Evaluation of the influence of tilt of optic disc on the measurement of optic disc variables obtained by optical coherence tomography and confocal scanning laser ophthalmoscopy

Purpose: To evaluate the relationship between optic disc variables measured by confocal scanning laser ophthalmoscopy (CSLO) and optical coherence tomography (OCT). Methods: Fifty-one eyes in 27 non-glaucomatous patients were scanned using a CSLO-TopSS™ and an OCT-OCT 3000™. The relationship between the following four optic disc variables - disc area (DA), cup area (CA), neuroretinal rim area (NRRA), and cup-disc area ratio (CDAR) - measured by CSLO and OCT were evaluated, and the relationship between these measurements and optic disc tilt was assessed. Horizontal (HD) and vertical diameters (VD) of the optic disc were measured from disc photographs, and by CSLO and OCT, and ratios (HD/VD) were then compared. Results: There was a good correlation in DA, CA, and CDAR except NRRA between OCT and CSLO measurements. In eyes with a tilt ≥4 degrees, DA and NRRA were measured larger, and CDAR and CA were measured smaller by OCT than by CSLO. However, in the eyes with a tilt of <4 degrees, no significant differences in measurement of disc variables were observed for the two measurement systems. HD/VD measured from disc photographs was well correlated with those determined by CSLO (r = 0.741, P < 0.0001), however, it correlated poorly with those measured by OCT in whole study eyes (r = 0.410, P = 0.008) and in eyes tilted by ≥4 degrees, respectively (P = 0.280). Conclusions: Although CSLO and OCT measurements of the optic disc are highly correlated, discrepancy becomes prominent in eyes with a disc tilted ≥4 degrees. Therefore, analysis of the optic nerve head by OCT must be cautiously interpreted in eyes with a highly tilted disc.