Contact Lens Materials Research Articles

Lubricity comparison of a silicone hydrogel contact lens material, the human cornea, and a wetting agent

Purpose: Narafilcon A (daily disposable, silicone hydrogel) has been previously shown to be equivalent to no lens wear after one year in several key areas of physiology including corneal staining and papillary changes (Morgan et al., CLAE 2013). The material contains a high molecular weight wetting agent, polyvinylpyrrolidone (PVP), which has individual repeating units similar in function to ocular mucins in providing a lubricious (low friction) surface. It is hypothesized this lubricious interface helps to minimize the interaction between the contact lens (CL) and the eye. The purpose of this study was to evaluate the coefficient of friction (CoF) of PVP, narafilcon A and human corneal tissue in vitro to help elucidate the previously published clinical performance findings.

Surface versus bulk activity of lysozyme deposited on hydrogel contact lens materials in vitro

To determine and compare the levels of surface versus bulk active lysozyme deposited on several commercially available hydrogel contact lens materials. 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. 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). 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.

Poly(2‐hydroxyethyl methacrylate)/boric acid composite hydrogel as soft contact lens material: Thermal, optical, rheological, and enhanced antibacterial properties

ABSTRACTThe present work proposes to fabricate a composite hydrogel material that well characterized, transparent, biocompatible, and self‐antibacterial as potential soft contact lens material. For this purpose, poly(2‐hydroxyethyl methacrylate) (PHEMA)/boric acid (BA) composite hydrogels were successfully prepared by chemical crosslinking with BA through in situ polymerization using different BA ratios between 1 and 10% w/w. Afterward, the compositions, thermal stability, transparence, oxygen permeability, water uptake capacity, swelling ratio as well as morphological and rheological properties, in vitro degradability, in vitro cytotoxicity, and antibacterial properties of the all prepared materials were analyzed using a series of different techniques. The thermal stability, hydrophilicity, water uptake, oxygen permeability gradually increased depending ratio of BA, which is desirable for biomaterial. While the transparence and refractive index decreased, the composite hydrogels, except for BA content of 10 wt %, maintained enough transparency to be used for contact lens. In addition, PHEMA/BA composite hydrogels exhibited good cytocompatibility (PHEMA‐1%BA and PHEMA‐3%BA) and excellent antibacterial activity against Gram‐positive (Staphylococcus aureus and Enterococcus faecium) and Gram‐negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Overall, the results demonstrated that the obtained PHEMA/BA composite hydrogels could be considered as self‐antibacterial contact lens and a potential composite biomaterial for other applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46575.

Microbial Keratitis Secondary to Therapeutic Contact Lens Wear

Therapeutic contact lenses are commonly used to treat various ocular surface conditions that require restoration or maintenance of the corneal epithelium. While this is a very successful treatment modality, it is not without risk. The primary risk associated with bandage contact lens wear is microbial keratitis. This paper will review the literature on the occurrence and outcomes of microbial keratitis in the setting of therapeutic contact lens use, including orthokeratology. Therapeutic contact lenses are used in various situations including ocular surface disease, post-keratorefractive surgery, and post-corneal crosslinking. Orthokeratology utilizes a rigid contact lens for therapeutic purposes. Though an uncommon occurrence in the setting of therapeutic contact lenses, microbial keratitis can occur and can lead to vision loss even in the setting of prophylactic topical antibiotics. Despite improvements in contact lens materials that would reduce infection rates, use of modern therapeutic contact lenses can still result in microbial keratitis, even with the use of prophylactic antibiotics. Although incidence rates for microbial keratitis in with therapeutic contact lens use are not available, numerous reports confirm that care must be taken when using therapeutic contact lenses to avoid sight-threatening infections.

The Effect of Denatured Lysozyme on Human Corneal Epithelial Cells.

