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Editors Selection IGR 18-1

Clinical Examination Methods: An OCT-A perspective on peripapillary capillaries and POAG

Comment by Tae-Woo Kim on:

71399 Peripapillary perfused capillary density in primary open-angle glaucoma across disease stage: an optical coherence tomography angiography study, Geyman LS; Garg RA; Suwan Y et al., British Journal of Ophthalmology, 2017; 101: 1261-1268

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With the emergence of optical coherence tomography angiography (OCTA), it became possible to image the papillary and peripapillary microvasculature in a non-invasive manner. It has been demonstrated that the peripapillary capillary density is decreased in eyes with glaucoma compared to healthy eyes. In addition, the decrease capillary density has been shown to coincide with the retinal nerve fiber layer defect identified by red-free photography. These observations raise the possibility that the peripapillary vessel density may be a viable modality for monitoring POAG. Geyman et al. assessed the peripapillary capillary density (PCD) in 60 POAG eyes with varying stages of disease and 24 healthy control eyes. The PCD was calculated as a percentage as the ratio of pixels associated with perfused capillaries to the total number of pixels in the corresponding region of interest (ROI). A custom automated algorithm was used to isolate the capillary microvasculature. They found a progressive stepwise decrease of PCD from control eyes throughout worsening POAG stage. PCD demonstrated a comparable diagnostic capability to the cpRNFL thickness and visual field parameters. In addition, PCD exhibited significant correlations with cpRNFL thickness and VF MD.

An intriguing finding of this study is that the temporal peripapillary sector exhibited a far smaller decrease across POAG stage relative to other sectors. The less decrease was contrasted with circumpapillary retinal nerve fiber layer thickness (cpRNFLT), particularly in late stage of disease: while the cpRNFLT demonstrated a marked thinning in the temporal sector, the temporal PCD was relatively preserved. This finding raises a possibility that the PCD may have better correlation with VF than cpRNFLT in the end stage of disease. The RNFLT may reach to its 'floor' despite remaining VF. Therefore, serial measurement of the RNFLT is often not useful to monitor disease progression in eyes with advanced VF defect. It would be of interest to see whether the PCD progressively attenuates along with the VF loss throughout the whole stage of disease. If so, the PCD may help clinicians to monitor the disease progression by enabling them to look at the vasculature-function consistent worsening of disease until the end stage of disease.

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