BLINDNESS
The most straightforward of the circadian rhythm
disorders is blindness. Many completely blind people
have circadian rhythms that are "free nmning" (they
are not synchronized to environmental time cues) and
oscillate on a cycle slightly longer than 24 hours
(approximately 24.5 hours) reflecting the intrinsic
period of the SCN. Consequently, most blind individuals
experience sleep-phase problems because this
internal pacemaker is not able to do the daily adjustment
necessary to remain synchronized with the 24-
hour day. These sleep-phase problems (either advanced
or delayed) underpin the sleep complaint,
which may vary over the course of months and
include sleep-onset insomnia, sleep maintenance insomnia,
difficulty awakening, and excessive daytime
sleepiness. Recent studies have revealed that the
optimal treatment for the sleep-phase problems experienced
by blind people is melatonin. 3~ As with
delayed sleep-phase syndrome, the timing of administration
is important. Melatonin was effective only
when it was given during the phase advance portion
of the patient's phase response curve.
BLINDNESSThe most straightforward of the circadian rhythmdisorders is blindness. Many completely blind peoplehave circadian rhythms that are "free nmning" (theyare not synchronized to environmental time cues) andoscillate on a cycle slightly longer than 24 hours(approximately 24.5 hours) reflecting the intrinsicperiod of the SCN. Consequently, most blind individualsexperience sleep-phase problems because thisinternal pacemaker is not able to do the daily adjustmentnecessary to remain synchronized with the 24-hour day. These sleep-phase problems (either advancedor delayed) underpin the sleep complaint,which may vary over the course of months andinclude sleep-onset insomnia, sleep maintenance insomnia,difficulty awakening, and excessive daytimesleepiness. Recent studies have revealed that theoptimal treatment for the sleep-phase problems experiencedby blind people is melatonin. 3~ As withdelayed sleep-phase syndrome, the timing of administrationis important. Melatonin was effective onlywhen it was given during the phase advance portionof the patient's phase response curve.
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