During contact lens wear, the amount of lysozyme deposited on contact lenses varies depending on the lens material. The binding of lysozyme to some contact lens materials may result in a conformational change that denatures the protein to an inactive form. This investigation evaluated the effect that denatured lysozyme has on human corneal epithelial cells (HCECs) by measuring cell viability and the release of inflammatory cytokines. HCECs were exposed to lysozyme that was denatured to various activity levels. After 24-hour exposure to the lysozyme (1.9 mg/mL) in growth media, the cells were evaluated for cell viability using confocal microscopy. The metabolic activity of the cells was determined using an alamarBlue assay. Cell supernatants were analyzed for inflammatory cytokines. Using confocal microscopy, there was no detectable change in the viability of the HCECs after exposure to the denatured lysozyme. However, using alamarBlue, a decrease in the metabolic activity of the HCECs exposed to denatured lysozyme was detected. HCECs exposed to lysozyme that was 67%, 47%, and 22% active showed a reduction in metabolic activity when compared with native (100% active) lysozyme and the media controls (P < 0.05). Exposure to the denatured lysozyme also caused an increase in the release of inflammatory cytokines (P < 0.05) from the HCECs. The results of this study show that denatured lysozyme can have a detrimental effect on HCECs. Both a reduction in metabolic activity and an increase in the release of inflammatory cytokines occurred after HCEC exposure to denatured lysozyme.

Impact of contact lens material and design on the ocular surface

BackgroundTo evaluate the impact on the ocular surface of a daily disposable hydrogel contact lens with high water content compared with two silicone hydrogel daily disposable lenses of lower water content.MethodsThe hydrogel lens assessed was made from nesofilcon A and the silicone hydrogel lenses were made of delefilcon A and stenfilcon A. Contact lens thickness was measured to assess material stability during daily wear, and ocular surface parameters such as tear film osmolarity, tear meniscus area and central corneal thickness were also assessed. Optical quality was analysed for all cases by means of wavefront aberrometry.ResultsThe nesofilcon A was shown to be the thinnest lens (p < 0.001), while no differences in lens thickness were found between the two silicone hydrogel lenses (p = 0.495). No significant differences were found in tear film osmolarity, tear meniscus area, central corneal thickness or corneal aberrations, either as a function of the lens measured or time of use (p > 0.05).ConclusionIn spite of having the thinnest lens and the highest water content, the hydrogel does not significantly impact on tear film and corneal swelling after one day of use in first‐time wearers.

Contact Lens Materials and Modalities

Contact Lens Materials and Modalities

A two-step method for rate-dependent nano-indentation of hydrogels

Soft, biphasic materials such as hydrogels are commonly used to mimic lubrication and confinement mechanics of biological tissue such as articular cartilage or the cornea. In-depth understanding of such mechanics is crucial for designing synthetic replacements for cartilage, contact-lens materials or soft coatings for medical devices. Using colloidal-probe atomic force microscopy (AFM), surfaces can be investigated at the nanoscale and information on the contact modulus, poro-viscoelastic properties and the permeability can be extracted. Yet, probing the surface of a soft material in a liquid environment is challenging, since the point of contact between a probe and sample surface during finite-rate indentation can be obscured by viscous squeeze-out effects of temporarily confined liquid. To address this issue, we have developed a 2-step indentation method that enables accurate alignment of finite-rate indentation curves with respect to the contact point of quasi-static indentation of soft matter in liquid. In this work, the issue and the method are illustrated by measurements on a commonly used poly(acrylamide) (PAAm) hydrogel. We have shown that liquid squeeze-out may cause non-negligible force offsets that can result in false contact-point determination during finite-rate indentation. The presented method allows accurate alignment of the indentation curves, enables one to accurately study the rate-dependent contact moduli and related stiffening effects, and thus greatly facilitates mechanical characterization of both biological as well as synthetic soft materials.

