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Radouil T Tzekov, David Drucker, Gonzalo Ortiz, Connor Hyde, Joseph Staffetti; From baseline or from preceding peak: effects of method of PhNR measurement on correlation with other parameters. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5034.
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© ARVO (1962-2015); The Authors (2016-present)
The photopic negative response (PhNR) is a negative deflection occurring after the b-wave peak of the photopic ERG and reflects mostly activity of the retina ganglion cells. As a relatively slow wave modified by a positive i-wave, its peak is often difficult to determine. The PhNR amplitude can be measured from the pre-stimulus baseline to the trough of the response; however, an alternative approach has been proposed too, namely, to be measured from the b-wave peak to the trough of the response. As a rigorous comparison between the effects of the two types of measurement on the correlation with other ERG parameters or with other variables (e.g. age) has not been published to date, the purpose of this work was to explore these relationships.
The full-field single flash photopic ERG (Photopic 3.0 ERG according to ISCEV standard) recordings of 97 patients (35 M; 62 F; age range 19.2 - 80.2 years; 187 eyes) with a variety of clinical diagnoses, but mostly having or being suspected to have retinal degenerations were analyzed. As under our recording conditions, i-wave interfered significantly with the PhNR peak, the trough was measured at two locations: immediately preceding the i-wave (PhNR1) and after the i-wave (PhNR2). A linear correlation between a- and b-wave amplitudes and the corresponding parameters of PhNR1 and PhNR2, and also the effects of age were examined.
Well-defined PhNR peaks were detectable in 97.3% of all records (PhNR1) and 85.6% (PhNR2). When amplitude dependencies were analyzed, the correlations were different based on which method of measurement was applied. Thus, measurement from baseline (fb) resulted in the following correlation coefficients: a-wave vs. PhNR1 (0.47), vs. PhNR2(0.51); b-wave vs. PhNR1 (0.19), vs. PhNR2 (0.35). Measurement from b-wave peak (fp) resulted in higher coefficients: 0.73, 0.68, 0.92, 0.93, respectively. Similarly, the effect of age was different depending on the method of measurement: fb resulted in no effect of age on PhNR1 or PhNR2 amplitudes (p=0.456; p=0.255); in contrast, fp resulted in noticeable age effects (-7.2 mV/decade; p=0.013 for PhNR1 and -6.8 mV/decade; p=0.04 for PhNR2).
Two different methods of measuring PhNR amplitude (from baseline and from b-wave peak) may have similar physiological context but result in different statistical outcomes, which needs to be taken into consideration.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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