Minutes Analysis Increases Sensitivity of Detecting Nerve Fiber Bundle Defects on Optical Coherence Tomography (OCT) Retinal Nerve Fiber Layer (RNFL) Thickness Measurements

Abstract

 

Purpose

 

To test the hypothesis that sectoring smaller than a clock hour on OCT RNFL thickness measurements improves sensitivity to detect nerve fiber bundle defects (NFBD).

 

Methods

 

Eighteen eyes, 10 glaucoma and 8 glaucoma suspects, were scanned with Cirrus HD-OCT (Zeiss, Dublin, CA; Optic Disc Cube 200x200 scan pattern). All eyes showed NFBD on the Cirrus native RNFL thickness deviation maps, but were categorized as normal based on global mean RNFL thicknesses. In addition to the conventional quadrants (90° sector) and clock hours (30°) measurements, minutes (6°) measurements were performed. Sensitivity and specificity were calculated in detecting NFBD. The gold standard was constructed by manually reading the cumulative arc length that showed at least borderline deviation (thinner than 5th percentile from the normative data) on the Cirrus RNFL thickness deviation map: larger than one clock hour arc length within one quadrant defined an abnormal quadrant, more than half of an arc length within one clock hour defined an abnormal clock hour, and any eligible deviation within one minute defined an abnormal minute as the size of super pixel (smallest unit indicating deviation from the normative data) on the deviation map is about the same size of the 6° arc along the 3.4mm circumpapillary ring.

 

Results

 

Sensitivity of the minutes analysis was significantly higher (50.4%) than global, quadrant, and clock hour analyses, while specificity was decreased modestly (97.9%) in the minutes analysis (Table).

 

Conclusions

 

Finer grained minutes analysis dramatically improves the OCT NFBD detection sensitivity with only a modest decrease in specificity. Minutes analysis may improve our ability to detect and follow early stage glaucoma. Also, this analysis can be applied in a retrospective fashion to all circumpapillary OCT RNFL measurements regardless of the modality (time and spectral domain).

 

 

Keywords: 550 imaging/image analysis: clinical • 610 nerve fiber layer • 549 image processing