Detecting Progression in Advanced Glaucoma: Are Optical Coherence Tomography Global Metrics Viable Measures?

ABSTRACT

SIGNIFICANCE: Optical coherence tomography (OCT) summary measures have been suggested as a way to detect progression in eyes with advanced glaucoma. Here, we show that these measures have serious flaws largely due to segmentation errors. However, inspection of the images and thickness maps can be clinically useful. PURPOSE: This study aimed to test the hypothesis that recently suggested global OCT measures for detecting progression in eyes with advanced progression are seriously affected by segmentation mistakes and other errors that limit their clinical utility. METHODS: Forty-five eyes of 38 patients with a 24-2 mean deviation worse than -12 dB had at least two spectral domain OCT sessions (0.8 to 4.4 years apart) with 3.5-mm circle scans of the disc and cube scans centered on the fovea. Average (global) circumpapillary retinal nerve fiber layer thickness, GcRNFL, and ganglion cell plus inner plexiform layer thickness, GGCLP, were obtained from the circle and cube scan, respectively. To evaluate progression, ΔGcRNFL was calculated for each eye as the GcRNFL value at time 2 minus the value at time 1, and ΔGGCLP was calculated in a similar manner. The b-scans of the six eyes with the highest and lowest ΔGcRNFL and ΔGGCLP values were examined for progression as well as segmentation, alignment, and centering errors. RESULTS: Progression was a major factor in only 7 of the 12 eyes with the most negative values of either ΔGcRNFL or ΔGGCLP, whereas segmentation played a role in 8 eyes and was the major factor in all 12 eyes with the largest positive values. In addition, alignment (one eye) and other (three eyes) errors played a secondary role in four of the six eyes with the most negative ΔGcRNFL values. CONCLUSIONS: For detecting the progression of advanced glaucoma, common summary metrics have serious flaws largely due to segmentation errors, which limit their utility in clinical and research settings.