Intraobserver and Interobserver Reliability Indices for Drawing Scanning Laser Ophthalmoscope Optic Disc Contour Lines With and Without the Aid of Optic Disc Photographs

Abstract

To investigate the effects on topographic optic disc analysis of defining regions of interest (ROIs) by drawing contour lines with and without photographic aid. Forty-five patients had optic disc imaging by stereoscopic photography and confocal scanning laser ophthalmoscopy using the Heidelberg Retinal Tomograph (HRT). Two experienced observers defined ROIs with a stereoscopic optic disc photograph, with a non-stereoscopic photograph and without any photographic guide. Intraclass coefficients and 95% tolerance limits for change were calculated for each HRT optic disc parameter for the following situations: (1) Intraobserver reliability for ROIs defined with non-stereoscopic photographs and no photograph compared against ROIs defined using stereoscopic photographs; (2) interobserver reliability for ROIs defined without the aid of a photograph, with stereoscopic photographs and with non-stereoscopic photographs; and (3) intraobserver reliability for ROIs defined twice for 23 patients using non-stereoscopic photographs. Intraclass correlation coefficients ranged from 0.63 to 1.00 (ie, 'substantial' to 'perfect' agreement). The 95% tolerance limits for change ranged from 3% to 34%. In general, intraobserver reliability indices were higher than interobserver reliability indices but no method of ROI definition appeared superior. The least reliable measurements were for rim area, rim volume, and disc area. Non-stereoscopic optic disc photographs are an acceptable alternative to stereoscopic photographs when defining ROIs for HRT analysis. Observers with impaired stereopsis may be able to define reliable ROIs. For HRT algorithms designed to determine a 'diagnosis' of glaucoma, rim area, rim volume, and disc area data should be used with caution.