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A. O. Amedo, J. T. Siegwart, Jr., T. T. Norton; The Effect of Age on Compensation to a Minus Lens and Recovery in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1028.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the effect of age on the development of myopia induced with a minus lens and on recovery from lens-induced myopia in tree shrews.
Starting at 16, 24, 35 or 48 days after natural eye-opening (e.g., days of visual experience [VE]), juvenile tree shrews (n ≥ 5 per group) wore a monocular -5 D lens for 11 days. A long-term lens-wear group (n=5) also began treatment at 16 days of VE but continued to wear the lens for 30 days. Daily non-cycloplegic refractive measurements were made during the first 11 days of treatment and then less frequently in the long-term group. The recovery phase in all groups was started by discontinuing -5 D lens wear. Daily measures were made for the first 10 days of recovery and then less frequently until at least 29 days of recovery.
The amount of myopia, measured without the lens, that developed after 11 days of lens wear was similar for the three younger groups (mean ± SEM, 16 VE, -4.7 ± 0.3 D; 24 VE, -4.9 ± 0.4 D; 35 VE, -4.1 ± 0.2 D) and slightly less (-3.3 ± 0.5 D) in the oldest group (48 days of VE). The rate of compensation decreased as a function of age. After 4.5 days the percent of full compensation was 16 VE, 68.1 ± 8.5%; 24 VE, 42.7 ± 9.5%; 35 VE, 26.1 ± 5.6%; 48 VE, 19.9 ± 5.1%. The long-term group remained stable after compensating for the -5 D lens. During recovery, 9 of the 26 treated eyes recovered quickly and completely (100% recovery after 10 days). Three of these were in the 48 VE group and had developed little myopia. The other 17 treated eyes recovered more slowly (13% to 70% recovery after 10 days). Most, but not all recovered by the end of the recovery period. Both quick and slow recovery occurred in all age groups and the speed of recovery from myopia of more than -3.2 D was unrelated to the amount of myopia or to age.
By 16 days after eye opening, tree shrew eyes respond quickly to minus lens wear. Continued lens wear maintains the compensation. The rate of compensation decreases with age. Recovery from induced myopia does not always occur. The time-course of recovery can be quite variable and some animals in all groups had residual myopia at the end of the recovery period.
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