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Peer-reviewed articles

2019

Phan,C -M., Walther,H., Qiao,H., Shinde,R., Jones,L. Development of an eye model with a physiological blink mechanism Translational Vision Science & Technology 2019;8(5):doi.org/10.1167/ tvst.8.5.1 [ Show Abstract ]

Purpose: To develop an eye model with a physiological blink mechanism.

Methods: All parts of the eye model were designed using computer-aided design software. The eyelid consisted of a unique 3D printed structure containing teeth to physically secure a flexible membrane. Both the eyeball and eyelid membrane were synthesized using polyvinyl alcohol (PVA). Four molecular weights of PVA (89–98, 85–124, 130, and 146–186 kDa) were tested at a range of concentrations between 5% and 30% weight/volume. The wettability and water content of these materials were compared with the bovine cornea and sclera. The model was connected to a microfluidic pump, which delivers artificial tear solution (ATS) to the eyelid. A corneal topographer was used to evaluate the tear break-up and tear film regeneration.

Results: The eyelid flexes and slides across the eyeball during each blink, which ensures direct contact between the two surfaces. When loaded with an ATS, this mechanism evenly spreads the solution over the eyeball to generate an artificial tear film. The artificial tear film in this eye model had a tear break-up time (TBUT) of 5.13 ± 0.09 seconds at 1.4 μL/min flow rate, 6 blinks/min, and <25% humidity.

Conclusions: This model simulates a physiological blink actuation and an artificial tear film layer. Future studies will examine variations in flow rates and ATS composition to simulate clinical values of TBUT.

Translational Relevance: The eye model could be used to study in vitro TBUT, tear deposition, and simple drug delivery.

Phan,C -M., Walther,H., Riederer,D., Lau,C.,Lorentz,H., Subbaraman,L., Jones,L. Analysis of polyvinyl alcohol release from commercially available daily disposable contact lenses using an in vitro eye model J Biomed Mater Res B Appl Biomater 2019;107(5):1662-1668 [ Show Abstract ]

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.

Walther,H., Subbaraman,L. N., Jones,L. Efficacy of Contact Lens Care Solutions in Removing Cholesterol Deposits From Silicone Hydrogel Contact Lenses. Eye & Contact Lens 2019;45(2):105-111 [ Show Abstract ]

PURPOSE: To determine the efficacy of multipurpose solutions (MPSs) on the removal of cholesterol deposits from silicone hydrogel (SH) contact lens materials using an in vitro model.
MATERIALS AND METHODS: Five SH lens materials: senofilcon A, comfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B were removed from the blister pack (n=4 for each lens type), incubated for 7 days at 37°C in an artificial tear solution containing C radiolabeled cholesterol. Thereafter, lenses were stored in a preserved saline solution control (Sensitive Eyes Saline Plus) or cleaned with 1 of the 5 MPSs incorporating different preservatives (POLYQUAD/ALDOX, polyquaternium-1/alexidine, polyquaternium-1/PHMB, and 2 based on PHMB alone) using a rub and rinse technique, according to the manufacturer's recommendations, and stored in the MPS for a minimum of 6 hr. Lenses were then extracted with 2:1 chloroform:methanol, analyzed in a beta counter, and μg/lens of cholesterol was determined.
RESULTS: Balafilcon A and senofilcon A lens materials showed the highest amounts of accumulated cholesterol (0.93±0.02 μg/lens; 0.95±0.01 μg/lens, respectively), whereas lotrafilcon A and lotrafilcon B deposited the lowest amounts (0.37±0.03 μg/lens; 0.47±0.12 μg/lens, respectively). For all lens materials, the MPS preserved with POLYQUAD/ALDOX removed more deposited cholesterol than any other test solution; however, the amount of removed cholesterol contamination from the individual contact lenses was only statistically significant for balafilcon A and senofilcon A (P=0.006 and P=0.042, respectively). Sensitive eyes and the other evaluated MPSs showed no significant effect on cholesterol removal (P>0.05).
CONCLUSION: Cholesterol-removal efficacy varies depending on the combination of lens material and solution. Only 1 MPS showed a statistically significant reduction of cholesterol deposit for only 2 of the 5 tested lens materials.

