Lakshman N Subbaraman | University of Waterloo (original) (raw)
Papers by Lakshman N Subbaraman
Investigative Ophthalmology & Visual Science, Jun 11, 2015
Investigative Ophthalmology & Visual Science, Apr 30, 2014
We compared microbial contamination of contact lens storage cases of asymptomatic contact lens we... more We compared microbial contamination of contact lens storage cases of asymptomatic contact lens wearers (Group 1; No. = 118; sampled once) and of contact lens wearers with manufacturer's lens-care instructions reinforced (Group 2; No. = 62; sampled three, six, 12, and 20 weeks after initial advisement). A significantly higher incidence of contamination of contact lens storage cases and solutions was observed among samples from Group 1 (132 of 247 samples) as compared to samples from Group 2 (30 of 500 samples; P = .000). Contact lens storage cases of individuals in Group 2 who used hydrogen peroxide systems (four of 78) showed a significantly lower incidence of contamination as compared to individuals who used other chemical disinfection (11 of 62 soft lens users; 10 of 59 rigid gas-permeable lens users; P = .041). Biofilms, adhered microorganisms embedded in a glycocalyx, in contact lens storage cases were not always inactivated by the addition of fresh solutions. Cleaning and periodic replacement of contact lens storage cases is recommended. DONZIS AND ASSOCIATESl found that some elements of the contact lens care system of 52 of 100 asymptomatic patients were contaminated with microorganisms. The frequency of contamination was higher with systems for extended-wear lenses compared to daily-wear lenses,
Investigative Ophthalmology & Visual Science, Jun 23, 2017
To determine and compare the levels of surface versus bulk active lysozyme deposited on several c... more To determine and compare the levels of surface versus bulk active lysozyme deposited on several commercially available hydrogel contact lens materials. Methods: Hydrogel contact lens materials [polymacon, omafilcon A, nelfilcon A, nesofilcon A, ocufilcon and etafilcon A with polyvinylpyrrolidone (PVP)] were incubated in an artificial tear solution for 16 h. Total activity was determined using a standard turbidity assay. The surface activity of the deposited lysozyme was determined using a modified turbidity assay. The amount of active lysozyme present within the bulk of the lens material was calculated by determining the difference between the total and surface active lysozyme. Results: The etafilcon A materials showed the highest amount of total lysozyme activity (519 ± 8 μg/lens, average of Moist and Define), followed by the ocufilcon material (200 ± 5 μg/lens) and these two were significantly different from each other (p < 0.05). The amount of surface active lysozyme on etafilcon and ocufilcon lens materials was significantly higher than that found on all other lenses (p < 0.05). There was no active lysozyme quantified in the bulk of the nelfilcon material, as all of the active lysozyme was found on the surface (1.7 ± 0.3 μg/lens). In contrast, no active lysozyme was quantified on the surface of polymacon, with all of the active lysozyme found in the bulk of the lens material (0.6 ± 0.6 μg/lens). Conclusions: The surface and bulk activity of lysozyme deposited on contact lenses is material dependent. Lysozyme deposited on ionic, high water content lens materials such as etafilcon A show significantly higher surface and bulk activity than many other hydrogel lens materials.
