Adduction induces large optic nerve head deformations in subjects with normal-tension glaucoma

Purpose To assess intraocular pressure (IOP)--induced and gaze--induced optic nerve head (ONH) strains in subjects with high--tension glaucoma (HTG) and normal-tension glaucoma (NTG). Design Clinic--based cross--sectional study. Methods The ONH from one eye of 228 subjects (114 subjects with HTG (pre--treatment IOP=21 mm Hg) and 114 with NTG (pre--treatment IOP<21 mm Hg)) was imaged with optical coherence tomography (OCT) under the following conditions: (1) OCT primary gaze, (2) 20 degrees adduction from OCT primary gaze, (3) 20 degrees abduction from OCT primary gaze and (4) OCT primary gaze with acute IOP elevation (to approximately 33 mm Hg). We then performed digital volume correlation analysis to quantify IOP--induced and gaze--induced ONH tissue deformations and strains. Results Across all subjects, adduction generated high effective strain (4.4%+/- 2.3%) in the LC tissue with no significant difference (p>0.05) with those induced by IOP elevation (4.5%+/- 2.4%); while abduction generated significantly lower (p=0.01) effective strain (3.1%+/- 1.9%). The lamina cribrosa (LC) of HTG subjects exhibited significantly higher effective strain than those of NTG subjects under IOP elevation (HTG: 4.6%+/- 1.7% vs NTG: 4.1%+/- 1.5%, p<0.05). Conversely, the LC of NTG subjects exhibited significantly higher effective strain than those of HTG subjects under adduction (NTG: 4.9%+/- 1.9% vs HTG: 4.0%+/- 1.4%, p<0.05). Conclusion We found that NTG subjects experienced higher strains due to adduction than HTG subjects, while HTG subjects experienced higher strain due to IOP elevation than NTG subjects-and that these differences were most pronounced in the LC tissue.