Walther,H., Subbaraman,L. N., Jones,L. Novel in vitro method to determine pre-lens tear break-up time of hydrogel and silicone hydrogel contact lenses Cont Lens Anterior Eye 2019;42(2):178-184 [ Show Abstract ]

PURPOSE:
To develop an in vitro model to determine pre-lens non-invasive break-up time (NIBUT) and to subsequently use this method to compare the NIBUT over contemporary daily disposable (DD) contact lenses (CL).
METHODS:
Three silicone hydrogel (SH) and two conventional hydrogel (CH) DD CLs were incubated in an artificial tear solution (ATS). A model blink cell (MBC) was utilised to mimic intermittent air exposure. CLs were repeatedly submerged for 3 seconds (s) and exposed to air for 10 s over periods of 2, 6, 12, and 16 hours (h). NIBUTs (n = 4) were determined out of the blister pack (T0) and at the end of each incubation period.
RESULTS:
Overall, nesofilcon A showed the longest NIBUTs (p < 0.001). At T0, CHs revealed significantly longer NIBUTs (p ≤ 0.001) than SHs. After 2 h, nesofilcon A showed the longest NIBUT, however, this was only statistically significant compared with delefilcon A (p ≤ 0.001). After 6 h, nesofilcon A NIBUT was significantly longer than all other CLs (p ≤ 0.001). Etafilcon A showed a significantly longer NIBUT (p ≤ 0.001) after 12 h and delefilcon A had the longest NIBUT (p ≤ 0.001) after 16 h. Statistically significant (p ≤ 0.05) changes of NIBUT within the lens materials varied between time points. After 16 h, all CLs showed significant reductions in NIBUTs (p ≤ 0.001) in comparison to T0.
CONCLUSION:
NIBUT values reduced gradually over time and varying levels of deposition impacted measured pre-lens NIBUTs. While NIBUT of CH materials are longer immediately out of the blister pack, after tear film exposure, the NIBUTs obtained using this methodology became very similar.

2018

Phan,C. -M, Walther,H., Smith,R. W., Riederer,D., Lau,C., Lorenz,K. O., Subbaraman,L. N., Jones L. Determination of the release of PEG and HPMC from nelfilcon A daily disposable contact lenses using a novel in vitro eye model. J Biomater Sci Polym Ed 2018;29(17):2124-2136 [ Show Abstract ]

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.

Qiao,H., Phan,C. -M., Walther,H., Subbaraman,L. N., Jones,L. Depth Profile Assessment of the Early Phase Deposition of Lysozyme on Soft Contact Lens Materials Using a Novel In Vitro Eye Model 2018;44(Suppl 2):S11-S18 [ Show Abstract ]

OBJECTIVE: To characterize the location of fluorescently labeled lysozyme on commercial contact lenses (CLs) using an in vitro eye model that simulates tear volume, tear flow, air exposure, and mechanical wear.
METHODS: One commercially available conventional hydrogel CL material (etafilcon A) and three silicone hydrogel CL materials (balafilcon A, lotrafilcon B, and senofilcon A) were evaluated in this study. The CLs were mounted on the in vitro eye model and exposed to artificial tear fluid containing fluorescein isothiocyanate (FITC)-labeled lysozyme for 2 and 10 hrs. After these short incubation periods, circular discs were punched from the CLs at the center and periphery and were prepared for confocal laser scanning microscopy (CLSM). The CLSM captured a series of consecutive images spaced 5 μm apart, and the resulting images were rendered into two dimensional cross-sectional views of the CL. The mean fluorescence at each 5 μm slice was used to generate a histogram depicting the penetration of FITC-lysozyme into CLs.
RESULTS: For both incubation periods, the CLSM images and histogram of etafilcon A showed that FITC-lysozyme is more concentrated at the lens surface, with a moderate amount of deposition in the lens matrix. For balafilcon A, FITC-lysozyme was evenly distributed throughout the lens. For lotrafilcon B, there was a greater amount of FITC-lysozyme deposition on the surfaces of the lens versus the matrix. Senofilcon A had differential FITC-lysozyme distribution profiles depending on the location of the lens. At the lens periphery, FITC-lysozyme primarily deposited on the surface, whereas FITC-lysozyme was uniformly distributed at the center of the lens.
CONCLUSIONS: With the use of a sophisticated in vitro eye model, the study revealed a complex deposition pattern of FITC-labeled lysozyme on various CL materials after short periods of exposure. An understanding of the early deposition pattern of lysozyme on different CL material may elucidate new insights into the processes behind CL discomfort.

