Case Report: Carbonic anhydrase inhibitor brinzolamide dramatically improved the morphology and also function of a patient with RS1 mutation.

X-linked retinoschisis (XLRS) is an inherited retinal disease caused by mutations in the RS1 gene, which encodes retinoschisin, a protein essential for maintaining the retinal structure during development. Here, we report the therapeutic evidence in a male patient diagnosed with X-linked retinoschisis (XLRS) before and after topical treatment with a carbonic anhydrase inhibitor (CAI), brinzolamide. XLRS-like typical retinal morphology and visual function before treatment and novel improvements gradually from one to 3 months following treatment were observed; then a recurrence of foveal retinoschisis and decreased retinal function occurred because the use of brinzolamide eye drops was disrupted by months-long recurrent upper respiratory tract infections; eventually retinal improvement after resuming brinzolamide were found again, confirming that brinzolamide eye drops could reduce retinoschisis and improve visual acuity. This individualized "dechallenge-rechallenge" evidence chain provides direct supports for the brinzolamide to be the cause in controlling XLRS progression rather than the natural occurring in the course of the disease itself.