Characterization of surface roughness of new nanophotonic soft contact lenses using lacunarity and AFM method

The aim of this study was to develop new soft contact lens (SCL) materials which would, after recommended and existing machining processes, improve surface roughness. Nanomaterials (fullerene, fullerol and methformin hydroxylate fullerene) were incorporated into commercial material for SCL (SL38) based on PHEMA, which were derived by the technology in the production lab of the company Soleko (Milan, Italy). Nanophotonic SCLs (SL38-A, SL38-B, SL38-C, respectively) were produced in the company Optix (Belgrade, Serbia) from the obtained materials. For the surface characterization of SCLs, AFM analysis and lacunarity method were performed. The results showed that for the SL38-B average roughness value is lower than those of SL38-A and SL38. The topography parameters of SL38-C were between the parameters of SL38-A and SL38-B. Lacunarity analysis of AFM images confirmed that SCLs surface state should belong to either group of adequate (slanted p-diagram) or inadequate (contorted p-diagram) roughness concerning tear film stability. Nanophotonic SCL SL38-C exibits more acceptable performance considering SCL surface functional behavior as compared to other SCLs. The positive result of incorporating nanomaterials into basic material for SCL is better quality of the nanophotonic SCLs surfaces. On the bases of these experiments, the assumption that incorporation of fullerene derivate will not increase surface roughness parameters is confirmed.

Materials and Applications of Smart Diagnostic Contact Lens Systems.

Contact lenses were originally developed for the purpose of vision correction, but they have recently been used for various purposes. Because contact lenses are minimally invasive, they are used in diagnostic and drug delivery applications. In particular, interest in using contact lenses for the purpose of diagnosing diseases by fusing contact lenses with information technology (IT), nanotechnology (NT), and biotechnology (BT) is increasing. These contact lens-based platforms are getting more attention as Google and Novartis develop contact lenses for diabetes diagnosis. Therefore, this chapter introduces materials that can be used for contact lens materials and diagnostic contact lenses, and discusses future prospects.

Are Contact Lens Discomfort or Soft Contact Lens Material Properties Associated with Alterations in the Corneal Sub-Basal Nerve Plexus?

ABSTRACTPurpose: To study whether contact lens (CL) discomfort and some properties of soft CL materials are associated with alterations in the nerve fibers morphology and density of dendritic cells of the corneal sub-basal nerve plexus.Materials and Methods: Forty soft CL wearers and 20 non-CL wearers were included. The Contact Lens Dry Eye Questionnaire-short form was administered to divide CL wearers based on their symptoms (20 symptomatic and 20 asymptomatic CL wearers were included). The CL material properties considered were the CL material type (16 hydrogel and 24 silicone hydrogel CL wearers were included), water content, oxygen transmissibility, and modulus of elasticity. Confocal microscopy was performed, and the number and density of corneal nerves, density of nerve branches, grade of nerve tortuosity, and density of dendritic cells were analyzed. The effects of CL discomfort and CL material properties on the confocal microscopy parameters were analyzed.Results: No significant differences were found among symptomatic and asymptomatic CL wearers and non-CL wearers in any of the confocal microscopy parameters evaluated. The density of dendritic cells was higher in the hydrogel CL wearers compared to the silicone hydrogel CL wearers and non-CL wearers (p = 0.002). The density of dendritic cells tended to be higher as the oxygen transmissibility decreased (β = −0.40, p = 0.07).Conclusions: CL discomfort appears not to be associated with alterations in the corneal sub-basal nerve plexus. Hydrogel CL wear might be involved in the recruitment of dendritic cells into the cornea, being a possible origin its lower oxygen permeability compared to silicone hydrogel materials. Future studies are required to confirm these results.

Chemical Functionalization of Polysaccharides-Towards Biocompatible Hydrogels for Biomedical Applications.

