Sequence of Changes in Ganglion Cell Layer Thickness and Perfusion Density in Early Glaucoma

Abstract

Purpose : We investigated whether macular ganglion cell layer (GCL) thinning detected by optical coherence tomography (OCT) precedes macular perfusion density (PD) loss by OCT angiography (OCTA) in early glaucoma, or vice versa. We also evaluated the effectiveness of GCL and PD measurements in detecting changes due to glaucoma after subtracting those related to normal aging.

Methods : This prospective study included glaucoma patients and healthy subjects undergoing OCT and OCTA imaging every four months. A 12° x 12° area centered on the fovea was segmented into 16 tiles of 3° squares, where GCL and PD were evaluated. For each tile, a single regression equation was formulated, incorporating the baseline age, and GCL or PD of healthy subjects. Estimated normal GCL and PD values were obtained by substituting the age of the glaucoma patient into the equation. The degree of loss in the actual value relative to the estimated value at baseline was defined as a percentage loss of GCL and PD. We assessed the relationship between the percentage loss of GCL relative to the percentage loss of PD at baseline and the subsequent slope of GCL and PD. Additionally, we determined the number of patients with steeper GCL and PD slopes than the threshold slope separating glaucoma patients from healthy subjects with 90% specificity in each tile.

Results : The study included 80 glaucoma patients and 42 healthy subjects with mean (SD) follow-up of 3.9 (0.4) years. In 9 (56%) tiles, patients with a significant PD slope showed a significantly greater percentage loss of GCL relative to the percentage loss of PD at baseline compared to those without a significant PD slope. (Figure 1) In contrast, only 1 (6%) tile showed this significant difference between patients with and without significant GCL slopes. Furthermore, in 15 (94%) tiles, there were significant trends indicating that a greater percentage loss of GCL relative to the percentage loss of PD was correlated with a faster PD slope. (Figure 2) No tiles showed this trend for GCL slope. The number of patients with faster GCL slopes than threshold slope was significantly larger than that with faster PD slope in 12 (75%) tiles.

Conclusions : A greater baseline percentage loss of GCL relative to PD is associated with a faster PD slope. These findings suggest that GCL reduction precedes PD loss in early glaucoma and have implications for understanding indices of glaucomatous progression.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.