Figure 8.

Repeatability (equation 2) of qAF measurements obtained from two images within a session, from two sessions on the same day (<5 minutes apart), and from two sessions on different days (28–64 days apart), and agreement (equation 2) between qAF measurements on the HRA2 and the Spectralis on the same day. Repeatability was better (smaller) within sessions than between sessions, suggesting that positioning of the subject's eye is a major source of measurement noise. Repeatability had the same pattern for all comparisons, improving with increasing sampling area and increasing fundus AF. The two cSLOs had similar repeatability (no significant differences between ΔqAF distributions, Kolmogorov-Smirnov two-sample; P ≥ 0.08). In one session, three to four images were acquired, separated by blinking and, if necessary, minor realignment of the camera. For between-session and between-instrument comparisons, two images from each session (randomly selected from session images) were averaged to provide the data. Repeatability and agreement computations included corrections for the use of multiple measurements per session.³⁸ Test–retest measurements were made in 12 subjects, 10 of whom had both eyes tested. As there were no significant correlations between the differences, ΔqAF, obtained from left and right eyes (three comparisons: ρ <0.3; P > 0.26) data for both eyes were used.