Axial eye growth and refractive error development can be modified by exposing the peripheral retina to relative myopic or hyperopic defocus

Abstract

Purpose: Bifocal contact lenses were used to impose hyperopic and myopic defocus on the peripheral retina of marmosets. Eye growth and refractive state were compared with untreated animals and those treated with single-vision or multizone contact lenses from earlier studies.

Methods: Thirty juvenile marmosets wore one of three experimental annular bifocal contact lens designs on their right eyes and a plano contact lens on the left eye as a control for 10 weeks from 70 days of age (10 marmosets/group). The experimental designs had plano center zones (1.5 or 3 mm) and +5 diopters [D] or -5 D in the periphery (referred to as +5 D/1.5 mm, +5 D/3 mm and -5 D/3 mm). We measured the central and peripheral mean spherical refractive error (MSE), vitreous chamber depth (VC), pupil diameter (PD), calculated eye growth, and myopia progression rates prior to and during treatment. The results were compared with age-matched untreated (N=25), single-vision positive (N=19), negative (N=16), and +5/-5 D multizone lens-reared marmosets (N=10).

Results: At the end of treatment, animals in the -5 D/3 mm group had larger (P<0.01) and more myopic eyes (P<0.05) than animals in the +5 D/1.5 mm group. There was a dose-dependent relationship between the peripheral treatment zone area and the treatment-induced changes in eye growth and refractive state. Pretreatment ocular growth rates and baseline peripheral refraction accounted for 40% of the induced refraction and axial growth rate changes.

Conclusions: Eye growth and refractive state can be manipulated by altering peripheral retinal defocus. Imposing peripheral hyperopic defocus produces axial myopia, whereas peripheral myopic defocus produces axial hyperopia. The effects are smaller than using single-vision contact lenses that impose full-field defocus, but support the use of bifocal or multifocal contact lenses as an effective treatment for myopia control.

Keywords: contact lenses; eye growth; myopia control; peripheral defocus; refractive error.

Figure 1

Diagrams of each contact lens design describing the peripheral zones of hyperopic or myopic imposed defocus, and the retinal zones with simultaneous plano and defocused vision based on calculations from Carkeet. The diagrams are for illustration only and not drawn to scale. The −5 D/3 mm lens (red) is shown to the left, the +5 D/3 mm (light blue) is show in the middle, and the + 5D/1.5 mm (dark blue) is shown to the right. In lenses with 3 mm central plano zones there was approximately 1° of clear vision on the optic axis for the average pupil diameter.

Figure 2

Average VC and refractive state for the experimental and control eyes in each experimental group, normalized to baseline. The −5 D/3 mm lens (red) is shown at the top, the +5 D/3 mm (light blue) is show in the middle, and the +5 D/1.5 mm (dark blue) is shown at the bottom. Asterisk indicates statistical significance P < 0.05.

Figure 3

Quadrant plots describing the relation between interocular differences (exp-con) in VC (x axis), and mean spherical refraction (y axis). Each plot shows data from an experimental lens design. The top graph (red) corresponds to animals treated with −5 D/3 mm lenses, the middle graph (light blue) corresponds to animals treated with +5 D/3 mm lenses, and the bottom graph (dark blue) corresponds to animals treated with +5 D/1.5 mm lenses. The interocular differences in VC depth or mean spherical refraction are shown for each animal as an individual arrow. Baseline measures are indicated by the tails of the arrows. The final experimental measurement is indicated at the arrowhead. The grey rectangle represents the 95% CI of age-matched untreated marmosets. Lines outside of the 95% CI indicate significant interocular differences. Data points in the top left quadrant indicate that the experimental eyes are smaller and more hyperopic than contralateral control eyes; points in the top right quadrant indicate eyes that are larger but more hyperopic; points in the bottom left quadrant show eyes that are smaller but more myopic than contralateral controls, and points in the bottom right quadrant show eyes that are larger and more myopic.

Figure 4

Box plots representing the interocular differences in ocular growth rate (exp-con) during the early (4–6 weeks into treatment), middle- (following four weeks of treatment) and late-periods (last four weeks into treatment) of treatment for the different treatment groups: untreated controls (white), single-vision −5D (dark red), single-vision +5D (dark blue), multizone +5/−5 D (black), −5 D/3 mm (light red), +5 D/3 mm (blue), and +5 D/1.5 mm (light blue). The data shown are means ± SE.

Figure 5

Scatter plots showing the correlations between changes (post baseline) in the interocular differences of VC (mm, top graph) or refraction (D, bottom graph) as a function of the contact lens area treatment zone (mm²) multiplied by the power of the treatment zone (D).