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.