| This study investigated whether adolescent guinea pigs can develop myopia induced by negative lenses, and whether they can recover from the induced myopia. Forty-nine pigmented guinea pigs (age of 3 weeks) were randomly assigned to 4 groups: 2-week defocus (n = 16), 4-week defocus (n = 9), 2-week control (n = 15) and 4-week control (n = 9). A -4.00 D lens was worn in the defocus groups and a plano lens worn in the control groups monocularly. The lenses were worn for 2 weeks in the 2-week treatment groups with the biometry measured at 2, 4, 6, 10 and 14 days of lens wear. The lenses were worn for 4 weeks in the 4-week treatment groups with the biometry measured immediately and at 2, 4, 6, 10 and 14 days after lens removal. Refractions in the defocused eyes developed towards myopia rapidly within 2 days of lens wear, followed by a slower development (p < 0.01 from 2 to 10 days, compared to the fellow eyes). The defocused eyes were at least 3.00 D more myopic with a greater increase in vitreous length by 0.08 mm compared to the fellow eyes at 14 days (p < 0.05). Choroidal thickness of the defocused eyes decreased rapidly within 2 days of lens wear, followed by a slower decrease over the next 4 days. Relative myopia induced by 4 weeks of negative-lens treatment declined rapidly following lens removal (p < 0.05). A complete recovery occurred 14 days after lens removal compared to the fellow eyes (p > 0.05). The refractive changes during the recovery corresponded to a slower vitreous lengthening and a rapid thickening of the choroid. The plano-lens wearing eyes showed a slight but significant myopic shift (< -0.80D) with no associated biometrical changes. Guinea pigs aged 3 weeks are still susceptible to negative lens induced myopia and this myopia is reversible after removal of the lens. The myopia and recovery are mainly due to changes in vitreous length and choroidal thickness. |
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