Auckland University researchers hope a new study will eventually help blind or vision-impaired people get a better night's sleep.
Dr Guy Warman, a lecturer in the Faculty of Medical and Health Sciences, said many blind people suffered chronic sleeping disorders because they could not perceive light, which helps to adjust
the internal body clock to 24 hours.
"It's like having jet lag without leaving home," he said.
"Light perception in sighted people allows them to make daily adjustments to this, which keeps their sleep patterns in line. However, those with poor or no light perception can find their body clock, and thus their sleep patterns, progressively drifting."
Chris Orr, a member of the Royal New Zealand Foundation of the Blind, has suffered disrupted sleep since losing his sight in an accident 30 years ago.
"I regularly wake at around 1.30 in the morning and then can't get back to sleep. Over the years I have accepted it and now just listen to the radio or read when I am awake at night. But I would obviously prefer a more regular sleep pattern."
Dr Warman said melatonin, a hormone produced by the pineal gland, had been successfully used to treat the problem but there was little information on the prevalence of sleep timing problems in blind and vision-impaired people. It was also unclear whether melatonin, taken in tablets, was being used appropriately.
The study, funded by the Health Research Council of New Zealand, will involve three groups of people: those with no conscious light perception (if you shine a torch in their eyes they cannot see it at all), those who are blind but have conscious light perception, and a group who are not visually impaired.
Dr Warman said the study results could be used to educate doctors, pharmacists and patients on the appropriate and effective use of melatonin.
