Cortical blindness in children: utility of flash VEPs

ERGs on the brain: the benefits of simultaneous flash retinal and cortical responses in paediatric cerebral visual impairment

Purpose

To highlight the importance of simultaneous flash electroretinogram (ERG) and visual evoked potential (VEP) recording to differentiate a true flash VEP response from an artefact caused by the intrusion of the ERG on a mid-frontal reference electrode in cases of severe cerebral visual impairment (CVI).

Methods

We report an observational case series of four children with severe CVI who underwent simultaneous flash ERG and VEP recordings. Flash VEPs from Oz–Fz and lower lid skin ERGs referred to Fz were recorded simultaneously to Grass intensity setting 4 flash stimulation.

Results

In all cases, atypical, but reproducible VEPs were evident. Comparison of the timing and waveform of the VEPs and ERGs showed the occipital responses were inverted ERGs and no true flash VEP was evident.

Conclusions

While ISCEV and neurophysiology standards do not require the simultaneous recording of the flash ERG with the VEP, these cases highlight the usefulness of this non-invasive technique particularly in suspected paediatric cerebral visual impairment to differentiate a true VEP from an artefact caused by ERG contamination.

The visual-evoked response in infants with central visual impairment

We studied ten children with central visual impairment with a known neurologic defect and an abnormal visual-evoked response who had results of repeat electrophysiologic testing evaluated at the Children's Hospital of Philadelphia from December 1989 through July 1991. Central visual impairment is defined as poor visual function with a normal anterior visual pathway. Age at first examination ranged from 5 to 48 months with a followup of two to 31 months. Repeat visual-evoked response testing showed improvement in seven patients and no change in three. Grating acuity as measured by the Teller acuity card procedure, performed in nine of ten patients, improved in seven, showed no change in one, and declined in one. We found a potentially favorable prognosis for those infants with central visual impairment, despite an initially abnormal visual-evoked response. We used a clinical approach to this disorder to improve diagnostic categorization and prognostic capabilities in central visual impairment.