Along with eye motion, pupillary response is controlled by cranial nerves III, IV, and VI. Normal pupils are of the same size bilaterally, about 2 to 6 mm and round.
About 15% of people have one pupil up to 1 mm smaller than the other; this is a normal variant known as anisocoria.
Occasionally, patients that have had cataract surgery will have irregular shaped pupils
A simple test any nurse can perform will determine if the eyes are normal. You will usually see one of two acronyms to describe this normal result:
To check pupil reactivity, bring a small beam of light in from the outer canthus (corner) of one eye; the normal response is for both pupils to react equally and briskly. There will be a slight increase in diameter a second or so after the light is applied and held on the eye.
Keep in mind that medications, surgery, and blindness can affect pupil size, shape, and reactivity. The hallmark sign of severe neurologic injury is a change in pupil size and reactivity.
Using a simple pen light is sufficient to do the test and takes only a minute or two. Please don’t try to do this just by shielding one eye from the ambient light with one hand. That’s just lazy.
Occasionally, people who have had cataract surgery will have a pupil that is not completely round, or people who have cataracts may have less brisk response to light since the opacity of the lens prevents light from entering the eye.
Also, medications such as OTC or prescription eye drops can affect the dilation of the pupil.