Targeting Contact Lens Induced Dryness and Discomfort: What Properties Will Make Lenses More Comfortable

Scleral Lenses for Managing Dry Eye Disease in the Absence of Corneal Irregularities: What Is the Current Evidence?

Scleral lenses (SLs) are large-diameter rigid contact lenses that are a mainstay treatment for eyes with corneal irregularities. In recent years, there has been increased interest in the role of managing dry eye disease (DED) with SLs, as many patients with DED have reported symptomatic relief with SL wear. The role of SLs for DED management when there are associated corneal irregularities is supported by individual case reports and studies. This has prompted practitioners to begin advocating using SLs in DED cases, even in the absence of associated corneal irregularities and other ocular surface diseases (OSDs). There have also been discussions on potentially placing SLs earlier in the treatment hierarchy of DED, where it currently sits at a more advanced level of intervention (Step 3) in the TFOS DEWS II Report. This review will present the currently available, albeit sparse, evidence that supports and suggests this practice, as well as ancillary evidence supporting the purported benefits of SL wear in DED. The advantages of SL wear, such as corneal healing, absence of tear evaporation and contact lens dehydration, and improved visual acuity with associated increased wear comfort, and how this will benefit DED patients will be explored. Conversely, the challenges associated with fitting SLs in DED patients, including increased midday fogging, poor wettability, and subjective patient satisfaction, will also be presented, as well as a discussion on the key considerations for SL fitting in this population. Overall, while more research is needed to support the use of SLs in DED patients without associated corneal irregularities and other forms of OSD, the use of these lenses may prove to have a potentially wider role given their reported ancillary benefits in these populations.

Protein and Polysaccharide-Based Optical Materials for Biomedical Applications

Recent advances in biomedical research, particularly in optical applications, have sparked a transformative movement towards replacing synthetic polymers with more biocompatible and sustainable alternatives. Most often made from plastics or glass, these materials ignite immune responses from the body, and their production is based on environmentally harsh oil-based processes. Biopolymers, including both polysaccharides and proteins, have emerged as a potential candidate for optical biomaterials due to their inherent biocompatibility, biodegradability, and sustainability, derived from their existence in nature and being recognized by the immune system. Current extraction and fabrication methods for these biomaterials, including thermal drawing, extrusion and printing, mold casting, dry-jet wet spinning, hydrogel formations, and nanoparticles, aim to create optical materials in cost-effective and environmentally friendly manners for a wide range of applications. Present and future applications include optical waveguides and sensors, imaging and diagnostics, optical fibers, and waveguides, as well as ocular implants using biopolymers, which will revolutionize these fields, specifically their uses in the healthcare industry.

Opportunities and threats to contact lens practice in Spain

OBJECTIVE

An international survey evaluated the opportunities and threats related to contact lens practice reported by eye care professionals worldwide. This study reports on the results specifically found in Spain and how these compare with those from other regions of the world.

METHODS

A questionnaire was distributed to eye care practitioners around the world through professional associations. The questionnaire consisted of 9, 5 and 12 questions about opportunities, interventions, and potential threats related to contact lens practice, respectively.

RESULTS

A total of 2,408 responses were obtained from practitioners worldwide, of which 436 responses were obtained from Spanish practitioners. Spain was found among the regions with the highest perception of opportunities (median: 6.5/10) along with Australasia, North America, Europe, and South America. Spanish (median: 7.3/10), along with South American practitioners, also reported the highest perception of threats. Continuously updating of knowledge/skills, recommending contact lens wearing options to potential patients, creating an efficient recall system for follow-up examinations and being competent in managing contact lens-related complications were reported as important interventions for contact lens practice growth by Spanish eye care practitioners.

CONCLUSIONS

Spain is one of the regions in the world with the highest perception of both opportunities and threats regarding future contact lens practice. As such, Spanish practitioners consider it important to continuously update knowledge/skills and to recommend and educate patients on the benefits of contact lens wear. Online sales were found to be one of the most important concerns reported by both Spanish and eye care practitioners worldwide.

A Microfluidic Contact Lens to Address Contact Lens-Induced Dry Eye

The contact lens (CL) industry has made great strides in improving CL-wearing experiences. However, a large amount of CL wearers continue to experience ocular dryness, known as contact lens-induced dry eye (CLIDE), stemming from the reduction in tear volume, tear film instability, increased tear osmolarity followed by inflammation and resulting in ocular discomfort and visual disturbances. In this article, to address tear film thinning between the CL and the ocular surface, the concept of using a CL with microchannels to deliver the tears from the pre-lens tear film (PrLTF) to the post-lens ocular surface using in vitro eye-blink motion is investigated. This study reports an eye-blink mimicking system with microfluidic poly(2-hydroxyethyl methacrylate) (poly(HEMA)) hydrogel with integrated microchannels to demonstrate eye-blink assisted flow through microchannels. This in vitro experimental study provides a proof-of-concept result that tear transport from PrLTF to post-lens tear film can be enhanced by an artificial eyelid motion in a pressure range of 0.1-5 kPa (similar to human eyelid pressure) through poly(HEMA) microchannels. Simulation is conducted to support the hypothesis. This work demonstrates the feasibility of developing microfluidic CLs with the potential to help prevent or minimize CLIDE and discomfort by the enhanced transport of pre-lens tears to the post-lens ocular surface.