Investigative Ophthalmology & Visual Science, Jun 16, 2013
Investigative Ophthalmology & Visual Science, Jul 13, 2018
Investigative Ophthalmology & Visual Science, May 10, 2007
Investigative Ophthalmology & Visual Science, Oct 18, 2013
Contact Lens Materials Given the fact that approximately 90% of the world's contact lens wearers ... more Contact Lens Materials Given the fact that approximately 90% of the world's contact lens wearers are wearing soft lenses with no recent change in this figure, 1 this report primarily concerns itself with the role of soft lens materials and designs and care solutions in CLD, with some discussion of rigid gas permeable lens (RGP) materials or designs where appropriate. Conventional Hydrogel Materials The pioneering work of Wichterle and colleagues 2,3 is well known as a basis for the development of hydrogel polymers for soft contact lenses, including lightly cross-linked polymers of 2
Clinical Ophthalmology, Apr 1, 2021
The amount of protein deposition on soft contact lenses and to what extent the proteins are denat... more The amount of protein deposition on soft contact lenses and to what extent the proteins are denatured may have an impact on comfortable wearing times of contact lenses. The purpose of this study was to evaluate the effects of two lens care systems on total protein and the quantity and activity of lysozyme deposited on worn senofilcon A, silicone hydrogel contact lenses. Participants and Methods: Thirty symptomatic soft contact lens wearers were enrolled into a 4-week prospective, randomized, bilateral eye, daily-wear, crossover, double-masked study. Participants were fitted with biweekly senofilcon A lenses and were assigned either a polyquaternium-1 and myristamidopropyl dimethylamine-containing system (OPTI-FREE RepleniSH) or a peroxide-based system (CLEAR CARE). After each wear period, proteins were extracted from the lenses and analyzed for total protein, total lysozyme quantity and activity. Results: The use of either the peroxide-based system or the polyquaternium-1 and myristamidopropyl dimethylamine-containing system resulted in no difference (P>0.05) to the amount of total protein deposited on the lenses (6.7 ± 2.8 micrograms/lens versus 7.3 ± 2.8 micrograms/lens, respectively) or to the amount of denatured lysozyme deposits (0.8 ± 0.7 versus 0.9 ± 0.7 micrograms/lens), respectively. The total amount of lysozyme deposited on the lenses was significantly lower when using the peroxide-based system (1.3 ± 0.9 micrograms/lens) compared to the polyquaternium-1 and myristamidopropyl dimethylaminecontaining system (1.7 ± 1.0 micrograms/lens) (P=0.02). Conclusion: The inactivation of lysozyme deposited on senofilcon A lenses when disinfected with the peroxide-based or the polyquaternium-1 and myristamidopropyl dimethylamine-containing systems were neither statistically nor clinically significant and the overall amounts of denatured lysozyme recovered from the lenses were low (<1 microgram/lens).
Journal of Visualized Experiments, Apr 6, 2016
Currently, in vitro evaluations of contact lenses (CLs) for drug delivery are typically performed... more 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 2piece 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.
Contact Lens and Anterior Eye, Jun 1, 2018
Journal of Biomedical Materials Research Part B, Oct 16, 2018
The purpose of this work was to determine the release of polyvinyl alcohol (PVA) from etafilcon A... more 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.
Journal of Biomaterials Science-polymer Edition, Sep 16, 2014
The antifungal agent natamycin can effectively form inclusion complexes with beta-cyclodextrin (β... more The antifungal agent natamycin can effectively form inclusion complexes with beta-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-βCD) to improve the water solubility of natamycin by 16-fold and 152-fold, respectively (Koontz, J. Agric. Food. Chem. 2003). The purpose of this study was to develop contact lens materials functionalized with methacrylated β-CD (MβCD) and methacrylated HP-βCD (MHP-βCD), and to evaluate their ability to deliver natamycin in vitro. Methods: Model conventional hydrogel (CH) materials were synthesized by adding varying amounts of MβCD and MHP-βCD (0, 0.22, 0.44, 0.65, 0.87, 1.08% of total monomer weight) to a monomer solution containing 2-hydroxyethyl methacrylate (HEMA). Model silicone hydrogel (SH) materials were synthesized by adding similar concentrations of MβCD and MHP-βCD to N,N-dimethylacrylamide (DMAA)/10% 3-methacryloxypropyltris(trimethylsiloxy)silane (TRIS). The gels were cured with UV light, washed with ethanol and then, hydrated for 24 h (h). The model materials were then incubated with 2 mL of 100 μg/mL of natamycin in phosphate buffered saline (PBS) pH 7.4 for 48 h at room temperature. The release of natamycin from these materials in 2 mL of PBS, pH 7.4 at 32 ± 2°C was monitored using UV-vis spectrophotometry at 304 nm over 24 h. Results: For both CH and SH materials, functionalization with MβCD and MHP-βCD improved the total amount of drugs released up to a threshold loading concentration, after which further addition of methacrylated CDs decreased the amount of drugs released (p < 0.05). The addition of CDs did not extend the drug release duration; the release of natamycin by all model materials reached a plateau after 12 h (p < 0.05). Overall, DMAA/10% TRIS materials released significantly more drug than HEMA materials (p < 0.05). The addition of MHP-βCD had a higher improvement in drug release than MβCD for both HEMA and DMAA/10% TRIS gels (p < 0.05). Conclusions: A high loading concentration of methacrylated CDs decreases overall drug delivery efficiency, which likely results from an unfavorable arrangement of the CDs within the polymer network leading to reduced binding of natamycin to the CDs. HEMA and DMAA/10% TRIS materials functionalized with MHP-βCD are more effective than those functionalized with MβCD to deliver natamycin.