Walther,H., Phan,C. -M., Subbaraman,L. N., Jones,L. Differential deposition of fluorescently tagged cholesterol on commercial contact lenses using a novel in vitro eye model Translational Vision Science and Technology 2018;7(2):18 [ Show 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.

2016

Phan,C. -M, Walther,H., Gao,H., Rossy,J., Subbaraman,L. N., Jones,L. Development of an in Vitro ocular platform to test contact lenses Journal of Visualized Experiments 2016;2016(110):e53907 [ Show Abstract ]

Currently, in vitro evaluations of contact lenses (CLs) for drug delivery are typically performed in large volume vials,1-6 which fail to mimic physiological tear volumes.7 The traditional model also lacks the natural tear flow component and the blinking reflex, both of which are defining factors of the ocular environment. The development of a novel model is described in this study, which consists of a unique 2-piece design, eyeball and eyelid piece, capable of mimicking physiological tear volume. The models are created from 3-D printed molds (Polytetrafluoroethylene or Teflon molds), which can be used to generate eye models from various polymers, such as polydimethylsiloxane (PDMS) and agar. Further modifications to the eye pieces, such as the integration of an explanted human or animal cornea or human corneal construct, will permit for more complex in vitro ocular studies. A commercial microfluidic syringe pump is integrated with the platform to emulate physiological tear secretion. Air exposure and mechanical wear are achieved using two mechanical actuators, of which one moves the eyelid piece laterally, and the other moves the eyeballeyepiece circularly. The model has been used to evaluate CLs for drug delivery and deposition of tear components on CLs.

Walther,H., Subbaraman,L., Jones,L. W. In vitro cholesterol deposition on daily disposable contact lens materials Optometry and Vision Science 2016;93(1):36-41 [ Show Abstract ]

Purpose. The goal of this study was to analyze how various incubation times affect the uptake of cholesterol on silicone hydrogel (SH) and conventional hydrogel (CH) daily disposable (DD) contact lens materials using an in vitro radiochemical detectionmethod. Methods. Three SH (somofilcon A, delefilcon A, and narafilcon A) and four CH (etafilcon A, nesofilcon A, ocufilcon A, and nelfilcon A) contact lenses were incubated in an artificial tear solution that contained major tear film components and a portion of radioactive 14C-cholesterol. Lenses (N = 4) were incubated for four incubation times (2, 6, 12, or 16 h) to assess the effects on cholesterol deposition. Subsequent to the incubation, the lenses were extracted using 2:1 chloroform:methanol, and the extracts were analyzed in a beta counter and (in nanograms per lens) extrapolated from standard curves. Results. In general, cholesterol deposited statistically significantly more on SH lenses than CHs (p e 0.033), with the exception of somofilcon A and nesolfilcon A materials (p = 0.067). Within the SH materials, narafilcon A accumulated the largest quantity of cholesterol (p G 0.05) and somofilcon A the lowest (p G 0.05). The uptake of cholesterol ranged from 22.63 T 2.98 ng/lens to 97.94 T 4.18 ng/lens for all lens materials. The accumulation of cholesterol was shown to be continuous throughout the 16 h of incubation, without reaching a plateau (p G 0.001). Conclusions. For the periods thatDDlens materials are worn, cholesterol deposits significantlymore ontoSHcontact lenses than CHs. This could have implications for wearers who have higher levels of lipid in their tears that are fitted with SH DD materials. Copyright © American Academy of Optometry.

