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.
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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:
PERL - Pupils Equal and Reactive to Light
PERRLA - Pupils Equal, Round and Reactive to Light and Accommodation.
RAPD - Relative Afferent Pupillary Defect
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.
This pen light should be part of your usual equipment that you bring to work along with your stethoscope, bandage scissors and Kelly clamps. (Usually the facility will have BP cuffs available, but if not, add that to your kit.)
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.
Watch an Eval of PERRLA
Silly story: I had an allergic reaction in one eye that caused intense itching so I used OTC allergy eye drops which did a great job stopping the itch but after repeated application of eye drops, I noticed that my vision had become very blurry in that eye. Looking in the mirror I noticed the difference in size. One pupil was totally blown for a while.
My first thoughts were wondering why I wasn’t noticing any other signs of a stroke. It took a few minutes to realize that one OTC allergy drops side effect is to dilate the pupil.