Color vision abnormality as an initial presentation of the complete type of congenital stationary night blindness
A 17-year-old male who was in a technical school of the transportation industry showed abnormalities in the color perception test for employment, and was referred to our hospital for a detailed examination. While he was in the elementary school, he received a color perception test during a health check. There were no abnormalities on the examination. He had no family history of color vision deficiency, and had no other symptoms. During the initial examination, his best-corrected visual acuity was 1.2, with no refractive error in either eye. The referral doctor, who specialized in color vision, investigated his color vision. Testing with Ishihara pseudoisochromatic plates, the patient could read only the first plate, and was diagnosed to have a color vision defect. However, he passed the panel D-15 dichotomous test with no errors. The patient’s color vision defect was mild, with no definite axis of error according to the 100-hue test performed at the referral hospital, and he showed normal match with an anomaloscope color blindness test.\nThe referring doctor also performed Standard Pseudoisochromatic Plates, part 2 to assess the type of color defect. The patient made two mistakes for blue–yellow differentiation and five mistakes for red–green differentiation in the right eye; and two mistakes for blue–yellow differentiation and four mistakes for red–green differentiation in the left eye, suggesting that the color vision defect had no definite axis.\nDuring the initial examination, his fundus showed no abnormalities except for a somewhat yellowish reflex in the fovea of both eyes. Fundus autofluorescence, optical coherence tomography, and multifocal ERG were normal (). Fluorescein fundus angiography also revealed no abnormalities (). Color vision deficiency with no apparent retinal abnormalities is sometimes associated with retinal diseases. Thus, these findings prompted us to obtain an ERG. Both the cone ERG and 30 Hz flicker ERG (recorded by International Society for Clinical Electrophysiology Vision [ISCEV] standard protocol ERG [using Tomei LE3000, Tomei, Tokyo, Japan]) showed a good response; however, the cone ERG showed wide a-wave trough. Bright flash, mixed rod and cone ERG showed a negative type with a reduced b-wave and a disappearance of oscillatory potential. No response was recorded in the rod ERG, either (). Based on the ERG findings, the patient was diagnosed with complete CSNB. Observation was recommended; he has been monitored for 5 years, and remains asymptomatic with no changes in visual acuity and fundus appearance since the first visit.