Background: To compare the measurement error of Cirrus HD-OCT and Heidelberg Retina Tomograph 3 (HRT3) in patients with early glaucomatous visual field defect.
Methods: Thirty-nine consecutive patients (39 eyes) with early glaucomatous visual field defect were included. One eye of a patient was examined with Cirrus HD-OCT and HRT3 in one session. Each instrument was used by two operators, each taking two measurements in turn. We performed measurements of average retinal nerve fiber layer (RNFL) thickness and RNFL thickness in four quadrants with Cirrus HD-OCT and 13 stereometric parameters of the optic nerve head and RNFL with HRT3.
Results: Cirrus HD-OCT parameters performed much better than HRT3 stereometric parameters. Mean (for both operators) intraoperator within-subject coefficient of variation of the best Cirrus HD-OCT parameter (average RNFL thickness) was 2.6-2.7 times lower than the best HRT3 parameters [mean cup depth and rim area (P < 0.001)]. Mean intraoperator variability of RNFL thickness in quadrants (except nasal quadrant) was also significantly lower with OCT than with HRT. The interoperator within-subject coefficients of variation for both average RNFL thickness and RNFL thickness in all quadrants were significantly lower than the interoperator variability of best HRT3 parameter [mean cup depth (P < 0.001)]. The within-subject coefficient of variation of the average/mean RNFL thickness assessed by both instruments was 5.4-7.3 times lower for Cirrus HD-OCT. Among HRT3 parameters, mean cup depth, rim area and linear cup/disk ratio were the least variable, while cup volume, cup area and cup/disc area ratio were the most variable parameters.
Conclusions: Cirrus HD-OCT provides excellent intrasession intra- and interoperator repeatability of the RNFL measurements, especially of the average RNFL thickness in primary open-angle glaucoma (POAG) patients and POAG suspects with early glaucomatous visual field defect. The measurement error (expressed as within-subject coefficient of variation) of RNFL measurements by Cirrus HD-OCT is much lower than the error of HRT3 measurements of stereometric parameters of the optic nerve head and RNFL.