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Timothy J Gawne, Alexander H Ward, Thomas T Norton; Temporal Non-linearity of Red-light Induced Hyperopia in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
In response to form deprivation (FD) or a minus lens (ML), the retina generates “GO” signals that produce axial elongation. Removal of FD or ML for as little as 2 hours per day produces “STOP” signals that block the axial elongation. In young tree shrews, long-wavelength (red) light also appears to produce STOP signals, slowing axial elongation during emmetropization. We asked if the red-light STOP signals are similarly effective when presented for only a few hours per day.
Tree shrews were raised by their mothers until 10 ± 1 days of visual experience (DVE, days after eye opening). They were housed in individual cages, illuminance 100-300 lux, from F34CW RS WM ECO fluorescent lights. One day later, 13 days of red-light treatment began. Each morning, the red lights (an array of LEDs [624 or 636 ± 10 nm]) atop the cage were turned on and the colony lights off, for 1 hr (n=4), 2 hrs (n=5) or 4 hrs (n=1). Illuminance on the floor of the cage was 500-1100 human lux. Refractive state was measured daily; ocular component dimensions were measured before and at the end of red-light treatment. After red-light treatment, the animals returned to colony lighting and the refractive state was followed for 26 days. Values were compared to normal animals (n=7) and to a previously-reported group that was exposed to red light 14 hrs per day.
At the end of treatment the refraction of the 2 hr group was 4.0 ± 0.8 D (diopters) hyperopic (mean ± SEM, see figure), significantly different (p < 0.05 t-test) from untreated controls at that age (1.2 ± 0.1 D). The 1 hr group was 2.7 ± 0.2 D hyperopic (ns). Vitreous chamber depth was: controls 2.80 ± 0.03 mm, 2 hr 2.70 ± 0.02 mm (significantly different from controls p < 0.05), and 1 hr 2.77 ± 0.03 mm (ns). The effect is nonlinear: 2 hours of red is 14% the duration of 14 hours of red but produced 42% of the hyperopia effect. A single 4 hr animal remained hyperopic, similar to animals exposed to 14 hrs of red light.
During the period of rapid emmetropization from hyperopia, brief periods of red light slow the refractive decrease, resulting in hyperopia at the end of treatment. The temporal non-linearity of the red-light treatment seems similar to that of removing FD or ML treatment, but the red light requires longer exposure time.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Refraction as a function of DVE for animals in colony lighting (black circles), and different durations of red light exposure.
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