ERG eases hereditary retinal disease diagnoses

SINGAPORE — Hereditary retinal diseases can be more easily defined because of advances in technology, specifically the electroretinogram, said Yozo Miyake, MD. He delivered the De Ocampo Lecture here during the Asia-Pacific Academy of Ophthalmology meeting.

Congenital stationary night blindness (CSNB) with normal fundi has been termed “Schubert-Bornschein type” when it shows negative electroretinogram (ERG) configuration, Dr. Miyake said. However, in an analysis of 92 patients at the National Institute of Sensory Organs in Tokyo, Dr. Miyake said two different diseases are mixed, and dubbed them incomplete and complete CSNB.

“The complete form has no rod function, and the incomplete form has moderate rod function,” he said. “Complete and incomplete types are definitely different entities.”

Fundus albipunctatus (FA) has been categorized as one of CSNB with unique fundus appearance, he said. The typical clinical characteristic of FA is “the enormous delay of rod adaptation.”

An analysis of 29 patients with FA who underwent ERG showed about 33% were associated with cone dystrophy, “sometimes showing bull’s eye maculopathy,” he said. Cone ERGs were virtually non-existent in the group, Dr. Miyake said. The patients also showed a specific gene mutation, namely RDH5.

“We cannot classify FA as a stationary disease because the cone dystrophy is progressive,” Dr. Miyake said.

Dr. Miyake added that occult macular dystrophy is a newly identified macular dystrophy where the fundi and fluorescein angiography are normal. He told attendees the key for diagnosis “is the abnormal focal macular ERG in spit of normal full-field ERG.”

An analysis of 46 patients indicated clinical findings of progressive decrease of bilateral visual acuity, color vision deficiency and autosomal dominant heredity. He warned most of these patients are misdiagnosed with psychological eye problems, optic nerve disease or central nervous system problems.