Macular hole morphology and measurement using an automated three-dimensional image segmentation algorithm

Abstract

Objective: Full-thickness macular holes (MH) are classified principally by size, which is one of the strongest predictors of anatomical and visual success. Using a three-dimensional (3D) automated image processing algorithm, we analysed optical coherence tomography (OCT) images of 104 MH of patients, comparing MH dimensions and morphology with clinician-acquired two-dimensional measurements.

Methods and analysis: All patients underwent a high-density central horizontal scanning OCT protocol. Two independent clinicians measured the minimum linear diameter (MLD) and maximum base diameter. OCT images were also analysed using an automated 3D segmentation algorithm which produced key parameters including the respective maximum and minimum diameter of the minimum area (MA) of the MH, as well as volume and surface area.

Results: Using the algorithm-derived values, MH were found to have significant asymmetry in all dimensions. The minima of the MA were typically approximately 90° to the horizontal, and differed from their maxima by 55 μm. The minima of the MA differed from the human-measured MLD by a mean of nearly 50 μm, with significant interobserver variability. The resultant differences led to reclassification using the International Vitreomacular Traction Study Group classification in a quarter of the patients (p=0.07).

Conclusion: MH are complex shapes with significant asymmetry in all dimensions. We have shown how 3D automated analysis of MH describes their dimensions more accurately and repeatably than human assessment. This could be used in future studies investigating hole progression and outcome to help guide optimum treatments.

Keywords: anatomy; diagnostic tests/investigation; imaging; macula; retina.

Figure 1

A. Schematic diagram of the macula hole 3D model; B. OCT of a macula hole with 2D labels; C. Representative example of a segmented 3D macular hole in 3 different orientations – base area marked by *, top area (i.e. at the ILM side) marked by #. The approximate zone of the minimal area is shown by the arrow.

Figure 2

Mapping of centre point of the hole to the base area (A) and the centre line of the hole at the apex compared with the retinal surface (B).

Figure 3

The relationship between the mean dimension of base area (BA) and the mean dimension of minimum area (MA).

Figure 4

Schematic diagrams of the extracted three-dimensional macular hole shapes using the following dimensions: mean of the base area, mean of the minimum area, height above the base of the minimal area, mean of the top area, and height of the hole from the retinal pigment epithelium to the inner retinal surface. The asymmetry in maximum and minimum dimensions is represented in the thickness of the sides of the schematic holes.

Figure 5

Bland-Altman plots for base diameter measurements with observer 1 against the algorithm and observer 2 against the algorithm superimposed. 95% CIs are shown for the mean differences (shaded) and 95% CIs for the differences (lines).