Agreement between Heidelberg Retina Tomograph-I and -II in detecting glaucomatous changes using topographic change analysis

Abstract

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 Z3 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-Imixed 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.

Comparison of Neuroretinal Rim Area Measurements Made by the Heidelberg Retina Tomograph I and the Heidelberg Retina Tomograph II

“…In the latest HRT software version (HRT 3), the alignment algorithm corrects for horizontal and vertical shifts, rotational and tilt misalignment, and differences in parabolic distortion [known as parabolic error correction (PEC)], between baseline and each follow-up topography in a longitudinal series. Because the field of view of HRT Classic imaging is smaller than that of HRT II imaging, PEC is not applied when an HRT Classic examination is included in the longitudinal series 24. In the image alignment algorithm between HRT II topographic images only, the HEE software performs a parabolic correction to account for the curved surface of the peripapillary retina.…”

Agreement between the Heidelberg Retina Tomograph (HRT) Stereometric Parameters Estimated Using HRT-I and HRT-II

“…Details of the sources of parabolic error in HRT exams and the parabolic error correction procedure currently available in the HRT software are presented elsewhere 6. In brief, when the eye being imaged is at an optimal distance of 10mm from the HRT, the focal plane of the HRT lies parallel to the retinal surface and therefore, the HRT images are optimal without any distortion.…”

“…Therefore, the current HRT software does not correct for differences in parabolic distortion between exams when there is at least one 10° HRT-I exam in a longitudinal series of topographies. Longitudinal study of HRT topographies with an HRT-I exam at baseline using HRT topographic change analysis (TCA) has shown that differences in parabolic distortion between HRT-I and HRT-II exams of each participant need to be corrected to provide good agreement between the TCA change parameters estimated from a longitudinal series with both HRT-I and HRT-II exams 6. In addition, a modified parabolic error correction procedure was proposed to improve the accuracy of the parabolic error correction for both between 2 HRT-II exams and between an HRT-I exam and an HRT-II exam to minimize the influence of deeper optic disk measurements on the parabolic error estimate and to adjust the parabolic error correction based on the imaging area.…”

“…In a recent study, we observed that when an HRT-I baseline exam (reformatted to HRT-II format) was combined with HRT-II follow-up exams in a single longitudinal series, HRT Topographic Change Analysis (TCA) detected significantly more locations with retinal height decrease than when HRT-II exams alone were used (the same baseline date and follow-up dates were used for both series with either HRT-I or HRT–II as the baseline exam) 6. HRT software (HRTS glaucoma module, ver.…”

“…It does not apply the parabolic error correction when HRT-I exams are included in the series with HRT-II exams. Application of the parabolic error correction procedure to longitudinal series containing both HRT-I and HRT-II exams improved the agreement of TCA parameters with that of longitudinal series from the same eyes with same exam dates containing only HRT-II exams 6. In addition, a modified parabolic error correction procedure was proposed to remove any influence of measurements within the optic disk margin on the parabolic error estimates 6…”