Toxic Anterior Segment Syndrome Following Implantable Collamer Lens Implantation in a Patient With Keratoconus and Nystagmus: A Case Report.

Toxic anterior segment syndrome (TASS) is a rare but serious postoperative inflammation that can occur after intraocular surgery, including after implantable collamer lens (ICL) implantation. A 27-year-old man with keratoconus and horizontal nystagmus developed severe anterior chamber inflammation two days after toric myopic ICL implantation in the right eye. Unlike endophthalmitis, which presents later with severe pain, conjunctival injection, and vitreous inflammation and requires intravitreal antibiotics, our patient had a rapid onset, no pain, no vitreous involvement, and a quick response to steroids, supporting a diagnosis of TASS. Intensive medical therapy led to full recovery, and subsequent left eye surgery was uneventful. This case highlights the importance of distinguishing TASS from infection through careful clinical reasoning and timely management, ensuring safe toric ICL implantation in patients with nystagmus.