Observer Experience and Cup:Disc Ratio Assessment

Background. The validity of the Cup:Disc (C:D) ratio as a clinical measure depends on the level of agreement among observers. In this study, we investigated the effect of observer experience on interobserver and intraobserver agreement in C:D ratio estimation. Methods. Nine 3rd‐year (Yr3) and nine 4th‐year (Yr4) optometry students and nine optometrists (Opt), determined C:D ratios from 26 optic disc photographs viewed monoscopically and stereoscopically. Observer agreement was investigated using weighted kappa (K W ) analysis. Results. Interobserver agreement was higher (p < 0.01) among optometrists than among 4th‐year students and higher (p < 0.01) among 4th‐year than among 3rd‐year students (mean K W : Opt = 0.61; Yr4 = 0.51; Yr3 = 0.39). Stereoscopic estimates of C:D ratios were higher (p < 0.0001) than monoscopic estimates, and interobserver agreement was higher (p < 0.001) when evaluating the vertical rather than the horizontal C:D ratio. Intraobserver agreement (mean K W : Opt = 0.67; Yr4 = 0.66; Yr3 = 0.62) did not vary significantly (p = 0.78) with experience. Conclusions. The extent to which an observer reproducibly assesses the C:D ratio from optic disc photographs (intraobserver agreement) does not increase with experience. However, the agreement between different observers in assessing the C:D ratio (interobserver agreement) increases with experience.