Retinal function in infants with optic nerve hypoplasia: electroretinograms to large patterns and photopic flash

Abstract

Aims Optic nerve hypoplasia (ONH), which is defined as a congenital deficiency of retinal ganglion cells, may also involve more distal layers of the retina. We investigated electrophysiological function of the retina in ONH using electroretinograms (ERGs). Methods ERGs were recorded from 48 subjects (3.5-35 months) with unilateral or bilateral ONH. Pattern reversal (41 checks) was presented under chloral hydrate sedation, using an optical system to correct a cycloplegic refraction. A photopic flash stimulus was also used. Fundus photographs were used to measure the disk diameter/disk macula ratio (DD/DM), and to document other clinical signs. Eyes were classified as moderate (0.15-0.3) or severe (o0.15) ONH, and those with DD/DM greater than 0.3 were used as reference eyes. Results Pattern ERG recording was completed in 89 eyes and was detectable in 80% of eyes with ONH (61/76 tested) and in all 13 reference eyes. Photopic flash ERGs were of good quality in all eyes. The severity of ONH correlates with the amplitude of the photopic flash b-waves and with the amplitude of the N95 component of the pattern ERG (Po0.01). However, the ERGs to large patterns were well preserved (43.5 lV) in 10 of 35 eyes with severe ONH. Tortuous retinal vessels in eyes with either moderate or severe ONH were associated with smaller amplitude photopic b-waves and markedly diminished or undetectable pattern ERGs. Conclusions This study supports the hypothesis that retinal dysfunction distal to the ganglion cells is common in ONH, but is not predictable on the basis of ONH severity alone. Additionally, tortuous retinal vessels in ONH may be a sign associated with retinal dysfunction.

Light-adapted electroretinograms in optic nerve hypoplasia

“…Electroretinograms (ERGs) to flash stimuli are typically normal in ONH [18][19][20], consistent with the notion that the deficit is isolated to the retinal ganglion cells. However, ERG abnormalities have been reported in some cases of ONH, suggesting retinal dysplasia distal to the ganglion cell layer in a subset of cases [21][22][23][24].…”

Clinical electrophysiology and visual outcome in optic nerve hypoplasia

“…The present data support our earlier hypothesis that the extent of cellular damage in the inner retina is variable in ONH 13 19. In the present series, the N95 of the PERG is selectively diminished, and while linked to the severity of visual impairment, there is considerable variability.…”

“…Each epoch was adjusted to a zero mean amplitude (DC correction routine, Neurosoft Inc.), and the mean slope, by linear regression, was also adjusted to zero (linear detrend, Neurosoft Inc.). Subsequently, epochs still containing artefacts greater than ±80 μV were rejected automatically, and two separate averaged waveforms were produced using half of the retained epochs for each average so that reproducibility could be evaluated 19. For the later participants, DC correction was applied to the raw data and epochs containing major artefacts were rejected manually, off line without additional filtering.…”

“…However, ERGs to pattern-reversal stimuli (PERGs) reflect middle and inner retinal function, including function of the ganglion cells 14–18. We have reported an association between PERGs and optic nerve size in a small group of children with ONH 19. VEPs also require functional ganglion cells and correlate with the severity of ONH 5 9 20 21…”

The syndrome of optic nerve hypoplasia

“…However, ERG abnormalities have been reported in some cases of ONH, suggesting retinal dysfunction distal to the ganglion cell layer [69][70][71]. It remains to be seen whether electroretinographic features now felt to be specifi c for ganglion cell function, such as the N95 peak of the pattern ERG, correlate with vision outcomes in patients with ONH [ 72 ].…”