Validation of the colour difference plot scoring system analysis of the 103 hexagon multifocal electroretinogram in the evaluation of hydroxychloroquine retinal toxicity

Purpose To evaluate sensitivity, specificity and reproducibility of colour difference plot analysis ( CDPA ) of 103 hexagon multifocal electroretinogram (mf ERG ) in detecting established hydroxychloroquine ( HCQ ) retinal toxicity. Methods Twenty‐three patients taking HCQ were divided into those with and without retinal toxicity and were compared with a control group without retinal disease and not taking HCQ . CDPA with two masked examiners was performed using age‐corrected mf ERG responses in the central ring ( R c ; 0–5.5 degrees from fixation) and paracentral ring ( R p ; 5.5–11 degrees from fixation). An abnormal ring was defined as containing any hexagons with a difference in two or more standard deviations from normal (colour blue or black). Results Categorical analysis (ring involvement or not) showed R c had 83% sensitivity and 93% specificity. R p had 89% sensitivity and 82% specificity. Requiring abnormal hexagons in both R c and R p yielded sensitivity and specificity of 83% and 95%, respectively. If required in only one ring, they were 89% and 80%, respectively. In this population, there was complete agreement in identifying toxicity when comparing CDPA using R p with ring ratio analysis using R5/R4 P 1 ring responses (89% sensitivity and 95% specificity). Continuous analysis of CDPA with receiver operating characteristic analysis showed optimized detection (83% sensitivity and 96% specificity) when ≥4 abnormal hexagons were present anywhere within the R p ring outline. Intergrader agreement and reproducibility were good. Conclusions Colour difference plot analysis had sensitivity and specificity that approached that of ring ratio analysis of R5/R4 P 1 responses. Ease of implementation and reproducibility are notable advantages of CDPA .