It seems likely that the influences of light upon circadian rhythms will decrease with aging, particularly those rhythms that are more influenced by light with a higher color temperature and richer in short wavelengths. More specifically, cataract patients' optical systems transmit light poorly, especially the shorter wavelengths that affect the circadian system more. The present study investigated melatonin secretion profiles and sleep patterns before and after cataract surgery. Fifteen subjects were studied for 3 consecutive weekdays before, and one month after, their cataract surgery. UV-cutting intra-ocular lenses were used for patients after surgery. No statistically significant differences between before and after surgery were observed in the amount of light received and the amount of activity. This means that there were no significant changes in their lifestyle during the experimental period. Considering the group as a whole, no significant differences were present in melatonin secretion, sleep parameters, or sleepiness before and after the surgery. However, individual subjects responded differently. The subjects showed a negative correlation between the wake-up ( p =0.067) or retiring times ( p =0.017) and sleep efficiency after surgery. The amount of light received during the nighttime influenced sleep more significantly than during the daytime.