RELATIONSHIP OF SILICON AND FLUORINE CONTENTS WITH WATER CONTENT OF SILICONE-HYDROGEL CONTACT LENS MATERIALS

Abstract

Purpose : A negative linear relationship between silicon content (Si) and water content (W) was found for 14 of 16 commercially available silicone hydrogel (SiHy) contact lens materials. The contents of Lotrafilcon A and B deviated from the relationship. These materials also contain fluorine. Accounting for fluorine content (F) showed that these materials contributed, as well, to a linear relationship between W and the combination of Si and F.

Methods : Si was assessed in percent (%) using Inductively Coupled Plasma-Optical Emissions Spectroscopy (ICP-OES). F was assessed in % using oxygen flask combustion and measurement with an ion-selective electrode. Lotrafilcon A and B were assessed for Si and F in powers of -3, -1, +3, +6 D. Thus, four lenses per material were evaluated for Si content and four lenses for F content, and the results averaged per material. Similarly, Si was evaluated for the 14 other materials. W was determined using a gravimetric method in powers -3, -2, -1, +1, +2, +3, +4, and +6 D. Two lenses per refractive power were assessed, and the results averaged per material. Thus, W was the average of 16 assessments per material. Si, F, and W were derived for lens samples having the same lot numbers for each material.

Results : The plot of mean Si and W for the 16 materials including those containing fluorine revealed a linear negative relationship: [Si = -0.2834(W) + 26.526, R² = 0.7466] in the dry state and [Si = -0.2615(W) + 19.776, R² = 0.9009] in the hydrated state. With the inclusion of F with Si of Lotrafilcon A and B, the linear relationship became for 16 materials: [(Si+F) = -0.345(W) + 29.694, R² = 0.9003] in the dry state and [(Si+F) = -0.3079 (W) + 22.151, R² = 0.9403] in the hydrated state.

Conclusions : Addition of F to Si in the analysis allowed the data points for Lotrafilcon A and B to fit the negative linear relationship established by the other 14 commercially available SiHy contact lens materials. The addition of fluorine allows Lotrafilcon A and B to contain lower W and lower Si than would otherwise occur in clinically successful SiHy contact lens materials.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.