The findings of a study based in Singapore have demonstrated that individuals with glaucoma exhibited tauter optic nerves and more protruding globes compared to unaffected eyes. Researchers believe that the tractional forces at work in the phenomenon could induce optic nerve head (ONH) deformations and initiate the development and progression of optic neuropathies such as glaucoma.

The team investigated optic nerve morphology in five high-tension primary open-angle (POAG) patients and five controls at primary gaze, adduction and abduction using magnetic resonance imaging. In each position, the ON tortuosity of normal eyes was significantly larger than that of the glaucomatous eyes. Globe proptosis at primary gaze was significantly higher in glaucoma subjects than in controls (19.14 ± 2.1mm, 15.32 ± 2.79mm, respectively).

Researchers speculate that that prolonged proptosis and/or muscle enlargement could restrict the free motion of the optic during eye movements, which may in turn result in more tension transmitted to the ONH. They believe that gaze-induced ONH deformations in normal tension glaucoma could play a larger role than intraocular pressure, while pressure might be more prominent in high tension-glaucoma.