Abstract
Purpose :
A previous study showed that reducing the contrast in the blue channel of a digital image (chromatically simulated myopic defocus or CSMD) protected tree shrews from myopia induced by small-cage rearing. The purpose of this study was to examine if proximity causes the small-cage myopia in tree shrews, the role of S-cone contrast in CSMD, and if CSMD is equally effective when applied on naturalistic image.
Methods :
Young tree shrews were reared in cubical cages with an internal dimension of 28cm (Gawne et al., 2022) for 12 days, and the binocularly averaged refraction and LenStar-measured ocular dimensions were compared: (1) Tree shrews reared in fully enclosed small cages (n = 7) were compared with those in small cages with one side covered by wire mesh (i.e., an open view. n = 5). (2): Small-cage-rearing tree shrews were exposed to Maltese cross pattern rendered with zero blue contrast (n = 8). (3): Small-cage-rearing tree shrews were exposed to a grayscale, "naturalistic" tree image rendered with CSMD (n = 7). For experiments 2 and 3, comparison data were obtained from small-cage tree shrews reared with CSMD-rendered Maltese cross pattern (n = 8. Gawne et al. 2022) (Figure 1 illustrates the visual patterns).
Results :
As illustrated in Figure 2, tree shrews reared in fully enclosed cages developed myopia (mean ± SD refraction: -1±1.0D), whereas those reared in a small cage with an open view remained mildly hyperopic (0.8±1.1D, one-way ANOVA with Bonferroni correction, p<.05). Tree shrews exposed to zero-blue-contrast images (2.1±1.3D) were also more hyperopic than tree shrews reared in fully enclosed cages (p<.05) but were less hyperopic than those of exposed to Maltese-cross-based CSMD (4.0±1.1D, p<.05). Finally, tree shrews reared with tree-pattern-based CSMD was less hyperopic than those reared with Maltese-cross-based CSMD (0.5±0.8D, p<.05). The refractive effects were consistent with alterations in vitreous chamber depth.
Conclusions :
Extreme proximity could cause myopia in tree shrews. The protection of CSMD against proximity myopia does not rely on S-cone contrast, although the elimination of S-cone contrast could reduce its efficacy. CSMD also had reduced efficacy if rendered using a naturalistic scene, suggesting that visual image structure plays a role in determining the efficacy of the chromatic optical cue.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.