The eyes and orbits are protected by reinforced folds of skin called the palpebrae, or eyelid. The eyelids serve three basic functions;
1. Blinking replenishes and spreads the tear film evenly
2. Pumps the tears through the lacrimal sac for drainage
3. Protects the eye from small foregin bodies and excessive light by rapidly and forcefully closing.
The rapid, forceful closure is called reflex blinking. The condition in which the eyes are so closed that they cannot be opened is called lepharospasm.
The space between the lids is called the palpebral fissure and measures approximately 10 mm at its widest point. If the palpebral fissure is too small (i.e. the upper lid droops) the condition is called ptosis.