Comparisons of ganglion cell-inner plexiform layer loss patterns and its diagnostic performance between normal tension glaucoma and primary open angle glaucoma: a detailed, severity-based study

AIM: To evaluate the patterns of macular ganglion cell-inner plexiform layer (GCIPL) loss in normal tension glaucoma (NTG) and primary open angle glaucoma (POAG) in a detailed, disease severity-matched way; and to assess the diagnostic capabilities of GCIPL thickness parameters in discriminating NTG or POAG from normal subjects. METHODS: A total of 157 eyes of 157 subjects, including 57 normal eyes, 51 eyes with POAG and 49 eyes with NTG were enrolled and strictly matched in age, refraction, and disease severity between POAG and NTG groups. The average, minimum, superotemporal, superior, superonasal, inferonasal, inferior, and inferotemporal GCIPL thickness, and the average, superior, temporal, inferior, and nasal retinal nerve fiber layer (RNFL) thickness were obtained by Cirrus optical coherence tomography (OCT). The diagnostic capabilities of OCT parameters were assessed by area under receiver operating characteristic (AUROC) curves. RESULTS: Among all the OCT thickness parameters, no statistical significant difference between NTG group and POAG group was found (all P>0.05). In discriminating NTG or POAG from normal subjects, the average and inferior RNFL thickness, and the minimum GCIPL thickness had better diagnostic capabilities. There was no significant difference in AUROC curve between the best GCIPL thickness parameter (minimum GCIPL) and the best RNFL thickness parameter in discriminating NTG (inferior RNFL; P=0.076) and indiscriminating POAG (average RNFL; P=0.913) from normal eyes. CONCLUSION: Localized GCIPL loss, especially in the inferior and inferotemporal sectors, is more common in NTG than in POAG. Among all the GCIPL thickness parameters, the minimum GCIPL thickness has the best diagnostic performance in differentiating NTG or POAG from normal subjects, which is comparable to that of the average and inferior RNFL thickness.