A 2017 study in Cornea involved 125 people —100 of whom had dry eye disease — and their sleep habits. Those who slept on their left or right side had more severe dry eye than those who slept on their backs.
Sleeping with a fan can soothe your mind and cool your body, but this can also aggravate dry eye. A 2014 article in the Saudi Journal of Ophthalmology studied 48 people who had dry eye and slept in a room with high air flow from air conditioning or a ceiling fan. Those who slept on their sides had more dry eye symptoms and lower production of tears in the contralateral eye. In other words, those who slept on their right side had more problems in their left eye than their right. This was particularly the case in people who had nocturnal lagophthalmos, which is when the eye doesn’t close completely during sleep. The authors suggested some options for people with this condition to reduce their symptoms of dry eye, such as sleeping on their back.