Elemental Composition at Silicone Hydrogel Contact Lens Surfaces.

Area of Science:

• Ophthalmic biomaterials science
• Surface chemistry of contact lenses
• Material characterization techniques

Background:

• Silicone hydrogel (SiHy) contact lenses are widely used for vision correction.
• Understanding the surface composition of SiHy lenses is critical for predicting their performance and biocompatibility.
• Surface wettability and interactions with the ocular environment are influenced by material properties.

Purpose of the Study:

• To analyze the outermost surface composition of 11 different SiHy contact lenses.
• To investigate variations in elemental composition, particularly silicon, fluorine, oxygen, and nitrogen.
• To correlate surface composition with lens wettability and potential ocular interactions.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) was employed to determine surface elemental composition.
• Lenses were prepared by soaking in phosphate-buffered saline and vacuum drying.
• XPS measurements were taken at two take-off angles (55° and 75°) to assess depth-related composition.

Main Results:

• Significant variations in surface elemental composition were observed among the 11 SiHy lens types.
• Silicon content ranged from 1.6% (lotrafilcon B) to 16.5% (comfilcon A).
• Fluorine was detected on comfilcon A and lotrafilcon A/B lenses; silicon enrichment was common at the outermost surface.

Conclusions:

• SiHy lens surface silicon concentration varied considerably, with comfilcon A showing the highest and lotrafilcon B/delefilcon A the lowest.
• Surface silicon's hydrophobic nature may affect lens wettability and interaction with the tear film.
• Elevated surface silicon correlates with adverse effects like enhanced lipid uptake, highlighting the need for monitoring.