GJD2 encodes connexin 36 (Cx36), a gap junction protein that forms intercellular channels allowing direct communication between adjacent cells 1. The protein is highly conserved across species (98% identity between human, mouse, and rat) and is predominantly expressed in neuronal cells of the mammalian central nervous system 1. In the brain, GJD2 shows intense expression in the inferior olivary complex, cerebellar cortex, cerebral cortex, hippocampus, and spinal cord gray matter 1. The gene is located on chromosome 15 1. Functionally, GJD2 plays a critical role in refractive error development, particularly myopia. Multiple genome-wide association studies have consistently identified GJD2 variants as top genetic risk factors for myopia 2. Genetic variants in GJD2, particularly rs524952 and rs634990, are associated with increased risk of myopia progression in children and hyperopia with astigmatism 34. The GJD2 risk genotype follows a dose-response pattern, with carriers showing longer axial length and deeper vitreous chambers already visible at age 6 years 5. Functional studies in zebrafish demonstrate that loss of gjd2 orthologs leads to refractive errors and retinal electrophysiological changes 6, supporting its role in ocular biometry regulation through retinal gap junctional communication.