Settling and deformation of a thin elastic shell on a thin fluid layer lying on a solid surface.

Area of Science:

• Ocular biomechanics
• Fluid dynamics
• Soft contact lens mechanics

Background:

• Soft contact lenses (SCLs) can shift during blinking due to fluid dynamics.
• The post-lens tear film (POLTF) plays a crucial role in SCL settling.
• Understanding SCL dynamics is vital for preventing corneal complications.

Purpose of the Study:

• To investigate the physical mechanisms governing SCL dynamics during blinking.
• To model the shape and distance of SCLs from the cornea over time.
• To analyze factors influencing SCL adherence and potential corneal abrasion.

Main Methods:

• Modeled SCL as a deformable elastic shell and cornea as a flat, nondeformable body.
• Applied lubrication equations for Newtonian fluid flow and thin-shell approximation for the SCL.
• Coupled solid and fluid mechanics via stress and velocity continuity at the interface.

Main Results:

• Lid pressure during blinking squeezes POLTF, deforming the lens and moving it towards the cornea.
• Interblink relaxation allows stored elastic energy to move the lens away from the cornea by imbibing fluid.
• SCL settling depends on the balance between inward blink motion and outward interblink motion, potentially leading to steady-state or continuous settling.

Conclusions:

• Elastohydrodynamic analysis predicts SCL settled state based on lens parameters.
• Continuous settling may lead to thin-film interactions, potentially causing lens adherence or corneal abrasion.
• This model aids in understanding SCL behavior to improve ocular health for contact lens wearers.