Retinal Ganglion Cells Count and Structure/Function Correlation in Glaucoma

Abstract

Purpose: To analyze the correlation between structural and functional parameters obtained by SD-OCT and Standard Automated Perimetry (SAP) and retinal ganglion cells (RGC) count, estimated applying an empirical model by Medeiros et al. in glaucoma patients

Methods: A sample of 89 eyes of 47 consecutive patients suspected for or affected by primary open angle glaucoma were selected. They were submitted to SITA Standard 24-2 program and staged according to Glaucoma Staging System 2 on the basis of Mean Defect (MD) and Pattern Standard Deviation (PSD). Three groups were created: group 0 (Stage 0 and borderline), group 1 (Stages 1 and 2) and group 2 (Stages 3, 4 and 5). All the eyes were scanned with iVue SD-OCT system using ONH and GCC scan pattern. RNFL total and sectorial (superior, inferior, temporal), GCC total, superior and inferior thicknesses were considered. RNFL temporal is the mean of all temporal sectors. Estimates of RGC count were obtained in circumpapillary and in macular regions from OCT and SAP data according to the empirical model. The 16 central points corresponding to GCC scanned area were considered as macular region of each visual field

Results: MD and PSD always show statistically significant difference (p < 0,01) comparing the three groups. Nevertheless VFI, RNFL and GCC show p > 0,01 comparing groups 0 and 1 with the exception of RNFL Temporal showing a substantial thinning between group 0 (99,64±14,03 μm) and group 1 (77,43±15,51 μm). RGC estimates seem to be able to discriminate patients at different stages of neuropathy. A good correlation exists between parameters obtained with the same algorithm (SAP or OCT) and also between the two structural algorithms (RNFL and GCC). A moderate correlation has been demonstrated between structural and functional parameters

Conclusions: SAP is nowadays considered the clinical standard for diagnosis and follow-up of glaucoma. RNFL and GCC are not much better than VFI in discerning between a substantial normality and a very early disease. Moderate correlation between functional and structural parameters is surely interesting considering all the differences between SAP and OCT. Estimates RGC counts are useful to discriminate between the three groups and they correlate in a very good way with structural and functional parameters

Keywords: 531 ganglion cells • 550 imaging/image analysis: clinical • 642 perimetry