CALORIE RESTRICTION DOES NOT AFFECT THE AGE-RELATED DECLINE IN OCULAR LENS CLARITY OR ACCOMMODATION IN RHESUS MONKEYS
J.A. Mattison*, M.A. Croft, P.L. Kaufman, W. Hubbard, B. Gabelt, J. Kiland, D. Dahl, G.S. Roth, D.K. Ingram, M.A. Lane
National Institute on Aging, Baltimore, MD 21224
Numerous degenerative changes in visual properties occur with age including a loss in accommodative function possibly related to hardening of the lens or loss of ciliary muscle mobility. Several recent studies have identified rhesus monkeys (Macaca mulatta) as a reliable animal model for studying age-related changes in ocular function. Calorie restriction (CR) is the only consistent intervention to slow aging and extend lifespan in rodents and more recently, the beneficial effects of CR have been evident in nonhuman primates. The goal of the present study was to evaluate age-related changes in ocular accommodation and the potential effect of long-term (>8 years) CR in male and female rhesus monkeys.
Refraction and accommodation (Hartinger coincidence refractometer), and lens thickness (A-scan ultrasound) were measured in 97 male and female rhesus monkeys age 8 to 36 yr under Telazol/acepromazine anesthesia. Refraction and accommodation measurements were taken before and after 40% carbachol iontophoresis to induce maximum accommodation. Age was estimated for each animal based on ocular clarity by an experienced ophthalmologist who did not know the real age. Half the animals were in the control (CON) group fed ad libitum while the CR group has received 30% less than age and weight-matched controls for 12 yr (males) or 8 yr (females).
With increasing age, accommodative ability declined in both CON and CR monkeys by 1.03 ± 0.09 (p= 0.001) and 1.18 ± 0.09 (p= 0.001) diopters/yr respectively. The age-related decline did not differ significantly between the groups (p=0.270). Baseline lens thickness increased with age in both groups by 0.03 ± 0.005 mm/yr (p= 0.001) and 0.02 ± 0.005 mm/yr (p= 0.001) for the CON and CR groups, respectively; again, the groups did not differ significantly (p=0.140). Baseline resting refraction was -2.3 ± 0.55 and -3.1 ± 0.54 diopters for CON and CR, respectively, and the regression of resting refraction on age was not significant. There was no difference in the slope of the age-related changes in accommodation, lens thickness, or refraction due to diet. The slopes of the regression of estimated age on real age was 0.79 ± 0.06 and 0.83 ± 0.06 estimated-years/real years for the CON and CR group, respectively. Thus, estimated age was about 20% less than true age for both groups but did not differ significantly between the groups.
These data are consistent with previous findings of decreased accommodative ability in aging rhesus monkeys, which is comparable to the age-dependent decrease in accommodative ability in humans. Although CR has been shown to slow many age-related changes, this study is the first to indicate that the accommodative system may not benefit from this intervention. The results are not entirely conclusive, however, because older animals may have already experienced an age-related decline before being placed on the CR diet; the late onset of CR could not be expected to reverse these changes. Nonetheless, this study does show that CR was not harmful to the accommodative system and can therefore be considered for its other advantages.
This study was supported in part by NIH grant numbers EY10213 and EY07119.
Key words:
vision, aging, calorie restriction, monkeys
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