Statistics from Altmetric.com
Glaucomatous damage typically causes retinal ganglion cell and retinal nerve fibre layer (RNFL) loss that can occur diffusely and focally. Optical coherence tomography (OCT) is a non-invasive, non-contact technology that allows cross-sectional high-resolution in vivo imaging of intraretinal layers. Since structural abnormalities may precede functional abnormalities, it might be expected that an OCT RNFL abnormality would be observed when glaucomatous visual field (VF) loss is present. We report two patients who demonstrated clinically evident focal RNFL defects with corresponding VF loss that failed to be recognised as outside normal limits by OCT analysis.
The first subject had normal-tension glaucoma with a best-corrected visual acuity (BCVA) of 20/25 in the right eye and marked optic nerve head (ONH) cupping, inferior disc haemorrhage and inferotemporal RNFL wedge defect (fig 1A). VF showed a superior nasal step with an early arcuate scotoma (fig 1B). The OCT RNFL thickness profile (StratusOCT; Carl Zeiss Meditec, Dublin, California) revealed a narrow depression into the abnormal zone (red colour) in the inferotemporal region and borderline depression (yellow) in the superior and superonasal regions. The OCT demonstrated borderline thin superior sectors on clock-hour analysis when compared with the OCT normative database but failed to demonstrate thinner than normal RNFL in the inferotemporal sectors (fig 1C). The cross-sectional scans showed an overt narrowing of the RNFL that was markedly underestimated by the RNFL edge detection analysis by failing to follow the surface (fig 1D).