Multifunctional glycoprotein coatings improve the surface properties of highly oxygen permeable contact lenses

To achieve and maintain good operability of medical devices while reducing putative side effects for the patient, a promising strategy is to tailor the surface properties of such devices as they critically dictate the tissue compatibility and the biofouling behavior. Indeed, those properties can be strongly improved by generating mucin coatings on such medical devices. However, using coatings on optical systems, e.g., contact lenses, comes with various challenges: here, the geometrical and optical characteristics of the lens may not be compromised by either the coating process or the coating itself. In this study, we show how mucin macromolecules can be attached onto the surfaces of rigid, gas permeable contact lenses while maintaining all critical lens parameters. We demonstrate that the generated coatings improve the surface wettability (contact angles are reduced from 105° to 40° and liquid film break-up times are increased from <1 s to 31 s) and prevent tribological damage to corneal tissue. Additionally, such coatings are highly transparent (transmission values above 98 % compared to an uncoated sample are reached) and efficiently reduce lipid deposition to the lens surface by 90 % but fully maintain the geometrical and mechanical properties of the lenses. Thus, such mucin coatings could also be highly beneficial for other optical systems that are used in direct contact with tissues or body fluids.

Nanomedicine and drug delivery to the retina: current status and implications for gene therapy

Blindness affects more than 60 million people worldwide. Retinal disorders, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma, are the leading causes of blindness. Finding means to optimize local and sustained delivery of drugs or genes to the eye and retina is one goal to advance the development of new therapeutics. Despite the ease of accessibility of delivering drugs via the ocular surface, the delivery of drugs to the retina is still challenging due to anatomic and physiologic barriers. Designing a suitable delivery platform to overcome these barriers should enhance drug bioavailability and provide a safe, controlled, and sustained release. Current inventions for posterior segment treatments include intravitreal implants and subretinal viral gene delivery that satisfy these criteria. Several other novel drug delivery technologies, including nanoparticles, micelles, dendrimers, microneedles, liposomes, and nanowires, are now being widely studied for posterior segment drug delivery, and extensive research on gene delivery using siRNA, mRNA, or aptamers is also on the rise. This review discusses the current state of retinal drug/gene delivery and highlights future therapeutic opportunities.

Evaluation of Wear Experience with Soft Daily Disposable Lenses for Astigmatism over 16 Hours of Wear

OBJECTIVE

The purpose of this study was to assess the wear experience of participants while wearing a toric daily disposable contact lens with water surface technology over long days of lens wear.

METHODS

Existing soft toric contact lens wearers were fit with the daily disposable study lenses. Participants assessed their initial comfort, vision, and satisfaction with the lenses by visual analog scale (VAS) survey. After a successful 1-week follow-up visit, participants were scheduled for 5 survey days, in which surveys were deployed to their smartphones for immediate assessments of comfort and quality of vision on a 1-10 scale at 10, 12, 14, and 16 hours of lens wear on 5 subsequent weeknights. The final study visit assessed visual acuity, and overall lens wear experience surveys were completed with VAS surveys. The overall median and interquartile (IQR) range of all surveys were calculated.

RESULTS

Thirty bilateral toric lens wearers completed the study. Median (IQR) initial impression VAS scores were 97(12) for quality of vision, 100(9) for comfort, and 96(10) for satisfaction. Median evening surveys resulted in comfort scores of 10(1) at 10 hours, 9(2) at 12 hours, 9(2) at 14 hours, and 8(2) at 16 hours of wear. Median evening surveys resulted in quality of vision scores of 10(1) at 10 hours, 10(2) at 12 hours, 9(2) at 14 hours, and 9(3) at 16 hours of wear. VAS scores for overall experience were 97(9) for comfort, 95(13) for vision, and 8(31) for dryness. End-of-day VAS scores were 93(21) for comfort, 90(15) for vision, and 21(38) for dryness. Mean (±standard deviation) OU LogMAR visual acuity with the study lenses was -0.19(0.06).

CONCLUSION

Surveys of wear experience resulted in high scores for comfort and vision over the course of a long day of wear with the daily disposable study lenses in this population of patients with astigmatism.

Sustained Release of a Polymeric Wetting Agent from a Silicone-Hydrogel Contact Lens Material

Uptake and release kinetics are investigated of a dilute aqueous polymeric-surfactant wetting agent, (ethylene oxide)₄₅-(butylene oxide)₁₀ copolymer, also referred to as poly(oxyethylene)-co-poly(oxybutylene), impregnated into a newly designed silicone-hydrogel lens material. Transient scanning concentration profiles of the fluorescently tagged polymeric surfactant follow Fick's second law with a diffusion coefficient near 10^-11 cm²/s, a value 3-4 orders smaller than that of the free surfactant in bulk water. The Nernst partition coefficient of the tagged polymeric wetting agent, determined by fluorescence microscopy and by methanol extraction, is near 350, a very large value. Back-extraction of the polymeric-surfactant wetting agent releases only ∼20% of the loaded amount after soaking the fully loaded lens for over 7 days. The remaining ∼80% is irreversibly bound in the lens matrix. Reverse-phase liquid chromatography of the lens-loaded and lens-extracted surfactant demonstrates that the released wetting agent is more hydrophilic with a higher polarity. Aqueous poly(oxyethylene)-co-poly(oxybutylene) is hypothesized to attach strongly to the lens matrix, most likely to the lens silicone domains. Strong binding leads to slow transient diffusion, to large uptake, and to significant irreversible retention. These characteristics indicate the suitability of using a poly(oxyethylene)-co-poly(oxybutylene) nonionic polymeric surfactant to maintain enhanced lens wettability over time. Methodology and findings from this study provide useful insights for designing sustained-release contact-lens wetting agents and materials.

Finite Element Analysis of Cornea and Lid Wiper during Blink, with and without Contact Lens

Ocular surface disorders such as Lid Wiper Epitheliopathy (LWE), Superior Epithelial Arcuate Lesion (SEAL), and contact lens-induced Limbal Stem Cell Deficiency (LSCD) as well as Superior Limbic Keratoconjunctivitis (SLK) affect one’s quality of life. Hence, it is imperative to investigate the underlying causes of these ocular surface disorders. During blink, the undersurface of the eyelid tends to interact with the cornea and the conjunctiva. The presence of a contact lens can add to the biomechanical frictional changes on these surfaces. To estimate these changes with and without a contact lens, a finite element model (FEM) of the eyelid wiper, eyeball, and contact lens was developed using COMSOL Multiphysics. Biomechanical properties such as von Mises stress (VMS) and displacement were calculated. Our study concluded that (a) maximum VMS was observed in the lid wiper in the absence of contact lens in the eye and (b) maximum VMS was observed in the superior 1.3 mm of the cornea in the presence of the contact lens in the eye. Thus, the development of friction-induced ocular surface disorders such as LWE, SLK, SEAL, and LSCD could be attributed to increased VMS. FEA is a useful simulation tool that helps us to understand the effect of blink on a normal eye with and without CL.

