Casado et al. explored the utility of the central macular full retinal (RTA) and GCL thickness measurements and their vertical asymmetry along the fovea-disc axis to peripapillary retinal nerve fiber layer (pRNFL) thickness measurements for discriminating glaucoma eyes with visual field loss from control eyes with no visual field defects. Three hundred and eighteen eyes of 161 subjects were included. The control group consisted of eyes that did not have visual field loss and therefore, could have been normal or have had early glaucoma. The investigators limited their analyses to the central 16 macular superpixels (called clusters).
They found similar performance for either GCL clusters (or superpixels) or GCL asymmetry measures comparable to pRNFL especially in eyes with superior VF loss while the pRNFL still performed better in eyes with inferior visual field loss. GCL and RTA asymmetry were measured subjectively. While subjective asymmetry in GCL and pRNFL were correlated with visual field loss, retinal thickness asymmetry did not show a significant difference between control and glaucoma eyes. GCL and pRNFL thickness meas-urements showed significant correlations with visual field severity stage (-0.334 for the best GCL superpixel and -0.303 for the average pRNFL).
Vertical asymmetry measures are useful for detection of early glaucoma
It is not clear how the proportion of eyes detected with macular measures overlaps with the eyes detected with pRNFL measures. This would have provided a better understanding of how complementary the two type of structural outcomes (macula-based vs. RNFLbased) would be. Myopic eyes were excluded limiting the generalizability of results to this important subset of patients. It is conceivable that macular thickness and asymmetry measures would have performed even better if the control group was composed of entirely normal eyes.
This paper adds to the already substantial amount of information in the literature suggesting that vertical asymmetry measures are useful for detection of early glaucoma. It is high time that a user-friendly marker based on vertical macular asymmetry is incorporated into commercial SD-OCT devices so as to facilitate clinical evaluation of eyes suspected of early glaucoma.