Nature of the refractive errors in rhesus monkeys (Macaca mulatta) with experimentally induced ametropias

Abstract

We analyzed the contribution of individual ocular components to vision-induced ametropias in 210 rhesus monkeys. The primary contribution to refractive-error development came from vitreous chamber depth; a minor contribution from corneal power was also detected. However, there was no systematic relationship between refractive error and anterior chamber depth or between refractive error and any crystalline lens parameter. Our results are in good agreement with previous studies in humans, suggesting that the refractive errors commonly observed in humans are created by vision-dependent mechanisms that are similar to those operating in monkeys. This concordance emphasizes the applicability of rhesus monkeys in refractive-error studies.

Figure 1

Frequency distributions for spherical-equivalent refractive error and anisometropia for Indian-derived (left) and Chinese-derived monkeys (right) obtained at the end of the treatment period for the treated monkeys and at equivalent ages for control monkeys. A & B. Refractive errors for right (black bar) and left eyes (white bar), the dashed lines in A & B represent ± 1 standard deviations from the mean refractive errors for the control monkeys. C & D. Anisometropia (right eye – left eye).

Figure 2

Simple correlation analyses between refractive error and vitreous chamber depth for all eyes (A), hyperopic eyes (B), emmetropic eyes (C) and myopic eyes (D). The filled and open circles represent individual Indian-derived right and left eyes, respectively. The filled and open triangles represent individual Chinese-derived right and left eyes, respectively. The correlations between refractive error and vitreous chamber depth are represented by the solid (Indian-derived monkeys) and dashed lines (Chinese-derived monkeys). Note that the slopes of the regression lines for emmetropic eyes were flatter than those for the myopic, hyperopic or combined subject groups.

Figure 3

Simple correlation analyses between ocular components (A. anterior chamber depth, B. lens thickness, C. vitreous chamber depth) and axial length. For details, see Figure 2.

Figure 4

Simple correlation analyses between corneal power and axial length in all eyes (A), hyperopic eyes (B), emmetropic eyes (C) and myopic eyes (D). For details, see Figure 2.

Figure 5

Box plots for Interocular differences (more myopic eye – less myopic eye) in ocular components of anisometropic monkeys. The horizontal solid line inside the box represents the median, the bottom and top of the box represent the 25^th and 75^th percentiles. The whiskers that extend vertically from the top and bottom of the box represent the 90^th and 10^th percentiles, respectively. Horizontal lines outside of the upper and lower limits represent outliers. Dashed horizontal lines are reference lines at zero differences. AC: anterior chamber depth; LT: lens thickness; VC: vitreous chamber depth; AL: axial length; CP: corneal power.

Figure 6

Simple correlation analyses between the interocular differences in refractive error and various axial dimensions (A. axial length; B. anterior chamber depth; C. lens thickness; D. vitreous chamber depth, and E. corneal power). Open symbols represent individual monkeys and the solid lines represent the regression function for each plot.