Power and radius changes induced in soft contact lens systems by flexure

Area of Science:

• Ophthalmology
• Biomechanical Engineering
• Optometry

Background:

• Soft contact lens fit and refractive power are influenced by lens flexure and tear layer dynamics.
• Accurate modeling of lens-cornea interaction is crucial for understanding optical performance.
• Previous models often assumed direct corneal contact, limiting their applicability.

Purpose of the Study:

• To develop a computational model for analyzing soft contact lens flexure without assuming posterior lens-cornea alignment.
• To quantify tear layer volume and its impact on the effective power of soft contact lenses.
• To investigate the relationship between lens design parameters and on-eye performance.

Main Methods:

• Development of a novel computer program for analyzing soft contact lens flexure.
• Simulation of tear layer entrapment and its effect on lens power for various lens designs.
• Mathematical modeling of the simultaneous flexure of front and back lens radii.

Main Results:

• Thin low-minus soft contact lenses entrap approximately 5.5 microliters of tear fluid, resulting in minimum power.
• Low-plus soft contact lenses can entrap approximately 9.5 microliters of tear fluid, leading to significant effective power changes (around -2.00 D).
• The relationship between the changes in posterior (r2) and anterior (r1) lens radii during flexure differs for plus and minus lenses (Δr2 ≈ 2Δr1 for plus, Δr2 ≈ 0.75Δr1 for minus).

Conclusions:

• The computational model provides insights into soft contact lens behavior on the eye, accommodating non-uniform corneal curvature.
• The findings support clinical observations of "power loss" in plus-powered soft contact lenses due to tear layer dynamics.
• Mathematical relationships describing lens radius changes during flexure can be specific to lens design and power.