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Eye movements may contribute to optic nerve damage in glaucoma
Repeated traction caused by eye movements may result in mechanical overloading of the optic nerve head and could explain the progression of glaucomatous damage in normal tension glaucoma, according to a study.
“The fact that a considerable portion of people develop glaucoma despite having never had elevated IOP suggests that there must be a mechanism that is independent of intraocular pressure that causes damage to the optic nerve,” Joseph Demer, MD, PhD, lead investigator of the study, said in a press release from the National Eye Institute.
MRI was used to record the effects on the optic nerve and surrounding sheath of central gaze, adduction and abduction eye movements in 34 eyes of 17 patients with primary open angle glaucoma (POAG) without elevated IOP and 59 eyes of 32 healthy subjects. While tethering and elongation were normal in abduction, adduction movements of eyes with POAG resulted in abnormal globe retraction of approximately 0.7 mm.
“In POAG without elevated IOP, we infer that the optic nerve and sheath are abnormally stiff and stretch less freely during adduction tethering, thus transferring the associated strain to the globe at the vulnerable peripapillary junction,” the authors wrote.
They noted that the adductions sustained during the MRI study are about half as large as transient saccades common in real life, both during day time and sleep.
“It’s certainly plausible that some of these rapid eye movements would involve degrees of adduction that could have a physiological effect,” Demer said in the press release.
Adduction tethering might, therefore, be an IOP-independent factor contributing to optic nerve damage in patients with glaucoma. These findings, if supported by further evidence, might pave the way to new therapeutic strategies, the authors stated. – by Michela Cimberle
Disclosure: The authors reported no relevant financial disclosures.
Perspective
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This study introduces a bold, compelling argument for biomechanical stress causing glaucomatous optic nerve damage during adducting eye movements. The striking MRI images almost make you wince as you see the optic nerve stretching within the orbit.
This is such a great reminder of the dynamic nature of the eye and glaucoma disease process, which is easy to forget when monitoring the often-sluggish changes typically observed with optic nerve cupping and visual field loss. It would only be fitting that a major missing piece of our understanding glaucoma disease was in plain sight.
Certainly, more study is required to even begin to understand how eye movements, optic nerve stretching and optic nerve sheath hysteresis fit into glaucoma pathogenesis; but, nonetheless, this is a fascinating and original study that has me rethinking my glaucoma perspective.