How many millimeters is the palpebral fissure normally?

• A. 8 millimeters
• B. 12 millimeters
• C. 9 millimeters
• D. 10 millimeters

Answer: (D)

The palpebral fissure is the opening between the upper and lower eyelids. When the eyes are in a straight-ahead gaze, the vertical height of that opening is normally about ten millimeters in adults. This single, round-number standard makes it a convenient reference in clinical observations and exams.

To measure it, have the patient look straight ahead and measure the distance from the upper lid margin to the lower lid margin at the center of the pupil. While ten millimeters is a common reference, there is natural variation among individuals, and some sources note a range roughly from about nine to twelve millimeters. Infants or individuals with ptosis may have smaller fissures, while other conditions can slightly increase the visible height.

So, among typical values, ten millimeters best represents the normal palpebral fissure height.