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Weizhong Lan, Marita Feldkaemper, Frank Schaeffel; Effect of bright light on choroidal thickness in chickens as measured with OCT. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5174.
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© ARVO (1962-2015); The Authors (2016-present)
Bright light was found to be a powerful inhibitor of myopia development in some animal models. We have studied whether its effect may involve changes in choroidal thickness (CT).
Three day old male white leghorn chickens were raised in temperature-controlled facilities under a 10/14 hour light/dark cycle either in “normal light”( 500 human lux, from 8AM to 6PM, n=14), or “bright light” (15,000 lux, 10AM to 4PM, n=14) for 5 days. CT in the posterior pole of right eyes was measured in alert, hand-held animals at 10AM, 4PM and 8PM every day, using small animal optical coherence tomography (Spectralis HRA+OCT, Heidelberg Engineering, Germany). Within-subject repeatability was high (SD 7.3µm or ± 4.4%; n=168, average CT=168.6µm). To uncover short-term effects of bright light, data collected at 4PM and 8PM were normalized to the individual CT data at 10AM every day. To determine long-term effects, individual CT at 10AM at day 1 was taken as baseline and changes between 10AM in day 1 and 10AM at day 5 were determined. Changes were analyzed using one-way repeated measures ANOVA and unpaired t-tests, respectively.
Among 28 chickens, 2 could not be properly measured and were excluded. In 3, one data point was lacking due to poor cooperation. Thus, complete data were available only for 21 chickens (9 in normal light and 12 in bright light). Immediately after bright light was switched off at 4PM, CT decreased by -5.2%±4.0% (mean±SEM). In contrast, in the normal light group, CT increased by 15.4%±4.7% (ANOVA: p=0.003). After further four hours, CT in the bright light group increased again by 17.8%±3.5%, but showed little further change in the normal light group (0.6%±4%; ANOVA, p=0.004). After 4 days in bright light, CT was thicker than the normal light group (7.6%±26.0% vs. -18.6%±26.9%, t-test: p=0.036), indicating that CT became thinner over time in normal light.
CT responds to ambient light intensity. Bright light modulated the diurnal CT cycling and increased CT over the 4 day period as a long-term effect. Since thicker choroids were previously shown to be associated with eye growth inhibition, it could be that the increase in CT induced by bright light also mediates the inhibition of myopia.
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