Purpose: To evaluate the sensitivity and specificity of measurements of retinal nerve fiber layer (RNFL) thickness in early to moderate glaucoma using Stratus time-domain and Cirrus spectral-domain optical coherence tomography (OCT; Carl Zeiss Meditec, Dublin, CA). Design: Evaluation of diagnostic test or technology. Participants: Fifty-four glaucoma subjects with early to moderate visual field defects and 50 age-matched normal subjects. Testing: Three peripapillary RNFL scans of 1 eye of each subject using Stratus and Cirrus OCT. Main Outcome Measures: Sensitivity and specificity of average, quadrant, and clock-hour RNFL thickness. Results: The average age standard deviation in the normal and glaucoma groups was 62.9 +/- 12.7 years (range, 40-84 years) and 67.6 +/- 11.4 (range, 42-85 years), respectively (P = 0.05). The glaucoma group consisted of 34 early (average mean deviation, -3.20 +/- 1.22 dB) and 20 moderate (average mean deviation, -8.05 +/- 1.87 dB) glaucomas. Cirrus OCT sensitivity and specificity for average RNFL abnormal at the 5% level were 83% and 88%, respectively, and at the 1% level were 65% and 100%, respectively. Stratus OCT sensitivity and specificity for average RNFL abnormal at the 5% level were 80% and 94%, respectively, and at the 1% level were 61% and 100%, respectively. For 1 or more abnormal quadrants at the 5% level, the sensitivity and specificity for Cirrus OCT were 98% and 80%, respectively, and at the 1% level were 87% and 92%, respectively. For 1 or more quadrants abnormal at the 5% level, the sensitivity and specificity for Stratus OCT were 96% and 76%, respectively, and at the 1% level were 74% and 94%, respectively. Cirrus OCT sensitivity and specificity using a criterion of 1 or more abnormal clock hours at the 5% level were 100% and 72%, respectively, and at the 1% level were 85% and 94%, respectively. Stratus OCT sensitivity and specificity for 1 or more abnormal clock hours at the 5% level were 98% and 66%, respectively, and at the 1% level were 85% and 90%, respectively. Conclusions: The sensitivity and specificity of various RNFL parameters using the Cirrus OCT for glaucoma with early to moderate visual field defects are excellent and are equivalent to Stratus OCT.