Miosis or Mydriasis? Here is a Quick Mnemonic to Remember

When it comes to the size of our pupils, two important terms come into play: miosis and mydriasis. These words describe opposite conditions of pupil size, which can provide insight into various medical conditions or reactions to light.

What is Miosis?

Miosis refers to the constriction of the pupil. This occurs when the pupil becomes smaller, typically less than 2 millimeters in diameter in daylight. It’s often a natural response to bright light or certain medications. Here is a mnemonic: You can remember that miosis means constricted pupils by noting that the word “miosis” has fewer letters (6), which corresponds to a smaller, tighter pupil.

What is Midriasis?

Mydriasis, on the other hand, describes the dilation of the pupil, where it becomes larger—usually more than 4 millimeters in daylight. This may occur in dim lighting or in response to specific drugs. A helpful way to recall that mydriasis means a dilated pupil is by recognizing that the word has more letters (9), just like the pupil widens.

Both conditions are normal responses to light or stimuli, but can also be indicative of underlying neurological or ophthalmic issues.