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Peer-reviewed articles

2021

Chan,V. W. Y., Phan,C-M., Walther,H., Ngo,W., Jones,L. Effects of Temperature and Blinking on Contact Lens Dehydration of Contemporary Soft Lens Materials Using an In Vitro Blink Model Translational Vision Science & Technology 2021;10(8):11 [ Show Abstract ]

Purpose: The purpose of this studywas to evaluate the effects of temperature and blinking on contact lens (CL) dehydration using an in vitro blink model.

Methods: Three silicone hydrogel (delefilcon A, senofilcon A, and comfilcon A) and two conventional hydrogel (etafilcon A and omafilcon A) CL materials were evaluated at 1
and 16 hours. The water content (WC) of the CLs was measured using a gravimetric method. Lenses were incubated on a blink model, internally heated to achieve a clinically relevant surface temperature of 35°C. An artificial tear solution (ATS) was delivered to the blink model at 4.5 μL/min with a blink rate of 6 blinks/min. A comparison set of lenses were incubated in a vial containing either 2 mL of ATS or phosphate-buffered saline (PBS) at 35°C.

Results: Increasing temperature to 35°C resulted in a decrease in WC for all tested CLs over time (P ≤ 0.0052). For most CLs, there was no significant difference in WC over time between ATS or PBS in the vial (P > 0.05). With the vial system, WC decreased and plateaued over time. However, on the blink model, for most CLs, the WC significantly decreased after 1 hour but returned toward initial WC levels after 16 hours (P > 0.05).

Conclusions: The reduction in WC of CLs on the eye is likely due to both an increase in temperature and dehydration from air exposure and blinking.

Translational Relevance: This study showed that the novel, heated, in vitro blink model could be used to provide clinical insights into CL dehydration on the eye.

Phan,C. M., Shukla,M., Walther,H., Heynen,M., Suh,D., Jones,L. Development of an In Vitro Blink Model for Ophthalmic Drug Delivery Pharmaceutics 2021;13(Article 300):1-10 [ Show Abstract ]

Purpose: The purpose of this study was to develop an advanced in vitro blink model that
can be used to examine the release of a wide variety of components (for example, topical ophthalmic
drugs, comfort-inducing agents) from soft contact lenses. Methods: The model was designed using
computer-aided design software and printed using a stereolithography 3D printer. The eyelid and
eyeball were synthesized from polyvinyl alcohol and silicone material, respectively. Simulated
tear fluid was infused through tubing attached to the eyelid using a syringe pump. With each
blink cycle, the eyelid slides and flexes across the eyeball to create an artificial tear film layer. The
flow-through fluid was collected using a specialized trough. Two contact lenses, etafilcon A and
senofilcon A, were incubated in 2 mL of a water-soluble red dye for 24 h and then placed on the eye
model (n = 3). The release of the dye was measured over 24 h using a tear flow rate of 5 µL/min.
Results: Approximately 25% of the fluid that flowed over the eye model was lost due to evaporation,
nonspecific absorption, and residual dead volume. Senofilcon A absorbed more dye (47.6 ± 2.7 µL)
than etafilcon A (22.3 ± 2.0 µL). For etafilcon A, the release of the dye followed a burst-plateau
profile in the vial but was sustained in the eye model. For senofilcon A, the release of the dye was
sustained in both the vial and the eye model, though more dye was released in the vial (p < 0.05).
Overall, the release of the dye from the contact lenses was higher in the vial compared with the eye
model (p < 0.05). Conclusion: The blink model developed in this study could be used to measure
the release of topical ophthalmic drugs or comfort agents from contact lenses. Simulation of a blink
mechanism, an artificial tear film, and nonspecific absorption in an eye model may provide better
results than a simple, static vial incubation model.

