Tear film dynamics of a new soft contact lens

PURPOSE

To present the objective metrics from a study that evaluated the clinical performance of a senofilcon A contact lens, both with and without a new manufacturing technique.

METHODS

This was a single-site, five-visit, controlled, randomised, subject-masked, 2 × 2 crossover study (May-August 2021) with a 2-week lens dispensing period (bilateral wear) and weekly follow-up visits. Healthy adult (18-39 years), habitual spherical silicone hydrogel contact lens wearers were included. The High-definition (HD) Analyzer™ was used to objectively measure the lens-on-eye optical system resulting from the study lenses at 1-week follow-up. Measurements assessed were vision break-up time (VBUT), modulation transfer function (MTF) cutoff, Strehl ratio (SR), potential visual acuity (PVA) for 100% contrast and objective scatter index (OSI).

RESULTS

Of the 50 enrolled participants, 47 (94.0%) were randomly assigned to one of the two possible lens wear sequences (test/control or control/test) and dispensed at least one study lens. The estimated odds ratio of VBUT > 10 s was 1.582 (95% confidence interval [CI]: 1.009 to 2.482) in test versus control lens. The least squares mean difference estimates of MTF cutoff, SR and PVA for 100% contrast between test versus control lens were 2.243 (95% CI: 0.012 to 4.475), 0.011 (95% CI: -0.002 to 0.023) and 0.073 (95% CI: -0.001 to 0.147), respectively. The estimated ratio of median OSI between test versus control lens was 0.887 (95% CI: 0.727 to 1.081). The test lens demonstrated superiority over the control lens with respect to VBUT and MTF cutoff. No serious adverse events were reported; eight adverse events (three ocular, five non-ocular) were indicated by six participants during the study.

CONCLUSION

The test lens demonstrated an increased probability of having a longer VBUT (>10 s). Future studies may be designed to assess the efficacy and long-term use of the test lens in a larger population.

In vitro Evaluation of the Location of Cholesteryl Ester Deposits on Monthly Replacement Silicone Hydrogel Contact Lens Materials

Purpose

The deposition profile of cholesteryl ester on the surface and throughout the matrix of silicone hydrogel contact lens (CL) materials was determined under conditions that mimic a daily wear regimen.

Methods

In this in vitro study, four SiHy CL materials (senofilcon C, lotrafilcon B, comfilcon A and samfilcon A) were incubated in an artificial tear solution (ATS) for up to 30 days. CL incubation was alternated between the ATS (16 hours) and a multipurpose care regimen (8 hours). The ATS included fluorescently tagged cholesteryl ester (5-cholesten-3ß-ol 6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]caproate; CE-NBD) and confocal laser scanning microscopy visualized the distribution of the lipid through the CLs.

Results

The distribution of CE-NBD was homogenous from the anterior to posterior surface in senofilcon C and comfilcon A, at all time points. For lotrafilcon B and samfilcon A, CE-NBD localization was heterogeneous, with greater amounts on the surfaces on Day 1 and Day 14 compared to the lens matrix; however, differences in concentration between the surface and bulk diminished by Day 30.

Conclusion

The distribution of the non-polar lipid CE-NBD varied with lens material chemistry. While some lens materials deposited the lipid primarily on the surface after 16 hours of exposure, all materials exhibited a homogenous distribution after one month.

Determination of the release of PEG and HPMC from nelfilcon A daily disposable contact lenses using a novel in vitro eye model

The traditional method to measure release of components from CLs is a vial containing a static volume of PBS (phosphate buffered saline). However, this model does not simulate physiologically relevant tear volume and natural tear flow, air exposure, and mechanical rubbing. These factors can significantly impact release kinetics. We have developed an in vitro eye model (OcuFlow) that simulates these parameters. The aim of the study was to measure the release of PEG (polyethylene glycol), and HPMC (hydroxypropyl methylcellulose) from a daily disposable hydrogel contact lens material (nelfilcon A; Dailies AquaComfort PLUS; DACP;) over 24 hrs using the OcuFlow platform. The elution of PEG and HPMC from DACP lenses was analyzed using LCMS (liquid chromatography mass spectrometry). The release of all wetting agents from the lenses followed a burst release pattern, which occurred within the first 1.5 hrs (P < 0.05). The release of PEG was greater than that of HPMC (P < 0.05). The amount of PEG and HPMC released at any given time was less than 1% of the amount in the blister pack solution. Our results suggest that HPMC and PEG are rapidly released from the CL.

Analysis of polyvinyl alcohol release from commercially available daily disposable contact lenses using an in vitro eye model

The purpose of this work was to determine the release of polyvinyl alcohol (PVA) from etafilcon A, omafilcon A, and nelfilcon A daily disposable hydrogel contact lenses using a novel in vitro model. PVA is an ocular lubricant that can be found in multiple formulations of artificial tears. Nelfilcon A innately contains PVA, so only the release of PVA from this lens was evaluated. Etafilcon A and omafilcon A lenses were incubated in a PBS solution containing PVA. The release of PVA was evaluated using a novel in vitro blink platform with Milli‐Q water and PBS under various blink conditions and flow rates. Nelfilcon A lenses significantly released more PVA than other lenses at 0.5 and 1.5 h in both PBS and Milli‐Q water (p < 0.001). For nelfilcon A, there was no statistical significance between the release profiles of PVA between the blink and no‐blink conditions, or for the various flow rates (p > 0.05). All tested groups and lenses showed a burst release within the first 4.5 h and rapidly plateaued thereafter. The current study demonstrates that releasable PVA (whether through uptake or through being inherently available from the material) is loosely bound on hydrogel lenses, and the majority is released within 4.5 h. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1662–1668, 2019.