Factors influencing the reliability of measurements in eyes with full-thickness macular holes: are we measuring incorrectly?

Purpose: The calliper function is used for manual measurements of full thickness macular holes (FTMHs). We aimed to investigate whether a reproducible difference could be detected beyond interobserver variability between two commonly used manufacturers in their manual calliper facility in spectral domain optical coherence tomography (OCT) for metrics related to FTMH.

Methods: This is a non-interventional, retrospective, observational study. Two independent observers examined 8 eyes (16 OCT) scans and 128 measurements (minimal linear diameter (MLD), basal diameter and hole height on both sides) of FTMHs, taken on Heidelberg Spectralis and Topcon Triton (OCT machines). The interobserver agreement and OCT machine agreement of measurements were analysed by Bland-Altman plots and intraclass correlation coefficient (ICC) analysis. Spectralis and Triton had 125 µm and 50 µm horizontal b-scan spacing, respectively.

Results: Overall, we report high absolute agreement in interobserver (ICC 0.991 (95% CI 0.985 to 0.995, p<0.001)) and OCT machine (ICC 0.993 (95% CI 0.987 to 0.996, p<0.001)) variability. Lower horizontal resolution in Triton compared with Spectralis leads to interobserver variability, in smaller horizontal measurements. Lower horizontal scanning density in Spectralis lead to relatively large interobserver variation if different reference scans were chosen, and consistently smaller MLD measurements than Triton. Vertical measurements without 1:1 scaling lead to inaccurate exaggerated oblique vertical measurements. Calliper function appears otherwise identically calibrated.

Conclusions: We report excellent interobserver and OCT machine agreement in measurements. However, the paper shows several factors that could influence the reliability of measurements acquired in eyes with FTMHs, such as the dimension of the hole as well as different image resolution, density scanning protocols or vertical scaling of the OCT machines viewing platform.