Purpose: To evaluate the suitability of including both Heidelberg Retina Tomograph-I (HRT-I) and HRT-II examinations in the same longitudinal series for HRT topographic change analysis (TCA) and to evaluate parabolic error correction (PEC) to improve the agreement between HRT-I and HRT-II examinations.
Methods: A total of 66 eyes from the University of California San Diego Diagnostic Innovations in Glaucoma Study with baseline HRT-I and HRT-II examinations obtained on the same day and ≥ 3 HRT-II follow-up examinations were included. Two TCA analyses, HRT-I examination at baseline (HRT-I-mixed series) and HRT-II examination at baseline (HRT-II-only series) were compared. Agreement between the HRT-I-mixed and HRT-II-only series were estimated using Bland-Altman plots. Agreement was assessed: (1) using the current HRT software settings (PEC applied only to HRT-II-only series), and (2) modified HRT settings (PEC also applied to HRT-I-mixed series).
Results: With current HRT software settings, the HRT-I-mixed series significantly overestimated change locations (ie, red pixels) compared with the HRT-II-only series as indicated by statistically significant proportional biases in the Bland-Altman analysis. By applying PEC to HRT-I-mixed series there were no statistically significant biases in the TCA parameter estimates compared with the HRT-II-only series.
Conclusion: In some eyes, HRT-I and HRT-II baseline examinations are not interchangeable in TCA analysis without parabolic error correction. HRT-I-mixed series detected more changes characteristic of glaucoma when there were only minimal changes in the HRT-II-only series. Our results suggest that in the majority of cases, with PEC, HRT-I examinations may be included in a longitudinal series containing HRT-II examinations.