Quantitative assessment of retinal nerve fiber layer defect depth using spectral-domain optical coherence tomography

To assess quantitatively the depth of retinal nerve fiber layer (RNFL) defects using a Cirrus high-definition (HD) optical coherence tomography (OCT)-derived RNFL thickness deviation map.

Prospective, cross-sectional study.

Three-hundred fifteen eyes with localized and diffuse RNFL defects of 315 glaucoma patients and 217 eyes of 217 healthy subjects.

For the glaucoma subjects, the severity of the RNFL defect was graded on red-free fundus photographs by 2 observers using a standardized protocol with a 3-level grading system. The RNFL defect depth on the RNFL thickness deviation map was expressed as an RNFL defect depth percentage index (RDPI): 100×(1-[summation of thicknesses of RNFL defects {red or yellow superpixels}/summation of RNFL thicknesses of upper 95th percentile range of age-matched healthy subjects in areas corresponding to RNFL defects]).

Retinal nerve fiber layer defect depth percentage index, average and segmental (4 quadrants and 12 clock-hour sectors) circumpapillary RNFL (cpRNFL) thicknesses according to the RNFL defect severity, and the area under the receiver operating characteristic curves (AUROCs) for various OCT parameters.

The RDPIs increased with the increasing severity of the RNFL defect in both the superior and inferior hemifields (P <0.05, 1-way analysis of variance test with Bonferroni correction). The AUROCs of the RDPIs (0.969 and 0.975 in the superior and inferior hemifields, respectively) were larger than those of all of the cpRNFL thicknesses in discriminating the mild from the moderate RNFL defects (P <0.05). Meanwhile, in discriminating the moderate from the severe RNFL defects, the AUROCs of the RDPIs (0.961 and 0.891 in the superior and inferior hemifields, respectively) were larger than those of the cpRNFL thicknesses in all areas except the inferior quadrant and the 6-, 7-, and 11-o'clock sectors (P <0.05).

The RDPI, a new parameter using a Cirrus HD OCT-derived RNFL thickness deviation map, can be a useful adjunct tool for objective quantification of RNFL defect depth. This parameter has an advantage over cpRNFL thickness in discriminating between mild and moderate RNFL defects, not in discriminating between moderate and severe defects.