CHANGES IN VISUAL FUNCTION WITH NORMAL AGING, CATARACT AND INTRAOCULAR LENSES

We have been able to separate the neural and optical components of vision with contrast sensitivity tests employing laser interferometry and direct viewing of a cathode ray tube display. In normal ageing, neural function declined markedly while optical function remained essentially unchanged. On the other hand, even the mildest degree of cataract was shown to degrade optical function to the extent that it exceeded the age-related neural deterioration. The satisfactory optical performance of the monofocal implant lens has been confirmed, though the diffractive bifocal implant lens was shown to have optical limitations. A major cause of these was shown, by simulation experiments, to be the dilution of the contrast of the in-focus image by the superimposed defocused image, particularly under conditions of reduced retinal sensitivity as would be present in the elderly.