Optometry and Vision Science, Jul 1, 2015
Within a few minutes of wear, contact lenses become rapidly coated with a variety of tear film co... more Within a few minutes of wear, contact lenses become rapidly coated with a variety of tear film components, including proteins, lipids, and mucins. Tears have a rich and complex composition, allowing a wide range of interactions and competitive processes, with the first event observed at the interface between a contact lens and tear fluid being protein adsorption. Protein adsorption on hydrogel contact lenses is a complex process involving a variety of factors relating to both the protein in question and the lens material. Among tear proteins, lysozyme is a major protein that has both antibacterial and anti-inflammatory functions. Contact lens materials that have high ionicity and high water content have an increased affinity to accumulate lysozyme during wear, when compared with other soft lens materials, notably silicone hydrogel lenses. This review provides an overview of tear film proteins, with a specific focus on lysozyme, and examines various factors that influence protein deposition on contact lenses. In addition, the impact of lysozyme deposition on various ocular physiological responses and bacterial adhesion to lenses and the interaction of lysozyme with other tear proteins are reviewed. This comprehensive review suggests that deposition of lysozyme on contact lens materials may provide a number of beneficial effects during contact lens wear.
Experimental Eye Research, Jun 1, 2021
The purpose of this study was to develop a standardized, accurate and efficient method for estima... more The purpose of this study was to develop a standardized, accurate and efficient method for estimating conjunctival goblet cell density (GCD) via optimizing sample storage conditions and quantification methods. Conjunctival impression cytology (CIC) membranes were collected from both eyes of 32 participants and were randomized to two storage durations (2-3 weeks, 6-7 weeks) and two storage container types (microcentrifuge tube, flat histology cassette). The CIC membranes were stained and subdivided into 25 areas (5 mm × 5 mm) for imaging and the GCs were counted under 200X magnification using three different methods: (1) full CIC membrane GC count of the 25 images with cell-counting software ("full"; reference method), (2) partial membrane GC count of 9 images with cell-counting software ("partial"), and (3) manual counting of the 25 images ("manual"). In all cases, GCD was determined by dividing the GC count by the counting area. The average time required for quantification was recorded to gauge efficiency. Results showed no significant difference in GC count between the two storage durations (p = 0.745) or storage container types (p = 0.552). The median (interquartile range (IQR)) time required to quantify a CIC membrane for the full, partial, and manual methods of GC counting, was 14.8(17.6), 4.6(5.2) and 5.0 (5.0) minutes, respectively. The agreement of GCD values between the full and manual methods (bias: 0.4, 95% LOA: [-4.6, 5.5]) was stronger than that comparing the full and partial methods (bias: 0.5, 95% LOA: [-18, 17]). All together, through systematic examination of key procedural variables, an optimized method for GCD quantification within 7 weeks of sample collection was outlined. Adaption of procedures described in this paper to facilitate accurate and efficient GCD quantification may serve as a valuable step in clinical trials investigating DED pathophysiology and/or novel DED treatment strategies.
