Advisory Committee Chair
William J Benjamin
Advisory Committee Members
Roderick Fullard
Robert Kleinstein
Michael Loop
Lee Moradi
Document Type
Dissertation
Date of Award
2017
Degree Name by School
Doctor of Philosophy (PhD) School of Optometry
Abstract
To more precisely determine the fundamental relationships between oxygen permeability (Dk), water content (WC), silicon (Si) content, and fluorine (F) content of clinically prescribed silicone-hydrogel (SiHy) materials, identical methodologies for 16 commercially available brands of SiHy materials were performed. Dk and WC were determined according to the ANSI and ISO standards and, with Si and F contents, on the same lot numbers of samples across a common range of available refractive powers. A negative linear relationship was found between Si content and water content. Lotrafilcon A, Lotrafilcon B, and the bulk polymer of Delefilcon A initially deviated from this relationship. However, they contributed to the relationship when their F contents (the former two) and hydrogel surface layers (the latter) were included in the analysis. There was a negative relationship of Dk with WC, positive relationship of Dk with the combination of Si and F [(Si+F)] content, and negative relationship of Dk with the combination of WC, Si, and F [WC+Si+F)] content. Plots of Log(Dk) with these contents were linear within the ranges of (Si+F) and WC in this study [0.76–16.7% (Si+F) and 21.8–73.8% water, respectively]. The quadratic and linear semi-logarithmic relationships were modeled in two-dimensional and three-dimensional plots to show the interrelationships between these three characteristics. A point of equality for water and (Si+F) contents of SiHy materials was located at 18.6 %, where Dk was 154.6 Fatt Dk units. Another point of equality for the WC of SiHy and conventional hydrogel materials was located at 73.3 %, where Dk was 46.3 Fatt Dk units. The SiHy materials that fell near these points were Lotrafilcon A and Efrofilcon A, respectively. The oxygen permeability of pure dimethylsiloxane (i.e., “silicone”) was found to be 8.8 times that of water, or approximately 900 Fatt Dk units. These relationships are of importance in the characterization of polymers in the contact lens field. They are the aspects of Dk, Si content, F content, and WC that can guide the formulation of new polymers for contact lenses and other devices, to supersede these relationships and to maintain them while biocompatibility and comfort are pursued.
Recommended Citation
Dupre, Terin E., "Oxygen Permeability (Dk) Of Silicone-Hydrogel Materials: Relationship With Water, Silicon, And Fluorine Contents" (2017). All ETDs from UAB. 1564.
https://digitalcommons.library.uab.edu/etd-collection/1564