Ophthalmic Sensors and Drug Delivery

Advances in multifunctional materials and technologies have allowed contact lenses to serve as wearable devices for continuous monitoring of physiological parameters and delivering drugs for ocular diseases. Since the tear fluids comprise a library of biomarkers, direct measurement of different parameters such as concentration of glucose, urea, proteins, nitrite, and chloride ions, intraocular pressure (IOP), corneal temperature, and pH can be carried out non-invasively using contact lens sensors. Microfluidic contact lens sensor based colorimetric sensing and liquid control mechanisms enable the wearers to perform self-examinations at home using smartphones. Furthermore, drug-laden contact lenses have emerged as delivery platforms using a low dosage of drugs with extended residence time and increased ocular bioavailability. This review provides an overview of contact lenses for ocular diagnostics and drug delivery applications. The designs, working principles, and sensing mechanisms of sensors and drug delivery systems are reviewed. The potential applications of contact lenses in point-of-care diagnostics and personalized medicine, along with the significance of integrating multiplexed sensing units together with drug delivery systems, have also been discussed.

CLEAR - Scleral lenses

Scleral lenses were the first type of contact lens, developed in the late nineteenth century to restore vision and protect the ocular surface. With the advent of rigid corneal lenses in the middle of the twentieth century and soft lenses in the 1970's, the use of scleral lenses diminished; in recent times there has been a resurgence in their use driven by advances in manufacturing and ocular imaging technology. Scleral lenses are often the only viable form of contact lens wear across a range of clinical indications and can potentially delay the need for corneal surgery. This report provides a brief historical review of scleral lenses and a detailed account of contemporary scleral lens practice including common indications and recommended terminology. Recent research on ocular surface shape is presented, in addition to a comprehensive account of modern scleral lens fitting and on-eye evaluation. A range of optical and physiological challenges associated with scleral lenses are presented, including options for the clinical management of a range of ocular conditions. Future applications which take advantage of the stability of scleral lenses are also discussed. In summary, this report presents evidence-based recommendations to optimise patient outcomes in modern scleral lens practice.

Design of a questionnaire for detecting contact lens discomfort: the Contact Lens Discomfort Index

Clinical relevance: Questionnaires can provide unique information regarding the status of a condition from the perspective of the patient. Contact lens (CL) discomfort (CLD) is a condition subjectively reported by CL users; thus, updated and reliable questionnaires are needed.Background: The objective of this study was to design a new questionnaire for identifying CLD, based on the currently established CLD definition considered in the Tear Film and Ocular Surface CLD Workshop.Methods: A survey to characterise CL wearers was created and administered. Some items of the survey were selected by a focus group and analysed using a Rasch model to develop a questionnaire to identify CLD. Unidimensionality was checked applying principal components analysis. To build a plausible CLD classification (symptomatic vs asymptomatic), an unsupervised cluster analysis was used. Gower's general similarity coefficient, the partitioning around medoids algorithm, and the silhouette width were calculated. The reliability of the questionnaire was assessed using the intraclass correlation coefficient and Cohen's kappa coefficient. A study was performed to compare this questionnaire with the Contact Lens Dry Eye Questionnaire (CLDEQ)-8.Results: The 31-item survey was completed by 1104 volunteers, and the posterior analysis resulted in a 9-item questionnaire, the Contact Lens Discomfort Index (CLDI). It showed a good fit with the model (mean square infit and outfit values range was 0.76-1.10), and good unidimensionality (eigenvalues ≤ 1.3). The CLDI score range was 0-18 and the cut-off score for identifying CLD was 8. The intraclass correlation coefficient was 0.88 (95% confidence interval, 0.75-0.94), and kappa was 0.67 (95% confidence interval, 0.41-0.93). Comparison of the CLDI with the CLDEQ-8 in a sample of 58 CL wearers showed that 70.7% were classified equally by both questionnaires.Conclusions: The CLDI is a well-structured instrument, with acceptable psychometric properties, making it a valid and reliable tool to measure CL-related symptoms.

Investigating the Synergistic Interactions of Surface Immobilized and Free Natural Ocular Lubricants for Contact Lens Applications: A Comparative Study between Hyaluronic Acid and Proteoglycan 4 (Lubricin)

The main reasons for the discontinuation of contact lens wear are ocular dryness and discomfort. Proteoglycan 4 (PRG4), a mucinous glycoprotein, and hyaluronic acid (HA), a nonsulfated linear glycosaminoglycan, are naturally present in the eye and contribute to ocular hydration and lubrication. This study aimed to investigate the impact of the structure of the recombinant human PRG4 (rhPRG4)/HA complex on contact lens properties, when one agent is grafted and the counterpart is physisorbed on the surface of model conventional or silicone contact lens materials. Investigation of the wettability, water retention, antifouling, and boundary lubricant properties of the prepared hydrogels showed that the rhPRG4/HA interactions varied with the rhPRG/HA configuration on the hydrogel surface as well as the composition of the underlying substrate used. The rhPRG4-physisorbed/HA-grafted sample was characterized by better antifouling and boundary lubricant properties on the model conventional hydrogels, while the HA-physisorbed/rhPRG4-grafted sample exhibited improved surface wettability, antifouling, and water-retentive properties on the model silicone hydrogels. The results of this study contribute to the design of biomimetic contact lens surfaces that work synergistically with ocular fluid-phase biological agents to enhance compatibility between the contact lens and the ocular environment, alleviating dry eye symptoms and improving comfort.