Translational Vision Science & Technology, Jun 29, 2020
To describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface... more To describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface potential of human meibum and to demonstrate successful use of this instrument on both human meibum and a meibum model system (six-lipid stock [6LS]) to elucidate nanoscale surface chemistry and self-assembly characteristics. Materials and Methods: 6LS and meibum were analyzed in this study. Mica-supported thin films were created using the Langmuir-Blodgett trough. Topography and electrical surface potential were quantified using simultaneous atomic force microscopy/KPFM imaging. Results: Both lipid mixtures formed thin film patches on the surface of the mica substrate, with large aggregates resting atop. The 6LS had aggregate heights ranging from 41 to 153 nm. The range in surface potential was 33.0 to 125.9 mV. The meibum thin films at P = 5 mN/m had aggregates of 170 to 459 nm in height and surface potential ranging from 15.9 to 76.1 mV, while thin films at P = 10 mN/m showed an aggregate size range of 147 to 407 nm and a surface potential range of 11.5 to 255.1 mV. Conclusions: This study showed imaging of the differences in electrical surface potential of meibum via KPFM and showed similarities in nanoscale topography. 6LS was also successfully analyzed, showing the capabilities of this method for use in both in vitro and ex vivo ocular research. Translational Relevance: This study describes the use of KPFM for the study of ocular surface lipids for the first time and outlines possibilities for future studies to be carried out using this concept.
Optometry and Vision Science, Aug 1, 2016
Purpose: To evaluate contact lens (CL) storage case contamination when used with four different C... more Purpose: To evaluate contact lens (CL) storage case contamination when used with four different CL care solutions, during daily wear of three different CL materials. Methods: A parallel, prospective, bilateral, randomized clinical trial (n=38) was conducted. Subjects were randomly assigned to use one of three CL materials (etafilcon A, senofilcon A or galyfilcon A) on a daily wear basis. Subsequently, each subject randomly used one of four different CL care solutions (Biotrue, OPTI-FREE PureMoist, RevitaLens OcuTec and CLEAR CARE) for two weeks, along with their respective storage cases. After every two-week period, their storage cases were collected and the right and left wells of each storage case were randomized for two procedures: (i) microbial enumeration by swabbing the storage case surface and (ii) evaluation of biofilm formation (multipurpose solution cases only) using a crystal violet staining assay. Results: More than 80% of storage cases were contaminated when used in conjunction with the four CL care solutions, irrespective of the CL material worn. Storage cases maintained with CLEAR CARE (mean Log colony forming units (CFU)/well ± SD, 2.0 ± 1.0) revealed significantly (p<0.001) greater levels of contamination, compared to those maintained with Biotrue (1.3 ± 0.8) and RevitaLens OcuTec (1.2 ± 0.8). Predominantly, storage cases were contaminated with Gram-positive bacteria (≥80%). There were significant differences (p=0.013) for the levels of Gram-negative bacteria Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation recovered from the storage cases maintained with different CL care solutions. Storage cases maintained with OPTI-FREE PureMoist (0.526 ± 0.629) showed significantly higher biofilm formation (p=0.028) compared to those maintained with Biotrue (0.263 ± 0.197). Conclusions: Levels of contamination ranged from 0 to 6.4 Log CFU/storage case well, which varied significantly (p<0.001) between different CL care solutions and storage case contamination was not modulated by CL materials. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Synopsis for "Microbial contamination of contact lens storage cases during daily wear use" This study evaluated the frequency and levels of microbial contamination in contact lens (CL) storage cases, during the daily wear of three different CL materials that were used in combination with three contemporary CL care solutions with dual disinfectants and a hydrogen-peroxide based solution. Overall, at least 80% of storage cases were contaminated. The levels of storage case contamination varied significantly between different CL care solutions and was not modulated by CL materials. It is worthwhile, to evaluate the association between microbial contamination and the occurrence of adverse events during CL wear in a future study. Short title for OVS announces: Microbial contamination of contact lens storage cases
Investigative Ophthalmology & Visual Science, Jun 16, 2013
Investigative Ophthalmology & Visual Science, Jun 11, 2015
Investigative Ophthalmology & Visual Science, Apr 30, 2014
We compared microbial contamination of contact lens storage cases of asymptomatic contact lens we... more We compared microbial contamination of contact lens storage cases of asymptomatic contact lens wearers (Group 1; No. = 118; sampled once) and of contact lens wearers with manufacturer's lens-care instructions reinforced (Group 2; No. = 62; sampled three, six, 12, and 20 weeks after initial advisement). A significantly higher incidence of contamination of contact lens storage cases and solutions was observed among samples from Group 1 (132 of 247 samples) as compared to samples from Group 2 (30 of 500 samples; P = .000). Contact lens storage cases of individuals in Group 2 who used hydrogen peroxide systems (four of 78) showed a significantly lower incidence of contamination as compared to individuals who used other chemical disinfection (11 of 62 soft lens users; 10 of 59 rigid gas-permeable lens users; P = .041). Biofilms, adhered microorganisms embedded in a glycocalyx, in contact lens storage cases were not always inactivated by the addition of fresh solutions. Cleaning and periodic replacement of contact lens storage cases is recommended. DONZIS AND ASSOCIATESl found that some elements of the contact lens care system of 52 of 100 asymptomatic patients were contaminated with microorganisms. The frequency of contamination was higher with systems for extended-wear lenses compared to daily-wear lenses,
Investigative Ophthalmology & Visual Science, Jun 23, 2017
To determine and compare the levels of surface versus bulk active lysozyme deposited on several c... more To determine and compare the levels of surface versus bulk active lysozyme deposited on several commercially available hydrogel contact lens materials. Methods: Hydrogel contact lens materials [polymacon, omafilcon A, nelfilcon A, nesofilcon A, ocufilcon and etafilcon A with polyvinylpyrrolidone (PVP)] were incubated in an artificial tear solution for 16 h. Total activity was determined using a standard turbidity assay. The surface activity of the deposited lysozyme was determined using a modified turbidity assay. The amount of active lysozyme present within the bulk of the lens material was calculated by determining the difference between the total and surface active lysozyme. Results: The etafilcon A materials showed the highest amount of total lysozyme activity (519 ± 8 μg/lens, average of Moist and Define), followed by the ocufilcon material (200 ± 5 μg/lens) and these two were significantly different from each other (p < 0.05). The amount of surface active lysozyme on etafilcon and ocufilcon lens materials was significantly higher than that found on all other lenses (p < 0.05). There was no active lysozyme quantified in the bulk of the nelfilcon material, as all of the active lysozyme was found on the surface (1.7 ± 0.3 μg/lens). In contrast, no active lysozyme was quantified on the surface of polymacon, with all of the active lysozyme found in the bulk of the lens material (0.6 ± 0.6 μg/lens). Conclusions: The surface and bulk activity of lysozyme deposited on contact lenses is material dependent. Lysozyme deposited on ionic, high water content lens materials such as etafilcon A show significantly higher surface and bulk activity than many other hydrogel lens materials.
