Abstract
PurposeTo introduce and evaluate the performance in detecting glaucomatous abnormalities of a novel method for extracting en face slab images (SMAS), which considers varying individual anatomy and configuration of retinal nerve fiber bundles.MethodsDense central retinal spectral domain optical coherence tomography scans were acquired in 16 participants with glaucoma and 19 age-similar controls. Slab images were generated by averaging reflectivity over different depths below the inner limiting membrane according to several methods. SMAS considered multiple 16 µm thick slabs from 8 to 116 µm below the inner limiting membrane, whereas 5 alternative methods considered single summary slabs of various thicknesses and depths. Superpixels in eyes with glaucoma were considered abnormal if below the first percentile of distributions fitted to control data for each method. The ability to detect glaucoma defects was measured by the proportion of abnormal superpixels. Proportion of superpixels below the fitted first percentile in controls was used as a surrogate false-positive rate. The effects of slab methods on performance measures were evaluated with linear mixed models.ResultsThe ability to detect glaucoma defects varied between slab methods, χ2(5) = 120.9, P < 0.0001, with SMAS showing proportion of abnormal superpixels 0.05 to 0.09 greater than alternatives (all P < 0.0001). No slab method found abnormal superpixels in controls.ConclusionsSMAS outperformed alternatives in detecting abnormalities in eyes with glaucoma. SMAS evaluates all depths with potential retinal nerve fiber bundle presence by combining multiple slabs, resulting in greater detection of reflectance abnormalities with no increase in surrogate false positives.Translational RelevanceSMAS may be used to objectively detect glaucoma defects in en face optical coherence tomography images.
Highlights
We previously showed that the configuration of retinal nerve fiber bundles (RNFBs) in healthy eyes varies with retinal location and individual anatomy.[19]
Part of the en face images of three participants with glaucoma were censored for similar reasons
All participants in the glaucoma group but one had a visual field defect according to the definition used for the control group’s exclusion criteria
Summary
Optical coherence tomography (OCT) is increasingly used to assess structural changes of the retina owing to glaucoma.[1,2,3] Such changes are conventionally evaluated in cross-sectional scans assessing the thickness of either the retinal nerve fiber layer (RNFL) or the ganglion cell and inner plexiform layers.[2,4] En face OCT imaging is a relatively new approach that uses transverse retinal images to assess reflectance properties of retinal nerve fiber bundles (RNFBs).[5]Compared with assessing RNFL reflectance in fundus photographs,[6,7] en face OCT has advantages in better visualization of narrow defects and preserved bundles, the ability to examine below the superficial RNFL, and being less affected by lens opacities and light fundus pigmentation.[8,9,10] En face OCT analysis of reflectivity has demonstrated potential for early glaucoma detection[11,12,13] and is a potential means to facilitate custom perimetry strategies that target specific regions of interest.[14,15,16,17,18] direct.
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