Integration of defocus by dual power Fresnel lenses inhibits myopia in the mammalian eye

Abstract

Purpose: Eye growth compensates in opposite directions to single vision (SV) negative and positive lenses. We evaluated the response of the guinea pig eye to Fresnel-type lenses incorporating two different powers.

Methods: A total of 114 guinea pigs (10 groups with 9-14 in each) wore a lens over one eye and interocular differences in refractive error and ocular dimensions were measured in each of three experiments. First, the effects of three Fresnel designs with various diopter (D) combinations (-5D/0D; +5D/0D or -5D/+5D dual power) were compared to three SV lenses (-5D, +5D, or 0D). Second, the ratio of -5D and +5D power in a Fresnel lens was varied (50:50 compared with 60:40). Third, myopia was induced by 4 days of exposure to a SV -5D lens, which was then exchanged for a Fresnel lens (-5D/+5D) or one of two SV lenses (+5D or -5D) and ocular parameters tracked for a further 3 weeks.

Results: Dual power lenses induced an intermediate response between that to the two constituent powers (lenses +5D, +5D/0D, 0D, -5D/+5D, -5D/0D and -5D induced +2.1 D, +0.7 D, +0.1 D, -0.3 D, -1.6 D and -5.1 D in mean intraocular differences in refractive error, respectively), and changing the ratio of powers induced responses equal to their weighted average. In already myopic animals, continued treatment with SV negative lenses increased their myopia (from -3.3 D to -4.2 D), while switching to SV positive lenses or -5D/+5D Fresnel lenses reduced their myopia (by 2.9 D and 2.3 D, respectively).

Conclusions: The mammalian eye integrates competing defocus to guide its refractive development and eye growth. Fresnel lenses, incorporating positive or plano power with negative power, can slow ocular growth, suggesting that such designs may control myopia progression in humans.

Keywords: Fresnel lens; guinea pig; myopia; spectacle lens compensation.

Figures

Figure 1

Fresnel lens. (A) Unmounted lens showing 16 concentric rings of alternating power. (B) Guinea pig wearing a mounted lens. Red bootie is worn on the nearest foot to buffer potential damage to the lens from scratching. (C) Diagrammatic representation of the two focal planes induced by a −5D/+5D dual power Fresnel lens in the nonaccommodated guinea pig eye. Without the lens, the eye is hyperopic at this age (green line). The +5D powered rings (+5.12 D effective power) foci is myopic, just in front of the retina (blue line). The −5D powered rings (−4.89 D effective power) foci is hyperopic and behind the retina (red line), exaggerating the preexisting hyperopia. The average of these two foci (+2.5 D) is shown by the hyperopic green plane (see Inset I for enlargement; eye and lens drawn to scale but focal planes exaggerated for clarity).

Figure 2

Mean difference between the lens-wearing and fellow eyes at the end of the lens-wearing period for each 50:50 dual lens power (plano combinations, white; power combination, striped red) and their corresponding single vision controls (black bars). (A) Difference in spherical equivalent refractive error. (B) Difference in ocular length measured with ultrasound. Grey bars show the arithmetic mean of the response to the two underlying single vision powers in each dual power lens. White asterisks indicate if this hypothetical average is significantly different from what was actually found. Bars are SE. The significant difference between each powered single vision control and the −5D/+5D Fresnel lens is shown by the square brackets. *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 3

Refractive errors in each eye in individual animals in Experiment 1 after 11 days of wearing a (A) +5D SV lens, (B) −5D/+5D Fresnel lens, (C) −5D SV lens, (D) +5D/0D Fresnel lens, (E) lens holder only, or a (F) −5D/0D Fresnel lens.The mean for each group is shown by the filled circles and dashed lines. Linked lines show each animal's response in the fellow eye and in the eye wearing a lens (or lens holder, 0D). Note that the mean differences observed between the two eyes do not arise because of any effect on the fellow eyes which remain relatively consistent between the different lens groups (F5,50 = 0.6, P = 0.8). Red lines in (B) show two animals that responded to the positive power only.

Figure 4

The effect of different lens types on the mean difference between the lens-wearing and fellow eye. (A) Difference in vitreous chamber depth. (B) Difference in lens thickness. (C) Difference in anterior chamber depth. (D) Difference in the combined thickness of the retina, choroid, and sclera. Grey bars show the arithmetic mean of the response to the two underlying single vision powers in each dual power lens. Bars are SEM. Statistical and shading conventions are the same as in Figure 2.

Figure 5

Comparison of the response of the eye to wearing lenses with different ratios of alternating −5D/+5D power (50:50 and 60:40) relative to SV controls. Mean difference between the lens-wearing and fellow eye is shown. (A) Spherical equivalent refractive error. (B) Ocular length. Bars are SE. The response of the eye is not significantly different from the expected response for a perfect integrator (dashed line). Grey-filled circles and grey lines show the average excluding the two animals that responded purely to the positive power.

Figure 6

Average lens-wearing and fellow eye responses. (A) Refractive error. (B) Vitreous chamber depth; during the period after the induction of myopia with a −5D lens worn on one eye for 4 days. At age 8 days, the lens either remained a −5D lens (left panel) or was swapped with a −5D/+5D (middle panel) or a +5D lens (right panel). Bars are SEM. Values at age 4 days were not measured in these animals but are based on the average taken from our database of untreated eyes at this age (n > 100). The statistical difference between the eyes is shown. *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 7

Animals were first made myopic by wearing −5D lenses on one eye for 4 days (grey zone). At age 8 days, the lens remained as a −5D lens or was swapped to a −5D/+5D or +5D lens. The mean difference between the two eyes is shown for 0, 1, and 2 weeks after the lens swap. (A) Spherical equivalent refractive error. (B) Ocular length measured with ultrasonography. Bars are SEM. P values from Holm-Sidak comparisons (between age 8 and 22 days) are shown for the difference between the response to: −5D and +5D SV lenses (*), and −5D/+5D and −5D lens designs ( ). Three symbols (*** or ), P < 0.001; two symbols (** or ), P < 0.01; one symbol (* or ), P < 0.05.

Figure 8

The mean difference between the two eyes in underlying ocular distances on axis at 0, 1, and 2 weeks after the lens swap occurred at 8 days of age following 4 days of −5D lens-wear (grey zone). (A) Vitreous chamber depth. (B) Crystalline lens thickness. (C) Anterior chamber depth. (D) Retinal thickness. (E) Choroid thickness. (F) Sclera thickness. After 2 weeks, the +5D/−5D Fresnel lens evoked an intermediate response in vitreous elongation, and retinal and choroidal thickening, while the remaining ocular components responded similarly to that induced by continuous SV negative lens-wear. Bars are SEM. P values from Holm-Sidak comparisons (between age 8 and 22 days) are shown for the difference between the response to: −5D and +5D SV lenses (*), and −5D/+5D and +5D ( ) lens designs. Three symbols (*** or ), P < 0.001; two symbols (** or ), P < 0.01; one symbol (* or ), P < 0.05.