Fouling in ocular devices: implications for drug delivery, bioactive surface immobilization, and biomaterial design

The last 30 years has seen a proliferation of research on protein-resistant biomaterials targeted at designing bio-inert surfaces, which are prerequisite for optimal performance of implantable devices that contact biological fluids and tissues. These efforts have only been able to yield minimal results, and hence, the ideal anti-fouling biomaterial has remained elusive. Some studies have yielded biomaterials with a reduced fouling index among which high molecular weight polyethylene glycols have remained dominant. Interestingly, the field of implantable ocular devices has not experienced an outflow of research in this area, possibly due to the assumption that biomaterials tested in other body fluids can be translated for application in the ocular space. Unfortunately, progression in the molecular understanding of many ocular conditions has brought to the fore the need for treatment options that necessitates the use of anti-fouling biomaterials. From the earliest implanted horsehair and silk seton for glaucoma drainage to the recent mini telescopes for sight recovery, this review provides a concise incursion into the gradual evolution of biomaterials for the design of implantable ocular devices as well as approaches used to overcome the challenges with fouling. The implication of fouling for drug delivery, the design of immune-responsive biomaterials, as well as advanced surface immobilization approaches to support the overall performance of implantable ocular devices are also reviewed.

Relationships between the material properties of silicone hydrogels: Desiccation, wettability and lubricity

Silicone hydrogels (SiHy), represent composite matrices composed of hydrophobic gas permeable silicone (Si) rich core and a surface enriched with hydrophilic polymer moieties. Their utilization in contact lens design requires number of SiHy properties (hydration, wettability, lubricity) to be optimized for the challenging conditions at the ocular surface. Typical limitations in literature are that (i) these properties are studied in isolation, monitoring only one parameter but not the rest of them, and (ii) measurements are performed with hydrated samples immediately after removal from storage solutions. Here we study the simultaneous evolution of critical material properties (evaporative loss of water, water contact angle, coefficient of friction) of different SiHy subjected to continuous blink-like desiccation/rehydration cycling. SiHy with wetting agents incorporated in their core (narafilcon A, senofilcon A) were particularly susceptible to extended desiccation. Stenfilcon A, a material with only 3% bulk Si content maintained its performance for 4 h of cycling, and delefilcon A (80% surface water content) resisted extended 8 h of desiccation/rehydration runs. Strong correlation exists between the evolution of SiHy wettability and lubricity at ≥4 h of blink-like cycling. Understanding the interplay between SiHy properties bears insights for knowledge based design of novel ophthalmic materials.

Lipid Analysis on Block Copolymer-containing Packaging Solution and Lens Care Regimens: A Randomized Clinical Trial

SIGNIFICANCE

Lotrafilcon B lenses packaged in and cared for with block copolymer-containing (polyoxyethylene-polyoxybutylene; EOBO) lens care solutions resulted in lower cholesterol extraction than each of the habitual silicone hydrogel lens/multipurpose solution (MPS) regimens tested.

PURPOSE

This study aimed to compare the extracted cholesterol of lotrafilcon B lenses packaged in and cared for with EOBO-containing lens care solutions with the extracted cholesterol of habitual silicone hydrogel lenses cared for with MPS not containing EOBO.

METHODS

In this prospective, randomized, observer-masked parallel study, habitual wearers of senofilcon C, senofilcon A, comfilcon A, and samfilcon A contact lenses using a non-EOBO MPS were randomized 1:1 to lotrafilcon B lenses packaged in and cared for with EOBO-containing solutions or to their habitual lenses and MPS. Subjects randomized to lotrafilcon B were further randomized to one of two EOBO-containing lens care solutions, OPTI-FREE PUREMOIST or CLEAR CARE PLUS with HydraGlyde (Alcon Laboratories, Inc., Fort Worth, TX). A subset of right eye lenses was collected after wear, and total cholesterol was extracted and measured using a fluorometric enzymatic assay.

RESULTS

Of 143 lenses analyzed, 95 were from subjects randomized to their habitual lenses/MPS and 48 to lotrafilcon B + EOBO lenses plus CLEAR CARE PLUS with HydraGlyde or OPTI-FREE PUREMOIST. The mean amounts of cholesterol extracted from lotrafilcon B + EOBO lenses cared for with CLEAR CARE PLUS with HydraGlyde (0.28 ± 0.18 μg/lens) and OPTI-FREE PUREMOIST (0.28 ± 0.48 μg/lens) were significantly lower than those extracted from senofilcon C (4.18 ± 3.25 μg/lens), senofilcon A (2.19 ± 2.69 μg/lens), comfilcon A (2.17 ± 1.47 μg/lens), and samfilcon A (2.07 ± 1.48 μg/lens) lenses used with MPS (P < .0001 each).

CONCLUSIONS

Cholesterol sorption was significantly lower in wearers of lotrafilcon B lenses cared for with polyoxyethylene-polyoxybutylene-containing lens care solutions than in users of habitual silicone hydrogel lenses cared for with non-polyoxyethylene-polyoxybutylene MPS.

Tear Film Characteristics During Wear of Daily Disposable Contact Lenses

Purpose

To evaluate changes induced over time by three daily disposable (DD) contact lenses on tear meniscus height (TMH), pre-lens non-invasive break-up time (pre-lens NIBUT), tear film osmolarity (TO) and objective quality of vision (OQV).

Patients and Methods

Forty-six subjects enrolled in this prospective open-label unmasked non-randomized simultaneous comparative cross-over study. For the first week of the study, subjects wore a nesofilcon A lens in the right eye and a delefilcon A lens in the left eye. After 3 days of washout, for the second week, subjects wore a nesofilcon A lens in the left eye and a stenfilcon A lens in the right eye. TMH, pre-lens NIBUT, TO and OQV were measured before contact lens fitting and for each contact lens combination on day 1 at 20 minutes and on day 7 after ≥8 hours of wear. OQV measurement included the changes of objective scatter index (OSI), the stability index (SI) and the fluctuation index (FI) calculated in a range of time of 20 s from a blink.