2013

Walther,H., Lorentz,H., Heynen,M., Kay,L., Jones,L. W. Factors that influence in vitro cholesterol deposition on contact lenses Optometry and Vision Science 2013;90(10):1057-1065 [ Show Abstract ]

PURPOSE: The purpose of this study was to analyze the impact that incubation time, lipid concentration, and solution replenishment have on silicone hydrogel (SiHy) and conventional hydrogel (CH) contact lens cholesterol deposition via in vitro radiochemical experiments. METHODS: Four SiHy (senofilcon A, lotrafilcon B, comfilcon A, balafilcon A) and two CH (etafilcon A and omafilcon A) contact lenses were incubated in an artificial tear solution (ATS) that contained major tear film proteins, lipids, salts, salts, and a trace amount of radioactive C-cholesterol. Lenses were incubated for various incubation times (1, 3, 7, 14, or 28 days), with three concentrations of lipid (0.5×, 1×, 2× tear film concentration) and with or without solution replenishment to assess each variable's impact on cholesterol deposition. After incubation, the lenses were extracted using 2:1 chloroform:methanol, extracts were analyzed in a beta counter and masses (micrograms per lens) were extrapolated from standard curves. RESULTS: Within the SiHy materials, balafilcon A deposited the greatest amount of cholesterol (p replenishing > 1× > 0.5×. CONCLUSIONS: Overall, SiHy lenses deposit significantly more cholesterol than CH lens materials, and the mass of lipid deposited is dependent on the contact lens material, length of incubation, concentration of lipids in the ATS, and the replenishment of ATS. Copyright © 2013 American Academy of Optometry.

Scientific Presentations

2019

Phan CM, Walther H, Jones L. Mass spectrometry detection of phosphatidyl choline from delefilcon A Canadian Biomaterials Society, Quebec, 2019

Phan CM, Walther H, Jones L. Development of a polymeric eye model for foreign body removal Canadian Biomaterials Society, Quebec, 2019

Phan CM, Walther H, Qiao H, Jones L. Development of a novel in vitro blink model Canadian Biomaterials Society, Quebec, 2019

Phan CM, Walther H, Qiao H, Jones L. The development of an eye model that truly blinks ISCLR, Singapore, 2019

Walther H, Chan V, Phan CM, Jones L. Modelling non-invasive tear break-up times of soft lenses using a sophisticated in vitroblink platform Invest Ophthalmol Vis Sci 2019;E-abstract 6328

2017

Gorbet M, Toameh D, Zhang J, Phan C-M, Walther H, Jones L. Development of a dynamic co-culture ocular cell in vitro model for ocular biocompatibility testing Invest Ophthalmol Vis Sci 2017;E-Abstract 4727

Kroeker D, van Doorn K, Walther H, Subbaraman L, Jones L. Development of a novel, objective metric to determine tear film stability Invest Ophthalmol Vis Sci 2017;E-Abstract 3089

2016

Phan C-M, Walther H, Riederer D, Smith R, Subbaraman L, Jones L. Determination of the release of wetting agents from nelfilcon a using a novel in vitro eye model Optom Vis Sci 2016;93: E-abstract 165114 [ PDF ]

Qiao H, Phan C-M, Walther H, Subbaraman L, Jones L. Localizing lysozyme deposition on contact lenses using a novel in vitro eye model Optom Vis Sci 2016;93: E-abstract 160100

Walther H, Phan C-M, Qiao H, Liu Y, Subbaraman L, Jones L. In vitro eye model to simulate the impact of blinking on contact lens deposition and drug delivery Optom Vis Sci 2016;93: E-abstract 160101

