Objective: To investigate changes in refraction and vitreous length during form-deprivation and visual re-exposure in guinea pig eyes.
Methods: It was an experimental study. Ninety-six guinea pigs with age of three weeks were randomly divided into form-deprivation and normal control groups (n = 48 in each group). The form-deprivation group was further divided into 4 subgroups (n = 12 in each subgroup) which underwent monocular form-deprivation for 1, 2, 4, and 6 weeks, respectively. At the end of each time point, the form-deprived eyes in all animals were visually re-exposed and followed for 3 (n = 6) and 7 days (n = 6). The control group was also divided into four subgroups (n = 12 in each subgroup) to match the time-points of the form-deprivation group. During form-deprivation and recovery, vitreous length and refraction in each group was measured and compared.
Results: There was significant difference in vitreous length (F = 6.108, 28.222, 19.195) and refraction (F = 12.504, 15.003, 6.829) when compared deprived eyes with contralateral eyes 2, 4, or 6 weeks after form-deprivation (P < 0.05). Difference in refraction between deprived eyes and contralateral eyes was -2.36 D, -3.64 D and -3.68 D at 2, 4, 6 week, respectively. Difference in vitreous length was 0.08 mm, 0.19 mm and 0.22 mm. During visual re-exposure, form-deprived eyes changed into hyperopia as compared with contralateral eyes. At day 3 point, there was no significant difference in refraction and vitreous length between form deprived eyes and contralateral eyes in 1 week and 2 weeks groups (F = 0.032, 0.280; P > 0.05). After 7 days recovery, vitreous length and refraction in deprived eyes almost backed to level of contralateral eyes in 1 and 2 weeks groups. At day 3 point, there was significant difference of refraction and vitreous length between form-deprived eyes and contralateral eyes in 4 weeks group and 6 weeks group. After 7 days recovery, there was significant difference in vitreous length for 4 weeks group and there was significant difference in both refraction and vitreous length for 6 weeks group (F = 4.108, 6.317; P < 0.05).
Conclusion: Form-deprivation causes myopic changes in deprived eyes, during visual re-exposure the refraction recovers and the extent depends on the length of form-deprivation. The recovery rate is faster during the first 3 days and then slower after 3 days. The mechanism of form-deprivation myopia in guinea pig eyes is similar to that of myopia in juvenile human beings.