Refractive Power and Biometric Properties of the Nonhuman Primate Isolated Crystalline Lens

Abstract

Purpose. To characterize the age dependence of shape, refractive power, and refractive index of isolated lenses from nonhuman primates. Methods. Measurements were performed on ex vivo lenses from cynomolgus monkeys (cyno: n = 120; age, 2.7-14.3 years), rhesus monkeys (n = 61; age, 0.7-13.3 years), and hamadryas baboons (baboon: n = 16; age, 1.7-27.3 years). Lens thickness, diameter, and surface curvatures were measured with an optical comparator. Lens refractive power was measured with a custom optical system based on the Scheiner principle. The refractive contributions of the gradient, the surfaces, and the equivalent refractive index were calculated with optical ray-tracing software. The age dependence of the optical and biometric parameters was assessed. Results. Over the measured age range isolated lens thickness decreased (baboon: -0.04, cyno: -0.05, and rhesus: -0.06 mm/y) and equatorial diameter increased (logarithmically for the baboon and rhesus, and linearly for cyno: 0.07 mm/y). The isolated lens surfaces flattened and the corresponding refractive power from the surfaces decreased with age (-0.33, -0.48, and -0.68 D/y). The isolated lens equivalent refractive index decreased (only significant for the baboon, -0.001 D/y), and as a result the total isolated lens refractive power decreased with age (baboon: -1.26, cyno: -0.97, and rhesus: -1.76 D/y). Conclusions. The age-dependent trends in the optical and biometric properties, growth, and aging, of nonhuman primate lenses are similar to those of the pre-presbyopic human lens. As the lens ages, the decrease in refractive contributions from the gradient refractive index causes a rapid age-dependent decrease in maximally accommodated lens refractive power.

Influence of Shape and Gradient Refractive Index in the Accommodative Changes of Spherical Aberration in Nonhuman Primate Crystalline Lenses

“…Studies in in vitro-human crystalline lenses 58 reported a positive conic constant in the anterior surface and scattered values of approximately 0 for the posterior. The values of asphericity reported here for the fully accommodated state agrees well with those reported by a previous study in isolated cynomolgus monkey lenses, 33 where a wide range (from À6 to þ4) was reported. The high value of lens anterior surface asphericity in monkeys in the unaccommodated state, never reported in humans, may be due to the differences in size between the species, to the young age of the monkey lenses compared with the humans from prior literature, and to the larger accommodative range of monkey lenses (up to 30 D) in comparison with the human lens (no more than 10 D).…”

“…Recent studies have investigated the lens power change with accommodation, and the role of the GRIN in cynomolgus monkeys and hamadryas baboons, assuming a value for the outer cortex refractive index. 33,34 The relative contribution of the GRIN to lens power appears to remain constant with accommodation. 9,34,35 This suggests that a homogenous index material in lens refilling procedure would be equally efficient in producing a refractive power change (assuming identical lens shape changes) than the natural lens GRIN material.…”

“…41,43 Nonhuman primates have been used in the literature as a model for myopia, emmetropization, or accommodation. 33,34,47,48 Both rhesus and cynomolgus monkeys are used as an experimental model to test emerging solutions for presbyopia correction. [49][50][51] Although there may be some differences in the growth of human and monkey lenses, the monkey's accommodation apparatus has been shown to be close to human (Augusteyn RC, et al IOVS 2011;52:ARVO EAbstract 1541), and to change in a similar way with age as the accommodation apparatus of a human does.…”

“…[49][50][51] Although there may be some differences in the growth of human and monkey lenses, the monkey's accommodation apparatus has been shown to be close to human (Augusteyn RC, et al IOVS 2011;52:ARVO EAbstract 1541), and to change in a similar way with age as the accommodation apparatus of a human does. 33,52,53 A full characterization of the cynomolgus monkey lens as a function of accommodation is therefore important to fully establish this species as a model for accommodation and presbyopia studies.…”

Noncoding origins of anthropoid traits and a new null model of transposon functionalization

“…GABA genes were also responsible for the enrichment of ASCs in eye lens development loci. GABA signaling influences lens growth (Schwirtlich et al 2011), and the primate lens is known for its ability to accommodate an exceptionally wide range of focal lengths (Borja et al 2010). Thus, widespread anthropoid gain of function in the GABA signaling pathway could potentially have played a role in primate visual acuity.…”