General Ophthalmology

Diagnostic Accuracy of Macular Ganglion Cell Layer Thickness Measured by Spectralis SD OCT versus Retinal Nerve Fibre Layer thickness in Discriminating Normal from Glaucomatous eyes

Dr Anna Elias

, Department of Ophthalmology

Purpose : The diagnosis of glaucoma in the early stages when structural and functional changes are not obvious, can be a dilemma. There is a need for newer diagnostic modalities for early and reliable diagnosis of glaucoma.The purpose of this prospective cross- sectional, observational study was to evaluate the accuracy of macular ganglion cell layer[GCL] thickness obtained by the macular retinal layer segmentation software of Spectralis SD OCT, in comparison with circumpapillary retinal nerve fibre layer [cpRNFL] thickness, in discriminating normal and glaucomatous eyes.

Methods : 100 patients diagnosed with primary open angle glaucoma[POAG], between the ages eighteen years and ninety years were recruited for the study. An equal number of healthy adults without glaucoma ,served as controls.There were 56 males and 44 females in each group. Exclusion criteria -Patients with a history of intraocular surgery and those with media opacity precluding good quality OCT Scans. For imaging the macula, the posterior pole horizontal scan protocol was used. Layer by layer segmentation was performed using the new software for the Spectralis OCT. The diagnostic capacity of each variable to differentiate between normal and glaucomatous eyes was determined by calculating the AUROC. Statistical analysis was carried out using SPSS version 16.0 and Medcalc software.

Results : One hundred patients (198 eyes) with glaucoma and one hundred controls (197 eyes) were evaluated for this study. GCL of all eight sectors of the ETDRS circles,except,cenrtal foveal thickness, showed a statistically significant difference between glaucoma patients and normal controls subjects (P<0.001). CpRNFL global average thickness had the highest diagnostic capacity[AUROC 0.816]. This was followed by GCL outer temporal zone[AUROC 0.796] The AUROC among the best discriminatory parameters were compared using the Delong test.

Conclusions : Our study showed that the ability of segmented macular GCL thickness to discriminate normal and glaucomatous eyes is high and comparable to that of cpRNFL. GCL thickness measurements did not outperform cpRNFL thickness in the diagnosis of glaucoma,but is valuable in certain clinical situations such as variation in the size and contour of the optic disc.