Purpose. The optical density of the human crystalline lens progressively increases with age and causes a shift in the spectral distribution of light reaching the retina. Yet color appearance is remarkably stable across the life span. When the lens is removed, cataract patients often report that the world looks much 'bluer' and this effect can last for many weeks. This suggests a process involving a long-term adaptive mechanism. We examined this adaptive mechanism by studying color appearance changes before and after cataract surgery. Methods. Lens absorption was measured by comparing absolute scotopic thresholds from 410 to 600 nm before and after surgery. Color appearance shifts were quantified using achromatic settings made on a calibrated CRT. Chromaticity was adjusted in CIE u'v' color space with luminance fixed at 30cd/m2, on a black background. The test area flashed on and off at 3s intervals. The achromatic settings were made before surgery and at various intervals after surgery up to one year. Results. Following surgery, there is an increase in short-wave light, mainly below 500 nm, reaching the retina. This has a large impact on S-cone quantal catch and a smaller impact on the M- and L-cones. The achromatic settings showed a large shift in the 'yellow' direction after surgery that gradually (but never fully) returned to the original setting over the course of a year. Conclusion. After cataract surgery, the intensity of the light at lower visible wavelengths increases substantially and results in a shift in color appearance. Over a period of several months, the visual system adapts to compensate for this change.
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