Walther,H., Lorentz,H., Heynen,M., Kay,L., Jones,L. W. The Impact of Incubation Conditions on in Vitro Phosphatidylcholine Deposition on Contact Lens Materials Optometry & Vision Science 2021;98(4):341-349 [ Show Abstract ]

SIGNIFICANCE: Previous in vitro measurements of contact lenses commonly investigate the impact of nonpolar
tear film lipids (i.e., sterols). Polar lipids, however, are equally important stabilizing components of the tear film.
This research explores and presents further knowledge about various aspects of polar lipid uptake that may impact
contact lens performance.

PURPOSE: This study evaluated the impact of incubation time, lipid concentration, and replenishment of an artificial
tear solution (ATS) on the uptake of phosphatidylcholine (PC) onto conventional hydrogel (CH) and silicone
hydrogel (SH) contact lens materials.

METHODS: Four SHs and two CH lens materials (n = 4) were soaked in a complex ATS containing radioactive
14C-PC as a probe molecule. Phosphatidylcholine uptake was monitored at various incubation time points (1, 3,
7, 14, and 28 days), with different ATS lipid concentrations (0.5, 1, 2) and with and without regular replenishment
of the ATS. Phosphatidylcholine was extracted from the lenses, processed, and counted by a β counter,
and accumulated PC (μg/lens) was extrapolated from standard lipid calibration curves.

RESULTS: All materials exhibited increasing PC deposition over time. Conventional hydrogel materials showed significantly lower PC uptake rates (P < .001) than any of the SH materials. Increasing lipid concentration in the ATS
resulted in increased PC binding onto the contact lens materials (P < .001). Replenishing the ATS every other day,
however, impacted the PC deposition differently, showing increased binding (P < .001) on CHs and reduced PC
deposition for SH materials (P < .001).

CONCLUSIONS: Length of incubation, lipid concentration in the ATS, and renewal of the incubation solution all
influenced the amount of PC that sorbed onto various lens materials and therefore need to be considered when
conducting future in vitro deposition studies.

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):Article 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

2023

Phan C-M, Chan V, Walther H, Pereira da Mota A, Lorenzo CA, Jones L. Developing a High-throughput in vitro Eye Model for Evaluating Ocular Drug Delivery with Contact Lenses XXV Biennial Meeting of the International Society for Eye Research, Feb 21, 2023 [ Show Abstract ]

Purpose: To develop a high-throughput in vitro eye model for evaluating ocular drug delivery with contact lenses (CLs).
Method: The eye model was designed using CAD software and manufactured using a combination of fabrication methods, including moulding, CNC machining, laser cutting, and 3D printing. The model consists of an eyeball, an upper and lower eyelid, and a collection tray to collect flow-through fluid. The portion of the upper eyelid that comes into contact with the eyeball is moulded with a highly wettable and durable polyvinyl alcohol hydrogel. The centre of the eyeball is designed with a 300 µm thick, 15 mm diameter cut-out that allows for a contact lens to be mounted. Simulated tear fluids can be delivered through an inlet located on the upper eyelid using a pump. During each blink cycle, the eyelid slides and flexes across the eyeball to create an artificial tear film layer. The blink distance, speed and rate are actuated using a motor controlled by an Arduino board and software. The release of a red dye from two CLs (etafilcon A and senofilcon A) and the release of two drugs (resveratrol and pravastatin sodium) from drug-loaded CLs were evaluated using the model and compared to the traditional vial testing method. Phosphate buffered saline (PBS) was used as the simulated tear fluid and infused into the model at 5 µL/min, at a blink rate of 1 blink/10 s.
Results: The fluid flows from the inlet, spreads across the eye, accumulates in the lower eyelid and then flows into the collection tray via gravity. During this process, approximately 25% of the fluid originally injected into the model was lost due to evaporation, nonspecific absorption, and residual dead volume. Overall, the release of the dye and drugs from the CLs was higher in a vial compared with the eye model. Interestingly, the drug release profiles from the drug-loaded CLs on the eye model were similar to in vivo results previously collected from a rabbit study, although the total amount of drugs released was significantly less. 9 or 24 CLs can be tested with one syringe or peristaltic pump, respectively.
Conclusion: The current eye model developed from this study could be used to measure the release of ophthalmic drugs or comfort agents from CLs in a high-throughput manner. However, further work is required to fine-tune the parameters of the model, such as the composition of the tear fluid, blink rate, tear flow rates, and temperature, to better simulate in vivo conditions.

