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Jane Yang, Kelsey Jordan, Kristen Totonelly, Debora L Nickla; The effects of brief periods of hyperopic defocus or form deprivation on eye growth in chicks depend on time of day. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2733.
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It is generally accepted that nearly continuous exposure to hyperopic defocus or form deprivation is required to elicit eye growth stimulation, in contrast to the robust responses to brief periods of myopic defocus for growth inhibition. We have found that the efficacy of brief myopic defocus to inhibit growth is dependent on time of day. Might the responses to brief hyperopic defocus (minus) or form deprivation (FD) be time-dependent as well?
Minus: Birds had one eye exposed to hyperopic defocus by the wearing of -10D lenses for 2 or 6 hrs at one of 3 times of day for 5d: Morning (7 am; n=13; n=6), Mid-day (12pm: n=20; 10am-4pm: n=8), Evening (7pm: n=12; 2-8pm: n=11). FD: Birds wore a diffuser over one eye for 2 hrs at one of 3 times of day for 5d: Morning (n=12); Noon (n=19) or Evening (n=6). Eyes were measured using high-frequency ultrasound on days 1 and 5. Refractive errors were measured on d5.
2 Hrs Minus: The effects of 2 hrs of defocus depended on time of day of exposure: it stimulated eye growth when exposure was in the morning and inhibited it at noon (change in vitreous chamber, X-C; ANOVA p<0.0005; 120 µm vs -77 µm respectively; one-sample t-tests: p=0.001; p=0.01; post-hoc test: p=0.002). For noon, experimental eyes were more hyperopic(X-C: 1.4 D; p<0.0001). Evening exposures had no effect. 6 Hrs Minus: Similar to 2 hrs defocus, exposures mid-day inhibited growth and produced hyperopia (X-C: -167 µm; t-test p=0.005; RE: 1.8 D; p=0.03). Morning and evening exposures had no effect. 2 Hrs FD: The effects of 2 hrs of FD were similar to those of both durations of hyperopic defocus in inhibiting growth for noon exposures, but FD inhibited growth in the morning as well (X-C: Morning: -78 µm; noon: -83 µm; ttests p=0.04 and p=0.002 respectively). Experimental eyes were more hyperopic (1.8 D; 1.0 D; p<0.05). Evening exposures had no effect.
Contrary to previous reports, relatively brief periods of hyperopic defocus can induce growth stimulation, but only if given early in the day, indicating a diurnal rhythm in response susceptibility. This suggests that early reading activities might be a risk factor for myopia development in children. The anomalous findings of growth inhibition by both hyperopic defocus and FD at noon might be due to more robust choroidal responses upon removal of the devices at these times.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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