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Byung Soo Kang, Li Ke Wang, Yong-Ping Zheng, Chea-su Kee; Form-deprived highly myopic chick eyes have lower than normal corneal stiffness than emmetropic eyes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2158.
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This study aimed to determine whether corneal stiffness differed between normal and highly myopic eyes in the chick model of myopia
Starting from day 5 post-hatching, the right eyes of 21 chicks (Gallus Gallus Domesticus) were covered with a translucent occluder for 7 days to induce form-deprived myopia. At the end of the treatment period, spherical equivalent (SE) refractive error was measured under anesthesia (1.5% Isoflurane) by Hartinger coincidence refractometry, and in-situ corneal stiffness (CS) was measured using a custom-made air-jet optical coherent tomography (OCT) system. Specifically, triplicate CS measurements were obtained, with corneal deformation (in mm) assessed in response to 5 cycles of increasing/decreasing air pressure (in N). A custom algorithm calculated the slope of CS load-deformation curve (N/mm) and the correlation between these parameters
Compared to fellow untreated eyes, form-deprived eyes developed significant myopia (mean±SEM: SE= -20.65 ± 1.41D vs. -1.22 ± 0.26D; paired t-test, p<0.001) and exhibited reduced corneal stiffness (mean±SEM: CS= 0.0203 ± 0.0008mm vs. 0.0239 ± 0.0009mm; paired t-test, p<0.05). When data from both eyes were used for correlation analyses, both SE (r=+0.462, p<0.002) and J45 astigmatic component (r=+0.351, p<0.05) were moderately correlated with corneal stiffness. Expressing the corneal stiffness as percentage of interocular difference in CS [100 %*( treated eye - fellow eye) / fellow eye], we found that in the 17 birds that showed a reduction in corneal stiffness in the treated eyes (range= -0.35% ~ -46.65%), eleven (64.7 %) of them had at least 15% reduction in corneal stiffness (mean= -24.46%, one-sample t-test, T= -4.57, p<0.01)
Form deprivation induced high myopia and reduced corneal stiffness. The correlation between SE and CS indicates that the changes occurring in the biomechanical properties of the cornea may be quantitatively related to those occurring in the sclera
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