Bilateral Acute Iris Transillumination Mimicking Anisocoria

Anisocoria, defined as a ≥0.4 mm difference in pupil diameter, may result from physiological or pathological causes. While often benign, it can occasionally indicate serious neurological or ophthalmological conditions. Bilateral acute iris transillumination (BAIT) is a rare, recently defined entity characterized by iris pigment dispersion and sphincter paralysis. A 54-year-old female presented to the emergency department on noticing unequal pupil sizes. Neurological examination and cranio-cervical magnetic resonance ımaging were unremarkable. She was referred to ophthalmology for further evaluation. Slit-lamp examination revealed bilateral iris transillumination defects and pupillary mydriasis, more prominent in the left eye. No signs of uveitis, glaucoma, or optic nerve pathology were observed. On detailed anamnesis, she reported systemic moxifloxacin use 1 month earlier for an upper respiratory tract infection. Clinical findings and drug history supported a diagnosis of BAIT. BAIT should be considered in the differential diagnosis of anisocoria, especially when neurological imaging is normal. Early recognition may prevent unnecessary investigations and optimize patient care.

Keywords: Anisocoria, uveitis, pupil disorders, moxifloxacin.