Vertical macular ganglion cell/inner plexiform thickness asymmetry for detection of early glaucoma

Abstract

 

Purpose

 

To investigate whether quantification of vertical asymmetry in macular ganglion cell/inner plexiform layer (GC/IPL) thickness measurements can improve detection of early glaucoma as compared to sectoral GC/IPL measures.

 

Methods

 

Sixty-nine normal control eyes (69 subjects) and 59 open-angle glaucoma eyes (47 subjects) [mean deviation (MD) >-6.0 dB] were enrolled. All patients underwent macular imaging with Cirrus HD-OCT (200x200 Macular Cube). The segmented macular GC/IPL thickness matrices (200x200) were exported and were centered in relation to the foveal center. The 40,000 A-scan measurements were clustered into a 20x20 grid of superpixels, and the superior superpixels were compared to their inferior counterparts by calculating an asymmetry ratio as =|log inferior/superior GC/IPL thickness|. An asymmetry index (AI) was defined as the grand mean of the asymmetry ratios in the central circular area (6 mm diameter). AI’s performance was compared to the best-performing GC/IPL sector based on areas under receiver operating characteristic curves (AUC) calculated after logistic regression.

 

Results

 

The glaucoma subjects were older (66.9±6.2 vs. 60.0±8.0 years, P˂0.001) and had longer axial length (24.6±1.1 vs. 23.8±1.1 mm, p˂0.001). Average MD in glaucoma and normal subjects was -2.4±1.7 and -0.2±1.2 dB (p˂0.001), respectively. The average AI was 0.034±0.016 and 0.052±0.023 in the normal and glaucoma groups (p˂0.001), respectively. The AUC for glaucoma discrimination was 0.790 for AI as compared to 0.909 for the inferotemporal GC/IPL sector (p=0.006, Figure 1).

 

Conclusions

 

The macular asymmetry index’s performance was worse with regard to detection of early glaucoma compared to the best macular sectoral thickness measure. Regional patterns of asymmetry in normal subjects and early glaucoma need to be further explored.