Hydrogels have emerged as a highly interdisciplinary topic as they play a significant role for a vast number of applications. They have been studied extensively as materials for contact lenses, wound dressing and as filler material in soft-tissue augmentation, in which classical polymer backbones such as hydroxyethylmethacrylate (HEMA) are typically employed. More recently, polysaccharides have received attention, particularly in the fields of regenerative medicine and tissue engineering, as ideal candidate materials for artificial extracellular matrices (ECM). The polysaccharides of choice are dextran, alginate, chitosan, hyaluronic acid and pullulan and in order to obtain suitable hydrogels from these polysaccharides, controlled chemical functionalization is of critical importance. This short review summarizes recent developments in the chemical derivatization of polysaccharides to pave the way for crosslinking and to decorate individual polysaccharide chains with bioactive ligands. The report covers convergent and divergent protocols for crosslinking, as well strategies for bisfunctionalization of polysaccharides. Additionally, information on biological properties and biomedical applications are covered.

Influence of soft contact lens material on corneal warpage: prevalence and time to resolution

ObjectiveCorneal warpage represents a reversible distortion of the corneal surface induced by soft contact lens (SCL) wear. The aim of the study is to assess the influence of SCL materials, age, wearing duration, cylindrical refraction, and spherical equivalence on the prevalence and time to resolution of corneal warpage. MethodsThis is an interventional prospective study in which SCL wearers volunteered to remove their SCLs and underwent, on each visit, a corrected distance visual acuity and anterior and posterior segment evaluation, along with keratometry measurement and corneal topography. Visits were scheduled 30 minutes after SCL removal, on day 4, day 7, and then weekly after SCL removal until warpage resolution. ResultsA total of 17 volunteers (34 eyes) were included, with 9 (18 eyes) in the hydrogel SCL group and 8 (16 eyes) in the silicone hydrogel SCL group. The difference in warpage prevalence between the hydrogel group (28%, 5 eyes) and silicone hydrogel group (31%, 5 eyes) was not statistically significant (p > 0.90). Duration necessary for warpage resolution ranged from 7 to 21 days with no statistically significant difference between the 2 groups (p = 0.12). ConclusionsBoth types of SCL had similar corneal warpage prevalence and time to resolution, with slightly longer mean time to resolution with silicone hydrogel. All eyes had resolution of warpage by 3 weeks. It seems more cautious to wait longer than the usual 1-week interval before performing refractive surgery, especially in patients wearing SCL for long periods and regardless of the type of material.

The effect of soft contact lens thickness in visual function after intracorneal ring segments surgery.

To study the influence of soft contact lens (SCL) central thickness and material in keratoconus on visual function after intracorneal ring segment (ICRS) surgery. A pilot, experimental, prospective, cross-sectional and double-blind study was performed. Fourteen keratoconus patients with age range of 34.75±9.22years (7 males and 7 females) with ICRS implanted were involved in the study. Two different SCL materials [Hioxifilcon A (G-5X/p-GMA/HEMA) and Lucifilcon A (silicone-hydrogel)] with four different central thicknesses (0.1, 0.2, 0.3 and 0.4mm) were fitted in one eye per patient, selected randomly. High and low corrected distance visual acuity (CDVA) and contrast sensitivity (CS), corneal topography and corneal and total aberrometry were measured. Corneal spherical like, coma like and root mean square (RMS) decreased significantly for 0.3 and 0.4mm in both SCL materials (p<0.05). Total RMS decreased significantly for 0.4mm with both SCL materials (p<0.05). High and low CDVA improved for 0.4mm of thickness for both materials (p<0.05). Statistically increasing were found in all thicknesses studied for CS in both materials (p<0.05). A central thickness of the SCL equal or superior to 0.4mm seems to decrease the ocular high order aberration (HOA) and to improve the visual function in keratoconus patients implanted with ICRS. However, the modulus of rigidity of the SCL would not influence the HOA correction.

Hyaluronan incorporation into model contact lens hydrogels as a built-in lubricant: Effect of hydrogel composition and proteoglycan 4 as a lubricant in solution.

