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Peer-reviewed articles

2021

Chan,V. W. Y., Phan,C-M., Ngo,W., Jones,L. Lysozyme Deposition on Contact Lenses in an In Vitro Blink-Simulation Eye Model Versus a Static Vial Deposition Model Eye & Contact Lens 2021;47(7):388-393 [ Show Abstract ]

Purpose:
To evaluate active lysozyme deposition on daily disposable (DD) contact lenses (CL) using a novel in vitro blink model.

Methods:
Three conventional hydrogel DD CL materials (etafilcon A, omafilcon A, nelfilcon A) and three silicone hydrogel DD CL materials (delefilcon A, senofilcon A, somofilcon A) were tested. The device blink rate was set to 6 blinks/min with a tear flow rate of 1 μL/min using an artificial tear solution (ATS) containing lysozyme and other typical tear film components. After incubation at 2, 4, or 8 hr, lenses were removed, and lysozyme activity was measured. A separate experiment was conducted with lenses incubated in a static vial containing 480 μL of ATS.

Results:
Etafilcon A deposited significantly higher amounts of active lysozyme (402±102 μg/lens) than other lens materials after 8 hr (P<0.0001). Etafilcon A had a higher amount of active lysozyme using the blink model compared with the static vial (P=0.0435), whereas somofilcon A (P=0.0076) and senofilcon A (P=0.0019) had a higher amount of lysozyme activity in the vial compared with the blink model.

Conclusion:
The blink model can be tuned to provide quantitative data that closely mimics ex vivo studies and can be used to model deposition of lysozyme on CL materials.

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.

Yee,A., Chan,V., Heynen,M., Phan,C. M., Jones,L. Uptake and release of a multipurpose solution biocide (MAP-D) from hydrogel and silicone hydrogel contact lenses using a radiolabel methodology Eye & Contact Lens 2021;47(5):249-255 [ Show Abstract ]

Purpose:
The purpose of this study was to evaluate the uptake and release of radiolabelled myristamidopropyl dimethylamine (MAP-D) on reusable daily wear contact lenses (CLs) over 7 days.

Methods:
Three silicone hydrogel (SH) CL materials (lotrafilcon B, balafilcon A, senofilcon A) and two conventional hydrogel (CH) materials (etafilcon A, omafilcon A) were tested. A short-term (experiment 1, N=4) and a longer-term (experiment 2, N=3) study was conducted. In experiment 1, the CLs were incubated in 2 mL of phosphate buffered solution (PBS) containing 14C MAP-D (5 μg/mL) for 8 hrs. The release of 14C MAP-D was measured at t=0.25, 0.5, 1, 2, 4, 8, and 24 hr in PBS. In experiment 2, the CLs were incubated in the 14C MAP-D solution for 8 hrs followed by a 16-hr release in PBS. This cycle was repeated daily for 7 days. At the end of both experiments, lenses were extracted to determine the total uptake of MAP-D. The radioactivity was measured using a beta scintillation counter.

Results:
In experiment 1, all three SH lenses sorbed similar amounts of MAP-D (P=0.99), all of which were higher than the two CH materials (P<0.01). However, the CH materials released a greater amount of MAP-D than the SH materials (P<0.01). In experiment 2, the uptake of MAP-D in SH materials increased over 7 days, whereas the amount of MAP-D remained constant in the CH materials (P=0.99). Similar to experiment 1, the CH lenses released more MAP-D than SH lenses after 7 days (P<0.01).

Conclusion:
The SH materials absorbed greater amounts of MAP-D compared to CH materials. However, the CH materials released the greatest amount of MAP-D. Radioactive labelling of MAP-D offers a highly sensitive method of assessing the uptake and release profiles of biocides to CL materials.

Scientific Presentations

2020

Chan V, Phan CM, Jones L. Evaluating lysozyme deposition on contemporary daily disposable contact lenses in a novel in vitro blink model The Association for Research in Vision and Ophthalmology, 2020 [ Show Abstract ][ PDF ]

Purpose : To evaluate total lysozyme deposition on daily disposable (DD) contact lenses (CL) using a novel in vitro eye-blink model.

