Research advances in claudin-1 in the eye.

Claudin-1, a transmembrane protein integral to tight junctions, is indispensable for paracellular barrier formation and the establishment and maintenance of cellular polarity. In the eye, claudin-1 exhibits tissue-specific expression in critical structures such as the cornea and retina, where it contributes fundamentally to corneal transparency, blood-retinal barrier integrity, and retinal homeostasis. This review comprehensively synthesizes current knowledge on the spatial distribution and physiological roles of claudin-1 across ocular tissues. We critically evaluate recent mechanistic and translational advances implicating claudin-1 dysregulation in a spectrum of ocular pathologies: anterior segment disorders (dry eye disease, pterygium, infectious keratitis, and gelatinous drop-like corneal dystrophy), retinal diseases (diabetic retinopathy, age-related macular degeneration, central serous chorioretinopathy, and retinoblastoma), and other conditions (uveitis, glaucoma, post-cataract macular edema, and cataract). Finally, we assess the emerging therapeutic potential of claudin-1-both as a molecular target for barrier modulation and as a facilitator of paracellular drug delivery in ophthalmology.