Intraobserver repeatability of macula measurements by confocal scanning laser tomography

To assess the repeatability of macula measurements provided by the Heidelberg Retina Tomograph II (HRT II) in normal subjects, patients with diabetic macular edema (DME), and patients with choroidal neovascularization (CNV).

Prospective, observational case.

Institutional-based study.

Ten normal eyes, 14 eyes with DME, and 14 eyes with CNV.

Three scans within a single day. An additional three scans of each of the 10 normal eyes on a different day.

Bland and Altman analysis for a 0.25 mm, 0.50 mm, and 0.75 mm radius circle.

Variability and repeatability of the measurements were not related to circle size for either group of patients. Coefficient of variability values of the normal group and a 0.50-mm radius circle were 17%, 5.7%, and 6.1% for mean surface height, signal width, and edema index, respectively. The corresponding values were 15.6%, 10%, and 10% for the DME group, and 10.5%, 7.4%, and 8.5% for the CNV group. The 95% confidence interval of the difference between single observations across days of the normal group was +/-106 microm, +/-80 microm, and +/-0.10 for mean surface height, signal width, and edema index, respectively. When three scans were combined, the corresponding values were +/-61.5 microm, +/-46.7 microm, and +/-0.06.

The repeatability and variability of measurements of normal subjects, patients with DME, and patients with CNV were determined. Differences between the three groups exist and are important for diagnosing a pathologic condition or measuring the effect of various treatments.