Bilateral Symmetric Circular Toxic Corneal Epitheliopathy Caused by Residual Disinfectant on an A-Scan Ultrasound Biometry Probe: A Case with Transient Visual Acuity Reduction

We report a rare case of bilateral, symmetric circular toxic corneal epitheliopathy caused by residual disinfectant solution (contains a foam from combination of citric acid and sodium chlorite) on an A-scan ultrasound biometry probe, producing transient visual acuity reduction. A 61-year-old woman underwent routine preoperative A-scan biometry prior to cataract surgery, minutes later, she presented with striking bilateral circular 5.5 - 6 mm central epithelial lesions containing dense necrotic precipitates. Visual acuity dropped unexpectedly from 0.7/0.6 pre-biometry to 0.4 OU. Although the optician initially stated that the probe had been dried, further questioning revealed that drying was inadequate, allowing residual disinfectant to remain on the probe tip. The patient works as a denture technician but denied any prior chemical or foreign-body exposure or previous contact lens use. Intensive lubrication and mild topical steroid led to complete recovery within 7 days. Disinfectant-induced corneal toxicity can occasionally produce substantial yet transient visual impairment when necrotic epithelium obstructs the visual axis. Perfect bilateral symmetry strongly supports instrument-mediated chemical transfer. Proper and optimal drying of A-scan probes is essential to prevent avoidable iatrogenic injury.