Clinical study of the pattern electroretinogram in patients with optic nerve damage

Comparison of human expert and computer-automated systems using magnitude-squared coherence (MSC) and bootstrap distribution statistics for the interpretation of pattern electroretinograms (PERGs) in infants with optic nerve hypoplasia (ONH)

PURPOSE

Pattern electroretinograms (PERGs) have inherently low signal-to-noise ratios and can be difficult to detect when degraded by pathology or noise. We compare an objective system for automated PERG analysis with expert human interpretation in children with optic nerve hypoplasia (ONH) with PERGs ranging from clear to undetectable.

METHODS

PERGs were recorded uniocularly with chloral hydrate sedation in children with ONH (aged 3.5-35 months). Stimuli were reversing checks of four sizes focused using an optical system incorporating the cycloplegic refraction. Forty PERG records were analysed; 20 selected at random and 20 from eyes with good vision (fellow eyes or eyes with mild ONH) from over 300 records. Two experts identified P50 and N95 of the PERGs after manually deleting trials with movement artefact, slow-wave EEG (4-8 Hz) or other noise from raw data for 150 check reversals. The automated system first identified present/not-present responses using a magnitude-squared coherence criterion and then, for responses confirmed as present, estimated the P50 and N95 cardinal positions as the turning points in local third-order polynomials fitted in the -3 dB bandwidth [0.25 … 45] Hz. Confidence limits were estimated from bootstrap re-sampling with replacement. The automated system uses an interactive Internet-available webpage tool (see http://clinengnhs.liv.ac.uk/esp_perg_1.htm).

RESULTS

The automated system detected 28 PERG signals above the noise level (p ≤ 0.05 for H0). Good subjective quality ratings were indicative of significant PERGs; however, poor subjective quality did not necessarily predict non-significant signals. P50 and N95 implicit times showed good agreement between the two experts and between experts and the automated system. For the N95 amplitude measured to P50, the experts differed by an average of 13% consistent with differing interpretations of peaks within noise, while the automated amplitude measure was highly correlated with the expert measures but was proportionally larger. Trial-by-trial review of these data required approximately 6.5 h for each human expert, while automated data processing required <4 min, excluding overheads relating to data transfer.

CONCLUSIONS

An automated computer system for PERG analysis, using a panel of signal processing and statistical techniques, provides objective present/not-present detection and cursor positioning with explicit confidence intervals. The system achieves, within an efficient and robust statistical framework, estimates of P50 and N95 amplitudes and implicit times similar to those of clinical experts.

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

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 (4 degrees 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 (<0.15) 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 (P<0.01). However, the ERGs to large patterns were well preserved (>3.5 microV) 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.

The incidence of abnormal pattern electroretinography in optic nerve demyelination

This report describes the pattern electroretinogram (PERG) findings in 141 patients with optic nerve demyelination in one or both eyes. The overall incidence of PERG abnormality in the 199 eyes with abnormally delayed pattern visual evoked potential (PVEP) P100 component was 39.2%, with 84.6% of these PERG abnormalities being confined to the N95 component. The incidence of abnormal PERG was greater (53.3%) in those eyes with a history of retrobulbar neuritis than in those with sub-clinical demyelination (22.8%). The importance of stimulus parameters is noted. The value of the PERG in the improved interpretation of an abnormal PVEP is discussed.

A review of the clinical applications of the pattern electroretinogram

The pattern electroretinogram (PERG) has recently been introduced as a clinical procedure. It has been thought by many to represent activity of the retinal ganglion cells, although this is still a matter of contention. The exciting prospect of a selective test of ganglion cell function led to the application of the PERG in a variety of ophthalmological conditions. In the course of these investigations the PERG was found to be diminished in cases of maculopathy, optic atrophy, optic neuritis, toxic optic neuropathy, neurotransmitter disorders, glaucoma and ocular hypertension and in retinal vascular disorders such as diabetes. It was also affected in some cases of amblyopia. This paper briefly describes the techniques used to record the PERG and reviews current literature pertaining to its clinical application.

Pattern ERG: effects of reference electrode site, stimulus mode and check size

We studied monocular pattern ERG (PERG) in 10 normal subjects and a patient with optic neuritis. No clinically significant PERG could be recorded from the occluded eye with any reference (ipsilateral ear or temple, or midfrontal), indicating that cross-contamination is not present with binocular testing. Ipsilateral temple reference minimized VEP (P100/N100) contribution to the PERG N95 which occurred with ipsilateral ear or midfrontal reference. The conclusions were confirmed by results from the patient, who had marked monocular delay of a normal amplitude P100. Twenty-four subjects were tested with monocular and binocular stimulation using an ipsilateral temple reference. There were differences in PERG latencies and amplitudes although the interside amplitude ratio showed smaller differences with binocular stimulation. Increasing check size (17, 35 and 70 min) decreased P50 and N95 latencies and increased P50 amplitude.

Pattern electroretinogram and optic nerve section in pigeons

We studied the effect of optic nerve section on the pattern electroretinogram (PERG) of 10 pigeons. Base line PERG and flash ERG were measured prior to surgery and then one optic nerve was cut. We measured PERG at various time intervals up to 24 weeks after the section. There was a sharp drop in PERG amplitude immediately following the section. It gradually returned to normal levels in the following 24 weeks. Significant decreases in time to peak were noted at 1 and 16 weeks for 0.5 cycle per degree checks and at 1, 2 and 9 weeks for 0.25 cycle per degree checks. The ERG generated by a TV stimulus did not change in amplitude but had a shorter time to peak at 24 weeks for a high intensity stimulus and at 16, 18, 24 weeks for a low intensity stimulus. Light and electron microscopic sections (at 24 weeks) revealed an almost complete loss of nerve fibers in the optic nerve. Retinal sections revealed only a few surviving ganglion cells and a few nerve fibers. This suggests that in pigeons, PERG is not generated by ganglion cells.

A comparison of oscillatory potential and pattern electroretinogram measures in diabetic retinopathy

Both basic and clinical electrophysiological investigations have established that the oscillatory potentials (OP) and pattern electroretinogram (PERG) appear to originate from retinal sites that are in proximity. The OPs, subcomponents of the flash ERG, have been shown to reflect disturbances in retinal circulation, and OP amplitude attenuation or loss may be a distinctive feature of diabetic retinopathy. The PERG has been shown to be abnormal in diseases of the optic nerve and ganglion cell body. Thus its relative sensitivity for detection of electroretinal abnormalities in diabetic retinopathy is in question. This study assessed the sensitivity of ERG and OP measures in their detection of abnormalities of electroretinal function in diabetic patients referred to our laboratory. Thirty-five adult Type I patients were studied: 21 with background retinopathy (BR group), 14 with no evidence of background retinopathy (No BR group), and 25 normal control subjects. Monocular OPs were recorded to full-field ganzfeld stimulation at four stimulus intensities. PERGs were obtained from checkerboard pattern reversal stimulation (check-size = 30' arc). Peak-to-peak amplitude and peak implicit time measures of PERGs and OPs were obtained. Subsequent multivariate analysis demonstrated significant differences between normals and diabetic patients, including diabetics with no clinical evidence of retinopathy. In addition, the OP and PERG implicit times appear to be unaffected while OP and PERG amplitudes were diminished in patients with background retinopathy. Only OP amplitudes were found to be significantly diminished in diabetic patients with no photographic evidence of background retinopathy. The PERGs were normal in these patients. Overall, the OP amplitude measures were more sensitive than PERG measures in detecting abnormalities in patients with no retinal photographic evidence of background retinopathy.