To report a case of adult-onset Coats' disease which showed decreased retinal edema and improved visual acuity following intravitreal ranibizumab injection.

A 21-year-old woman visited our hospital for decreased visual acuity in left eye from 3 months ago. Her best corrected visual acuity was 1.0 in the right eye, and 0.4 in the left eye. The intraocular pressure was 19 mmHg in the right eye and 16 mmHg in the left eye. At anterior segment examination, no abnormal findings were found. On fundus examination, subretinal exudates, superior retinal edema at posterior pole, and telangiectasia along superortemporal vascular arcade were observed in the left eye. Upon diagnosis as Coats' disease, intravitreal ranibizumab was performed, and laser photocoagulation was done around the retinal telangiectasia and nonperfusion area. Then, the second and third intravitreal ranibizumab injections were performed by a month, and her best visual acuity was improved to 0.8 and optical coherence tomography revealed decreased retinal edema.

We report a case of adult-onset Coats' disease. Intravitreal ranibizumab injection is effective in rapid visual improvement and decrease of retinal edema as combination therapy with laser photocoagulation which was a generalized treatment of choice in Coats' disease.