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I.G. Morgan, M.P. Ambadeniya; Imposed Peripheral Myopic Defocus Can Prevent the Development of Lens–Induced Myopia . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3328.
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To determine whether myopic defocus imposed on the peripheral retina is able to prevent the development of lens–induced myopia (LIM), and to determine the minimum time of exposure to myopic defocus to prevent otherwise constant stimulation of eye growth.
PMMA contact lenses were obtained from Australian Contact Lenses (Doveton, Victoria), and were fitted over the eyes of 5 day–old chickens, using Velcro mounts glued to the feathers around the eyes. Positive lenses were custom–made in 3 configurations – full +10D, and +10D with 3mm or 5 mm plano central zones (PCZ). The effects of the positive lenses were assessed after 7 days of constant wear. LIM was induced with –5D lenses for 7 days, and its development was interrupted by replacement of the –5D lenses with positive lenses for 1h, 30 or 15 minutes each day at noon. Axial lengths were measured by ultrasonography using a Mentor A–scan ultrasound, and inter–ocular differences (IOD) were calculated.
After 7 days of constant wear, +10D lenses with 3mm PCZ were as effective as full +10D lenses in slowing axial elongation, with experimental eyes significantly shorter than control eyes (p<0.01). +10D lenses with 5 mm PCZ were ineffective (p=0.76). Both full +10D lenses and +10D lenses with 3mm PCZ were able to block axial elongation induced by –5D lenses, with a minimum exposure of 30 minutes per day to both full +10D and +10D with 3 mm PCZ required to substantially counter the increased axial elongation induced by otherwise constant wearing of –5D lenses.
These results show that +10D contact lenses with 3mm plano central zones are as effective as full +10D lenses in suppressing normal eye growth, and excessive eye growth induced by –5D lenses. The results suggest that imposed peripheral myopic defocus may be able to be used to control on–axis axial elongation, even with normal central vision.
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