While you are sleeping, the eyes continue to produce tears. Because of the position in which you are lying down, not all of the tears drain in the usual fashion. Some of them leak out at the corners of the eye and then dry, which gives some crusting. Therefore, a small amount of crusting is normal. Larger amounts of crusting might not be normal, depending on whether or not there are other symptoms. For example, conjunctivitis, which can be both allergic or an infection, is characterized by red, itching, water eyes. At night this extra drainage will crust over. Both forms of conjunctivitis are easily treated. An infection of the eyelid, known as blepharitis, will also cause crusting. In this condition, the eyelids will be inflamed and reddened right at the edge where the eyelashes are located. As always the diagnosis and the management of your particular condition will require a physical examination by your personal physician. Setting up an office visit with your primary care doctor
might be indicated.