2022

Chan V, Phan CM, Walther H, Ngo W, Jones L. Effects of temperature and blinking on contact lens dehydration using an in vitro blink model 10th Canadian Optometry School Research Conference, Montréal, Canada, Dec 3, 2022

Chan VWY, Phan CM, Walther H, Jones L. Fabrication of an in vitro eye model for practicing corneal foreign body removal 10th Canadian Optometry School Research Conference, Montréal, Canada, Dec 3, 2022

2020

Phan CM, Shukla M, Heynen M, Walther H, Jones L. Development of an In Vitro Blink Model for Measuring Drug and Comfort Agent Elutes from Soft Contact Lens Polymers Academy at Home, 2020 [ Show Abstract ]

Purpose: To develop an advanced in vitro blink model that could be used to examine release of a wide variety of components (topical drugs; comfort agents etc) from soft contact lenses.
Methods: The model was designed using CAD software and 3D printed using an SLA printer. A UV-curable resin polymer was used to fabricate the main components of the eye model to ensure water-sealed parts. The eyelid and eyeball were synthesized from a polyvinyl alcohol and a silicone material respectively. Simulated tear fluid is delivered through tubing attached to the eyelid. With each blink cycle (1 blink/10s), the eyelid slides and flexes across the eyeball to create an artificial tear film. The flow-through fluid is collected in a specialized trough. Two contact lenses, etafilcon A and senofilcon A, were incubated in 2 mL of a water-soluble red dye for 24 hours and then placed on the eye model. The release of the dye was measured at t= 0.5, 1, 2, 4, 8, 12, and 24 hours (n=3) in phosphate buffered saline (flow rate = 5 µL/min). The dye release from the lenses was also evaluated in a vial containing 2 mL of PBS over 24 hours (n=3). The amount of dye in the samples was determined using a UV/Vis spectrophotometer at 520 nm.
Results: All of the contact lenses were visibly red after the incubation with the dye. After the release studies, the etafilcon A lenses became transparent with a slight red tint, whereas the senofilcon A lenses retained a moderate red colour. For the vial study, the release of the dye from the contact lenses was rapid within the first 4 hours, which was then followed by a slower release phase. In contrast, dye release from the lenses on the eye model was significantly slower and was sustained over the 24-hour period. The total amounts of dye released in the eye model were also significantly lower compared to the vial (p<0.05), which could be attributed to the absorption of the dye into the eyelid. From the total amount of tear fluid (7.2 mL) that was infused into the eye model, approximately 5.2 ± 0.6 mL of flow-through was collected. The loss of fluid can be attributed to fluid absorption into the eyelid and contact lenses, as well as evaporation.
Conclusion: The blink model developed in this study could be used to measure the release of topical ophthalmic drugs or comfort agents from contact lenses. The results showed that the release kinetics of a dye from contact lenses on the eye model was significantly different than that of a vial. The model also simulated non-specific absorption of the dye into the eyelid. Future work will focus on developing polymers to simulate the absorption of drugs on the eye.

Yee A, Phan CM, Heynen M, Walther H, Jones L. The uptake and release kinetics of myristamidopropyl dimethylamine (MAP-D) from contact lenses using radioactive labelling he Association for Research in Vision and Ophthalmology, 2020 [ Show Abstract ][ PDF ]

Purpose : Biocides are an important disinfecting component commonly found in contact lens (CL) multipurpose solutions (MPS). During the disinfection step, the uptake of biocides into CL materials can significantly reduce the efficacy of the MPS to disinfect the lens. An increased release of biocides from the CL can lead to clinical complications such as discomfort and corneal staining. However, detection methods using chromatography and spectrometry can be time-consuming and have low sensitivity. The purpose of this study was to evaluate the uptake and release of myristamidopropyl dimethylamine (MAP-D; ALDOX®) using a radiolabel method.

