Cone dysfunction with negative electroretinogram and ring scotoma

Abstract

Objective: To report an unusual case of cone dysfunction (CD) in which ring scotoma and negative electroretinogram (ERG) were found. Patient and methods: The patient was a 28-year-old Japanese man, who had been aware of an aversion to bright light since the age of eight years.The corrected visual acuity was 0.8 in each eye.Bilateral broad ring scotomas were demonstrated by kinetic perimetry. Almost five degrees of the central visual field were preserved. No nystagmus was noted.The standard full-field scotopic and photopic ERGs were recorded. Results: The photopic ERGs, including bright flash and flicker stimuli under rod-saturating background illumination, showed very little response. Negative ERG, i.e. reduced b-wave amplitude, was evident in the scotopic bright flash ERG.The scotopic responses to dim flashes were within the normal range. Conclusions: On the basis of the ERG findings, the patient was diagnosed as having CD.The central scotomas, usually detected in CD by conventional perimeter, were not found in this patient. Our results suggested that the cone function of this patient was reduced more severely in the parafoveal retina than in the central retina.