Peripheral vision can influence eye growth and refractive development in infant monkeys

Abstract

Purpose: Given the prominence of central vision in humans, it has been assumed that visual signals from the fovea dominate emmetropization. The purpose of this study was to examine the impact of peripheral vision on emmetropization.

Methods: Bilateral, peripheral form deprivation was produced in 12 infant monkeys by rearing them with diffusers that had either 4- or 8-mm apertures centered on the pupils of each eye, to allow 24 degrees or 37 degrees of unrestricted central vision, respectively. At the end of the lens-rearing period, an argon laser was used to ablate the fovea in one eye of each of seven monkeys. Subsequently, all the animals were allowed unrestricted vision. Refractive error and axial dimensions were measured along the pupillary axis by retinoscopy and A-scan ultrasonography, respectively. Control data were obtained from 21 normal monkeys and 3 infants reared with binocular plano lenses.

Results: Nine of the 12 treated monkeys had refractive errors that fell outside the 10th- and 90th-percentile limits for the age-matched control subjects, and the average refractive error for the treated animals was more variable and significantly less hyperopic/more myopic (+0.03 +/- 2.39 D vs. +2.39 +/- 0.92 D). The refractive changes were symmetric in the two eyes of a given animal and axial in nature. After lens removal, all the treated monkeys recovered from the induced refractive errors. No interocular differences in the recovery process were observed in the animals with monocular foveal lesions.

Conclusions: On the one hand, the peripheral retina can contribute to emmetropizing responses and to ametropias produced by an abnormal visual experience. On the other hand, unrestricted central vision is not sufficient to ensure normal refractive development, and the fovea is not essential for emmetropizing responses.

Figures

Figure 1

Refractive error along the pupillary axis, specified as the spherical-equivalent, spectacle-plane refractive correction, plotted as a function of age for the right eyes of individual control animals (lines) and treated monkeys (symbols) reared with diffusers with (A) 4- and (B) 8-mm apertures. (C) Right eye refractive errors for treated (•, 4-mm apertures; ♦, 8-mm apertures) and control animals (⋄) at ages corresponding to the end of the treatment period. Open and filled bars: median and the 10th, 25th, 50th, and 90th percentiles for the control and treated monkeys.

Figure 2

Mean ± SD vitreous chamber depth along the pupillary axis plotted as a function of age for the right eyes of individual control animals (lines) and treated monkeys (symbols) reared with diffusers with (A) 4- and (B) 8-mm apertures. (C) Vitreous chamber depth plotted as a function of spherical-equivalent refractive error for treated (•, 4-mm apertures; ♦, 8-mm apertures) and control animals (⋄) at ages corresponding to the end of the treatment period. Solid line: results of the regression analysis of the data from the treated monkeys.

Figure 3

Recovery from experimentally induced refractive errors. Spherical equivalent, spectacle plane refractive correction (top) and mean vitreous chamber depth along the pupillary axis (bottom; the SDs were smaller than the symbol size) are plotted as a function of age in the right eyes of individual control animals (lines) and the right (•) and left eyes (○) of a representative monkey that wore the peripheral diffusers.

Figure 4

Effects of foveal ablation on recovery from experimentally induced refractive errors. Top: retinal photographs illustrating the foveal ablations in the treated eyes. Spherical equivalent, spectacle plane refractive corrections (middle) and mean vitreous chamber depths along the pupillary axis (bottom) are plotted as a function of age, in the right eyes of individual control animals (lines) and the laser-treated (•) and nontreated (○) eyes of two monkeys that wore the peripheral diffusers (the SDs for the mean vitreous chamber depths were smaller than the symbol size). Middle, filled horizontal bars: lens-rearing periods. The laser photoablations were performed immediately after the lens-rearing period (arrows). Monkey LAU was selected because it was the only lens-reared monkey that was relatively hyperopic at the end of the treatment period. Monkey MIT was representative of the treated monkeys that exhibited relative myopic errors during the lens-rearing period.

Figure 5

Interocular differences in refractive error (laser treated eye or right eye–fellow eye) plotted as a function of age for the seven diffuser-reared monkeys that had the fovea of one eye ablated by laser photocoagulation at the end of the lens-rearing period. Data shown were obtained during (•) and (○) after the lens-rearing period. Lines: data from the control monkeys.