Purpose: To better understand the effects of severe glaucoma on the thickness of the retinal ganglion cell (RGC) and inner plexiform (IP) layers measured with frequency-domain optical coherence tomography.
Methods: In experiment 1, macular cube scans were obtained in 11 patients with glaucoma and the thickness of both the RGC and IP layers were measured at locations corresponding to 3, 5, and 7° eccentricity. For patients, only locations with total deviation losses of -15 dB or worse on perimetry were included. In experiment 2, higher resolution, horizontal midline scans were obtained from 30 controls in order to obtain a precise measure of the thickness of the RGC and IP layers of the healthy retina.
Results: In regions of severe field loss (experiment 1), glaucoma decreased the thickness of both layers, leaving a residual layer. The residual thickness of the IP layer was larger than the residual thickness of the RGC layer. In healthy controls (experiment 2), the RGC layer was about 57% of the RGC+IP layer thickness at 3° as compared with only 36% at 10°, in agreement with a recent histological study.
Conclusion: Glaucomatous optic neuropathy, with severe losses in visual field sensitivity, decreases the thickness of both the RGC and IP layers, but leaves a residual thickness of both. The IP layer contributes slightly more than the RGC to this residual, even just outside the center of the fovea where the RGC layer thickness exceeds the IP layer thickness in controls.