Differential Deposition of Fluorescently Tagged Cholesterol on Commercial Contact Lenses Using a Novel In Vitro Eye Model

Abstract

Purpose: We evaluate the differences in lipid uptake and penetration in daily disposable (DD) contact lenses (CL) using a conventional "in-vial" method compared to a novel in vitro eye model.

Methods: The penetration of fluorescently labelled 22-(N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino)-23,24-Bisnor-5-Cholen-3beta-Ol (NBD)-cholesterol on three silicone hydrogel (SH) and four conventional hydrogel (CH) DD CLs were investigated. CLs were incubated for 4 and 12 hours in a vial, containing 3.5 mL artificial tear solution (ATS), or were mounted on an in vitro eye-blink platform designed to simulate physiologic tear flow (2 mL/24 hours), tear volume and "simulated" blinking. Subsequently, CLs were analyzed using laser scanning confocal microscopy and ImageJ.

Results: Penetration depth and fluorescence intensities of NBD-cholesterol varied between the incubation methods as well as lens materials. Using the traditional vial incubation method, NBD-cholesterol uptake occurred equally on both sides of all lens materials. However, using 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.

Conclusions: The traditional "in-vial" incubation method exposes the CLs to an excessively high amount of ATS, 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.

Translational relevance: In vitro measurements of CLs are a common approach to predict their interactions and performance on the eye. Traditional methods, however, are rudimentary. Therefore, this study presents a novel in vitro model to evaluate CLs, which consequently will enhance elucidations of the interactions between CLs and the eye.

Keywords: cholesterol; contact lens; conventional hydrogel; daily disposable; deposition; eye model; laser scanning confocal microscopy; lipid; silicone hydrogel.

Figure 1

Chemical structure of cholesterol (386.65 g/mol) and NBD-cholesterol (494.63 g/mol).

Figure 2

Lateral motion produces intermittent air exposure (A). Circular motion simulates rubbing action during blinking (B). TF infusion into eyelid (C). OcuFlow platform (D).

Figure 3

Confocal images showing a cross-section of etafilcon A, nelfilcon A, nesofilcon A, ocufilcon, delefilcon A, somofilcon A, narafilcon A after incubation with NBD-cholesterol in the vial and OcuFlow model after 4 (A) and 12 (B) hours.

Figure 4

Histograms representing the different incubation methods: OcuFlow after 4 (blue line) and 12 (broken red line) hours, vial incubation after 4 (purple line) and 12 (black line) hours; as well as depth of absorption of NBD-cholesterol of various contact lenses: etafilcon A (A), nelfilcon A (B), nesofilcon A (C), ocufilcon A (D), delefilcon A (E), somofilcon A (F), narafilcon A (G). The values plotted are the relative intensity fluorescence values (RIF).

Figure 5

Drawbacks of using a simple vial model to evaluate CLs.