Unilateral sectoral heterochromia and myelinated retinal nerve fibers: A rare coexistence in an 8-year-old male monozygotic twin

We report a rare case of an 8-year-old male presenting with unilateral sectoral heterochromia and localized myelinated retinal nerve fibers (MRNFs) in the same eye. A detailed ophthalmological examination was performed on the patient and his monozygotic twin, including anterior segment and fundus evaluations. The patient demonstrated sectoral heterochromia and localized MRNF along the superior retinal arcade in the left eye, without any reduction in visual acuity. In contrast, his twin showed normal iris pigmentation and no MRNF, although both siblings exhibited bilateral congenital vessel tortuosity. No systemic disease was identified. The unique unilateral presentation and the absence of systemic involvement raise the possibility of either a coincidental coexistence or a shared embryological origin affecting both iris pigmentation and retinal myelination. This unusual case underscores the importance of further research into the developmental mechanisms that may link these ocular findings.