Multi-parametric MRI demonstrates age-related changes in the human eye

Abstract

Purpose : The dense connective tissues in the corneoscleral shell interact dynamically with the retina and optic nerve under changing physiological conditions, and can play an important role in ocular hypertension, myopia and aging. Multi-parametric MRI can provide a non-invasive means of evaluating the microstructural organization and macromolecular compositions of the whole eye without depth limitations. Here, we tested the feasibility and sensitivity of submillimeter-resolution T2 relaxometry, magnetization transfer MRI (MTI) and diffusion tensor MRI (DTI) in detecting age-dependency across different structures of the human eyes.

Methods : Twelve fresh human eyes from healthy sighted donors (63.3±6.7 yrs, mean±S.D.) were suspended in agarose gel and subjected to T2 relaxometry, MTI and DTI using a 7-Tesla Bruker scanner. T2 relaxometry and MTI had a spatial resolution of 256x256x500 µm³, while DTI had a 128x128x500 µm³ resolution. The regions of interest for the ocular structures assessed were illustrated in Fig. 1 and were used to measure the absolute T2 value, magnetization transfer ratio (MTR), fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD). These multi-parametric MRI values were then compared between ocular structures and correlated with age.

Results : Among the ocular structures, the lens cortex, myelinated optic nerve and sclera had the highest MTR and FA and the lowest AD, RD and MD. Lens cortex and sclera yielded the lowest T2 while the anterior chamber and vitreous body had the highest T2, AD, RD and MD but the lowest MTR and FA (Post-hoc Tukey’s tests: p<0.05) (Fig 1). MTR, AD, RD and MD of the posterior sclera had strong negative correlations with age, while MTR and FA of the myelinated optic nerve negatively correlated with age (p<0.05) (Fig 2).

Conclusions : Given that T2 and MTR are sensitive to mobile water and macromolecules such as collagen, proteoglycans, and myelin, respectively, the decreases in MTR and diffusivities in the posterior sclera suggest an age-related loss of macromolecular contents and restricted water diffusion without change in mobile water contents. The negative FA and MTR correlations with age in the myelinated optic nerve indicate disrupted fiber organization and myelin contents during aging. Multi-parametric MRI demonstrated the susceptibility of the microstructural integrity and macromolecules to aging at the back of the eye.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.