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

Abstract

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. In group 1 (79 eyes), VCDR measurements obtained by StratusOCT (using the default cup-offset of 150 microm above 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. 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 microm and 191.6 +/- 70 microm 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). Adjusting the StratusOCT cup-offset according to the cup depth improves agreement between StratusOCT and stereophotography in measuring the VCDR.