Shining a bright light directly into your patient’s pupil, you have one second to catch the speed of dilation, 8-10 seconds to estimate size, about 4 seconds to determine whether those approximations are relatively normal—and you do it all relying on nothing more than years of practice and your own naked eye. And for the most part, it’s worked. As long as you have plenty of elbow room for error.
Physicians have trusted the pupillary light reflex (PLR) to assess a number of clinical conditions for more than 100 years. Popular for its role in concussion analysis, PLR has also been used to gauge depth level of sedation, detect consciousness and diagnose brain death in comatose patients, and screen for retinoblastoma in infants.