| Sumario: | Background: The cup-to-disc (C/D) ratio is a commonly used measurement for assessing the optic nerve requiring the use of monocular and binocular visual processing. Interobserver agreement is known to be poorer than intra-observer agreement with regard to the precision of C/D ratio measurements, but studies evaluating reproducibility in live subjects and across different experience groups are scarce. While previous studies use stereoscopic photographs and expert observers to estimate reproducibility, this study evaluated interobserver variability in live subjects among both students and practicing clinicians. Methods: Eleven observers from each of four experience groups measured the right optic nerves of three subjects via slit lamp fundoscopy. For each experience group, limits of reproducibility were constructed for vertical and horizontal C/D ratio measurements by subject and analyzed for significant differences. Furthermore, data were analyzed in a categorical fashion in which differences between corresponding intra-class measurements were classified as falling within 0.05, 0.10, 0.15, or more than 0.15 C/D ratio units of one another and analyzed for trends. Results: Limits of reproducibility ranged from 0.07 to 0.32 C/D ratio units, with no significant trend toward superior reproducibility in the groups with more clinical experience. Furthermore, a significant trend indicating improvement in agreement corresponding with increased experience was not exhibited in the higher experience levels via the categorical approach. Conclusions: Reproducibility of C/D ratio measurements between observers is relatively broad and does not appear to correlate strongly with practitioner experience. When possible, multi-clinician practices should attempt to have the same clinician monitor C/D ratios in order to eliminate inter-observer variability. Poor binocularity and/or visual processing skills of some clinicians may contribute to these findings.
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