Optical coherence tomography quantifies gradient refractive index and mechanical stiffness gradient across the human...

Area of Science:

• Ophthalmology
• Biomedical Optics
• Biomechanics

Background:

• The crystalline lens's mechanical stiffness gradient and gradient refractive index (GRIN) are crucial for ocular accommodation, influencing deformability and optical function.
• Quantifying these lens properties can enhance diagnosis and management of lenticular disorders and guide refractive surgery.

Purpose of the Study:

• To present and demonstrate a novel optical coherence elastography technique for in vivo assessment of human crystalline lens mechanical properties and GRIN distribution.
• To validate the technique using mechanical deformation stimuli and compare results with existing literature.

Main Methods:

• Developed an optical coherence elastography system to measure lens displacement and strain in vivo.
• Applied external (pressure modulation) and intrinsic (accommodation micro-fluctuations) mechanical stimuli to a cohort of 12 human subjects.
• Acquired high-resolution strain maps of the crystalline lens.

Main Results:

• Demonstrated excellent agreement between high-resolution strain maps and established lens stiffness profiles.
• Observed age-dependent stiffness variations: young lenses are 2.0-2.3x stiffer in the cortex, while old lenses are 1.0-7.0x stiffer in the nucleus.
• Successfully quantified in vivo lens mechanical characteristics and GRIN distribution.

Conclusions:

• Optical coherence tomography is a viable tool for quantifying in vivo crystalline lens internal stiffness and refractive index distribution.
• This methodology offers new possibilities for ophthalmic pre-surgical evaluations and fundamental research into the eye's optical mechanisms.