Reproducibility of Macular Thickness Measurements in Eyes Affected by Dry Age-Related Macular Degeneration From Two Different SD-OCT Instruments

BACKGROUND AND OBJECTIVE: To compare macular thickness measurement algorithms of two different spectral-domain optical coherence tomography (SD-OCT) devices in eyes affected by dry age-related macular degeneration (AMD). PATIENTS AND METHODS: Patients with dry AMD and healthy volunteers from the retina clinic of the Doheny Eye Center - UCLA were imaged using two different SDOCT devices: the RS-3000 Advance (Nidek, Padova, Italy) and the Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA). All patients had been previously diagnosed with drusen or geographic atrophy due to AMD. The commercial instrument software was used to generate the macular retinal thickness measurements, and measurements were compared between devices. RESULTS: Eighty-five diseased eyes from 49 patients and 16 healthy control eyes from eight normal volunteers were included in this study. The macular thickness measurements generated by the two instruments in eyes with AMD differed significantly in mean retinal thickness in the foveal center subfield (257.34 mu m +/- 51.72 mu m using the Nidek OCT vs. 238.20 mu m +/- 51.89 mu m using the Cirrus OCT; P < .001). The mean difference in macular thickness between the two devices was 19.14 mu m +/- 5.84 mu m for diseased eyes and 17.06 mu m +/- 5.28 mu m in normal control eyes, and this was not statistically different between the two groups (P > .05). The macular thickness measurements in diseased eyes, as evaluated by the two different instruments, however, showed excellent correlation (r = 0.99; P < .001), with an intraclass correlation coefficient of 0.99 (95% confidence interval, 0.98-0.99). Post hoc evaluation of cases with larger differences also showed differences in foveal center selection and variabilities in boundary selection with specific pathology. CONCLUSION: Macular thickness measurements provided by the Nidek and Cirrus OCT instruments in eyes with dry AMD are highly correlated but show a consistent difference, which may allow the use of a standard correction factor to be applied to better interrelate measurements between the devices.