Results

TMH was unchanged at 20 minutes wear of all lenses but was significantly reduced after 8 or more hours wear (on day 7) of delefilcon A and stenfilcon A, respectively. Pre-lens NIBUT was significantly reduced with all lenses, while no significant change in TO was observed with any lens. SI and FI increased significantly for all lenses at both wear times.

Conclusion

While the presence of any contact lens on the eye challenges the tear film, nesofilcon A contact lenses, despite their high water content, compared to delefilcon A and stenfilcon A contact lenses, showed a lower overall effect. We speculate that superior tear film behavior while wearing nesofilcon A lenses may translate to improved subjective comfort, but this remains to be evaluated.

Hydrogel-based commercial products for biomedical applications: A review

Hydrogels are hydrophilic polymer networks, able to absorb large amount of water, increasing their volume and showing a plethora of different material behaviors. Since their first practical application, dating from sixties of last century, they have been employed in several fields of biomedical sciences. After more than half a century of industrial uses, nowadays a lot of hydrogels are currently on the market for different purposes, and offering a wide spectra of features. In this review, even if it is virtually impossible to list all the commercial products based on hydrogels for biomedical applications, an extensive analysis of those materials that have reached the market has been carried out. The hydrogel-based materials used for drug delivery, wound dressing, tissue engineering, the building of contact lens, and hygiene products are enlisted and briefly described. A detailed snapshot of the set of these products that have reached the commercial maturity has been then obtained and presented. For each class of application, the basics of requirements are described, and then the materials are listed and classified on the basis of their chemical nature. For each product the commercial name, the producer, the chemical nature and the main characteristics are reported.

Contact Lens Technology: From Fundamentals to Applications

Contact lenses are ocular prosthetic devices used by over 150 million people worldwide. Primary applications of contact lenses include vision correction, therapeutics, and cosmetics. Contact lens materials have significantly evolved over time to minimize adverse effects associated with contact lens wearing, to maintain a regular corneal metabolism, and to preserve tear film stability. This article encompasses contact lens technology, including materials, chemical and physical properties, manufacturing processes, microbial contamination, and ocular complications. The function and the composition of the tear fluid are discussed to assess its potential as a diagnostic media. The regulatory standards of contact lens devices with regard to biocompatibility and contact lens market are presented. Future prospects in contact lens technology are evaluated, with particular interest given to theranostic applications for in situ continuous monitoring the ocular physiology.

Surface modification of model hydrogel contact lenses with hyaluronic acid via thiol-ene "click" chemistry for enhancing surface characteristics

Discontinuation of contact lens wear as a result of ocular dryness and discomfort is extremely common; as many as 26% of contact lens wearers discontinue use within the first year. While patients are generally satisfied with conventional hydrogel lenses, improving on-eye comfort continues to remain a goal. Surface modification with a biomimetic, ocular friendly hydrophilic layer of a wetting agent is hypothesized to improve the interfacial interactions of the contact lens with the ocular surface. In this work, the synthesis and characterization of poly(2-hydroxyethyl methacrylate) surfaces grafted with a hydrophilic layer of hyaluronic acid are described. The immobilization reaction involved the covalent attachment of thiolated hyaluronic acid (20 kDa) on acrylated poly(2-hydroxyethyl methacrylate) via nucleophile-initiated Michael addition thiol-ene "click" chemistry. The surface chemistry of the modified surfaces was analyzed by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy. The appearance of N (1s) and S (2p) peaks on the low resolution X-ray photoelectron spectroscopy spectra confirmed successful immobilization of hyaluronic acid. Grafting hyaluronic acid to the poly(2-hydroxyethyl methacrylate) surfaces decreased the contact angle, the dehydration rate, and the amount of nonspecific sorption of lysozyme and albumin in comparison to pristine hydrogel materials, suggesting the development of more wettable surfaces with improved water-retentive and antifouling properties, while maintaining optical transparency (>92%). In vitro testing also showed excellent viability of human corneal epithelial cells with the hyaluronic acid-grafted poly(2-hydroxyethyl methacrylate) surfaces. Hence, surface modification with hyaluronic acid via thiol-ene "click" chemistry could be useful in improving contact lens surface properties, potentially alleviating symptoms of contact lens related dryness and discomfort during wear.

Self-Cleaning Interfaces of Polydimethylsiloxane Grafted with pH-Responsive Zwitterionic Copolymers

Self-cleaning surfaces allow the reversible attachment and detachment of microorganisms which show great promise in regards to their reusability as smart biomaterials. However, a widely used biomaterial such as polydimethylsiloxane (PDMS) suffers from high biofouling activity and hydrophobic recovery that results in decreased efficiency and stability. A current challenge is to modify and fabricate self-cleaning PDMS surfaces by incorporating antifouling and pH-sensitive properties. To address this, we synthesized a zwitterionic and pH-sensitive random poly(glycidyl methacrylate- co-sulfobetaine methacrylate- co-2-(dimethylamino)ethyl methacrylate) polymer, poly(GMA- co-SBMA- co-DMAEMA). In this work, chemical modification of PDMS was done by grafting onto poly(GMA- co-SBMA- co-DMAEMA) after surface activation via UV and ozone for 90 min to ensure the formation of covalent bonds necessary for stable grafting. The PDMS grafted with G20-S40-D40 exhibit antifouling and pH-sensitive properties by mitigating fibrinogen adsorption, blood cell adhesion, and releasing 98% adhered E. coli bacteria after immersion at basic pH. The grafting of poly(GMA- co-SBMA- co-DMAEMA) presented in this work shows attractive potential for biomedical and industrial applications as a simple, smart, and effective method for the modification of PDMS interfaces.

