Unilateral negative electroretinogram presenting as photophobia

Purpose We aimed to describe four cases with an acquired unilateral negative electroretinogram (ERG) and severe unilateral photophobia and assess the underlying pathology. Methods We performed a retrospective chart view of the four cases by visiting two independent hospitals. Results Over the last 10 years, a 65-year-old man, 71-year-old woman, 68-year-old man, and 73-year-old woman presented to the hospitals with unilateral photophobia. Symptom onset was relatively obvious in all the patients. Comprehensive examinations, including visual acuity and visual field assessment, optical coherence tomography, and fluorescein angiography, showed minimal change in the eye with photophobia. However, only in the affected eye, the mixed rod–cone response in full-field ERG showed a markedly electronegative pattern, namely the amplitude of a-wave was preserved and larger than that of b-wave, and the rod and cone responses were very low. In fact, the cone responses were almost absent in all four patients. ERG findings indicate dysfunction of both rod and cone visual pathways, and the preserved a-wave in the mixed rod–cone ERG suggests that the disturbance of the rod visual pathway exists in post-photoreceptors. Moreover, although multifocal ERG showed a very low amplitude in the entire area, the preservation of the responses was detected to some extent only in the center. These symptoms and examination findings remained unchanged for more than 4 years. Conclusions Four patients with acquired unilateral negative ERG associated with severe photophobia showed similar clinical findings. To our knowledge, no known disorders can explain these conditions.