Diagnostic capability of ganglion cell complex thickness in primary open angle glaucoma

Background

Glaucoma is characterized by loss of retinal ganglion cells (RGCs) followed by visual field defects.Spectral domain OCT(SD-OCT) enabled more precise and quantitative assessments of macular ganglion cell complex (GCC) thickness.

Objective

This study was to evaluate the diagnostic ability of GCC thickness in identifying primary open angle glaucoma (POAG).

Methods

A prospective study was performed.Seventy POAG patients and 30 healthy volunteers were enrolled in Beijing Tongren Hospital from November 2015 to April 2016.Macular GCC thickness and peripapillary retinal nerve fiber layer (RNFL) thickness were measured with RTVue SD-OCT, and Humphrey perimetry was performed on the eyes.The patients were assigned to the early stage POAG group, advanced POAG group and later stage POAG group based on the mean defect (MD) of visual field.The average, superior, inferior GCC and RNFL, focal loss volume (FLV), and global loss volume (GLV) were measured and compared among the groups.The correlations between GCC thickness or RNFL thickness with MD were evaluated in the POAG eyes.The discrimination capabilities of GCC thickness or RNFL thickness were assessed and compared by using areas under the receiver operating characteristic (ROC) curves (AUC).

Results

Compared with the normal control group, the average, superior, inferior GCC thickness and RNFL values were evidently reduced, the FLV and GLV were significantly increased in the early stage POAG group, advanced POAG group and later stage POAG group (all at P<0.001). Compared with the early stage POAG group, the average GCC and RNFL thickness values were significantly reduced, and GLV was increased in the advanced POAG group and later stage POAG group (all at P<0.05). In the later stage POAG group, superior RNFL was thinner than that in the early stage POAG group (P=0.003). The superior GCC value were lower in the later stage POAG group than that in the early stage POAG group and advanced POAG group (all at P<0.001). Compared with the early stage POAG group, the inferior GCC and RNFL thicknesses were decreased and the FLV was increased in the advanced POAG group and the later stage POAG group (all at P≤0.01). Linear positive correlations were found between average GCC, superior GCC, inferior GCC, average RNFL, superior RNFL or inferior RNFL and MD (r=0.624, 0.583, 0.601, 0.571, 0.447, 0.537, all at P<0.001), and the positive correlations were also seen between average GCC and average RNFL, between superior GCC and superior RNFL or between inferior GCC and inferior RNFL (r=0.648, 0.630, 0.602, all at P<0.001). The AUCs were 0.965, 0.979, 0.924, 0.985, 0.980, 0.990, 0.979 and 0.992 in the average GCC, superior GCC, inferior GCC, FLV, GLV, average RNFL, superior RNFL and inferior RNFL, with the largest AUCs in the FLV and inferior RNFL thickness.No significant difference was found in the AUC between FLV and inferior RNFL thickness (P>0.05).

Conclusions

Inferior GCC is more susceptible to glaucomatous damage.FLV and GLV from GCC pattern parameters are sensitive indicators for diagnosis of POAG.GCC thickness could be a valid structural parameter for detecting glaucoma and can be used as a marker in glaucoma assessment.