09/19/2026
Pupillary light reflexes (PLRs) are vital to localizing a lesion.
In the above case, I couldn’t see the retina or optic nerve in the left eye, but I know there’s a problem there. The left pupil remains mydriatic when stimulated and the right pupil also doesn’t move either. This indicates the left retina or optic nerve are affected. I looked at the right retina and there was severe retinal degeneration.
Tips:
• Dilated pupil + no direct PLR, but consensual PLR works → problem with the nerve controlling that pupil or iris atrophy
• Shine light in one eye → neither pupil constricts → problem with the retina or optic nerve (CN II) of the eye you’re testing
• Blind + normal PLRs + normal dazzle → think brain/visual pathway/SARDS
• Blind + no PLRs + no dazzle → think severe retina or optic nerve disease, like optic neuritis
