Repeatability of Heidelberg Retinal Tomography 3 and effect of alignment algorithm on glaucoma suspects.

Background: The Heidelberg Retina Tomograph (HRT) is a commonly-used clinical instrument for glaucoma diagnosis; however, the repeatability of the two most commonly used analysis tools, Moorfield regression analysis (MRA) and 'glaucoma probability score' (GPS) is not known and could have significant implications for patients at risk or suspected of developing glaucoma. Thus, the intra-visit repeatability of the HRT3 (an objective measure of instrument-induced variability) was investigated in a glaucoma suspect cohort.

Methods: Two repeat 15° × 15° optic nerve head scans were taken from 164 eyes of 84 patients using the HRT (HRT3, software version 3) during a single visit. The variability of global and sectoral rim area, rim volume and GPS were analysed with and without image alignment using SPSS 22.0. Repeatability was evaluated as absolute difference between the two measurements.

Results: Repeatability of the global rim area, rim volume and GPS were high with and without image registration. Variability increased by a small, yet significant amount without image alignment (p < 0.001 to p = 0.002). This increase was more prominent for sectoral analysis with the exception of the rim area and volume in the temporal sector (p = 0.034 to p < 0.001). Increase in the variability of the GPS was also significant (p < 0.001).

Conclusion: HRT3 demonstrated high short-term repeatability, which significantly improved with image registration for all global measurements. Sectoral analysis demonstrated higher repeatability with image registration for some of the sectors in rim area and volume analysis and all sectors for the GPS. Therefore, depending upon the assessed parameters, image registration may play a significant role in the interpretation of results in glaucoma suspects.