Macular coloboma is a congenital defect of the retina and choroid in the macular region. It may appear due to an intrauterine inflammation or a developmental abnormality. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a result of malformation of the renal tubule. Its combination with ocular manifestations may be genetic, specifically in case of claudin-19 (CLDN-19) gene mutations. The combination of FHHNC and ocular manifestations is not always present in these patients. Optical coherence tomography (OCT) helps us diagnose this condition by allowing us to evaluate and confirm the absence of retina layers without histological examination. Although genetic testing is necessary to diagnose mutational alterations of the CLDN-19 gene, in our case, it was not necessary to diagnose the FHHNC patient with macular coloboma, since the diagnosis of ocular damage had been already accurately established by the OCT.