The Effects of the Relative Strength of Simultaneous Competing Defocus Signals on Emmetropization in Infant Rhesus Monkeys

Abstract

Purpose: We investigated how the relative surface area devoted to the more positive-powered component in dual-focus lenses influences emmetropization in rhesus monkeys.

Methods: From 3 to 21 weeks of age, macaques were reared with binocular dual-focus spectacles. The treatment lenses had central 2-mm zones of zero-power and concentric annular zones that had alternating powers of either +3.0 diopters (D) and 0 D (+3 D/pL) or -3.0 D and 0 D (-3 D/pL). The relative widths of the powered and plano zones varied from 50:50 to 18:82 between treatment groups. Refractive status, corneal curvature, and axial dimensions were assessed biweekly throughout the lens-rearing period. Comparison data were obtained from monkeys reared with binocular full-field single-vision lenses (FF+3D, n = 6; FF-3D, n = 10) and from 35 normal controls.

Results: The median refractive errors for all of the +3 D/pL lens groups were similar to that for the FF+3D group (+4.63 D versus +4.31 D to +5.25 D; P = 0.18-0.96), but significantly more hyperopic than that for controls (+2.44 D; P = 0.0002-0.003). In the -3 D/pL monkeys, refractive development was dominated by the zero-powered portions of the treatment lenses; the -3 D/pL animals (+2.94 D to +3.13 D) were more hyperopic than the FF-3D monkeys (-0.78 D; P = 0.004-0.006), but similar to controls (+2.44 D; P = 0.14-0.22).

Conclusions: The results demonstrate that even when the more positive-powered zones make up only one-fifth of a dual-focus lens' surface area, refractive development is still dominated by relative myopic defocus. Overall, the results emphasize that myopic defocus distributed across the visual field evokes strong signals to slow eye growth in primates.

Figure 1

Photographic images of the +3 D/pL dual-focus lenses (top) and a magnified view of the annular power zones for the 50:50, 33:67, 25:75, and 18:82 power ratio lenses (bottom). The width of the +3 D annular zones was 0.4 mm for all lenses; the widths of the zero-powered zones varied from 0.4 to 1.8 mm.

Figure 2

Spherical-equivalent, spectacle-plane refractive corrections (top) and vitreous chamber depths (bottom) plotted as a function of age for the right (filled symbols) and left eyes (open symbols) for individual +3 D/pL 33:67 lens-reared monkeys. The thin gray lines in each plot represent data for the right eyes of the 35 control monkeys. The plots for treated subjects are arranged from left to right according to the maximum degree of hyperopia observed during the treatment period.

Figure 3

Spherical-equivalent, spectacle-plane refractive corrections (top) and vitreous chamber depths (bottom) plotted as a function of age for the right (filled symbols) and left eyes (open symbols) for individual +3 D/pL 25:75 lens-reared monkeys. See Figure 2 for details.

Figure 4

Spherical-equivalent, spectacle-plane refractive corrections (top) and vitreous chamber depths (bottom) plotted as a function of age for the right (filled symbols) and left eyes (open symbols) for individual +3 D/pL 18:82 lens-reared monkeys. See Figure 2 for details.

Figure 5

Refractive errors for the right eyes plotted as a function of age for all of the individual lens-reared monkeys in the FF+3D, +3 D/pL 50:50, 33:67, 25:75, and 18:82 subject groups (A–E). The large symbols to the right in each panel represent the averages (±SD) for the lens-reared monkeys at the end of the treatment period. The shaded areas in each plot show the 10th to 90th percentile range of ametropias for the 35 control monkeys. The filled and open symbols represent animals that appeared to compensate for the anterior and posterior focal planes, respectively.

Figure 6

Spherical-equivalent, spectacle-plane refractive corrections (top) and vitreous chamber depths (bottom) plotted as a function of age for the right (filled symbols) and left eyes (open symbols) individual −3 D/pL 67:33 lens-reared monkeys. See Figure 2 for details.

Figure 7

Refractive errors for the right eyes plotted as a function of age for all of the individual lens-reared monkeys in the FF−3D, −3 D/pL 50:50 and 67:33 subject groups (A–C). The large symbols to the right in each panel represent the averages (±SD) for the lens-reared monkeys at the end of the treatment period. See Figure 5 for details. In (B) and (C), the filled and open symbols represent animals that appeared to compensate for the anterior and posterior focal planes, respectively.

Figure 8

Refractive errors are plotted as a function of the AL/CR for the right eyes of all the monkeys treated with dual-focus lenses. The circles, down triangles, up triangles, diamonds, and filled and open squares represent data for the monkeys treated with the +3 D/pL 50:50, 33:67, 25:75, 18:82, −3 D/pL 50:50, and 67:33 lenses, respectively. The solid line is the best-fitting regression line.

Figure 9

The average ametropias (±SEM) plotted as a function of the percentage of surface areas that was devoted to the powered portions of the treatment lenses. The control monkeys reared with unrestricted vision are represented at the 0 point on the abscissa. The monkeys reared with the FF−3D and FF+3D single-vision lenses are represented at the “100% −3 D” and “100% +3 D” positions, respectively. The dual-focus groups are positioned according to the proportion of lens surface areas devoted to the −3 D and +3 D power zones.