Measuring Macular Holes: Is It Actual Growth or Measurement Error?
Translational Vision Science & Technology
Errors in measurement can be mistaken for enlargement of a macular hole (MH). Moreover, MHs are not perfectly round, and their minimum linear diameter (MLD) can lie in any meridian. Baumann et al. reviewed data for patients with MHs measured from high-density radial OCT scans, with the goal of establishing a cutoff point for progression of concern. Their findings indicate that 31 μm is an effective cutoff point for distinguishing true change from a mistake in measurement.
The analysis included 51 consecutively managed patients (51 MHs) who had a waiting period of four weeks leading up to MH surgery. For each MH, two qualified observers obtained three repeated sets of measurements from high-density radial OCT scans, conducted at initial presentation and four weeks later (before the surgery). The objective was to define a cutoff point to differentiate MH enlargement from measurement error. Another goal was to identify risk factors for changes in MLD and best-corrected visual acuity (BCVA).
The mean hole size in the study group was 334 μm (range, 39-793 μm). The cutoff point for an increase in MLD, calculated as the outer confidence limit for the 99.73% limit of agreement, was 31 μm and independent of MH size. With this cutoff applied, MLD increased during the waiting period in nine (26.5%) of 34 patients without vitreomacular traction (VMT) and in 14 (82.4%) of 17 patients with VMT (p < .001). In patients with MH progression, mean BCVA deteriorated from .62 to .82 logMAR (p < .001). Patients without progression experienced no meaningful change in BCVA.
Obtaining mean values from repeated measurements of MHs is crucial to determine bona fide changes in size, said the authors. If only one measurement per rater had been used in their study, the cutoff point would have exceeded 60 μm. MH progression occurred more quickly than in other studies, particularly when VMT was present. Such findings may help to guide treatment decisions, said the authors, who recommend repeating OCT shortly before surgery. As a next step, they suggest assessing inter-OCT precision so that cutoffs can be generalized for different centers.
The original article can be found here.