The effects of simultaneous dual focus lenses on refractive development in infant monkeys

Abstract

Purpose: We investigated the effects of two simultaneously imposed, competing focal planes on refractive development in monkeys.

Methods: Starting at 3 weeks of age and continuing until 150 ± 4 days of age, rhesus monkeys were reared with binocular dual-focus spectacle lenses. The treatment lenses had central 2-mm zones of zero power and concentric annular zones with alternating powers of +3.0 diopter [D] and plano (pL or 0 D) (n = 7; +3D/pL) or -3.0 D and plano (n = 7; -3D/pL). Retinoscopy, keratometry, and A-scan ultrasonography were performed every 2 weeks throughout the treatment period. For comparison purposes data were obtained from monkeys reared with full field (FF) +3.0 (n = 4) or -3.0 D (n = 5) lenses over both eyes and 33 control animals reared with unrestricted vision.

Results: The +3 D/pL lenses slowed eye growth resulting in hyperopic refractive errors that were similar to those produced by FF+3 D lenses (+3 D/pL = +5.25 D, FF +3 D = +4.63 D; P = 0.32), but significantly more hyperopic than those observed in control monkeys (+2.50 D, P = 0.0001). One -3 D/pL monkey developed compensating axial myopia; however, in the other -3 D/pL monkeys refractive development was dominated by the zero-powered portions of the treatment lenses. The refractive errors for the -3 D/pL monkeys were more hyperopic than those in the FF -3 D monkeys (-3 D/pL = +3.13 D, FF -3D = -1.69 D; P = 0.01), but similar to those in control animals (P = 0.15).

Conclusions: In the monkeys treated with dual-focus lenses, refractive development was dominated by the more anterior (i.e., relatively myopic) image plane. The results indicate that imposing relative myopic defocus over a large proportion of the retina is an effective means for slowing ocular growth.

Keywords: Fresnel lenses; emmetropization; eye growth; hyperopia; myopia; refractive error.

Figure 1

Spherical-equivalent, spectacle-plane refractive corrections plotted as a function of age for the right (filled symbols) and left eyes (open symbols) of individual +3 D/pL monkeys (A–G). The average (±SD) refractive errors for all of the +3 D/pL monkeys are shown in (H). The gray lines in each plot represent data for the right eyes of the 33 control monkeys.

Figure 2

Vitreous chamber depths for the right (filled symbols) and left eyes (open symbols) of individual +3 D/pL monkeys plotted as a function of age (A–G). The average vitreous chamber depths for all of the +3 D/pL monkeys are shown in (H). See Figure 1 for details.

Figure 3

Spherical-equivalent, spectacle-plane refractive corrections plotted as a function of age for the right (filled symbols) and left eyes (open symbols) of individual −3 D/pL monkeys (A–G). The average (±SD) refractive errors for all of the −3 D/pL monkeys are shown in (H). See Figure 1 for details.

Figure 4

Vitreous chamber depths for the right (filled symbols) and left eyes (open symbols) of individual −3 D/pL monkeys plotted as a function of age (A–G). The average vitreous chamber depths for all of the −3 D/pL monkeys are shown in (H). See Figure 1 for details.

Figure 5

(A) Refractive errors for the right eyes plotted as a function of age for individual lens-reared monkeys in the FF +3 D (open symbols) and +3 D/pL (filled symbols) groups. (B) Refractive errors for the right eyes plotted as a function of age for individual lens-reared monkeys in the FF −3 D (open symbols) and −3 D/pL (filled symbols) groups. The large symbols to the right in (A, B) represent the averages ± SD for the lens-reared monkeys at the end of the treatment period. (C) The average (±SD) refractive errors for all of the +3 D/pL lens (filled symbols) and −3 D/pL lens-reared monkeys (open symbols) plotted as a function of age. The shaded areas in each plot show the 10^th to 90^th percentile range of ametropias for the 33 control monkeys.

Figure 6

Refractive errors are plotted as a function of vitreous chamber depth for individual right eyes. The filled and open diamonds represent data from +3 D/pL and −3 D/pL lens-reared monkeys, respectively. The solid line is the best fitting regression line. The small gray circles represent data from control monkeys.

Figure 7

Comparisons of the effects of dual focus, Fresnel-like lenses (50:50 area ratios) on refractive error development in macaques (present study), chicks, marmosets, and guinea pigs. The left scale indicates the relative percentage change in ametropias at the end of treatment. For binocularly treated animals (present study), the ametropias for the right eyes are represented relative to that for control animals. For monocularly treated animals (all other studies), the ametropias for the treated eyes are expressed relative to that of the fellow eye. Values of 0% and 100% indicate complete compensation for the most hyperopic and myopic image planes, respectively. Values of 50% indicate that the animals compensated for the average power of the dual focus treatment lenses.