Investigative Ophthalmology & Visual Science, Jun 16, 2013
Investigative Ophthalmology & Visual Science, Jul 13, 2018
Investigative Ophthalmology & Visual Science, May 10, 2007
Investigative Ophthalmology & Visual Science, Oct 18, 2013
Contact Lens Materials Given the fact that approximately 90% of the world's contact lens wearers ... more Contact Lens Materials Given the fact that approximately 90% of the world's contact lens wearers are wearing soft lenses with no recent change in this figure, 1 this report primarily concerns itself with the role of soft lens materials and designs and care solutions in CLD, with some discussion of rigid gas permeable lens (RGP) materials or designs where appropriate. Conventional Hydrogel Materials The pioneering work of Wichterle and colleagues 2,3 is well known as a basis for the development of hydrogel polymers for soft contact lenses, including lightly cross-linked polymers of 2
Clinical Ophthalmology, Apr 1, 2021
The amount of protein deposition on soft contact lenses and to what extent the proteins are denat... more The amount of protein deposition on soft contact lenses and to what extent the proteins are denatured may have an impact on comfortable wearing times of contact lenses. The purpose of this study was to evaluate the effects of two lens care systems on total protein and the quantity and activity of lysozyme deposited on worn senofilcon A, silicone hydrogel contact lenses. Participants and Methods: Thirty symptomatic soft contact lens wearers were enrolled into a 4-week prospective, randomized, bilateral eye, daily-wear, crossover, double-masked study. Participants were fitted with biweekly senofilcon A lenses and were assigned either a polyquaternium-1 and myristamidopropyl dimethylamine-containing system (OPTI-FREE RepleniSH) or a peroxide-based system (CLEAR CARE). After each wear period, proteins were extracted from the lenses and analyzed for total protein, total lysozyme quantity and activity. Results: The use of either the peroxide-based system or the polyquaternium-1 and myristamidopropyl dimethylamine-containing system resulted in no difference (P>0.05) to the amount of total protein deposited on the lenses (6.7 ± 2.8 micrograms/lens versus 7.3 ± 2.8 micrograms/lens, respectively) or to the amount of denatured lysozyme deposits (0.8 ± 0.7 versus 0.9 ± 0.7 micrograms/lens), respectively. The total amount of lysozyme deposited on the lenses was significantly lower when using the peroxide-based system (1.3 ± 0.9 micrograms/lens) compared to the polyquaternium-1 and myristamidopropyl dimethylaminecontaining system (1.7 ± 1.0 micrograms/lens) (P=0.02). Conclusion: The inactivation of lysozyme deposited on senofilcon A lenses when disinfected with the peroxide-based or the polyquaternium-1 and myristamidopropyl dimethylamine-containing systems were neither statistically nor clinically significant and the overall amounts of denatured lysozyme recovered from the lenses were low (<1 microgram/lens).
Journal of Visualized Experiments, Apr 6, 2016
Currently, in vitro evaluations of contact lenses (CLs) for drug delivery are typically performed... more 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 2piece 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.
Contact Lens and Anterior Eye, Jun 1, 2018
Journal of Biomedical Materials Research Part B, Oct 16, 2018
The purpose of this work was to determine the release of polyvinyl alcohol (PVA) from etafilcon A... more 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.
Journal of Biomaterials Science-polymer Edition, Sep 16, 2014
The antifungal agent natamycin can effectively form inclusion complexes with beta-cyclodextrin (β... more The antifungal agent natamycin can effectively form inclusion complexes with beta-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-βCD) to improve the water solubility of natamycin by 16-fold and 152-fold, respectively (Koontz, J. Agric. Food. Chem. 2003). The purpose of this study was to develop contact lens materials functionalized with methacrylated β-CD (MβCD) and methacrylated HP-βCD (MHP-βCD), and to evaluate their ability to deliver natamycin in vitro. Methods: Model conventional hydrogel (CH) materials were synthesized by adding varying amounts of MβCD and MHP-βCD (0, 0.22, 0.44, 0.65, 0.87, 1.08% of total monomer weight) to a monomer solution containing 2-hydroxyethyl methacrylate (HEMA). Model silicone hydrogel (SH) materials were synthesized by adding similar concentrations of MβCD and MHP-βCD to N,N-dimethylacrylamide (DMAA)/10% 3-methacryloxypropyltris(trimethylsiloxy)silane (TRIS). The gels were cured with UV light, washed with ethanol and then, hydrated for 24 h (h). The model materials were then incubated with 2 mL of 100 μg/mL of natamycin in phosphate buffered saline (PBS) pH 7.4 for 48 h at room temperature. The release of natamycin from these materials in 2 mL of PBS, pH 7.4 at 32 ± 2°C was monitored using UV-vis spectrophotometry at 304 nm over 24 h. Results: For both CH and SH materials, functionalization with MβCD and MHP-βCD improved the total amount of drugs released up to a threshold loading concentration, after which further addition of methacrylated CDs decreased the amount of drugs released (p < 0.05). The addition of CDs did not extend the drug release duration; the release of natamycin by all model materials reached a plateau after 12 h (p < 0.05). Overall, DMAA/10% TRIS materials released significantly more drug than HEMA materials (p < 0.05). The addition of MHP-βCD had a higher improvement in drug release than MβCD for both HEMA and DMAA/10% TRIS gels (p < 0.05). Conclusions: A high loading concentration of methacrylated CDs decreases overall drug delivery efficiency, which likely results from an unfavorable arrangement of the CDs within the polymer network leading to reduced binding of natamycin to the CDs. HEMA and DMAA/10% TRIS materials functionalized with MHP-βCD are more effective than those functionalized with MβCD to deliver natamycin.
