea pigs have significantly thicker choroid than the NZ animals (NZ vs EH, 11 days old: 125±71 vs. 144±26 μm, p<0.05). After just one day of lens treatment, EH animals showed bidirectional responses (minus: -20.2±0.56 µm, n=5; plus: 6.86±12.05 µm, n=7, p<0.05), while NZ animals showed choroidal thinning with both minus and plus lenses (-6±8.72 vs. -7.75±6.99 µm, n=4 resp.). After four days of lens wear, both NZ and EH showed bidirectional response patterns, although EH animals showed greater choroid thinning than NZ ones with -2 D lenses (EH: -21.6±4.43 µm, n=5; NZ: -8±8.98 µm, n=4, n.s.). OCT images suggest better well-defined choroidal layering in EH compared to NZ animals to (putative Haller’s layer, indicated by stars, and Sattler’s layer, indicated by black arrows).
Chorioidal thickness and structural differences appear linked to differential responses to imposed optical defocus, with thicker choroids showing more capacity to thin, perhaps also contributing to myopiagenic protection.
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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