Sleeping with eyes open is caused by incomplete lid closure, which can be caused by a variety of reasons, such as facial nerve paralysis and thyroid-related eye disease. The facial nerve innervates the orbicularis oculi muscle. When the orbicularis oculi muscle is stimulated by electrical signals from the facial nerve, it will contract, thus closing the eyelid slit. If the facial nerve is paralyzed, the orbicularis oculi muscle will not be able to move properly, and the eyelids will not be able to close completely when the patient sleeps, so the patient may sleep with his/her eyes open. Thyroid-related ophthalmopathy may be caused by hyperplasia of the orbital contents, which pushes the eyeballs to protrude, resulting in the patient’s eyelids not being able to close completely when sleeping. In addition, if the patient is overly tired, he or she may also sleep with incomplete lid closure, which is not a pathologic change. It is recommended that patients with incomplete eyelid closure and other discomfort seek medical attention to evaluate their condition and follow the doctor’s instructions.