MAY 13, 2011
The authors conducted this retrospective study to compare the detection of retinal nerve fiber layer (RNFL) progression using the fast and the regular RNFL scan protocols of the Stratus optical coherence tomography (OCT) device (Carl Zeiss Meditec, Dublin, Calif.). The results indicate that the agreement of progression analysis between the fast and regular RNFL scans was only fair to moderate. The authors conclude that the longer scan time required for the regular RNFL scan may increase the probability of scan circle displacement error with a resulting reduced sensitivity and specificity for detecting change. They say that the fast RNFL scan seems to be preferable for monitoring RNFL damage in glaucoma patients.
Subjects in the study were 72 glaucoma patients (129 eyes) followed for between 2.9 and 6.1 years. All eyes had at least four serial RNFL measurements obtained with both the fast (256 A-scans in each scan circle) and the regular (512 A-scans in each scan circle) RNFL scan protocols, with visual field assessment also performed on the same d
The authors analyzed 1,373 fast and 1,373 regular RNFL scans and 1,236 visual field tests. The fast RNFL scan detected more eyes with progression (21 eyes from 19 patients vs. 15 eyes from 13 patients) than the regular scan at a comparable level of specificity (96.9 vs. 96.1 percent). More eyes were found to have increasing RNFL thickness with age at individual clock hours (except for 3, 5, 6 and 11 o'clock) when measurements were obtained with the regular scan. K values ranged between 0.14 and 0.49 for agreement between the fast and regular scan for detection of RNFL progression. The rate of average RNFL thickness progression calculated was -1.01 µm per year with the fast scan and -0.77 µm per year with the regular scan.
The authors conclude that the choice of Stratus OCT scan protocol has a significant impact on the evaluation of RNFL progression. They say that these results were unexpected because previous studies have found the test-retest measurement variability between the fast and regular scans to be similar. Although the estimated specificity for average RNFL thickness was similar between the scan protocols, the authors note that the fast scan was able to detect more eyes with progression, whereas the regular scan generally identified more eyes with improvement (in particular at 7 o'clock, where RNFL defects are located most frequently).