Methods : Radioactive (14C) MAP-D was purchased from Moravek Inc. (CA, USA). Five soft CL materials (lotrafilcon B, balafilcon A, senofilcon A, etafilcon A, omafilcon A) were tested (N=4). The lenses were incubated in PBS (ISO 18369-3) solution containing 2mL of 14C radioactive MAP-D (5µg/mL) for 8 hours, followed by a release period in PBS for 16 hours. The cycle was continued over a 7-day period with a new replenishing solution for each day. The samples were counted for their radioactive signal (CPM) using the LS6500 Beckman Coulter liquid scintillation beta counter (ON, CA). A standard curve was used to convert CPM to µg of MAP-D.

Results : After 7-days, the silicone hydrogel (SH) lenses, lotrafilcon B (36.21±0.42µg), balafilcon A (36.29±1.15µg) and senofilcon A (35.54±1.37µg) had a significantly greater uptake of MAP-D compared to the conventional hydrogel (CH) lenses, etafilcon A (7.66±1.19µg) and omafilcon A (6.54±0.94µg) (p<0.01). However, the percent of MAP-D released was higher for CH lenses, etafilcon A (80%), omafilcon A (93%) compared to SH lenses, lotrafilcon B (25%), balafilcon A (19%) and senofilcon A (19%) over the 7-days (p<0.01).

Conclusions : Radioactive labelling offers a highly sensitive and accurate way of assessing the uptake and release kinetics of MAP-D to CL materials. Greater uptake of MAP-D occurs to SH materials, and the release of MAP-D is relatively minor. While CH materials take up only low amounts of MAP-D, the majority of it is easily released from these materials.

This is a 2020 ARVO Annual Meeting abstract.

2019

Phan C, Walther H, Jones L.. Development of a blink model for testing contact lenses American Academy of Optometry, Orlando, 2019 [ Show Abstract ][ PDF ]

Purpose: To develop an eye model with a physiological blink mechanism to test contact lenses.

Methods: All parts of the eye model were designed using CAD software. The eyeball moulds were CNC machined to ensure a smooth finish for the corneal surface. A chamber to house the eye model was cut using a laser cutter, assembled, and sealed using methylene chloride. 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 kDa, 85-124 kDa, 130 kDa, and 146-186 kDa) were tested at a range of concentrations between 5 – 30 % w/v. The wettability and water content of these materials were compared with the bovine cornea and sclera. The rotational motion of the eyelid was controlled by a stepper motor and an Arduino. 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 speed, degree of actuation, and rate of blinking can be controlled using the open source Arduino software. The artificial tear film layer 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.

Conclusion: 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. The model could be used to study in vitro TBUT, tear deposition, and drug delivery from contact lenses.

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

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 [ PDF ]

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;60, E-abstract 6328 [ Show Abstract ][ PDF ]

Purpose : To evaluate the feasibility of a novel in vitro eye model to determine the pre-lens non-invasive tear breakup times (NIBUT) of two daily disposable (DD) contact lenses (CLs).

Methods : An artificial eyeball synthesized from polyvinyl alcohol (15% w/t, 89-98 kDa) was used on a novel in vitroeye model (OcuBlink), incorporating a blink and constant tear flow. A flat black disc was incorporated into the eyeball for contrast. The OcuBlink’s flexible eyelid design ensures contact with the eyeball, thereby enabling an even spread of the tear solution over the front of the CL. The blink interval was set to 10 seconds, and the flow rate of an artificial tear solution was set to 1.4 µL/min. A silicone hydrogel (SH; delefilcon A), and conventional hydrogel (CH; nelfilcon A) DD were placed over the corneal section and the NIBUT was evaluated after 1 h of blinking. A corneal topographer (Atlas, Zeiss Canada) was used to illuminate the lens surfaces and capture changes of the placido ring images. The humidity during the experiment was between 22-23%.

