OCT Measurements in Patients with Optic Disc Edema

Abstract

This study investigated the influence of disc edema (DE) caused by inflammatory optic neuropathies or retinal vein occlusions on optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness measurements. OCT RNFL circle scans centered on the optic disc were made for 13 patients with DE (7 with retinal vein occlusions and 6 with inflammatory optic neuropathies) and 13 controls. RNFL thickness was assessed using the OCT normative database. The same circle scans were also used for peripapillary total retinal thickness measurements. The RNFL percentage of total retinal thickness was calculated, normalized (nRNFL%), and averaged separately for affected and unaffected regions of each eye. Average RNFL thickness was 122 +/- 23 microm in the DE group, and 91 +/- 8 microm in the control group (P = 0.0001). Mean peripapillary total retinal thickness was 329 +/- 56 microm in the DE group and 255 +/- 12 microm in the control group (P < 0.001). Comparison of the averaged nRNFL% values at measurement locations above the range of the normative database with averaged nRNFL% values at measurement locations within the range of the normative database in the optic neuropathy group showed a significant difference (P = 0.024); however, the same analysis in the retinal vein occlusion group revealed no significant difference. OCT measurements are influenced by DE and show significantly greater thickness values in those patients than in controls. The presence of a significant difference within the averaged nRNFL% values in the optic neuropathy group and the absence of such a difference in the retinal vein occlusion group could be explained by edema primarily affecting the RNFL in optic neuropathy in contrast to what occurs in retinal vein occlusion, where edema affects all retinal layers.