Interpretation of electroretinograms in children–know your equipment

Introduction
Electroretinograms (ERGs) are useful for diagnosis of congenital retinal dystrophies. However, the ERG is challenging to perform in children. There are several instruments and types of electrodes available for testing in children including stationary vs handheld devices and corneal fiber or skin electrodes. The purpose of our study was to determine potential causes of misinterpretation by comparing results from a handheld system with skin electrodes to a stationary system with corneal fiber electrodes.
Methods
Retrospective chart review of 5 pediatric patients referred for possible retinal dystrophies who had both handheld/skin electrode (HH/Skin) and stationary/corneal fiber (S/Corneal) ERGs.
Results
Average age of 5 patients (4M, 1F) was 3 and 9/12years (range, 3 months to 11 and 9/12 years). Final diagnosis was retinal dystrophy in 2 patients, normal retinal function in 3. HH/Skin vs S/Corneal ERGs: Amplitudes obtained with HH/Skin were significantly lower than with S/Corneal. Both patients with retinal dystrophy had abnormal HH/Skin and S/Corneal ERG. However 3/3 normal patients had abnormal HH/Skin ERG but normal S/Corneal ERG. These 3/3 normal children had essentially nonrecordable dark adapted dim flash waveforms with HH/Skin ERG.
Conclusion/relevance
ERG amplitudes in the same patient are different depending on the instrumentation used. Amplitudes were lower with a handheld/skin electrode system than with a stationary/corneal fiber electrode. The largest disparity was in the dark-adapted dim flash waveforms which were essentially nonrecordable in three normal children. Clinicians should be wary of interpreting pediatric handheld/skin electrode ERGs as abnormal.