Blind people with no light perception can suffer from a variety of sleep problems. Its now been proved that for the majority of blind people with no light perception, the lack of light makes it impossible for a gland situated in the brain to produce sufficient levels of a hormone called melatonin. This can lead to circadian sleep disorders which can occur when the body clock does not fall into a regular rhythm. Blind listeners tell In Touch about the impact poor sleep can have on their quality of life. We also hear from Lynn McGovern of The Circadian Sleep Disorders Network, a support and advocacy group which works on raising awareness of disrupted sleep, . Russell Foster, a Professor of Circadian Neuroscience and Head of Ophthalmology at Nuffield Department of Clinical Neurosiences, Oxford University has spent many years researching sleep problems in blind people and he tells Peter about the current thinking on why blind people persistently suffer from problems sleeping. Producer: Lee Kumutat Presenter: Peter White.