Were you visited by the sandman during the night and woken up to find crusty sand like stuff called “sleep in your eyes”? Sleep can make it hard to open your eyes in the morning. What is the sleep in your eyes and why does it form? 

‘Sleep’ is a type of rheum which is a type of mucus and is referred to as gound. It is made up of mucus, skin cells, oils and dust. Gound has a protective function by removing waste products and potentially harmful debris from the tear film and the front surface of your eyes.

Eyes produce gound throughout the day. However, when you blink throughout the day, the gound is flushed out before it can harden in your eyes. When you're asleep — and not blinking — eye discharge collects and crusts in the corners of your eyes and sometimes along the lash line, hence the term "sleep in your eyes."

Eye discharge is a function of your tear film and a necessary component of good eye health and waking with some sleep in your eyes is normal. Obscene amounts of gound build up, sometimes to the point where it prevents people from opening their eyes.  

Thus it is due to the lack of blinking while we sleep that gound is able to build up in the corner of the eyes and along the lash line. The gound then dries forming the white ‘sandy’ substance that we know as “sleep in the eyes.”