Sequential-digital image correlation for mapping human posterior sclera and optic nerve head deformation.

Area of Science:

• Biomedical Engineering
• Ophthalmology
• Biomechanics

Background:

• Optic nerve head (ONH) deformations are implicated in glaucoma, even with normal intraocular pressures (IOPs).
• Understanding posterior scleral biomechanics under physiological pressures is crucial for elucidating ONH mechanical changes and retinal ganglion cell death.
• Current methods for measuring scleral deformation may lack sufficient resolution or comprehensive mapping capabilities.

Purpose of the Study:

• To develop and validate a novel sequential 3D digital image correlation (S-DIC) method for precise quantification of posterior scleral deformations.
• To improve in-depth (z-axis) resolution in deformation measurements without compromising in-plane sensitivity.
• To accurately contour and map deformations of the complex-shaped ONH under pressure.

Main Methods:

• Developed an S-DIC approach combining two orthogonal axes of parallax with standard 3D DIC using a single high-resolution camera.
• Validated the S-DIC method through a benchmark on an object with known complex geometry for shape, deformation, and strain measurement.
• Applied the S-DIC methodology to a human posterior scleral shell, encompassing the peripapillary sclera and optic nerve.

Main Results:

• The S-DIC method achieved a reconstruction accuracy of 0.17%.
• Demonstrated an uncertainty in z-position measurement of 8 μm, indicating high in-depth resolution.
• Successfully applied the technique to map deformations in a human posterior scleral sample.

Conclusions:

• The developed S-DIC approach offers enhanced capabilities for measuring complex deformations compared to standard 3D DIC.
• This relatively inexpensive S-DIC technique provides a new tool for investigating ONH biomechanics.
• Findings may offer new insights into retinal ganglion cell death mechanisms in primary open-angle glaucoma.