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Bright Senyo Ashimatey, William Howard Swanson, Brett J King, Stephen A Burns; Defining RNFB abnormality in peripapillary OCT en face imaging. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3994.
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© ARVO (1962-2015); The Authors (2016-present)
The details of glaucomatous abnormality have been suggested to be seen better on en face images than on circumpapillary retinal nerve fiber layer thickness (cRNFLT) measures (Hood et al. 2015). The evidence for this assertion is currently based on eyes with deep visual field defects near fixation. Given the availability of OCT en face imaging in clinical devices and its potential to influence clinical decision making, we investigated the patterns of abnormality on en face imaging of the retinal nerve fiber bundles (RNFBs) in a group of patients with clinically diverse glaucomatous damage
We analyzed Heidelberg Spectralis OCT en face images from 30 patients participating in an ongoing research project in our lab. We compared the findings of the en face images in the superior temporal (ST) and inferior temporal (IT) disc sectors to the ST and IT findings of the cRNFLT. We defined a sector from an en face image as abnormal when a wedge defect traceable to the disc was found between the inner limiting membrane and 72μm depth in that sector, and defined a sector on the cRNFLT protocol as abnormal when the average sector thickness was less than the 1% reference value of the machine norms. To better understand the nature of the defect, we used adaptive optics SLO imaging in two of the subjects with a thickness abnormality but without an en face OCT abnormality
The table in Figure 1 shows the findings of en face images relative to the findings of cRNFLT. The Cohen's kappa assessing agreement between the cRNFL and the en face imaging was 0.56, p<0.05 and 0.65, p<0.05 for ST and IT respectively. AOSLO confirmed an en face abnormality (traceable to the disc) in one of the two subjects who were imaged on the AOSLO (shown in figure 2).
When a well defined wedge defect was present on the en face image, the details of glaucomatous damage were better seen on the en face images than the cRNFLT profiles as suggested by Hood et al. However, when wedge defects were not explicitly defined on the OCT en face images (as is expected in diffuse loss), cRNFLT showed a more convincing abnormality. The presence of deep indistinct wedge defects on OCT en face imageing can sometimes be confirmed with the AOSLO when imaged at a suitable depth. In addition to viewing the details of glaucomatous abnormality en face, carefully characterizing the depth and thickness parameters of the RNFBs may be helpfull in detecting abnomality.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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