Contact lens friction significantly correlates with subjective comfort. Hyaluronan (HA) and proteoglycan 4 (PRG4) are natural boundary lubricants present in the body. The objective of this study was to assess the effect of crosslinked HA into the bulk of model contact lens materials pHEMA, pHEMA/TRIS, and DMAA/TRIS on surface wettability, protein sorption, and boundary lubricating properties at a material-cornea biointerface, both alone and synergistically with PRG4 in solution. Surface wettability was assessed by water contact angle measurement, protein sorption by lysozyme sorption assay, and boundary lubricating properties using an in vitro friction test method. HA incorporation (HAinc ) increased the surface wettability of all materials, and reduced protein sorption for pHEMA and DMAA/TRIS. HAinc increased friction for pHEMA, and DMAA/TRIS, whereas a decrease was observed for pHEMA/TRIS. A combination of HAinc and PRG4sol had a synergistic effect of reducing friction only for pHEMA/TRIS. This combination had similar friction reduction compared with PRG4sol alone for DMAA/TRIS. These results indicate HA incorporation could be an effective internal wetting agent, antiadhesive, and boundary lubricant for pHEMA/TRIS silicone hydrogels. In conclusion, HA incorporation can reduce friction of hydrogels alone and in combination with PRG4 in solution, though in a hydrogel composition-dependent (e.g., TRIS) manner. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1818-1826, 2018.

A Review of Techniques to Measure Protein Sorption to Soft Contact Lenses.

To compare and critically evaluate a variety of techniques to measure the quantity and biological activity of protein sorption to contact lenses over short time periods. A literature review was undertaken investigating the major techniques to measure protein sorption to soft contact lens materials, with specific reference to measuring protein directly on lenses using in situ, ex situ, protein structural, and biological activity techniques. The use of in situ techniques to measure protein quantity provides excellent sensitivity, but many are not directly applicable to contact lenses. Many ex situ techniques struggle to measure all sorbed proteins, and these measurements can have significant signal interference from the lens materials themselves. Techniques measuring the secondary and tertiary structures of sorbed proteins have exhibited only limited success. There are a wide variety of techniques to measure both the amount of protein and the biological activity of protein sorbed to soft contact lens materials. To measure the mass of protein sorbed to soft contact lenses (not just thin films) over short time periods, the method of choice should be I radiolabeling. This technique is sensitive enough to measure small amounts of deposited protein, provided steps are taken to limit and measure any interaction of the iodine tracer with the materials. To measure the protein activity over short time periods, the method of choice should be to measure the biological function of sorbed proteins. This may require new methods or adaptations of existing ones.

Non-invasive pre-lens tear film assessment with high-speed videokeratoscopy.

To evaluate the effect of two types of daily contact lenses (delefilcon A and omafilcon A) on the tear film and establish whether it is dependent on pre-corneal tear film characteristics using a new method to analyse high-speed videokeratoscopy recordings, as well as to determine the sensitivity of the method in differentiating between contact lens materials on eye. High-speed videokeratoscopy recordings were analysed using a custom made automated algorithm based on a fractal dimension approach that provides a set of parameters directly related to tear film stability. Fifty-four subjects participated in the study. Baseline measurements, in suppressed and natural blinking conditions, were taken before subjects were fitted with two different daily contact lenses and after four hours of contact lens wear. The method for analysing the stability of the tear film provides alternative parameters to the non-invasive break up time to assess the quality of the pre-corneal and pre-lens tear film. Both contact lenses significantly decreased the quality of the tear film in suppressed and natural blinking conditions (p<0.001). The utilised method was able to distinguish between contact lens materials on eye in suppressed blinking conditions. The pre-corneal tear film characteristics were not correlated with the decrease in pre-lens tear film quality. High-speed videokeratoscopy equipped with an automated method to analyse the dynamics of the tear film is able to distinguish between contact lens materials in vivo. Incorporating the assessment of pre-lens tear film to the clinical practice could aid improving contact lens fitting and understand contact lens comfort.