Lipid-hyaluronan synergy strongly reduces intrasynovial tissue boundary friction

Hyaluronan (HA)-lipid layers on model (mica) surfaces massively reduce friction as the surfaces slide past each other, and have been proposed, together with lubricin, as the boundary layers accounting for the extreme lubrication of articular cartilage. The ability of such HA-lipid complexes to lubricate sliding biological tissues has not however been demonstrated. Here we show that HA-lipid layers on the surface of an intrasynovial tendon can strongly reduce the friction as the tendon slides within its sheath. We find a marked lubrication synergy when combining both HA and lipids at the tendon surface, relative to each component alone, further enhanced when the polysaccharide is functionalized to attach specifically to the tissue. Our results shed light on the lubricity of sliding biological tissues, and indicate a novel approach for lubricating surfaces such as tendons and, possibly, articular cartilage, important, respectively, for alleviating function impairment following tendon injury and repair, or in the context of osteoarthritis. STATEMENT OF SIGNIFICANCE: Lubrication breakdown between sliding biological tissues is responsible for pathologies ranging from dry eye syndrome to tendon-injury repair impairment and osteoarthritis. These are increasing with human longevity and impose a huge economic and societal burden. Here we show that synergy of hyaluronan and lipids, molecules which are central components of synovial joints and of the tendon/sheath system, can strongly reduce friction between sliding biological tissues (the extrasynovial tendon sliding in its sheath), relative to untreated tissue or to either component on its own. Our results point to the molecular origins of the very low friction in healthy tendons and synovial joints, as well as to novel treatments of lubrication breakdown in these organs.

Review of Contact Lens-Related Complications

The purpose of this article is to provide a review of existing literature describing complications with contemporary contact lenses and their management. It is envisioned that this will serve as a useful summary of noninfectious and infectious complications associated with contact lens wear.

Determination of the release of PEG and HPMC from nelfilcon A daily disposable contact lenses using a novel in vitro eye model

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.

Use of a novel extended blink test to evaluate the performance of two polyvinylpyrrolidone-containing, silicone hydrogel contact lenses

Background

Sustained digital display viewing reduces eye blink frequency and tear film stability. To retain water and preserve a smooth optical surface, contact lens manufacturers have integrated the humectant polyvinylpyrrolidone (PVP) into silicone hydrogel contact lenses. In this study, extended blink time (EBT) was used to assess visual stability over a prolonged blink interval of two PVP-containing silicone hydrogel lenses, samfilcon A (SAM) and senofilcon A (SEN).

Materials and methods

This randomized, bilateral, masked, crossover study assessed lens performance in ten subjects after 16 hours of wear. EBT, ie, the time elapsed between cessation of blinking and blur-out of a threshold letter on the acuity chart, was measured. At the end of the wear period, subjects reported duration of computer use and rated visual quality (VQ) and comfort while wearing the assigned lens, and the investigator evaluated lens surface wetting characteristics. Each lens was removed and immediately weighed to determine total water content.

Results

EBTs were 10.42 seconds for SAM and 8.04 seconds for SEN (p = 0.015). Subjective ratings of VQ after 16 hours of wear were 84.6 for SAM and 74.4 for SEN (p = 0.049). Comfort ratings were 85.9 for SAM and 80.2 for SEN (p > 0.05). Median times of computer use were 6-8 hours for both lens types. Post blink, 70.0% of SAM and 30.0% of SEN lenses were completely wet (p = 0.021). Total water content after wear was 43.7% for SAM and 35.5% for SEN (p < 0.001).

Conclusion

EBT measurement indicated more stable vision with the PVP-containing SAM polymer compared with the PVP-containing SEN polymer. The SAM polymer also demonstrated better surface wetting and maintained higher water content after a prolonged period of wear. EBT can be valuable in assessing vision stability of patients after hours of computer use.

Reliability of Blotting Techniques to Assess Contact Lens Water Content

OBJECTIVES

To determine the reliability of wet and modified dry blotting techniques used in the gravimetric method to assess contact lens (CL) water content (WC), the accuracy of both techniques in comparison with the nominal WC, and also their agreement.

METHODS

We evaluated hydrated and dry CL mass values and WC using the gravimetric method in 440 daily disposable CLs. Samples assessed corresponded to Dailies Total 1, Dailies AquaComfort Plus, 1-Day Acuvue TruEye, and Biotrue ONEday. Back vertex power ranged from +3.00 diopters (D) to -6.00 D. Within-subject coefficient of variation (CVw) and intraclass correlation coefficients were calculated. Bland-Altman analysis was also performed.

RESULTS

The modified dry blotting technique yielded significantly (P≤0.0001) higher hydrated CL mass values. The wet blotting technique provided significantly (P≤0.04) better consistency than the modified dry one. Values of CVw for wet and modified dry blotting techniques ranged from 1.2% to 2.1% and from 3.7% to 5.4%, respectively. As for dry CL mass values, CVw values were not significantly different (P≥0.05) between wet (range: 1.1%-1.9%) and dry (range: 1.0%-5.1%) blotting techniques, except for Dailies AquaComfort Plus (P=0.03). Bland-Altman analysis showed poor agreement between the techniques. The wet blotting technique yielded WC values close (around 1%) to nominal ones, in contrast to modified dry blotting technique (≥2.5%).

CONCLUSIONS

The wet blotting technique is not only more reliable than the modified dry one when obtaining hydrated CL mass but also provides more accurate nominal WC measurements. Agreement between the techniques was poor.

Evaluation of the safety and efficacy of therapeutic bandage contact lenses on post-cataract surgery patients

AIM

To evaluate the safety of therapeutic bandage contact lens for post-cataract surgery patients and to illustrate its efficacy on post-operative comfort and tear-film stability.

