The interrelationship of lens anatomy and optical quality. II. Primate lenses

We have quantified the influence of lens sutural anatomy on optical quality (focal length variability, i.e. spherical aberration) in adult monkeys (Macaque nemestrina). Adult lenses (n = 6) were initially scanned by a low-power helium-neon laser beam that was passed at a series of acute angles to, and/or directly through, lens sutures. Optical analysis showed that while the 'star' sutures of primate lenses exerted a quantifiable negative effect on focal length variability, this detrimental effect was far less significant than that attributable to 'line' and 'Y' sutures in non-primate lenses. Correlative morphological and 3-D computer-assisted drawing (CAD) analysis of the laser-scanned lenses areas, as well as of variably aged lenses (n = 30), revealed that primates have a more complex lens architecture than non-primates. Non-primate lenses feature suture planes, aligned along the visual axis that are responsible for a significant quantifiable increase in spherical aberration. Primate lenses are characterized by an absence of continuous suture planes aligned along the visual axis. Rather, 3-D-CADs of primate lenses demonstrate that distinct generations of progressively more complex sutures are produced as a function of development, growth, and age. In succession, 'Y' sutures (three branches) are formed throughout embryonic development, 'simple star' sutures (three-six branches) evolve after birth and through infancy, 'star' sutures (six-nine branches) are made in young adult lenses and, finally, 'complex star' sutures (nine-15 branches) are laid down from middle through old age. In view of the fact that slit-lamp evaluation of cataractous lenses often reveals abnormally thin zones of discontinuity, it is significant to note that the temporal development of the zones of discontinuity in normal human lenses is essentially identical to the progressive iteration of offset monkey lens sutures. In conclusion, these studies describe a specific structural aspect of lenses that adversely influences optical quality, and relates it to the most commonly employed clinical technique to identify and monitor the progress of cataracts.