Hendrik Walther is a PhD student at the Centre for Contact Lens Research, School of Optometry and Vision Science, University of Waterloo.
Download the poster (.pdf), which was originally shared at the Association for Research in Vision and Ophthalmology (ARVO) annual meeting, 2016.
Hendrik Walther, Chau-Minh Phan, Lakshman Subbaraman, Lyndon Jones
Centre for Contact Lens Research, School of Optometry & Vision Science, University of Waterloo
Purpose: Current in vitro models to evaluate tear film (TF) deposition on various contact lenses (CLs) do not adequately simulate physiological ocular conditions. The aim of this study was to evaluate the differences in lipid uptake and penetration in daily disposable (DD) CLs using the conventional “in-vial” method compared to a novel in vitro eye model.
Methods: The penetration of NBD-cholesterol (7-nitrobenz-2-oxa-1,3-diazol-4-yl-cholesterol) on three silicone hydrogel (SH) (delefilcon A, somofilcon A, narafilcon A) and 4 conventional hydrogel (CH) (etafilcon A, ocufilcon B, nesofilcon A, nelfilcon A) DD CLs were investigated. The CLs were incubated for 4 and 12 hrs in an artificial tear solution (ATS) containing fluorescently labeled NBD-cholesterol at room temperature (21oC). For the vial condition, the CLs were incubated in a vial containing 3.5 mL of ATS. In the in vitro eye model, the CLs were mounted on our eye-blink platform, designed to simulate physiological tear flow (2 mL/24 hrs), tear volume, and ‘simulated’ blinking. After the incubation period, the CLs were analyzed using a laser scanning confocal microscopy technique (LSCM). Quantitative analysis for penetration depth and relative fluorescence intensity values was determined using ImageJ.
Results: The depth of penetration of NBD-cholesterol varied between the vial and the eye-blink platform. Using the traditional vial incubation method, NBD-cholesterol uptake occurred equally on both sides of all lens materials. However, employing our eye-blink model, cholesterol penetration was observed primarily on the anterior surface of the CLs. In general, SH lenses showed higher intensities of NBD-cholesterol than CH materials. Fluorescence intensities also varied between the incubation methods as well as the lens materials.
Figure 1: NBD-cholesterol depth of penetration on various lens materials
Conclusions: This study provides a novel in vitro approach to evaluating deposition and penetration of lipids on CLs. We show that the traditional “in-vial” incubation method exposes the CLs to an excessively high amount of ATS on both the front and back surface of the lens, which results in an overestimation for cholesterol deposition. Our model, which incorporates important ocular factors such as intermittent air exposure, small tear volume, and physiological tear flow between blinks, provides a more natural environment for in vitro lens incubation. Consequently, this will better elucidate the interactions between CLs and TF components.
