Diagnostic capability of ganglion cell complex thickness using spectral domain optical coherence tomography in glaucoma

BACKGROUND: This study had two main aims: first, aimed to document the normal values of macular ganglion cell complex (GCC) thickness among control eyes and glaucoma suspects and second, to evaluate the diagnostic ability of GCC parameters in distinguishing Primary Open Angle Glaucoma (POAG), Glaucoma Suspects and Controls in a tertiary eye centre in Nepal. METHODS: A hospital-based cross-sectional observational study was conducted in Kathmandu, Nepal, from June 2020 to June 2021. GCC parameters (Average GCC, Superior GCC, and Inferior GCC) were measured using spectral-domain Optical Coherence Tomography (OCT). These parameters were compared among groups using Linear Mixed-effect Models, considering considerable inter-eye correlation. Receiver operating characteristic (ROC) curves were constructed, and area under the curve (AUC) values were calculated to assess diagnostic performance. RESULTS: A total of 203 patients (406 eyes) were included - 76 with POAG, 62 Glaucoma suspects, and 65 Controls. Average GCC, superior GCC and Inferior GCC thickness were 96.54 ± 10.09 μm, 96.68 ± 10.91 μm and 96.43 ± 9.60 μm, in controls; 83.30 ± 11.46 μm, 83.88 ± 12.29 μm, and 81.94 ± 13.19 μm in POAG, and 93.76 ± 7.74 μm, 94.02 ± 8.03 μm, and 93.82 ± 8.27 μm, respectively in glaucoma suspects. All GCC parameters were significantly lower in the POAG group compared with both glaucoma suspects and controls (p < 0.05), even after adjustment for age. The highest diagnostic accuracy was observed for average GCC (AUC = 0.83, 95% C.I. - 0.77-0.92) and inferior GCC (AUC = 0.83, 95% C.I. - 0.76-0.90), both demonstrating excellent discrimination between POAG and controls (AUC = 0.83). CONCLUSIONS: All GCC parameters demonstrated a significant diagnostic capability in detecting POAG, with average GCC and inferior GCC thickness showing the best performance. The single-centre cross-sectional study design, and lack of randomisation were the main limitations of this study.