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Jacob Lewis, Mariana Garcia, Christine Wildsoet; The effect of induced myopia on the scleral creep response of whole chick eyes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5179.
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To determine the effect of induced form deprivation myopia on the scleral creep response of intact chick eyes. Testing involved pressurized intact globes as a more physiologically representative model for testing the mechanical properties of the sclera than traditional uniaxial tensile testing of scleral strips.
Diffusers were applied to one eye of 6 one-day old chicks, while the fellow eye was left uncovered as a contralateral control. Retinoscopy and A-scan ultrasonography were performed on days 1 and 5. After enucleation on day 5, each eye was cannulated via a 25G needle passed through the cornea and lens into the vitreous chamber of the eye, and connected externally to a column of phosphate buffered saline (PBS) solution; the eye was also immersed in PBS. Intraocular pressure (IOP) was adjusted by altering the height of the column stepwise to 80 mmHg where it was held for one hour during which time changes in eye shape were recorded at a sampling frequency of 0.1 hz. Four 2 mm beads were glued to the sclera at the equator and posterior pole, as an aid to visualizing scleral changes. Image processing software was subsequently used to determine the position of the beads in each photograph, to measure the deformation of the posterior sclera over the course of the experiment and thus its creep.
After 5 days of form deprivation, the axial lengths of deprived eyes had increased by an average of 0.44 mm compared to 0.04 mm for control eyes. The form-deprived eyes, which were also myopic, exhibited significantly larger sclera creep compared to that of control eyes. With IOP held at 80 mmHg, form-deprived eyes elongated by 0.33% compared to 0.21% for control eyes (p < 0.05). The scleral creep rates determined for the final half hour of testing were 0.26 and 0.13 %/hour for myopic and control eyes respectively, averaged across eyes (p < 0.05).
Myopic chick eyes exhibit a higher scleral creep rate than control eyes when tested as intact globes. These results are consistent with results from earlier studies involving uniaxial loading of scleral strips.
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