Evaluation of retinal nerve fiber layer thickness in swollen optic disc

Purpose: To evaluate the retinal nerve fiber layer thickness in patients with optic disc swelling by using Heidelberg Retina Tomography (HRT) and Optical Coherence Tomography (OCT).Patients and Methods: 40 patients with swollen optic disc and 41 age and sex matched healthy subjects were enrolled in the study. Detailed ophthalmological examinations, computerized visual field, HRT III and OCT analysis were performed on the study group. Mean retinal nerve fiber layer (RNFL) thickness of peripapillary zone was measured by OCT and HRT III and quadrantial analysis was performed by OCT.Results: The mean age of the study population was 44.6 ± 14.4 (11?72) years. There were 17 (42.5 %) women and 23 men (57.5 %) in the group with optic disc swelling and the mean age was 41.3 ± 17.3 years however; mean age was 47.8 ± 10.1 years in the control group. More seriously affected eyes of the patients with bilateral involvement were considered. The causes of optic disc swelling were pseudotumor cerebri (PTC) in 11 patients (27.5%), nonarteritic anterior ischemic optic neuropathy (NAION) in 11 patients (27.5%), optic disc drusen (ODD) in 8 patients (20%), central retinal vein occlussion (CRVO) in 6 patients (15%), and optic neuritis in 4 patients (10%). The mean RNFL thickness were 176.10 µm and 251.47 µm in the group with optic disc swelling and 98.85 µm and 275.60 µm in the control group with OCT and HRT respectively. In the patient group, there was a statistically significant positive correlation between the measurements of these two methods (r=0.42, p=0.007). However positive correlation was also found in the control group (r=0.27, p=0.094) but there was no statistical significance in this group. When the relationship of mean RNFL thickness measurements by using HRT between each subgroup and controls was evaluated, only statistically significant difference was detected between the NAION subgroup and controls (p=0.02). Statistically significant differences were found between each subgroup and controls in the mean RNFL thickness measurements by OCT (p<0.05). Statistically significant difference was detected only between PTC and ODD subgroups when the study subgroups were compared with each other using OCT (p=0.04). Comperison of superior quadrant RNFL thickness by OCT of each subgroup with controls revealed statistical significance in PTC, NAION and CRVO subgroups (p=0.000, p=0.002, p=0.003, respectively). Inferior quadrant RNFL thickness measurements by using OCT were compared between the study subgroups and controls, differences were statistically significant in each subgroups (p<0.05). When the study subgroups were compared to each other, statistically significant differences were found between PTC and ODD subgroups and, PTC and CRVO subgroups (p=0.04, p=0.01, respectively). Temporal and nasal quadrant RNFL thickness measurements by using OCT were statistically thicker than controls in PTC, NAION and CRVO subgroups (p<0.05).Conclusion: Besides, positive correlation of RNFL thickness measurements between HRT and OCT was found in patients with optic disc swelling; much more thicker results were obtained by using HRT than OCT in control patients. OCT measurements for detecting RNFL thickness may be more useful in differential diagnosis of optic disc swelling with different etiologies.Keywords: Anterior ischemic optic neuropathy, Heidelberg Retinal Tomography, optic disc drusen, swollen optic disc, Optical Coherence Tomography, optic neuritis, retinal nerve fiber layer thickness, central retinal vein occlussion.