Preparation and characterization of protein-resistant hydrogels for soft contact lens applications via radical copolymerization involving a zwitterionic sulfobetaine comonomer

We aimed to introduce hydrophilic sulfobetaine-type zwitterionic groups to macromolecular chains of copolymers to construct novel copolymer hydrogels with anti-protein-fouling performance that could be used as soft contact lens (SCL) materials. Using hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidinone (NVP) and sulfobetaine methacrylate (SBMA) as comonomers, several copolymer hydrogels with different SBMA contents, poly(HEMA-NVP-SBMA), are synthesized via radical copolymerization in an aqueous phase. Surface chemistry, structural morphologies, water contact angle (WCA), equilibrium water content (EWC), visible light transmittance and tensile mechanical properties are investigated. The prepared hydrogels exhibit a closed-type porous structure. With increasing SBMA content in the comonomer mixture, the prepared copolymer hydrogel pore size gradually increases up to the micron level, WCA tends to decrease, EWC tends to increase, and visible light transmittance slightly increases, but their tensile mechanical properties decline. The amounts of protein Lyz and BSA adsorbed on the copolymer hydrogels and on commercially available EASY DAY® SCLs as a control are also determined by protein adsorption tests. The amount of protein adsorbed on the copolymer hydrogel decreases with increasing SBMA content. For the hydrogel prepared using the comonomer mixture with 5.0 wt % SBMA, the amount of adsorbed Lyz is 0.91 μg/cm2, which corresponds to only 56.8% of the amount adsorbed on EASY DAY® SCLs. Thus, novel SCL materials with high water content and excellent anti-protein-fouling performance were efficiently constructed by introducing sulfobetaine-type zwitterionic groups into a traditional polymer hydrogel system.

PALS, MIR and UV–vis–NIR spectroscopy studies of pHEMA hydrogel, silicon- and fluoro-containing contact lens materials

Studies on polymeric materials used in contactology for manufacturing of contact lenses are presented in the paper. Different types of brand new contact lenses were investigated: hydrogel, silicone-hydrogel and rigid gas permeable. Positron annihilation lifetime spectroscopy (PALS) was used to characterize geometrical sizes and fraction of the free volume holes in the investigated samples. Measurements reveal significant differences between the materials. Namely differences in size and fraction of free volume were observed. These changes are strongly correlated with oxygen permeability in contact lenses. Middle infrared (MIR) spectroscopy was carried out in order to investigate the internal structure of materials. Furthermore, UV–vis–NIR studies were performed in order to determine the transmittance properties of contact lenses.

Hydrophilic surface modification of poly(methyl methacrylate)-based ocular prostheses using poly(ethylene glycol) grafting

Ocular prostheses are custom-made polymeric inserts that can be placed in anophthalmic sockets for cosmetic rehabilitation. Prosthetic eye wearers have reduced tear amount, and they often experience dry eye symptoms including dryness, irritation, discomfort, and discharge. Most modern ocular prostheses are made of poly(methyl methacrylate) (PMMA), which is highly hydrophobic. Previous research has shown that improving the wettability of contact lens materials decreases its wearers discomfort by increasing lubrication. Therefore, hydrophilic modification of PMMA-based ocular prostheses might also improve patient discomfort by improving lubrication. We modified the surfaces of PMMA-based ocular prostheses using poly(ethylene glycol) (PEG), which is hydrophilic. To do this, we used two strategies. One was a “grafting from” method, whereby PEG was polymerized from the PMMA surface. The other was a “grafting to” method, which involved PEG being covalently bonded to an amine-functionalized PMMA surface. Assessments involving the water contact angle, ellipsometry, and X-ray photoelectron spectroscopy indicated that PEG was successfully introduced to the PMMA surfaces using both strategies. Scanning electron microscopy and atomic force microscopy images revealed that neither strategy caused clinically significant alterations in the PMMA surface morphology. In vitro bacterial adhesion assessments showed that the hydrophilic modifications effectively reduced bacterial adhesion without inducing cytotoxicity. These results imply that hydrophilic surface modifications of conventional ocular prostheses may decrease patient discomfort and ocular prosthesis-related infections.