Methods : Three conventional hydrogel (CH) DD CL materials (etafilcon A, omafilcon A, nelfilcon A) and three silicone hydrogel (SH) DD CL materials (delefilcon A, senofilcon A, somofilcon A) were tested. The lenses were removed from their blister packs and placed directly on the eye model. An artificial tear solution (ATS) was flown over the lenses at a flow rate of 1 µl/min. The blink rate was set to 6 blinks per minute and the model was incubated at room temperature (23-26°C) and >45% humidity. After exposure periods of 2, 4 or 8 hours the lenses were removed and the lysozyme was extracted using acetonitrile: 0.2% trifluoroacetic acid (n=3). A separate experiment was conducted with lenses incubated in a vial containing 480 µL of ATS on an orbital shaker at 60 rpm for 8 hours (n=3). The lysozyme activity was measured using a spectrophotometric assay.

Results : Etafilcon A had the highest amount of active lysozyme absorption at all time points (p>0.001). After 8 hours, a cumulative total of 402 ± 102µg/lens of active lysozyme was absorbed on etafilcon A. Delefilcon A had the highest cumulative amount of active lysozyme (26 ± 1µg/lens) for SH materials (p<0.05). Nelfilcon A, senofilcon A and somofilcon A had the lowest amount of lysozyme activity (p<0.05). Overall, CH had a higher amount of lysozyme activity than SH after 8 hours (p>0.05). The amount of active lysozyme sorption for certain lens types was different when measured using the eye-blink model as compared to a vial (p<0.05). Etafilcon A had a higher amount of active lysozyme when incubated on the blink model as compared to the vial (p<0.05), whereas somofilcon A and senofilcon A had a higher amount of lysozyme activity in the vial compared to the eye model (p<0.05). Both methods, however, showed no differences in the amount of active lysozyme sorption for omafilcon A, nelfilcon A, and delefilcon A (p>0.05).

Conclusions : The in vitro eye-blink model provides quantitative data that is close to that determined from ex vivo studies and is an excellent model to assess the deposition of lysozyme on DD CL materials.

This is a 2020 ARVO Annual Meeting abstract.

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.

Yee A, Chan V, Heynen M, Jones L. A radioactive labelling technique for evaluating the uptake and release of myristamidopropyl dimethylamine (MAP-D) from contact lenses Invest Ophthalmol Vis Sci 2019;E-abstract 6370 [ Show Abstract ][ PDF ]

Purpose: The uptake and subsequent release of biocides from contact lens (CL) materials is of relevance as it has been linked with outbreaks of microbial keratitis and potential cytotoxic responses. Previous uptake and release studies of myristamidopropyl dimethylamine (MAP-D; ALDOX®) have used light-scattering techniques, which are time consuming and have relatively low sensitivity. The purpose of this study was to develop a radioactive labelling technique in order to improve the accuracy and sensitivity of biocide uptake and release to CL materials.

Methods: Four soft CL materials (lotrafilcon A, balafilcon A, senofilcon A, etafilcon A) were tested (N=4). Radioactive (14C) MAP-D was purchased from Moravek Inc. (California, USA). The lenses were incubated in PBS (ISO 18369-3) solution containing radioactive MAP-D (5µg/mL) for 8 hours. After the incubation period of 8 hours, the lenses were placed into the release condition. The release of MAP-D was assessed over 24 hours in 2 mL of PBS. Aliquots were removed at 0.25, 0.5, 1, 2, 4, 8, and 24 hour time points and added to scintillation fluor (PerkinElmer, USA). The samples were counted for their radioactive signal (CPM) using the LS6500 Beckman Coulter liquid scintillation beta counter (Beckman Coulter, ON, CA). The CPM was converted to µg of MAP-D based on a standard curve.

Results: After the incubation period of 8 hours, the uptake of MAP-D by etafilcon A (2.78±0.19µg) was significantly different than lotrafilcon A (4.69±0.1µg, p<0.01), balafilcon A (4.55±0.31µg, p<0.01), and senofilcon A (4.35±0.13µg, p<0.01). The total amount of MAP-D released by etafilcon A (1.41±0.09µg) was significantly greater than lotrafilcon A (0.27±0.02µg, p<0.01), balafilcon A (0.23±0.04µg, p<0.01), and senofilcon A (0.21±0.01µg, p<0.01). The results demonstrate that the uptake of MAP-D was higher for all silicone hydrogel (SH) lenses and lower for the conventional hydrogel lens. The release profile of etafilcon A was greater than the SH lenses, with a burst release of 0.33µg at 0.25 hr.

Conclusions: Radioactive labelling of MAP-D offers a highly sensitive, accurate way of assessing the uptake and release profiles of biocides to CL materials. Future studies using this methodology will investigate the profiles for other biocides, such as polyhexamethylene biguanide (PHMB), a common biocide used in CL solutions.