Reproducibility of peripapillary retinal nerve fiber layer thickness and optic nerve head parameters measured with cirrus HD-OCT in glaucomatous eyes - PubMed (original) (raw)

Reproducibility of peripapillary retinal nerve fiber layer thickness and optic nerve head parameters measured with cirrus HD-OCT in glaucomatous eyes

Jean-Claude Mwanza et al. Invest Ophthalmol Vis Sci. 2010 Nov.

Abstract

Purpose: To assess the reproducibility of peripapillary retinal nerve fiber layer (RNFL) thickness and optic nerve head (ONH) parameters measured with Cirrus HD-OCT in glaucomatous eyes.

Methods: Fifty-five glaucomatous eyes were included in the study. The optic disc cube 200 × 200 protocol was used to obtain three scans during the same visit to evaluate the intravisit reproducibility. One scan on 4 additional days within a 2-month period of the first session was obtained to assess intervisit reproducibility. Intraclass correlation coefficient (ICC), coefficient of variation (CV), and test-retest SD (TRT SD) were calculated for each RNFL and ONH parameter. The formula 1.645 × √2 × intervisit TRT SD provides an upper tolerance limit to variability beyond which nonphysiologic change should be considered.

Results: All ICCs were excellent, ranging from 83.9% to 99.2% for intravisit measurements and from 80.8% to 99.1% for intervisit measurements. Cup/disc area ratio had the lowest CV (1.1%) in either type of measurement, followed by average RNFL thickness (1.9% and 2.7%). Nasal clock hours and quadrants showed the poorest reproducibility as did the clock hour directly temporally. The intervisit tolerance limit for average RNFL thickness was 3.89 μm.

Conclusions: Intravisit and intervisit measurements of peripapillary RNFL thickness and ONH parameters with Cirrus HD-OCT showed excellent reproducibility, indicating that this instrument may be useful in monitoring glaucoma progression. When comparing two measurements from the same eye on two different visits, a reproducible decrease in average RNFL thickness of approximately 4 μm or more may be considered a statistically significant change from baseline.

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Figures

Figure 1.

Figure 1.

Vertical (A) and horizontal (B) tomograms of the same eye showing the end of the Bruch's membrane (black dots) as determined by the Cirrus HD-OCT ONH analysis software. The end of the Bruch's membrane corresponds to the disc margin, whereas white dots represent reference points for the cup margin. The distance between the black dots and the white dots represents the rim width or precisely VRT (A) and HRT (B). En face image (C) showing the disc margin (outer black) and the cup margin (inner red) as detected and drawn by with Cirrus HD-OCT 5.0 software. The region between disc and cup margins represents the neuroretinal rim area (mm2); the region inside the cup margin corresponds to the cup area (mm2); the disc area (mm2) is the rim area the plus the cup area. The CDR is given by the square root of the ratio of the area of the cup to the area of the disc. The VCDR is the ratio of the vertical line through the cup center to the same vertical line extending to the disc margin: BC/(AB+BC+CD) or BC/AD. The HCDR is the ratio of the horizontal line through the cup center to the same line extending to the disc margin: FG/(EF+FG+GH) or FG/EH. VRT (μm) is the total rim thickness measured in the vertical meridians: AB-BC or simply AB+CD. HRT (μm) is the total rim thickness measured in the horizontal meridian: EH-FG or simply EF+GH.

Figure 2.

Figure 2.

Tomogram of an optic disc showing the cup volume (light blue shaded area, mm3) as determined and calculated by Cirrus HD-OCT 5.0 software. Red spots indicate reference points to cup margin; green spots represent the end of the Bruch's membrane. The blue horizontal line is the RPE/Bruch's membrane plane or simply the optic disc plane. The black horizontal line is located 200 μm above the disc plane. The cup volume is a three-dimensional measurement defined as the volume between a plane at a fixed offset located 200 μm from the plane of the optic disc and the vitreoretinal interface/inner limiting membrane.

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