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Abstract
The biometric, optical and physical properties of 19 pairs of isolated human eye-bank
lenses ranging in age from 5 to 96 years were compared. Lens focal length and spherical
aberration were measured using a scanning laser apparatus, lens thickness and the
lens surface curvatures were measured by digitizing 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 force to the lens. The lens capsule was then removed from each lens
and each measurement was repeated to ascertain what role the capsule plays in determining
these optical and physical characteristics. Age dependent changes in lens focal length,
lens surface curvatures and lens resistance to physical deformation are described.
Isolated lens focal length was found to be significantly linearly correlated with
both the anterior and posterior surface curvatures. No age dependent change in equivalent
refractive index of the isolated lens was found. Although decapsulating human lenses
causes similar changes in focal length to that which we have shown to occur when human
lenses are mechanically stretched into an unaccommodated state, the effects are due
to nonsystematic changes in lens curvatures. These studies reinforce the conclusion
that lens hardening must be considered as an important factor in the development of
presbyopia, that age changes in the human lens are not limited to the loss of accommodation
that characterizes presbyopia but that the lens optical and physical properties change
substantially with age in a complex manner.