Photopic Negative Response in Healthy Adults: Normative Values and Test-Retest Reliability

Abstract

Purpose : To determine normative values and test-retest reliability for a range of parameters derived from the photopic negative response (PhNR) in healthy normal adults.

Methods : Light-adapted flash full-field electroretinograms (ERGs) were recorded from a randomly-selected eye of 50 subjects (16-55 years; mean 28.8± 10.1; 30 females), and 13 of them were tested on two separate days. Stimuli were brief 1 cd*s/m2 red flashes (<5ms) on a 10 cd/m2 blue background. PhNR amplitude (µV) was measured using through to baseline (BT) and from the preceding b-wave peak (PT). BT/b and PT/b amplitude ratios were also calculated. Normal limits were determined as 5% percentile for amplitudes and 95% percentile for latencies. Test–retest reliability was assessed with Wilcoxon signed-rank test, intraclass correlation coefficient (ICC) and the coefficient of reliability (COR).

Results : Amplitude (µV) mean values and lower normal limits were, respectively, 25.88±7.16; 16.44 for a-wave and 88.01±33.01;48.01 for b-wave, whereas for latency (ms) the values were, respectively, 15.34±0.59; 16.33 for a-wave and 29.75±1.52; 32.66 for b-wave. Mean PhNR amplitude (µV) and lower limit were respectively 26.26±5.30; 21.15 for BT, 114.27±34.49;69.30 for PT, 1.33±0.12;1.16 for PT/b and 0.33±0.12;0.16 for BT/b. Mean values and normal limit of latency (ms) were respectively 15.34±0.59; 16.33 for a-wave and 29.75±1.52; 32.67 for b-wave. Mean PhNR latency (ms) and normal limit was 60.65±2.52; 65.33. There were no significant differences between test-retest for all PhNR measurements. Amplitudes for a- and b-waves were reproduced, respectively, with moderate (ICC, 0.74; CoR%, 37.03%) and excellent reliability (ICC, 0.87; CoR%, 25.12%). For PhNR, the most reliable measurement was PT (ICC, 0.86; CoR%, 9.06%) followed by BT (ICC,0.84; CoR%, 27.01%). The PT/b was more reproduced (ICC, 0.73; CoR%, 9.43) than all other PhNR measurement parameters.

Conclusions : The normative values provided by this study will be clinically useful to help in the diagnosis of innermost retinal disorders, especially those affecting retinal ganglion cells as glaucoma and other forms of optic neuropathy. PT/b amplitude ratio showed less variability and might be a more consistent measure than absolute PhNR amplitude. Further studies including a larger sample with variable age range are desirable to confirm and extend the current results.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.