Changes in hydrogel contact lens power due to flexure.

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Materials Science

Background:

• Hydrogel contact lenses can change power when worn due to corneal flexing.
• Existing calculations of lens power on the eye may not fully account for lens deformation.
• Discrepancies between calculated and measured lens powers have been observed.

Purpose of the Study:

• To investigate the power changes of hydrogel lenses on the eye.
• To determine the influence of lens flexing and fluid layer formation on effective lens power.
• To identify conditions where measured and calculated lens powers agree.

Main Methods:

• Comparing measured correcting power of Hydrocurve lenses on the eye with calculated values.
• Developing a model that incorporates lens flexing and the presence of a fluid lens.
• Analyzing power changes for various lens powers (minus and plus) and thicknesses.

Main Results:

• A fluid lens between the hydrogel lens and cornea can explain power discrepancies.
• Moderate to high minus lenses showed a shift towards more plus power.
• Low minus and all plus lenses shifted towards more minus power.
• Agreement between measured and calculated powers was found for -2.00 D regular-thickness and -0.75 D thin Hydrocurve lenses.

Conclusions:

• The fluid lens effect is significant in determining the effective power of hydrogel contact lenses.
• Specific lens powers and thicknesses (-2.00 D regular, -0.75 D thin) approximate corneal conformity, minimizing the fluid lens effect.
• Understanding these optical principles is crucial for accurate contact lens fitting and prescription.