Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis.

Effects of age and sex on pattern electroretinograms and visual evoked potentials

The pattern electroretinogram (PERG) findings in 72 patients with disease of the anterior visual pathways are presented in relation to the site of dysfunction. Two components of the PERG are described which are selectively involved in different pathologies. In particular, the main positive P50 component is invariably affected in retinal/macular dysfunction, whereas the late negative N95 component is principally affected in optic nerve disease.

https://bjo.bmj.com/content/bjophthalmol/71/3/166.full.pdf

Significance of abnormal pattern electroretinography in anterior visual pathway dysfunction.

A TV monitor was used to evoke either a pattern ERG to a contrast-reversing checkerboard (PERG), or a focal ERG to alternate increases and decreases of luminance of the blank screen within a bright surround (FERG). Both responses are small (approx 2 microV) and fast (approx 50 msec to peak) and are similar in several other properties. However, they differ in timing and respond differently to changes in contrast. Each frame of a TV picture evokes a "raster ERG," even though the screen is blank. The response is focal and specific to a small central strip of the screen. It is simpler to record than the FERG, where the whole screen is flashing. Because the FERG summation area is about 4 deg, small squares (checks) reversing in contrast produce little luminance response. In 5 of 7 cases where the PERG is unilaterally reduced, the FERGs or raster responses were not affected. Thus clinical evidence also suggests that the PERG may be a separate phenomenon to the FERG and produced at a different site. Toxic, traumatic, congenital, and degenerative diseases of the optic nerve reduce the PERG. The comparison is most easily made in unilateral disease. Ten weeks after an optic nerve insult, the PERG becomes reduced in the affected eye as if retrograde degeneration was occurring. In 27 amblyopes of various types, the PERG was reduced in 23 where orthoptic treatment had failed. In 4 patients responding to treatment, PERGs of the amblyopic eye were as large as, or larger than, those of the fellow eye. The loss is greater with smaller checks. Retinal changes do occur after age 4 but so slowly that responses in heavily occluded eyes are not reduced. An additional level in the visual pathway is thus accessible to evoked potential investigation.

Clinical and experimental evidence that the pattern electroretinogram (perg) is generated in more proximal retinal layers than the focal electroretinogram (ferg)

Pattern-reversal and flash electroretinograms (ERG), and oscillatory potentials (OP) were recorded from 11 patients with unilateral glaucoma. The pattern-reversal ERG amplitudes were reduced below the level of normal variation in 10 of the 11 glaucomatous eyes. The difference in amplitude means was statistically significant. No differences were observed in flash ERGs or OPs. The histopathological correlate to the visual field defects in glaucoma is retinal ganglion cell degeneration. The present electrophysiological findings support the view, based on results from animal experiments, that the pattern-reversal ERG reflects ganglion cell activity.

Pattern-reversal electroretinograms in unilateral glaucoma.

We have used a pattern-reversing chequerboard (1 degree squares, or smaller: 84 per cent contrast, or less: 2 to 16 reversals/sec: field size 22 degrees x 16 degrees: mean luminance 50 cd/m2) to evoke responses from the eyes of young adults and children. ERGs were recorded with gold foil electrodes, which did not interfere with the normal optics. All patients were affected accurately. The fixation point was adjusted so that squinters received the stimulus on corresponding areas of each retina. The normal ERG obtained is 1.5 to 3 mu V in amplitude, and in thirteen normal subjects right and left eyes gave equal responses. The extreme asymmetry detected was c. 10 per cent. In all amblyopes, including children of 6 years old and upwards, satisfactory recordings were obtained. In most amblyopes, the response from the affected eye was 50 per cent or less of the response from the fellow eye. In all cases of failure to respond to treatment, the asymmetry was highly significant. In adults, occluding the screen area corresponding to the area of amblyopic suppression, reduces the ERG in the fellow eye, but does not reduce the ERG in the amblyopic eye. We conclude that amblyopic retina produces very little electrical activity that we can record. The timing, response to frequency of stimulation, and other parameters in the pattern ERG are dissimilar from those in the ERG produced by small changes of luminance. We have little evidence about the class of cell generating the response we observe, but evidently there is peripheral abnormality in the visual system even of amblyopic children.

Pattern ERGs are abnormal in many amblyopes.

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Clinical and experimental evidence that the pattern electroretinogram (perg) is generated in more proximal retinal layers than the focal electroretinogram (ferg)

Pattern ERGs are abnormal in many amblyopes.