Steps to Measurement Floor of an Optical Microangiography Device in Glaucoma

Purpose

To compare dynamic ranges and steps to measurement floors of peripapillary and macular metrics from a complex signal-based optical microangiography (OMAGC) optical coherence tomography angiography (OCTA) device for glaucoma with those of OCT measurements.

Design

Cross-sectional study.

Methods

Imaging of 252 eyes from 173 glaucoma subjects and 123 eyes from 92 non-glaucoma subjects from a glaucoma clinic was quantified using custom and commercial software. Metrics from OCT (retinal nerve fiber layer [RNFL], ganglion cell-inner plexiform layer [GCIPL]) and OCTA (custom: peripapillary vessel area density [pVAD], macular vessel area density [mVAD], macular vessel skeleton density [mVSD]; commercial: peripapillary perfusion density [pPDZ], macular perfusion density [mPDZ], macular vessel density [mVDZ]) were plotted against visual field mean deviation (MD) with linear change-point analyses, measurement floors, and steps to floors.

Results

Mean MD (dB) for glaucomatous eyes was -5.77 (-6.45 to -5.10). The number of eyes with mild glaucoma (MD >-6), moderate glaucoma (MD -6 to -12), and severe glaucoma (MD <-12) were 164, 50, and 38, respectively. pPDZ yielded the lowest estimated floor at -26.6 dB (standard error [SE] 1.53), followed by OCTA macular metrics (-25 to -21 dB; SE 1.03) and pVAD (-17.6 dB, SE 1.06). RNFL and GCIPL produced floors at -17.8 (SE 0.927) and -23.6 dB (SE 1.14). The highest number of steps to measurement floor belonged to RNFL (7.20) and GCIPL (7.33), followed by pPDZ (4.25), mVAD (3.87), and mVSD (3.81), with 2.5 or fewer steps for pVAD, mPDZ, and mVDZ.

Conclusions

pPDZ, mVAD, and mVSD had approximately 4 steps within their dynamic ranges, without true measurement floors, and thus may be useful in evaluating advanced glaucomatous progression. Improving OCTA test-retest repeatability could augment number of steps for OCTA metrics, increasing their clinical utility.

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