Palpebral fissures

The anatomic openings between the upper and lower eyelid margins (rimae palpebrarum). It determines how much of your eye is visible, averaging about 10 mm vertically and 30 mm horizontally in healthy adults. Vertical widening (larger openings) are seen in Graves' disease, facial nerve paralysis, and Cri-du-chat syndrome. Vertical narrowing (smaller opening) is seen in ptosis, blepharophimosis, trisomy 21, Marfan syndrome, Noonan syndrome, and fetal alcohol syndrome.