Retinal Oximetry in Subjects With Glaucomatous Hemifield Asymmetry

Although some studies suggest a strong link between retinal vessel oxygenation and damage to the retinal nerve fiber layer (RNFL) seen in glaucoma, it has yet to be conclusively proven. This study compares intraocular retinal oximetry in glaucomatous eyes displaying asymmetrically affected hemifields across different subgroups of glaucoma, namely primary angle closure glaucoma (PACG), primary open-angle glaucoma (POAG), and normal tension glaucoma (NTG).

In this prospective cross-sectional study, 99 patients (PACG, n=28; POAG, n=37; NTG, n=34) underwent retinal oxygenation and vessel caliber measurements using the Oxymap T1 Retinal Oximeter, Cirrus optical coherence tomography, and Humphrey visual field testing. For the comparison between different subtypes of glaucoma, an analysis of variance with Bonferroni method was performed. Intraeye differences were compared with a paired t test. Determination of the more affected and less affected hemifield was made using the Humphrey visual field pattern deviation plot.

Considering the mean deviation and Advanced Glaucoma Interventional Study score, the visual field defects were milder in NTG as compared with POAG and PACG (P<0.05).Arteriole diameter was smaller in the more affected hemifield compared with the less affected hemifield in patients with PACG (109.30±18.07 vs. 120.57±17.92; P=0.023) and NTG (109.36±13.79 vs. 117.46±17.72; P=0.04). The more affected hemifield had a significantly thinner RNFL than the less affected hemifield in patients across all 3 groups, though this was only significant in PACG (P=0.02) and NTG patients (P<0.01). In all 3 groups, although the less affected hemifield tended to have a marginally higher arteriole and venule oxygen saturation than the more affected hemifield, no statistical significance was reached. There were no significant differences in arteriovenous difference between the more and less affected hemifield in all 3 groups.

In our study, localized visual field losses were not associated with changes in retinal oximetry but were associated with narrower retinal arteriolar diameters in PACG and NTG. The RNFL was thinner in the more affected hemifield in these 2 groups but this was not so marked in the POAG sample, possibly limiting our ability to find a difference in arteriolar diameter there.