METHODS

A total of 40 participants were recruited and randomly divided into two groups. Group one was instructed to wear bandage contact lenses for a week and use antibiotic eye drops for a month since the first day after surgery. Group two received sub-conjunctival injection of tobramycin and was asked to wear eye pads on the first day after surgery and then were instructed to use antibiotic eye drops as the first group did. Ocular surface disease index (OSDI) questionnaire, slit-lamp microscope examination of tear break-up time (TBUT), corneal fluorescein score (CFS), tear meniscus height (TMH) together with anterior segment optical coherence tomography (AS-OCT) and corneal topography were evaluated preoperatively and postoperatively.

RESULTS

The subjective feeling (P=0.004), TBUT (P<0.001) and TMH (P=0.02) post-surgery had improved in patients who used bandage contact lenses compared with those who did not at 1wk post-surgery. Until three month postoperatively, the comfort degree (P=0.004) and TMH (P=0.01) of group two were still worse than group one. Moreover, TBUT (P<0.001) and CFS (P=0.004) of the group with eye pads got worse than the results before, whereas the group with bandage contact lenses recovered to normal. None of these patients had infections or other complications.

CONCLUSION

Wearing therapeutic bandage contact lens after cataract surgery, compared with traditional eye-pads, is a safe method to improve tear-film stability and reduce post-operative discomfort without hindering corneal incision recovery.

Can artificial tears prevent Acanthamoeba keratitis? An in vitro approach

BACKGROUND

The use of contact lenses has increased in recent years as has the incidence of Dry Eye Syndrome, partly due to their use. Artificial tears are the most common treatment option. Since these changes can facilitate Acanthamoeba infection, the present study has been designed to evaluate the effect of three artificial tears treatments in the viability of Acanthamoeba genotype T4 trophozoites. Optava Fusion™, Oculotect®, and Artelac® Splash were selected due to their formulation.

METHODS

Viability was assessed using two staining methods, Trypan Blue stain and CTC stain at different time intervals (2, 4, 6, 8 and 24 h). Trypan Blue viability was obtained by manual count with light microscopy while the CTC stain was determined using flow cytometry.

RESULTS

Trypan Blue staining results demonstrated a decrease in viability for Optava Fusion™ and Artelac® Splash during the first 4 h of incubation. After, this effect seems to lose strength. In the case of Oculotect®, complete cell death was observed after 2 h. Using flow cytometry analysis, Optava Fusion™ and Oculotect® exhibited the same effect observed with Trypan Blue staining. However, Artelac® Splash revealed decreasing cell respiratory activity after four hours, with no damage to the cell membrane.

CONCLUSIONS

The present study uses, for the first time, CTC stain analyzed by flow cytometry to establish Acanthamoeba viability demonstrating its usefulness and complementarity with the traditional stain, Trypan Blue. Artelac® Splash, with no preservatives, and Optava Fusion TM, with Purite®, have not shown any useful amoebicidal activity. On the contrary, promising results presented by Ocultect®, with BAK, open up a new possibility for Acanthamoeba keratitis prophylaxis and treatment although in vivo studies should be carried out.

A single vectored thermal pulsation treatment for meibomian gland dysfunction increases mean comfortable contact lens wearing time by approximately 4 hours per day

Purpose

To evaluate the effect of a single vectored thermal pulsation (VTP) treatment in contact lens wearers with meibomian gland dysfunction (MGD) and dry eye symptoms.

Methods

The prospective, nonsignificant risk, open-label, randomized, multi-center clinical trial included 55 soft contact lens (SCL) wearers with MGD and evaporative dry eye. Subjects were randomized to the single VTP treatment group or an untreated control. The controls received a crossover VTP treatment at 3 months (crossover treatment group). Primary effectiveness measures were meibomian gland secretion (MGS) score and Standard Patient Evaluation of Eye Dryness (SPEED) that were evaluated at baseline, at 1 and 3 months post-VTP treatment, and at 1 month post-VTP treatment in the crossover treatment group. Exploratory variables included fluorescein tear break-up time (TBUT), lid wiper epitheliopathy (LWE), lid parallel conjunctival folds (LIPCOF), ocular surface staining, frequency of over-the-counter (OTC) drop use, and hours of comfortable contact lens wear.

Results

At 3 months, the treatment group showed significantly greater mean change from baseline in MGS (12.4±9.1 vs 1.4±6.4, p<0.0001), SPEED (−8.4±4.7 vs −0.7±4.4, p<0.0001) and significantly greater improvement in exploratory variables (TBUT, LWE, and frequency of OTC drop use) relative to the controls. Mean comfortable contact lens wearing time increased by 4.0±3.9 hours at 1 month. This was sustained for 3 months with no change in the control group. The crossover treatment group demonstrated similar results to the treatment group at 1 month post-VTP.

Conclusion

In SCL wearers with MGD, a single VTP treatment significantly improved mean meibomian gland function and significantly reduced dry eye signs and symptoms compared to an untreated control. The treatment increased mean comfortable lens wearing time by 4 hours (approximately doubling the pretreatment findings). This was sustained for up to 3 months post-treatment on average.

Mechanical response of transient telechelic networks with many-part stickers

A central question in soft matter is understanding how several individual, weak bonds act together to produce collective interactions. Here, gel-forming telechelic polymers with multiple stickers at each chain end are studied through Brownian dynamics simulations to understand how collective interaction of the bonds affects mechanical response of the gels. These polymers are modeled as finitely extensible dumbbells using an explicit tau-leap algorithm and the binding energy of these associations was kept constant regardless of the number of stickers. The addition of multiple bonds to the associating ends of telechelic polymers increases or decreases the network relaxation time depending on the relative kinetics of association but increases both shear stress and extensional viscosity. The relationship between the rate of association and the Rouse time of dangling chains results in two different regimes for the equilibrium stress relaxation of associating physical networks. In case I, a dissociated dangling chain is able to fully relax before re-associating to the network, resulting in two characteristic relaxation times and a non-monotonic terminal relaxation time with increasing number of bonds per polymer endgroup. In case II, the dissociated dangling chain is only able to relax a fraction of the way before it re-attaches to the network, and increasing the number of bonds per endgroup monotonically increases the terminal relaxation time. In flow, increasing the number of stickers increases the steady-state shear and extensional viscosities even though the overall bond kinetics and equilibrium constant remain unchanged. Increased dissipation in the simulations is primarily due to higher average chain extension with increasing bond number. These results indicate that toughness and dissipation in physically associating networks can both be increased by breaking single, strong bonds into smaller components.

