Optical Power of the Isolated Human Crystalline Lens

PURPOSE. To characterize the age dependence of isolated human crystalline lens power and quantify the contributions of the lens surfaces and refractive index gradient. METHODS. Experiments were performed on 100 eyes of 73 donors (average 2.8 Ϯ 1.6 days postmortem) with an age range of 6 to 94 years. Lens power was measured with a modified commercial lensmeter or with an optical system based on the Scheiner principle. The radius of curvature and asphericity of the isolated lens surfaces were measured by shadow photography. For each lens, the contributions of the surfaces and the refractive index gradient to the measured lens power were calculated by using optical ray-tracing software. The age dependency of these refractive powers was assessed. RESULTS. The total refractive power and surface refractive power both showed a biphasic age dependency. The total power decreased at a rate of Ϫ0.41 D/y between ages 6 and 58.1, and increased at a rate of 0.33D/y between ages 58.1 and 82. The surface contribution decreased at a rate of Ϫ0.13 D/y between ages 6 and 55.2 and increased at a rate of 0.04 D/y between ages 55.2 and 94. The relative contribution of the surfaces increased by 0.17% per year. The equivalent refractive index also showed a biphasic age dependency with a decrease at a rate of Ϫ3.9 ϫ 10 Ϫ4 per year from ages 6 to 60.4 followed by a plateau. CONCLUSIONS. The lens power decreases with age, due mainly to a decrease in the contribution of the gradient. The use of a constant equivalent refractive index value to calculate lens power with the lens maker formula will underestimate the power of young lenses and overestimate the power of older lenses. (Invest Ophthalmol Vis Sci. 2008;49:2541-2548) DOI: 10.1167/iovs.07-1385 T he optical power of the crystalline lens is determined by the surface curvatures, the refractive index differences at the aqueous lens and lens vitreous interfaces, and the refractive index gradient distribution within the lens. 1 Studying the optical properties of the lens (i.e., optical power, refractive index distribution, and the surface refractive contributions) in vivo is difficult because of the position of the lens behind the cornea and pupil, as well as the distortions of the posterior lens surface caused by the lens refractive index gradient. Two approaches have been used to measure the lens power in vivo. In the first approach the curvatures of the lens surface and lens thickness are measured by phakometry and ultrasonic or optical biometry. The lens power is then calculated assuming an equivalent uniform refractive index (typically, ϳ1.42). 2,3 In the second approach, the lens power is calculated from measurements of axial eye length, anterior chamber depth, corneal power, and refractive state of the eye. These parameters are input into an eye model to calculate the power required for the lens to produce an optical system that matches the measurements. 3-6 Both techniques derive the lens power from measurements of other ocular parameters. Even though recent studies have cross-validated in vivo lens biometry techniques 9 -15 A comparison of in vivo -21 The isolated lens power has been shown to decrease with age

Age-related development of a refractive index plateau in the human lens: evidence for a distinct nucleus

The human lens comprises two distinct regions in which the refractive index changes at different rates. The periphery contains a rapidly increasing refractive index gradient, which becomes steeper with age. The inner region contains a shallow gradient, which flattens with age, due to formation of a central plateau, of RI = 1.418, which reaches a maximum size of 7.0 × 3.05 mm around age 60 years. Formation of the plateau can be attributed to compression of fibre cells generated in prenatal life. Present in prenatal but not in postnatal fibre cells, γ-crystallin may play a role in limiting nuclear cell compression

Evaluation of equilibrium constants from precipitin curves: interaction of α-crystallin with an elicited monoclonal antibody

A simple procedure, based on the precipitin curve and the antibody:antigen ratios of the precipitates, is described for evaluation of the intrinsic association constant (k) governing the interaction between a multivalent antigen and a bivalent antibody. Its application is illustrated with a study of the interaction between alpha-crystallin and an elicited monoclonal antibody, which is shown to exhibit essentially identical affinities (k = 9 X 10(4) M-1) for the alpha m and alpha c forms of the antigen

Growth of the human lens in the Indian adult population: Preliminary observations

Context: The eye lens grows throughout life by the addition of new cells inside the surrounding capsule. How this growth affects the properties of the lens is essential for understanding disorders such as cataract and presbyopia. Aims: To examine growth of the human lens in the Indian population and compare this with the growth in Western populations by measuring in vitro dimensions together with wet and dry weights. Settings and Design: The study was conducted at the research wing of a tertiary eye care center in South India and the study design was prospective. Materials and Methods: Lenses were removed from eye bank eyes and their dimensions measured with a digital caliper. They were then carefully blotted dry and weighed before being placed in 5% buffered formalin. After 1 week fixation, the lenses were dried at 80 °C until constant weight was achieved. The constant weight was noted as the dry weight of the lens. Statistical Analysis Used: Lens parameters were analyzed as a function of age using linear and logarithmic regression methods. Results: Data were obtained for 251 lenses, aged 16-93 years, within a median postmortem time of 22 h. Both wet and dry weights increased linearly at 1.24 and 0.44 mg/year, respectively, throughout adult life. The dimensions also increased continuously throughout this time. Conclusions: Over the age range examined, lens growth in the Indian population is very similar to that in Western populations