Optometry and Vision Science, Jul 1, 2015
Within a few minutes of wear, contact lenses become rapidly coated with a variety of tear film co... more Within a few minutes of wear, contact lenses become rapidly coated with a variety of tear film components, including proteins, lipids, and mucins. Tears have a rich and complex composition, allowing a wide range of interactions and competitive processes, with the first event observed at the interface between a contact lens and tear fluid being protein adsorption. Protein adsorption on hydrogel contact lenses is a complex process involving a variety of factors relating to both the protein in question and the lens material. Among tear proteins, lysozyme is a major protein that has both antibacterial and anti-inflammatory functions. Contact lens materials that have high ionicity and high water content have an increased affinity to accumulate lysozyme during wear, when compared with other soft lens materials, notably silicone hydrogel lenses. This review provides an overview of tear film proteins, with a specific focus on lysozyme, and examines various factors that influence protein deposition on contact lenses. In addition, the impact of lysozyme deposition on various ocular physiological responses and bacterial adhesion to lenses and the interaction of lysozyme with other tear proteins are reviewed. This comprehensive review suggests that deposition of lysozyme on contact lens materials may provide a number of beneficial effects during contact lens wear.
Experimental Eye Research, Jun 1, 2021
The purpose of this study was to develop a standardized, accurate and efficient method for estima... more The purpose of this study was to develop a standardized, accurate and efficient method for estimating conjunctival goblet cell density (GCD) via optimizing sample storage conditions and quantification methods. Conjunctival impression cytology (CIC) membranes were collected from both eyes of 32 participants and were randomized to two storage durations (2-3 weeks, 6-7 weeks) and two storage container types (microcentrifuge tube, flat histology cassette). The CIC membranes were stained and subdivided into 25 areas (5 mm × 5 mm) for imaging and the GCs were counted under 200X magnification using three different methods: (1) full CIC membrane GC count of the 25 images with cell-counting software ("full"; reference method), (2) partial membrane GC count of 9 images with cell-counting software ("partial"), and (3) manual counting of the 25 images ("manual"). In all cases, GCD was determined by dividing the GC count by the counting area. The average time required for quantification was recorded to gauge efficiency. Results showed no significant difference in GC count between the two storage durations (p = 0.745) or storage container types (p = 0.552). The median (interquartile range (IQR)) time required to quantify a CIC membrane for the full, partial, and manual methods of GC counting, was 14.8(17.6), 4.6(5.2) and 5.0 (5.0) minutes, respectively. The agreement of GCD values between the full and manual methods (bias: 0.4, 95% LOA: [-4.6, 5.5]) was stronger than that comparing the full and partial methods (bias: 0.5, 95% LOA: [-18, 17]). All together, through systematic examination of key procedural variables, an optimized method for GCD quantification within 7 weeks of sample collection was outlined. Adaption of procedures described in this paper to facilitate accurate and efficient GCD quantification may serve as a valuable step in clinical trials investigating DED pathophysiology and/or novel DED treatment strategies.