Walther H, Phan C, Subbaraman L, Jones L. Cholesterol Penetration into Daily Disposable Contact Lenses Using a Novel In Vitro Eye-Blink Model Invest Ophthalmol Vis Sci 2016;57: E-abstract 1476 [ PDF ]

2015

Phan C, Walther H, Gao H, Bajgrowicz M, Subbaraman L, Jones L. Developing a novel in vitro eye-blink platform for drug delivery and deposition research ISCLR Budapest, Hungary, 2015

Walther H, Phan C, Subbaraman L, Jones L. Cholesterol Penetration into Daily Disposable Contact Lenses Using a Novel In Vitro Eye-Blink Model ISCLR Budapest, Hungary, 2015

Walther H, Subbaraman L, Jones L. Novel in vitro method to determine pre-lens tear break up time of hydrogel and silicone hydrogel contact lenses Invest Ophthalmol Vis Sci 2015;56: E-abstract 6105 [ PDF ]

2014

Walther H, Subbaraman L, Wettig S, Jones L. In vitro surface pressure measurements of various tear film lipids Invest Ophthalmol Vis Sci 2014;55: E-abstract 43 [ PDF ]

2013

Schulze M, Simpson T, Situ P, Menzies K, Walther H, Jones L. Effects of magnification on tear meniscus parameters using optical coherence tomography (OCT) images Canadian Optometry Schools Research Conference, Waterloo, Canada, 2013

Subbaraman L, Walther H, Kay L, Jones L. In vitro efficiency of contact lens care solutions in removing cholesterol deposits from silicone hydrogel contact lenses Contact Lens & Anterior Eye 2013;36, S2:e41

Walther H, Subbaraman L, Jones L. Efficacy of multi-purpose solutions in removing cholesterol desposits from silicone hydrogel contact lenses Invest Ophthalmol Vis Sci 2013;54: E-Abstract 517

Walther H, Subbaraman L, Jones L. Method optimization to quantify oxidative stress in tear film lipids Canadian Optometry Schools Research Conference, Waterloo, Canada, 2013

2012

Walther H, Subbaraman L, Jones L. In Vitro Dehydration of Daily Disposable and Silicone Hydrogel Contact Lens Materials Invest Ophthalmol Vis Sci 2012;53:ARVO E-Abstract 6121

2011

Jones L, Lorrentz H, Walther H, Heynen M, Kay L. Impact of lipid concentration, exposure time and tear film components on in vitro model lipid deposition to silicone hydrogel and hydrogel contact lens materials International Society for Contact Lens Research (Napa Valley, California), 2011

Lorentz H, Walther H, Heynen M, Kay L, Jones L. Radiochemical kinetic uptake of three lipids on silicone hydrogel and conventional hydrogel contact lens materials Invest Ophthalmol Vis Sci 2011;52:E-Abstract 6479

Muntz A, Lorentz H, Walther H, Heynen M, Joyce E, Sickenberger W, Jones L. Utility of a pulsating contact lens case to aid cholesterol removal from contact lens materials soaked in a no-rub MPS regimen Contact Lens & Anterior Eye 2011;34, S1:S9

Schulze M, Simpson T, Situ P, Menzies K, Walther H, Jones L. Effects of magnification on tear meniscus parameters using optical coherence tomography (OCT) images Optom Vis Sci 2011;88:E-abstract 115482

Situ P, Simpson T, Schultze M, Menzies K, Walther H, Jones L. Intra- and inter-operator variability of meridional corneal and epithelial thickness measurements obtained using optical coherence tomography (OCT) Optom Vis Sci 2011;87: E-abstract 115021

Walther H, Lorentz H, Heynen M, Kay L, Jones L. The effect of in vitro lipid concentration on lipid deposition on silicone hydrogeland conventional hydrogel contact lens materials Contact Lens & Anterior Eye 2011;34, s21: