Original article
Accuracy of the Heidelberg Spectralis in the Alignment Between Near-Infrared Image and Tomographic Scan in a Model Eye: A Multicenter Study

https://doi.org/10.1016/j.ajo.2013.04.030Get rights and content

Purpose

To evaluate temporal changes and predictors of accuracy in the alignment between simultaneous near-infrared image and optical coherence tomography (OCT) scan on the Heidelberg Spectralis using a model eye.

Design

Laboratory investigation.

Methods

After calibrating the device, 6 sites performed weekly testing of the alignment for 12 weeks using a model eye. The maximum error was compared with multiple variables to evaluate predictors of inaccurate alignment. Variables included the number of weekly scanned patients, total number of OCT scans and B-scans performed, room temperature and its variation, and working time of the scanning laser. A 4-week extension study was subsequently performed to analyze short-term changes in the alignment.

Results

The average maximum error in the alignment was 15 ± 6 μm; the greatest error was 35 μm. The error increased significantly at week 1 (P = .01), specifically after the second imaging study (P < .05); reached a maximum after the eighth patient (P < .001); and then varied randomly over time. Predictors for inaccurate alignment were temperature variation and scans per patient (P < .001). For each 1 unit of increase in temperature variation, the estimated increase in maximum error was 1.26 μm. For the average number of scans per patient, each increase of 1 unit increased the error by 0.34 μm.

Conclusion

Overall, the accuracy of the Heidelberg Spectralis was excellent. The greatest error happened in the first week after calibration, and specifically after the second imaging study. To improve the accuracy, room temperature should be kept stable and unnecessary scans should be avoided. The alignment of the device does not need to be checked on a regular basis in the clinical setting, but it should be checked after every other patient for more precise research purposes.

Section snippets

Methods

Six ophthalmologic sites were involved in this multicenter study beginning in March of 2012. Sites included were: (1) Jacobs Retina Center and (2) Hamilton Glaucoma Center at the Shiley Eye Center, University of California San Diego, La Jolla, California, USA; (3) Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico and (4) Luigi Sacco Hospital, University of Milan, Milan, Italy; (5) Azienda Ospedaliera Sant’Anna, Como, Italy; and (6) Department of Ophthalmology,

Results

A summary of all results of the 12-week study is presented in the Table. After the calibration procedure at baseline, the mean horizontal error among the 6 sites was 0.54 ± 0.31 pixels, equivalent to 3.10 ± 1.80 μm; the mean vertical error was 0.69 ± 0.12 pixels, equivalent to 3.93 ± 0.68 μm. During the 12-week study, the mean horizontal error among the 6 sites was 2.43 ± 1.20 pixels, equivalent to 13.90 ± 6.89 μm; the mean vertical error was 2.46 ± 1.14 pixels, equivalent to 14.08 ± 6.55 μm.

Discussion

The present study showed that, overall, the alignment between simultaneous NIR images and OCT scans of the Heidelberg Spectralis is excellent. The mean error in the alignment was 13.90 μm (horizontal) and 14.08 μm (vertical), and the mean maximum error was 15.35 μm. Interestingly, the maximum error increased significantly at week 1 compared to baseline (P = .01), then varied randomly without significant changes during the 12-week follow-up period. During the first day after calibration, the

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