Rationale. The PERG is arguably the only way to probe the activity of retinal ganglion cells. The PERG is reported to be altered in the early stages of glaucoma and may predict future visual field losses. We have developed a user-friendly adaptation of the PERG for screening and follow up of glaucoma, called PERGLA. Methods. The PERGLA is recorded simultaneously from both eyes by means of skin electrodes on the lower eyelids (reference ipsilateral temple), in response to horizontal gratings (1.7 c/d, 25 deg circular field, 95% contrast, 40 cd/m2 mean luminance), alternating at 8.14 Hz. Signals are conventionally amplified and averaged. The actual test lasts 3 minutes (two blocks of 1.5 minutes each) and subjects are allowed to blink freely. The amplitude and phase of the component at the reversal rate are automatically evaluated by Discrete Fourier Transform. Deviations from age-corrected norms are expressed in SD units and visualized on a polar diagram. The internal variability of the response and a noise index are also simultaneously evaluated. Results. Normative data (n=100 eyes) have been obtained in healthy subjects aged 12-85 years. On average, the signal-to-noise ratio is above 10 for all ages, and the coefficient of variation between partial averages is 10% for amplitude and 2% for phase. Test-retest, and interocular asymmetry have similar variability. We have also recorded the PERGLA from 132 glaucoma suspects (n=261 eyes) with normal standard visual fields. Overall, more than 40% of patients showed abnormal responses from normal average (exceeding 2 SDs) in amplitude, latency or interocular asymmetry. Conclusions. The signal-to-noise ratio, reproducibility, and sensitivity of the PERGLA in glaucoma are at least as good as other PERG techniques with corneal electrodes. The PERGLA has a potential value for a non-invasive screening and follow up of glaucoma in the early stages.
- Glaucoma &fields
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