Comparison between Optic Disc Torsion of Fellow Eyes in Unilateral Normal-tension Glaucoma and Normal Eyes

Purpose: To determine the association between optic disc tilt and torsion of glaucomatous and fellow eyes of unilateral normal-tension glaucoma (NTG) patients and normal. Methods: We measured optic disc tilt and torsion of 23 unilateral NTG patients and 23 normal controls by analyzing fundus photography and compared 3 groups. We also measured retinal nerve fiber layer (RNFL) thickness through optical coherence tomography in 23 unilateral NTG patients and compared the findings with those of normal eyes. Results: The mean values of optic disc tilt ratio and torsion degree in glaucomatous eyes were 1.17 +/- 0.19 degrees and 15.57 +/- 8.16 degrees, respectively, while those in fellow eyes were 1.10 +/- 0.10 degrees and 8.26 +/- 5.20 degrees. There was no significant difference in tilt ratio (p = 0.109), but there was a significant difference in torsion degree (p = 0.001). The mean values of optic disc tilt ratio and optic disc torsion in the controls were 1.11 +/- 0.07 degrees and 3.25 +/- 2.69 degrees, respectively. Also, there was no significant difference in optic disc tilt ratio (p = 0.601), but a significant difference in optic disc torsion between fellow eyes and controls (p < 0.001). The RNFL thickness of the same torsion direction in unilateral NTG eyes was measured to be 49.35 +/- 17.18 mu m smaller than the normal value (mean RNFL thickness: 71.91 +/- 16.92 mu m). Reduced RNFL thickness of the same torsion direction between glaucomatous eyes and fellow eyes was significantly different (p < 0.001). In addition, it was confirmed that RNFL thickness was significantly decreased according to the degree of disc torsion (p = 0.024). Conclusions: The optic disc torsion showed a significant difference between glaucomatous and fellow eyes in unilateral NTG patients and normal controls. Also, the RNFL thickness significantly decreased according to the degree of the optic disc torsion. Therefore, fellow eyes of unilateral NTG patients need to be carefully monitored for the progression of glaucoma.