Agreement between optical coherence tomography and digital stereophotography in vertical cup-to-disc ratio measurement

Background: Given the increasing popularity of optical coherence tomography in the diagnosis of glaucoma, we aimed to assess agreement between StratusOCT and stereophotography in measuring the vertical cup-to-disc ratio (VCDR) and examine whether it can be improved by changing the StratusOCT cup-offset. Methods: In group 1 (79 eyes), VCDR measurements obtained by StratusOCT (using the default cup-offset of 150 μm bove the retinal pigment epithelium) and stereophotography were compared. For each eye, the cup-offset was moved upward or downward until the difference disappeared and an adjusted cup-offset was identified. In group 2 (41 eyes), the stereophotography VCDR was compared to the StratusOCT value obtained by using the mean adjusted cup-offset. StratusOCT was used to classify optic disc cups as shallow or deep. Results: In group 1, StratusOCT overestimated VCDR in optic discs with deep cups and underestimated it in those with shallow cups (p <0.0001). Mean adjusted cup-offsets were 72.8±92 μm and 191.6±70 μm for eyes with deep and shallow cups. The 95% limits of agreement (LOA) ranged from -0.21 to 0.17. In group 2, the adjusted cup-offsets enabled us to eliminate the statistical differences in VCDR measurements and improve the 95% LOA (from -0.13 to 0.14). Conclusion: Adjusting the StratusOCT cup-offset according to the cup depth improves agreement between StratusOCT and stereophotography in measuring the VCDR.