What does the term "Bell's phenomenon" relate to?

Bell's phenomenon refers specifically to the upward eye movement that occurs when the eyelid is closed. This reflexive action is a protective mechanism for the eye, ensuring that when the eye is closed (such as during sleep or when blinking), the cornea is somewhat elevated and protected. The upward movement is mediated by the ocular muscles, particularly involving the action of cranial nerves, primarily the third cranial nerve (oculomotor nerve), which controls most of the eye movements.

Understanding this phenomenon can be important in clinical assessments, especially when evaluating the integrity of cranial nerve function in conditions that may affect facial nerve control or eye closure, such as in Bell's palsy or other neurological conditions. It highlights the way the eyes can respond even when voluntary control over eyelid movements is compromised.