Precision and reliability of retinal thickness measurements in foveal and extrafoveal areas of healthy and diabetic eyes.

PURPOSE To determine the precision and reliability of retinal thickness measurements with an optical coherence tomograph (Stratus OCT 3; Carl Zeiss Meditec, Dublin, CA) and a retinal thickness analyzer (RTA; Talia Technology Ltd., Neve-Ilan, Israel) in foveal, parafoveal, and perifoveal areas. METHODS Three measurements of all areas were performed within 1 hour on the same day with each instrument in the eyes of healthy volunteers and diabetic patients. The latter group was divided into eyes with and without macular edema. RESULTS Measurement precision, expressed as the 95% limits of agreement (LA 95%), was significantly higher (i.e., a lower LA 95%, P < 0.01) for the OCT in comparison to the RTA in virtually all areas of the retina. Moreover, measurement reliability, expressed as the intraclass correlation coefficient, was high with the OCT (>0.90) and moderate to low with the RTA (0.26-0.89). A direct influence of macular edema itself on measurement precision of para- and perifoveal areas was found in the OCT measurements. CONCLUSIONS The high measurement precision and reliability of the OCT suggests that this instrument is currently the most suitable technique for detection and follow-up of diabetic macular edema. When macular edema is present, the OCT can reliably detect changes of at least 36 microm at the fovea, 55 microm in parafoveal areas below a thickness of 744 microm, and 42 microm in perifoveal areas below a thickness of 1011 microm.