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S. Backhouse, K. Bumsted O'Brien, J. R. Phillips; The Effect of Induced Myopia on Ocular Compliance in the Guinea Pig. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1031.
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1. Determine the effect of induced refractive error on ocular compliance in the guinea pig. 2. Confirm the presence of contractile cells in guinea pig sclera.
One week old guinea pigs (n = 29) were monocularly deprived of form vision (FD) for 14 days. Refractive error measures were taken under cycloplegia with an IR Optometer. Ocular compliance (change in length/mmHg change in IOP) was compared between the FD and control eyes of 8 anaesthetised animals. 15 MHz A-scan ultrasound measures were taken every 10 minutes with IOP increased to 50 mmHg for one hour. Further ultrasound measures were taken 20 minutes after returning the IOP to 15 mmHg. Immunocytochemistry with antibodies to DAPI and α-smooth muscle actin (α-SMA) was used to determine scleral cell density and cell contractile potential in guinea pig sclera.
FD induced -4.06 ± 1.88 D of myopia, which was correlated with 169 ± 267 µm of vitreous chamber depth (VCD) elongation (n = 29; R2 = 0.37). There was a significant increase in the VCD after one hour of raised IOP in the deprived eye only (p = 0.016), while the control eye remained similar in length to baseline (p = 0.469). After reducing the IOP to 15 mmHg from 50 mmHg there was shortening of the VCD relative to baseline in the control eye of 71.93 µm, while the deprived eye remained 80.25 µm longer than baseline. However, these differences did not reach statistical significance. Cells displaying the contractile marker α-SMA were identified in guinea pig sclera.
In the guinea pig the in vivo ocular compliance response differs between myopic and control eyes, with myopic eyes being less able to recover from expansion induced by increases in IOP. The presence of contractile cell markers in guinea pig sclera suggests they may play a role in determining the ocular compliance response.
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