Biometric, optical and physical changes in the isolated human crystalline lens with age in relation to presbyopia

The biometric, optical and physical properties of 19 pairs of isolated huma n eye-bank lenses ranging in age from 5 to 96 years were compared. Lens foc al length and spherical aberration were measured using a scanning laser app aratus, lens thickness and the lens surface curvatures were measured by dig itizing the lens profiles and equivalent refractive indices were calculated for each lens using this data. The second lens from each donor was used to measure resistance to physical deformation by providing a compressive forc e to the lens. The lens capsule was then removed from each lens and each me asurement was repeated to ascertain what role the capsule plays in determin ing these optical and physical characteristics. Age dependent changes in le ns focal length, lens surface curvatures and lens resistance to physical de formation are described. Isolated lens focal length was found to be signifi cantly linearly correlated with both the anterior and posterior surface cur vatures. No age dependent change in equivalent refractive index of the isol ated lens was found. Although decapsulating human lenses causes similar cha nges in focal length to that which we have shown to occur when human lenses are mechanically stretched into an unaccommodated state, the effects are d ue to nonsystematic changes in lens curvatures. These studies reinforce the conclusion that lens hardening must be considered as an important factor i n the development of presbyopia, that age changes in the human lens are not limited to the loss of accommodation that characterizes presbyopia but tha t the lens optical and physical properties change substantially with age in a complex manner. (C) 1999 Elsevier Science Ltd. All rights reserved.