Translational Vision Science & Technology, Jun 29, 2020
To describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface... more To describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface potential of human meibum and to demonstrate successful use of this instrument on both human meibum and a meibum model system (six-lipid stock [6LS]) to elucidate nanoscale surface chemistry and self-assembly characteristics. Materials and Methods: 6LS and meibum were analyzed in this study. Mica-supported thin films were created using the Langmuir-Blodgett trough. Topography and electrical surface potential were quantified using simultaneous atomic force microscopy/KPFM imaging. Results: Both lipid mixtures formed thin film patches on the surface of the mica substrate, with large aggregates resting atop. The 6LS had aggregate heights ranging from 41 to 153 nm. The range in surface potential was 33.0 to 125.9 mV. The meibum thin films at P = 5 mN/m had aggregates of 170 to 459 nm in height and surface potential ranging from 15.9 to 76.1 mV, while thin films at P = 10 mN/m showed an aggregate size range of 147 to 407 nm and a surface potential range of 11.5 to 255.1 mV. Conclusions: This study showed imaging of the differences in electrical surface potential of meibum via KPFM and showed similarities in nanoscale topography. 6LS was also successfully analyzed, showing the capabilities of this method for use in both in vitro and ex vivo ocular research. Translational Relevance: This study describes the use of KPFM for the study of ocular surface lipids for the first time and outlines possibilities for future studies to be carried out using this concept.
Optometry and Vision Science, Aug 1, 2016
Purpose: To evaluate contact lens (CL) storage case contamination when used with four different C... more Purpose: To evaluate contact lens (CL) storage case contamination when used with four different CL care solutions, during daily wear of three different CL materials. Methods: A parallel, prospective, bilateral, randomized clinical trial (n=38) was conducted. Subjects were randomly assigned to use one of three CL materials (etafilcon A, senofilcon A or galyfilcon A) on a daily wear basis. Subsequently, each subject randomly used one of four different CL care solutions (Biotrue, OPTI-FREE PureMoist, RevitaLens OcuTec and CLEAR CARE) for two weeks, along with their respective storage cases. After every two-week period, their storage cases were collected and the right and left wells of each storage case were randomized for two procedures: (i) microbial enumeration by swabbing the storage case surface and (ii) evaluation of biofilm formation (multipurpose solution cases only) using a crystal violet staining assay. Results: More than 80% of storage cases were contaminated when used in conjunction with the four CL care solutions, irrespective of the CL material worn. Storage cases maintained with CLEAR CARE (mean Log colony forming units (CFU)/well ± SD, 2.0 ± 1.0) revealed significantly (p<0.001) greater levels of contamination, compared to those maintained with Biotrue (1.3 ± 0.8) and RevitaLens OcuTec (1.2 ± 0.8). Predominantly, storage cases were contaminated with Gram-positive bacteria (≥80%). There were significant differences (p=0.013) for the levels of Gram-negative bacteria Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation recovered from the storage cases maintained with different CL care solutions. Storage cases maintained with OPTI-FREE PureMoist (0.526 ± 0.629) showed significantly higher biofilm formation (p=0.028) compared to those maintained with Biotrue (0.263 ± 0.197). Conclusions: Levels of contamination ranged from 0 to 6.4 Log CFU/storage case well, which varied significantly (p<0.001) between different CL care solutions and storage case contamination was not modulated by CL materials. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Synopsis for "Microbial contamination of contact lens storage cases during daily wear use" This study evaluated the frequency and levels of microbial contamination in contact lens (CL) storage cases, during the daily wear of three different CL materials that were used in combination with three contemporary CL care solutions with dual disinfectants and a hydrogen-peroxide based solution. Overall, at least 80% of storage cases were contaminated. The levels of storage case contamination varied significantly between different CL care solutions and was not modulated by CL materials. It is worthwhile, to evaluate the association between microbial contamination and the occurrence of adverse events during CL wear in a future study. Short title for OVS announces: Microbial contamination of contact lens storage cases
Investigative Ophthalmology & Visual Science, Jun 16, 2013