The Parameters Governing the Anti-Myopia Efficacy of Chromatically Simulated Myopic Defocus in Tree Shrews.

Abstract

We previously showed that exposing tree shrews (Tupaia belangeri, small diurnal mammals closely related to primates) to chromatically simulated myopic defocus (CSMD) counteracted small-cage myopia and instead induced hyperopia (approximately +4 diopters [D]). Here, we explored the parameters of this effect. Tree shrews were exposed to the following interventions for 11 days: (1) rearing in closed (n=7) or open (n=6) small cages; (2) exposed to a video display of Maltese cross images with CSMD combined with overhead lighting (n=4); (3) exposed to a video display of Maltese cross images with zero blue contrast ("flat blue," n=8); and (4) exposed to a video display of black and white grayscale tree images with different spatial filtering (blue pixels lowpass <1 and <2 cycles per degree [CPD]) for the CSMD. (1) Tree shrews kept in closed cages, but not open cages, developed myopia. (2) Overhead illumination reduced the hyperopia induced by CSMD. (3) Zero-blue contrast produced hyperopia but slightly less than the CSMD. (4) Both of the CSMD tree images counteracted small cage myopia, but the one low pass filtering blue <1 CPD was more effective at inducing hyperopia. Any pattern with reduced blue contrast at and below approximately 1 CPD counteracts myopia/promotes hyperopia, but maximal effectiveness may require that the video display be the brightest object in the environment. Chromatically simulated myopic blur might be a powerful anti-myopia therapy in children, but the parameter selection could be critical. Issues for translation to humans are discussed.