The effect of age on compensation for a negative lens and recovery from lens-induced myopia in tree shrews (Tupaia glis belangeri)

Abstract

We examined in tree shrews the effect of age on the development of, and recovery from, myopia induced with a negative lens. Starting at 11, 16, 24, 35 or 48 days after natural eye-opening (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=6) began treatment at 16 days of VE and wore the lens for 30 days. A young adult group (n = 5) began to wear a −5 D lens between 93 and 107 days of VE (mean ± SD, 100 ± 6 days of VE) and wore the lens for 29 to 54 days (mean ± SD, 41.8 ± 9.8 days). The recovery phase in all groups was started by discontinuing −5 D lens wear. Contralateral control eyes in the three youngest groups were compared with a group of age-matched normal eyes and showed a small (<1 D), transient myopic shift. The amount of myopia that developed during lens wear was measured as the difference between the treated and control eye refractions. After 11 days of lens wear, the induced myopia was similar for the four younger groups (near full compensation: 11 day, −5.1 ± 0.4 D; 16 day, −4.7 ± 0.3 D, 24 day, −4.9 ± 0.4 D; 35 day, −4.0 ± 0.02) and slightly less in the oldest juvenile group (48 day, −3.3 ± 0.5 D). The young adult animals developed −4.8 ± 0.3 D of myopia after a longer lens-wear period. The rate of compensation (D/day) was high in the 4 youngest groups and decreased in the 48-day and young adult groups. The refractions of the long-term lens-wear juvenile group remained stable after compensating for the −5 D lens. During recovery, all animals in the youngest group recovered fully (< 1 D residual myopia) within seven days. Examples of both rapid (< 10 days) and slow recovery (> 12 days) occurred in all age groups except the youngest. Every animal showed more rapid recovery (higher recovery slope) in the first 4 days than afterward. One animal showed extremely slow recovery. Based on the time-course of myopia development observed in the youngest age groups, the start of the susceptible period for negative lens wear is around 11 to 15 days after eye opening; the rate of compensation remains high until approximately 35 days of VE and then gradually declines. Compensation is stable with continued lens wear. The emmetropization mechanism, both for negative lens compensation and recovery, remains active into young adulthood. The time-course of recovery is more variable than that of compensation and seems to vary with age, with the amount of myopia (weakly) and with the individual animal.

Multi-scale Modeling of Vision-Guided Remodeling and Age-Dependent Growth of the Tree Shrew Sclera During Eye Development and Lens-Induced Myopia

“…Similar to the growth rate (1), the maximum remodeling rate is assumed to be genetically determined and to decrease with age. These assumptions are based on the observation that the relative axial elongation rate (treated eye minus control eye) decreases with age in lens treated tree shrews [32]. …”

“…Our G&R model was fitted to previously published data from Norton et al [32] consisting of 6 groups of tree shrews G 1−6 that were treated with a -5D lens on one eye at different ages ( n = 5 per group) and one new group of normal animals (no treatment) G 0 ( n = 7). One group of Norton et al [32] was disregarded here as it didn’t enrich the cost function used to fit our model.…”

“…One group of Norton et al [32] was disregarded here as it didn’t enrich the cost function used to fit our model. The lens wear started at 11, 16, 24, 35, 48, and 100 DVE in G 1−6 , respectively.…”

“…In addition to refractive measurements, the axial dimensions were obtained for the new normal group G 0 using a Lenstar LS-900 optical biometer (Haag-Streit USA, Mason, OH). Details about the experimental procedures can be found in Norton et al [32]. The LenStar biometer is known to be calibrated for human eyes [44].…”

“…In Section 3 we fit our model to new and previously published tree shrew data [32]. In Section 4 we investigate the predictive power of our new model by validating it against data that was not used to fit the model [24; 33].…”