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Byung Soo Jeremy Kang, Li Ke Wang, Yong-Ping Zheng, Chea-Su Kee; Reduced corneal stiffness under IOP-controlled conditions in form-deprived highly myopic chicks. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5710.
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© ARVO (1962-2015); The Authors (2016-present)
Form-deprived myopic eye was found to exhibit reduced corneal stiffness (CS) in chicks. However, it is unclear whether this reduced CS was due to altered intraocular pressure (IOP). This study aimed to determine the effects of high myopia on CS under controlled IOP in chicks
High myopia was induced in chicks (n=23) monocularly by wearing diffuser from 5 days of age for a week (P5-P12); an age-matched controlled group (n=11) received no treatment. At P12, after the refractive status (Spherical equivalent, SE) was measured by a modified Hartinger refractometer under anesthesia, the birds were sacrificed for CS measurement. To monitor and control IOP, a needle connecting to a manometer and a pressure transducer was inserted into the vitreous chamber. Three sets of CS was measured by using a custom-made air-jet optical coherent tomography (OCT) for each of the two IOP levels: 0mmHg or 5mmHg. For each CS measurement, the data of corneal deformation (in mm) in response to 5 cycles of ascending-descending air pressures (N) were recorded and analyzed by a custom MATLAB algorithm. CS was expressed as the slope of load-deformation curve (N/mm). All parameters were expressed as mean±SEM
Both treatment (treated eyes vs. fellow control eyes) and IOP (0mmHg vs. 5mmHg) had significant effects on CS (Two-way ANOVA, both p<0.001). Compared to fellow untreated eyes, the form-deprived eyes in the treated group developed high myopia (SE= -24.56 ± 1.40D vs. -1.41 ± 0.32D; paired t-test, p<0.001) and reduced CS at both IOP levels (0mmHg: 0.0188 ± 0.001 N/mm vs. 0.0236 ± 0.001 N/mm; 5mmHg: 0.0171 ± 0.0008 N/mm vs. 0.0254 ± 0.002 N/mm; paired t-test, both p<0.01). No significant differences were found between the fellow untreated eyes of the treated group and the right and left eyes of the control group (One-way ANOVA, p>0.393). When data from both eyes of treated birds were combined, CS was significantly correlated with SE (IOP0: r= +0.449, IOP5: r= +0.449, p<0.01) and J0 astigmatic component (IOP5: r= -0.314, p<0.05)
Highly myopic eyes showed notable reduction in CS even when CS was measured under IOP-controlled conditions. These results strengthen the hypothesis that structural remodeling during myopia progression might involve not only the scleral but also corneal tissue, leading to a weakened CS. Further investigations on the origin/s of these corneal biomechanical changes are needed
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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