Simulated myopic defocus counteracts a myopiagenic environment in juvenile tree shrews producing hyperopia

Abstract

Purpose : To examine the effects of a video display of simulated myopic blur on refractive development (emmetropization) in juvenile tree shrews.

Methods : Seven tree shrews (Tupaia belangeri, diurnal mammals closely related to primates) were removed from standard colony housing at 24 days of visual experience (DVE; days after eye opening) and placed in closed solid-wall cubical cages, 28 cm on a side internal dimension, with black and white patterns on the walls, until 35 DVE. Five animals were placed in the same size cage, but one wall consisted of a video display of simulated myopic blur (see Figure 1) of brightness 147 cd/m2, that was achieved by blurring the blue channel. Non-cycloplegic refractions and ocular dimensions were measured in awake animals using an autorefractor and an optical biometer, respectively. Data were compared with those obtained from seven animals previously reared in standard colony conditions with open-view wire mesh cages.

Results : At the end of the treatment period, the animals in the closed cages without the simulated myopic blur become slightly myopic: -1.0±0.4 (stderr) Diopters (see Figure 2). Animals in the open-view colony caging were slightly hyperopic at this age: 1.0±0.2 Diopters, significantly different from the animals in the closed view cage by t-test (P<0.001, t=4.805, df=12). In contrast, animals exposed to simulated myopic blur were hyperopic: +4.1±0.6 Diopters. The closed cage vs. myopic defocus group difference was 5.1 diopters, significant by t-test (P<0.001, t=7.3638, df=10). Changes in vitreous chamber depth were consistent with the refractive effects.

Conclusions : Cages with restricted viewing distance cause significant myopia in juvenile tree shrews. However, under these conditions simulated myopic blur more than overcomes the effect of restricted viewing distance and causes robust hyperopia. This emphasizes the importance of chromatic cues in emmetropization. This effect could potentially be developed into a powerful anti-myopia visual therapy for children.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1. Simulated myopic blur presented on one wall of the small cages.

 

Figure 2. A. Mean refractions as a function of time (average refraction from each animal OD and OS treated as single data points) for normal open-view colony animals, animals in small cages with closed views, and animals in small cages with simulated myopic blur. B. Same, but change in vitreous chamber depth over time.