RELATIONSHIP BETWEEN MELATONIN RHYTHMS AND VISUAL-LOSS IN THE BLIND

Melatonin rhythms were assessed in 49 registered blind individuals by measurement of the urinary metabolite of melatonin, 6-sulfatoxymelaton in (aMT6s). Subjects had different causes of visual loss and were clas sified as having light perception or better (LP; n = 19) or having no perception of light (NPL; n = 30). Subjects collected four-hourly urin e samples (eight-hourly overnight) for 48 h at weekly intervals for 3- 5 weeks. The majority of LP subjects (14 of 19) had normally entrained aMT6s rhythms (mean acrophase range, 2.4-6.2 h), 4 were abnormally en trained to 24 h (mean acrophase range, 8.9-1.0 h), and 1 was unclassif ied. Conversely, most NPL subjects had abnormal rhythms (23 of 30), th e incidence of which was greater in uni- and bilaterally enucleated su bjects. The majority of NPL subjects (17 of 30) had free-running aMT6s rhythms (period range, 24.13-24.79 h), 5 were abnormally entrained to 24 h (acrophase range, 7.2-20.6 h), and 1 was unclassified. Output (m icrograms of aMT6s per 24 h) and amplitude (micrograms per h) of aMT6s production did not vary between LP and NPL subjects (mean 24-h output +/- SD, 12.7 +/- 7.5 and 9.4 +/- 6.4 mu g aMT6s/24 h, respectively; m ean amplitude +/- SE, 0.6 +/- 0.4 and 0.5 +/- 0.3 mu g/h, respectively ). These results indicate that a higher proportion of NPL subjects hav e abnormal melatonin rhythms compared to those with LP.