Surface morphology of contact lenses probed with microscopy techniques

Area of Science:

• Ophthalmology
• Materials Science
• Surface Science

Background:

• Contact lens surface properties are crucial for comfort and wearability.
• Understanding surface morphology differences between various lens types is essential for material selection and design.

Purpose of the Study:

• To compare the surface morphology of different contact lens materials and manufacturing methods.
• To evaluate the utility of cryo-scanning electron microscopy (cryo-SEM) and atomic force microscopy (AFM) for analyzing hydrated contact lenses.

Main Methods:

• Investigated 10 types of contact lenses (silicone hydrogel and conventional hydrogel) from five manufacturers.
• Utilized cryo-scanning electron microscopy (cryo-SEM) for high-magnification imaging (up to 2000x).
• Employed atomic force microscopy (AFM) in aqueous media for nanoscale surface roughness analysis.

Main Results:

• Surface roughness varied significantly based on manufacturing techniques (lathe-cutting, cast-moulding, spin casting).
• Lathe-cut lenses exhibited considerably higher surface roughness (4-140 nm) compared to other methods.
• For cast-moulded lenses, surface roughness decreased as water content increased.
• Plasma oxidation treatment resulted in a porous surface structure on some lenses.

Conclusions:

• Manufacturing method is a key determinant of contact lens surface roughness.
• Cryo-SEM and AFM are effective tools for characterizing hydrated contact lens surfaces.
• Surface characteristics can be tailored by manufacturing processes and post-treatments, influencing lens performance.