Finite Element Analysis Predicts Large Optic Nerve Head Strains During Horizontal Eye Movements

Area of Science:

• Ophthalmology
• Biomechanics
• Medical Imaging

Background:

• The optic nerve head (ONH) is crucial for vision and susceptible to damage.
• Understanding biomechanical forces on the ONH is vital for diagnosing and treating optic neuropathies like glaucoma.

Purpose of the Study:

• To quantify optic nerve head (ONH) strains during horizontal eye movements using finite element (FE) analysis and dynamic magnetic resonance imaging (MRI).
• To compare ONH strains induced by eye movements with those caused by elevated intraocular pressure (IOP).
• To investigate the influence of connective tissue stiffness on ONH strains.

Main Methods:

• Dynamic MRI visualized ocular globes and orbits during horizontal eye movements (up to 13°).
• A baseline FE model of the ONH was created, incorporating orbital and ONH tissues.
• FE-derived ONH strains from eye movements were compared to strains from an IOP of 50 mm Hg.
• A sensitivity study varied connective tissue stiffness to assess its impact on ONH strains.

Main Results:

• Horizontal eye movements induced posterior pulling of the ONH by the optic nerve.
• ONH strains during a 13° lateral eye movement were substantial and exceeded those from an IOP of 50 mm Hg.
• Stiffer sclerae reduced prelamina and lamina cribrosa strains, while stiffer optic nerve sheaths significantly increased them.

Conclusions:

• High ONH strains occur during eye movements, exacerbated by stiffer optic nerve sheaths.
• Further research is needed to link eye movement-induced ONH strains to axonal loss in glaucoma.