SANDMAN- A randomised placebo-controlled trial to assess the effect of melatonin on circadian sleep-wake disturbances in ocular disease
Our sleep/wake cycles are fine-tuned by specialist cells located at the back of the eye. These cells are sensitive to blue light and are known as the photosensitive retinal ganglion cells (pRGC). The amount of light entering the eye in daylight hours is very different from night time. The pRGCs are activated by light and send a signal to a receptive area in the brain, which controls the sleep/wake cycle. When working properly sleep is triggered to happen at night and being awake occurs with onset and in daylight. This ensures that we are in synch with our environment. There are a number of reasons why the message does not reach the brain. From our studies investigating ocular disease and its impact on sleep and mood, we know that disorders that affect the eye may in some cases damage the pRGCs, particularly if they have damaged the retina extensively as seen in advanced glaucoma, optic nerve disease and end stage retinal disorders.
Where no eyes are present either due to being born without eyes or removal due to trauma or diseases, no pRGCs are present so no message can be sent to the brain. Melatonin is a hormone triggered as part of this pathway to ‘inform’ the body that night time is imminent. It is, naturally produced by the body and is important in controlling body clock. It activates certain types of chemical receptors in the brain and thereby helps to induce sleep. Melatonin has been prescribed by doctors to help people with sleep disorders and does not have the side effects typically associated with other sleep medications. We are carrying out a trial to see if melatonin supplements can be used to improve sleep cycles in people with ocular disease who have sleep disorders, to try to help initiate sleep at night, and thus improving wakefulness in the day.