A new digital optic disc stereo camera: intraobserver and interobserver repeatability of optic disc measurements

Aims-To investigate the intraobserver and interobserver repeatability of op tic disc measurement using a new digital optic disc stereo camera. Methods-112 consecutive new patients presenting to a glaucoma service had d ilated optic disc photography performed using a new digital stereo camera ( Discam, Marcher Enterprises Ltd, Hereford). The images were analysed by two masked observers using a stereo viewer and computer simulated stereopsis. Vertical and horizontal cup:disc ratios (CDR), cup area:disc area, and cup circumference:disc circumference were computed. Intraobserver and interobse rver repeatability analyses were performed. Intraclass correlation coeffici ents (ICC) and 95% tolerance for change (TC) were computed. Results-220 optic discs were photographed, of which 196 were suitable for a nalysis (10 were of poor image quality and 14 had anomalous discs). Mean ag e of patients was 65 years, 60 were male and 48 female. For intraobserver m easurements of: horizontal CDR, ICC = 0.94, TC = 0.11 (15% of range); verti cal CDR, ICC = 0.92, TC = 0.14 (16% of range); cup area:disc area, ICC = 0. 95, TC = 0.10 (13% of range), and cup circumference:disc circumference, ICC = 0.95, TC = 0.09 (14% of range). For interobserver measurements of: horiz ontal CDR, ICC = 0.89, TC = 0.14 (19% of range); vertical CDR, ICC = 0.90, TC = 0.14 (16% of range); cup area:disc area, ICC = 0.92, TC = 0.13 (16% of range), and cup circumference:disc circumference, ICC = 0.90, TC = 0.12 (1 7% of range). Systematic bias between observers was within acceptable limit s. Conclusions-Digital stereo disc photography and analysis provide repeatable measures of optic disc variables. The results compare favourably with opht halmoscopic and stereophotographic methods of assessment of the optic disc.