Retinal Nerve Fiber Layer Thickness Measurement by Fourier-domain Optical Coherence Tomography: A Comparison Between Cirrus-HD OCT and RTVue in Healthy Eyes

Purpose: To compare retinal nerve fiber layer (RNFL) thickness measurements by 2 Fourier-domain optical coherence tomography (OCT) instruments: Cirrus-HD OCT and RTVue. Materials and Methods: Twenty-three eyes of 23 healthy participants underwent RNFL thickness measurement using both devices on the same day. The NMH4 and Optic Disk Cube 200 x 200 protocols were used, respectively, for scan acquisition with RTVue and Cirrus-HD OCT. Measurements were compared by means of a paired t test. Results: RTVue gave higher mean RNFL thickness values than Cirrus-HD OCT in the superior (128.44 +/- 22.48 vs. 119.73 +/- 18.22 mu, P = 0.0002), inferior (137.15 +/- 21.99 vs. 124.94 +/- 22.51 mu, P < 0.0001), nasal (77.58 +/- 15.61 vs. 70.21 +/- 11.53 mu, P = 0.0009), and temporal (78.09 +/- 10.05 vs. 67.08 +/- 9.60 mu, P< 0.0001) quadrants, as well as a higher 360 degrees average measurement (105.88 +/- 14.59 vs. 95.21 +/- 12.45 mu, P < 0.0001). The average difference between the 2 instruments showed a standard deviation too high to calculate a reliable correcting factor for comparing a pair of individual scans taken with the 2 instruments (superior quadrant 8.70 +/- 9.19 mu; inferior quadrant 13.11 +/- 5.4 mu; nasal quadrant 7.37 +/- 9.18 mu; temporal quadrant 11.01 +/- 8.50 mu; average measurement: 10.67 +/- 4.88 mu). Conclusions: In healthy eyes RNFL measurements taken with RTVue and Cirrus-HD OCT show significant differences that make the measurements themselves noninterchangeable.