Purpose To evaluate and compare the diagnostic classification of retinal nerve fiber layer (RNFL) measurement using time-domain and spectral-domain optical coherence tomography (OCT) in healthy myopic eyes.

Design Prospective, observational study

Methods A total of 97 eyes from 97 healthy myopia subjects were included. The RNFL in each eye was imaged sequentially with Stratus OCT and Cirrus OCT (Carl Zeiss Meditec, Dublin, CA). Based on the internal normative databases, categorization (within normal limits, borderline, or outside normal limits) provided by each device was calculated and compared by using the likelihood ratio chi-square test. Multiple logistic regression analysis was performed to evaluate the potential factors associated with abnormal diagnostic classification.

Results The Cirrus OCT classified a significantly higher percentage of eyes as outside normal limits/borderline in at least one clock-hour (Stratus, 14.4% / 24.8%; Cirrus, 21.6% / 34.1%; all p<0.01). Analyses at individual clock hours showed that RNFL measurement at 1 o’clock (Cirrus, 23.6%) and 2 o’clock (Stratus, 23.5%) was the location most frequently classified as abnormal. Eyes with smaller optic disc size and longer axial length were found to be associated with higher percentage of abnormal diagnostic classification.
Conclusions  While nasal sectorial RNFL measurement was frequently classified as borderline or outside normal limits, abnormal classification of RNFL measurement was significantly higher in Cirrus OCT than Stratus OCT. Eyes with smaller optic disc size and longer axial length were associated with higher percentage of abnormal diagnostic categorization in both OCTs. Caution should be exercised in interpreting the results of Stratus OCT and Cirrus OCT in myopic eyes (especially in eyes with small optic disc size).