A 78-year-old man had exanthema on his head and visited the Department of Dermatology in the general hospital in October 2009. It was removed by surgery. Pathological examinations of the removed specimens led to a diagnosis of malignant melanoma. He received a course of follow-up examinations for 4 years because the cancer did not metastasize. Then, the malignant lesions were found to have spread to the right lung, which were then removed during an additional surgery. He was subsequently diagnosed as T4aN0M1 Stage IV. Based on a second opinion, he visited the Department of Dermatology in our hospital and he elected to receive 4 cycles of dacarbazine, nimustine, vincristine, and interferon-beta starting in January 2014. After finding new metastasis in the liver and lungs, he was additionally administered nivolumab. However, 3 months later, further metastasis to the bones, pleura, and peritoneum were found. Therefore, in June 2017, it was decided to start the patient on a new treatment with ipilimumab. He had received ipilimumab at 3mg/kg (weight of him was 55.5kg) every 3 weeks for 4 cycles according to the protocol. After 2 cycles of ipilimumab, the patient noticed impairment of the visual field in both of his eyes at 22 days after the last administration and visited our department in August. At his initial visit, best corrected visual acuity was 16/20 in both eyes and there were no abnormal findings in either the anterior chamber or optic media. Fundus examination revealed serous retinal detachment (SRD) and several retinal pigment epithelial detachments in both eyes (). Fluorescein angiography (Spectralis HRA+OCT; Heidelberg Engineering GmbH) revealed no obvious leakage in either of the SRD areas. Indocyanine green angiography (Spectralis HRA+OCT; Heidelberg Engineering GmbH) showed neither leakage during both the early and late phases nor any abnormal choroidal hyperpermeability (). SS-OCT (Topcon DRI OCT Triton Swept Source OCT, Topcon, Japan) identified SRD accompanied by a widely distributed high reflection of the photoreceptor outer segment when using the horizontal and vertical 12 mm B-scanned images. High reflection of the photoreceptor outer segment was detected in both areas where the SRD appeared and did not appear. In normal retina, ellipsoid zone and interdigitation zone are distinguishable, however in these suffered areas, the distribution of the high reflection was not used to differentiate between the interdigitation zone and the ellipsoid zone. SS-OCT also detected thickening (maximum diameter 75 μm) of the photoreceptor outer segment (). Fundus autofluorescence (FAF) showed there were no abnormalities (). After this evaluation, he was administered 4 cycles of ipilimumab. During his course of follow-up examinations, initially there was a slight increase in the SRD during 4 cycles of ipilimumab, after which the SRD then gradually decreased, and the impairment of his visual field stabilized. Although best corrected visual acuity was 16/20 in both eyes, the SRD and obscurity of the interdigitation zone remained (). He had hyperopia at the initial visit and no shift occurred during a course of follow-up examinations.