The Test-Retest Reliability of the Photopic Negative Response (PhNR)

Jessica Tang; Thomas Edwards; Jonathan G Crowston; Marc Sarossy

doi:10.1167/tvst.3.6.1

The Test-Retest Reliability of the Photopic Negative Response (PhNR)

Transl Vis Sci Technol. 2014 Nov 3;3(6):1. doi: 10.1167/tvst.3.6.1. eCollection 2014 Oct.

Authors

Jessica Tang¹, Thomas Edwards², Jonathan G Crowston³, Marc Sarossy⁴

Affiliations

¹ Centre for Eye Research Australia, Melbourne, Australia.
² The Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
³ Centre for Eye Research Australia, Melbourne, Australia ; The Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
⁴ Centre for Eye Research Australia, Melbourne, Australia ; RMIT University, Melbourne, Australia.

Abstract

Purpose: The photopic negative response (PhNR) may be useful as a tool to monitor longitudinal change in retinal ganglion cell (RGC) function. The goal was to assess PhNR test-retest reliability, and to estimate the amount of change between tests that is likely to be statistically significant for an individual test subject.

Methods: Photopic electroretinograms (ERGs) were recorded from 49 visually normal subjects (mean age, 38.9 years; range, 21-72 years). Signals were acquired using Dawson-Trick-Litzkow (DTL) electrodes in response to red stimulus at four flash energies (0.5, 1, 2.25, 3 cd·s/m²) on a blue background (10 cd/m²). The PhNR amplitude was recorded from prestimulus baseline to trough (BT), prestimulus baseline to fixed time point (BF), and b-wave peak to trough (PT). The ratio of baseline PhNR to b-wave amplitude (BT/b-wave) was calculated. Reliability was assessed using the intraclass correlation coefficient (ICC_2,1) and coefficient of repeatability (CoR).

Results: Flash energy of 1.00 cd·s/m² produced reliable, well-defined traces. At this stimulus, the a- and b-wave amplitudes were reproduced with moderate reliability (ICC, 0.62; CoR%, 90.0%; and ICC, 0.74; CoR%, 54.3%; respectively). For PhNR, the order from most to least reliable measurement was: PT (ICC, 0.64; CoR%, 59.1%), BT (ICC, 0.40; CoR%, 148.3%), and BF (ICC, 0.22; CoR%, 166.1%). The BT/b-wave did not improve reliability (ICC, 0.37; CoR%, 181.5).

Conclusion: The b-wave peak-to-PhNR trough amplitude produced the most reliable measurement.

Translational relevance: A relatively large magnitude of change in PhNR amplitude is required to make clinical inferences about changes in RGC function. Refinement to the technique of acquisition and/or processing of the PhNR is recommended to improve reliability.

Keywords: electroretinogram; glaucoma; photopic negative response; reliability; statistics.