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Hannah Bowrey, Guang Zeng, Amelia Leotta, Christine Wildsoet, Sally McFadden; The effect of two-zone concentric bifocal lenses on refractive error and eye shape in guinea pigs. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5176.
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© ARVO (1962-2015); The Authors (2016-present)
The phenomena of relative peripheral hyperopia in myopic eyes has led to the idea that lenses which correct the peripherial hyperopia may inhibit the progression of myopia. We studied the changes in eye shape which occur in mammalian eyes wearing a concentric bifocal lens which contained either plus or minus defocus in its periphery.
Guinea pigs wore one of 5 lens types on one eye from 8 days of age for 12 days. Lenses were 14mm in diameter and contained either a single power (-4D, 0D, or +4D, n=85) or dual power with a 4mm plano center and minus or plus power in the surround (0/-4D or 0/+4D, n=31). At the end of the lens-wear period, refractive error was measured centrally and 30° off-axis in the temporal and nasal fields under cycloplegia . Eyes were enucleated immediately after death and rapidly frozen and sectioned in the horizontal plane. Eye shape was analyzed from high-resolution images of the section with maximum lens thickness and distances calculated relative to the center of the lens axes.
Eye shape analysis showed that -4D lens wear caused elongation around the optic nerve (peri-papilliary zone, PPZ) with relatively little change in the periphery. A similar reduced pattern occurred with 0/-4D lens wear, showing that lenses containing peripheral hyperopic defocus induce growth in the PPZ. +4D lenses inhibited peripheral growth, particularly in nasal retina, but little change occurred in the PPZ, suggesting that myopic defocus predominantly influences peripheral eye shape. 0/+4D lenses caused an identical inhibition in nasal retina, but there was significant expansion in the PPZ, very similar to that seen with 0/-4D lenses. Since single vision 0D lenses did not significantly change posterior eye growth, it suggests that the PPZ is sensitive to peripheral lens defocus of either sign when combined with a 0D central lens zone.
Regional sensitivity to defocus is differentially affected by the sign of defocus. Minus lenses caused elongation in the PPZ and plus lenses caused peripheral inhibition in eye shape. However, when the center of an imposed lens contained no additional defocus, the remaining peripheral power induced elongation in the PPZ regardless of its sign. If human eyes act like guinea pig eyes, it suggests that lenses with peripheral defocus will change eye shape asymmetrically in the zone surrounding the optic disk.
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