Abstract
Purpose :
Previously we showed fibrous scleral changes in response to recovery from induced myopia. Here we investigate changes in cartilaginous and fibrous sclera and total scleral thickness change in response to refractive errors induced in chick eyes by myopic and hyperopic defocus.
Methods :
Refractive error was induced by applying +10D or -10D lenses unilaterally to chicks (Gallus gallus domesticus) on the day of hatching. Chicks were raised in a 14/10 hour light/dark cycle with food and water ad libitum. Birds were assigned randomly to 3 groups; induced myopia (n=6), induced hyperopia (n=5), and normal control (n=6). After 14 days, eyes were enucleated immediately after euthanasia, fixed in 10% neutral buffered formalin, routinely processed and embedded in paraffin. Blocks were sectioned in 5-μm thick sections, stained with Hematoxylin and Eosin and evaluated using bright field microscopy for fibrous, cartilaginous, and total scleral thickness. Analysis of variance with Bonferoni corrected post-hoc testing was used to determine differences between treatment groups.
Results :
Birds wearing -10D lenses developed average myopia of -13.67 +/- 2.48D. Refractive errors were not available for untreated birds. Previous work has shown that this breed is about 2.50D hyperopic at age 14 days. Birds wearing +10D lenses became hyperopic by 10.00 +/- 2.12D. There was a significant treatment effect on total scleral thickness (F=4.3; p=0.035). Hyperopic birds had thicker sclera’s (190 +/- 22 µm) than myopic birds (151 +/- 16 µm) p<0.05. Total thickness change was largely the result of significant changes in the fibrous sclera (F=47.17; p<0.0001). Fibrous scleral thickness was 16 +/- 3, 26 +/- 3, 64 +/- 15 µm for myopic, control and hyperopic birds respectively. Differences were significant between myopic and hyperopic birds (p<0.001), hyperopic and control birds (p<0.001) but not between myopic and control birds (p>0.05). There was no significant effect of treatment on cartilaginous scleral thickness (myopic 135 +/- 15; control 135 +/- 30: hyperopic 126 +/- 17 µm; F=0.29; p=0.755).
Conclusions :
There is a differential effect of refractive error direction on chick scleral thickness. Sclera’s are thicker in hyperopic than myopic eyes. This is a result of fibrous sclera changes with little or no effect on cartilaginous scleral thickness. This differential effect suggests an active role of the fibrous sclera in the control of eye size and refractive error.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.