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D. Y. Tse, H. E. Bowrey, C.-H. To, C. F. Wildsoet, S. A. McFadden; Modulation of Mammalian Ocular Growth and Myopia Progression With Competing Defocus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1727.
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© ARVO (1962-2015); The Authors (2016-present)
The exact mechanism of how emmetropization functions in the presence of multiple defocus planes is unclear. Using concentric dual-power lenses, we have previously shown that avian retina can recognise and integrate longitudinal competing defocus. Here we sought to investigate whether competing plus and minus defocus are integrated to facilitate recovery from myopia in the mammalian eye.
38 guinea pigs were raised under diffuse white light on a 12/12hr light-dark cycle. In the first phase, myopia was induced in all animals by applying a -5D lens over one eye from 4-8 days of age. In the second phase (8-29 days of age), the -5D lens was swapped with +5D single power lens in one group, a +5/-5D Fresnel lens in the second group, and left as a -5D lens in the third group. Refractive errors using retinoscopy and axial dimensions of the eyes using ultrasound A-scan were measured repeatedly during phase 2 at 8,15, 22, and 29 days of age.
Eyes became -3D myopic after 4 days of -5D lens wear. Eyes left with a -5D lens, stayed myopic over the next 3 weeks, while those changed to +5D rapidly recovered from myopia by decreasing their rate of elongation. Eyes switched to a +5/-5D lens showed intermediate changes with a slight bias towards the +5D response in refractive error, ocular length, and vitreous chamber depth; while choroid thickness was biased towards -5D. One week after lens switching, the mean interocular refractive error for the groups +5D, +5/-5D and -5D were -4.57, -1.48 and -0.44D respectively. The +5/-5D group was significantly more hyperopic than the -5D group (p<0.05). The corresponding mean interocular differences in vitreous chamber depth were -14, +39 and +56 µm respectively.
The mammalian eye is able to integrate opposite signs of defocus to modulate its growth and when myopic defocus is included in a dual-power Fresnel lens, it can inhibit the progression of myopia. This implies that similar dual-power lenses may inhibit myopia progression in humans while at the same time providing clearly corrected vision.
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