KRT3 (keratin 3) is a type II cytokeratin located on chromosome 12-q13 1 that functions as a structural component of corneal epithelial intermediate filaments. KRT3 is a marker of differentiated corneal epithelial cells (CECs), with expression increasing upon limbal epithelial stem cell (LESC) differentiation 23. The protein is downregulated in undifferentiated stem cells and upregulated during corneal epithelial maturation, where it participates in keratinization and epithelial cell differentiation 45. KRT3 mutations cause Meesmann corneal dystrophy (MECD), an anterior corneal dystrophy characterized by bilateral epithelial microcysts and corneal opacities 67. Disease-associated variants include missense mutations and indels affecting the keratin protein structure, with some arising de novo 6. The clinical severity varies from minimal visual impairment to corneal blindness, depending on the specific mutation and phenotypic variability 7. KRT3 expression is regulated by multiple signaling pathways, including retinoic acid signaling and transcriptional factors like ETS1 and NRG1, which suppress KRT3 expression in stem cells to maintain proliferative capacity 423. Understanding KRT3 function enables molecular diagnosis and potential therapeutic targeting of corneal dystrophies.