Whole-globe biomechanics using high-field MRI

Area of Science:

• Ocular biomechanics
• Medical imaging
• Ophthalmology

Background:

• The eye's structural integrity relies on interconnected tissues resisting intraocular pressure (IOP).
• Previous ocular biomechanics studies often focused on localized eye regions, not the whole globe.
• Understanding global ocular deformation is crucial for diagnosing and treating eye conditions related to IOP.

Purpose of the Study:

• To utilize high-field MRI for measuring IOP-induced displacements and deformations across the entire ocular globe.
• To quantify changes in global dimensions (axial length, equatorial diameter) and optic nerve head structures (scleral canal diameter, peripapillary sclera bowing) under varying IOP.
• To assess the non-linear biomechanical response of the eye to IOP elevation.

Main Methods:

• Seven sheep eyes were imaged using high-field MRI (9.4 T) at multiple IOP levels (0, 10, 20, 40 mmHg).
• IOP was controlled via a gravity perfusion system and anterior chamber cannula.
• Manual morphometry and 3D visualization software were used to quantify global and optic nerve head scale deformations.

Main Results:

• High-field MRI visualized outward posterior scleral bowing and anterior corneal bulging with increasing IOP.
• Axial length increased significantly (7.9% ± 5.7%) with IOP increments (10-40 mmHg) in most eyes.
• Equatorial diameter changes were negligible (<0.4%), and nasal-temporal scleral canal diameter increased (13.4% ± 9.7%) between 0-20 mmHg, unlike the superior-inferior diameter.

Conclusions:

• High-field MRI effectively visualizes and quantifies whole-globe ocular biomechanical responses to IOP.
• The minimal change in equatorial diameter supports the use of fixed boundary conditions in ocular models.
• This technique offers valuable insights into ocular biomechanics and IOP effects in large animal models.