Comparison of scanning laser ophthalmoscopy and high-definition optical coherence tomography measurements of optic disc parameters.

Objective: To investigate the agreement between scanning laser ophthalmoscopy (Heidelberg retinal tomograph 3; HRT-3) and high-definition optical coherence tomography (HD-OCT) for measurements of optic nerve head (ONH) parameters.
Methods: As part of a population-based cross-sectional study, 913 consecutive Chinese subjects aged 40 years and older underwent HRT-3 and HD-OCT imaging of the ONH after pupillary dilation. Limits of agreement (LOA) derived from Bland-Altman analysis were calculated for ONH measurements.
Results: The mean age (± SD) of study participants was 54.2 ± 7.2 years and 52.0% were men. The two instruments showed no difference in mean optic disc area measurements (1.98 ± 0.37 for HD-OCT vs 1.98 ± 0.39 mm for HRT-3, p=0.95). HD-OCT showed smaller rim area (1.29 ± 0.24 vs 1.46 ± 0.27 mm, p<0.001), but bigger cup-related parameters (p<0.001 for all) than HRT-3. The highest correlations between the instruments were observed for cup volume (r(2)=0.74, p<0.001) and disc area (r(2)=0.62, p<0.001). The correlations for cup-to-disc ratio (CDR), vertical CDR and rim area were lower (r(2)=0.59, 0.48 and 0.24, respectively, p<0.001 for all). The Bland-Altman plots demonstrated significant proportional bias for differences in all ONH parameters (p<0.01 for all), with LOA greater for disc-related parameters (0.98-1.0) than cup-related parameters (0.26-0.50).
Conclusions: There are substantial disagreements between HRT-3 and HD-OCT in ONH measurements. Although optic disc area measurements were similar, HD-OCT underestimates the rim area and overestimates cup parameters compared with HRT-3.