Results : A stable artificial tear film layer was formed over the artificial eyeball and the CLs. This layer was regenerated after each blink. The NIBUTs for delfilcon A, nelfilcon A, and the artificial eyeball were 7.55 ± 1.59 seconds, 8.16 ± 0.81 seconds, and 5.13 ± 0.09 seconds respectively. There were no significant differences between the two lens types (p>0.05), and between nelfilcon A and the artificial eyeball (p>0.05). However, delfilcon A had a longer NIBUT than the artificial eyeball (p<0.05).

Conclusions : The measured NIBUT values over the artificial eyeball and CLs are similar to those found in vivo. The OcuBlink simulates the blink motion and physiological tear flow rates, and could be used to measure in vitro pre-lens NIBUT values for various CLs.

Walther H, Phan CM, Jones L.. Detection of Phosphatidylcholine from Delefilcon A Contact Lenses using Mass Spectrometry American Academy of Optometry, Orlando, 2019 [ Show Abstract ][ PDF ]

Purpose: The gradual release of phospholipids from contact lenses could potentially stabilise the tear film over the front surface of the lens and increase comfort during wear. Delefilcon A (Dailies Total 1) contact lenses inherently contain phosphatidylcholine (PC), a zwitterionic phospholipid that is a potent wetting agent and lubricant found in the human tear film.Due to its molecular structure, PC is relatively difficult to detect using standard spectrophotometric techniques. However, it has been detected previously at low concentrations using ultra-high performance liquid chromatography mass spectrometry (UHPLC-MS). The aim of this study was to detect the presence of PC from contact lens extracts of delefilcon A lens materials and its blister packaging solution using UHPLC-MS.

Methods: PC was extracted from the contact lens and the blister pack using 3 mL of 2:1 chloroform: methanol and 0.5 mL of monosodium phosphate aqueous buffer. The chloroform layer containing PC was collected, dried down using nitrogen gas, and then resuspended in 100 µL sample buffer. A PC standard, L-α-Phosphatidylcholine (Sigma Aldrich, St. Louis, MO), was prepared at 8 pmol/µL. The samples were analyzed using UHPLC-MS on a Waters and Thermo/Dionex system using a multi-step, reversed-phase gradient consisting of A: 60:40 acetonitrile: water and B: 90:10 isopropanol: acetonitrile, both with 10mM ammonium formate and 0.1% formic acid. The flow was set at 250 uL/min, the column was kept at 45C, sample tray at 4C, and injection volume was 10 uL.

Results: During the electrospray process, L-α-Phosphatidylcholine, also known as 1,2-diacyl-sn-glycero-3-phosphocholine, protonates to form C42H10NO8P+, with a theoretical mass m/z = 758.57. Elution peaks from the UHPLC-MS corresponding to PC were detected in the PC standard at m/z = 758.5-758.6. Other elution peaks for PC were also detected at m/z = 760.58-760.60, 786.60-786.61, and 788.62-788.63. These same peaks, with nearly identical retention times, were detected in both the blister pack solution and contact lens extracts for delefilcon A.

Conclusion: These results indicate that PC is present within the delefilcon A material and also in its blister pack solution. Future studies will determine if PC is released over time from the contact lens using a novel in vitro blink platform.

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:

Continuing Education Presentations

2021

Muntz A, Walther H.. Das trockene Auge im digitalen Alter: Updates aus der Forschung Sichtkontakte, Virtual Conference, October 9, 2021

Professional Publications

2019

Phan C., Walther H., Jones L. Development of a polymeric eye model for foreign body removal Optometric Education 2019;45, 1: 1-6