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Timothy Gawne, Alexander Ward, Thomas T Norton; Wavelength Cues Are Essential to Maintain Emmetropia in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2744.
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To examine the effects of narrow-band flickering blue light in juvenile tree shrews (diurnal mammals closely related to primates) that had completed the initial emmetropization decrease from hyperopia toward emmetropia.
Nine tree shrews were raised with their mothers in fluorescent colony lighting until they began treatment at 24 days of visual experience (DVE) at which age they had achieved age-normal emmetropia (mean ± SEM, 1.2 ± 0.5 D). Arrays of LEDs (peak, either 457 or 464 ± 10 nm) placed atop the cage provided illuminance on the floor of the cage of 300 to 500 human lux. The LEDs were flickered in a pseudo-random pattern that we previously demonstrated is myopiagenic in infant animals (starting at 11 DVE) (Gawne et al. 2014, Soc. Ns. Abstr. 59.09). Non-cycloplegic refractive state was measured daily for a minimum of 11 days. These groups were compared with animals raised in colony light and with a group that had been treated with monocular –5 D lenses (Norton et al. 2010).
All wavelength-treated animals developed increased refractive error. Refractions in six animals initially moved toward hyperopia (+1.4 to +4.8 D, max.) and then became myopic (–0.9 to –6.1, min., when followed to the maximum time period, Fig. 1A). After 11 days of treatment, the refraction of 7/9 animals was outside the normal range, and the variance of refractions of the blue-treated animals (Fig. 1B) was significantly greater than for age-matched animals in colony light or treated with a –5 D lens (Bootstrap, P<0.05).
The maintenance of emmetropia is an active process that no doubt uses multiple visual cues. This restricted wavelength/flicker condition removed cues essential to maintain emmetropia. Animals whose refraction initially moved toward hyperopia and became myopic passed through emmetropia but, in this visual environment, the eyes were unable to stop. The blue light significantly stimulated both long (LWS) and short (SWS) wavelength sensitive cones and their relative stimulation did not change with the refractive state. This result is consistent with the hypothesis that feedback from changes in the relative activation of LWS and SWS cones is necessary to maintain emmetropia. Without this feedback refraction drifted. One wonders if this may have been a factor in the variable results of previous narrow-band wavelength studies.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
A: Refraction vs. age for individual animals B: Group means and variances.
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