Mizuo–Nakamura phenomenon in X-linked retinoschisis

PURPOSE: To determine whether the Mizuo–Nakamura phenomenon, which is an important diagnostic sign of Oguchi's disease, also occurs in patients with genetically proven X-linked retinoschisis (XLRS). METHODS: We examined three patients with a clinical and genetic diagnosis of XLRS and one patient who was clinically diagnosed with Oguchi's disease, with an emphasis on the Mizuo–Nakamura phenomenon. We obtained color fundus photographs, especially in the fully dark-adapted state, using the non-mydriatic mode on a digital retinal camera and infrared observation monitor to avoid the bleaching effects caused by the viewing light, which alters the fundus color in a short time. RESULTS: The Mizuo–Nakamura phenomenon was observed in all patients with molecularly proven XLRS, similar to that in the patient with Oguchi's disease. The sets of photographs were obtained in the light- and dark-adapted states using our newly devised techniques needed to witness the Mizuo-Nakamura phenomenon. CONCLUSIONS AND IMPORTANCE: The Mizuo–Nakamura phenomenon was identified in three patients with genetically proven XLRS. To the best of our knowledge, this study provided the first genetic evidence of the Mizuo–Nakamura phenomenon in a patient with molecularly proven XLRS without the causative genetic abnormalities for Oguchi's disease. Our findings suggest that XLRS is responsible for the Mizuo–Nakamura phenomenon and its presence in XLRS is not a rare exception but may be a consistent manifestation of XLRS.