Optical Assessment of Soft Contact Lens Edge-Thickness

PURPOSE

To assess the edge shape of soft contact lenses using Gabor-Domain Optical Coherence Microscopy (GD-OCM) with a 2-μm imaging resolution in three dimensions and to generate edge-thickness profiles at different distances from the edge tip of soft contact lenses.

METHODS

A high-speed custom-designed GD-OCM system was used to produce 3D images of the edge of an experimental soft contact lens (Bausch + Lomb, Rochester, NY) in four different configurations: in air, submerged into water, submerged into saline with contrast agent, and placed onto the cornea of a porcine eyeball. An algorithm to compute the edge-thickness was developed and applied to cross-sectional images. The proposed algorithm includes the accurate detection of the interfaces between the lens and the environment, and the correction of the refraction error.

RESULTS

The sharply defined edge tip of a soft contact lens was visualized in 3D. Results showed precise thickness measurement of the contact lens edge profile. Fifty cross-sectional image frames for each configuration were used to test the robustness of the algorithm in evaluating the edge-thickness at any distance from the edge tip. The precision of the measurements was less than 0.2 μm.

CONCLUSIONS

The results confirmed the ability of GD-OCM to provide high-definition images of soft contact lens edges. As a nondestructive, precise, and fast metrology tool for soft contact lens measurement, the integration of GD-OCM in the design and manufacturing of contact lenses will be beneficial for further improvement in edge design and quality control. In the clinical perspective, the in vivo evaluation of the lens fitted onto the cornea will advance our understanding of how the edge interacts with the ocular surface. The latter will provide insights into the impact of long-term use of contact lenses on the visual performance.

Dry Eye Treatment Based on Contact Lens Drug Delivery: A Review

Dry eye disease affects a substantial segment of the word population with increasing frequency. It is a multifactorial disease of the ocular surface and tear film, which causes ocular discomfort, visual disturbances, and tear instability with potential damage to the cornea and conjunctiva. Because of its multifactorial etiology, the use of different pharmacological treatment for dry eye treatment has been proposed, which include anti-inflammatory molecules, lubricants or comfort agents, and secretagogues. However, in some cases these pharmacological approaches only relieve symptoms temporarily, and consequently, eye care professionals continue to have difficulties managing dry eye. To improve pharmacological therapy that allows a more efficient and long-term action, effective ocular drug delivery of the currently available drugs for dry eye treatment is required. Contact lenses are emerging as alternative ophthalmic drugs delivery systems that provide an increased residence time of the drug at the eye, thus leading to enhanced bioavailability and more convenient and efficacious therapy. In this article, we reviewed the different techniques used to prepare contact lens-based drug delivery systems and focused on articles that describe the delivery of compounds for dry eye treatment through contact lenses.

Contact Lens-Induced Discomfort and Inflammatory Mediator Changes in Tears

PURPOSE

Studies indicate that contact lens (CL) discontinuation mostly occurs because of dryness and discomfort symptoms. This study aimed to investigate relationships between changes in the concentration of tear inflammatory mediators with subjective comfort ratings with CL wear and no contact lens wear between morning and evening.

METHOD

Forty-five subjects collected tears twice daily in the morning and in the evening with or without lenses. Comfort was rated subjectively on a scale from 1 to 100 (where 100 was extremely comfortable) just before each tear collection. Tear samples were assayed for complement components (C3 and C3a), leukotriene B4 (LTB4), secretory phospholipase A2 (sPLA2), secretory immunoglobulin A (sIgA), and bradykinin using commercially available immuno-based assay kits.

RESULTS

Comfort ratings showed a statistically significant decline from morning to evening both with CL (89.0±10.1 AM vs. 76.7±15.2 PM; P<0.001) and without CL (89.1±10.2 AM vs. 84.2±12.6 PM; P<0.005) wear. The decline was steeper with lens wear (P<0.001). Bradykinin and sPLA2 levels did not change between morning and evening or with CL wear (P>0.05). Leukotriene B4 levels were slightly higher in CL (CL 43.4±12.6 pg/ml vs. No CL 39.4±13.4 pg/mL; P=0.034), whereas the concentration of LTB4, C3, C3a, and sIgA dropped by the end of the day in the presence or absence of lens wear (P<0.001). For most mediators, tear levels were not correlated with comfort ratings in any of the conditions. Leukotriene B4 had a higher concentration in the evening, and when measured as a ratio to sIgA, there was a trend for increased concentration of this mediator during CL wear.

CONCLUSION

Although specific mediators showed changes from morning to evening with and without lens wear, most of these were not correlated with subjective comfort ratings in lens wear. The only mediator that showed an increase in concentration during the day and during lens wear was LTB4, and further studies on this mediator are warranted.

Understanding the Presence and Roles of Ap4A (Diadenosine Tetraphosphate) in the Eye

Diadenosine tetraphosphate abbreviated Ap₄A is a naturally occurring dinucleotide, which is present in most of the ocular fluids. Due to its intrinsic resistance to enzyme degradation compared to mononucleotides, this molecule can exhibit profound actions on ocular tissues, including the ocular surface, ciliary body, trabecular meshwork, and probably the retina. The actions of Ap₄A are mostly carried out by P2Y₂ receptors, but the participation of P2X2 and P2Y₆ in processes such as the regulation of intraocular pressure (IOP), together with the P2Y₂, is pivotal. Beyond the physiological role, this dinucleotide can present on the ocular surface keeping a right production of tear secretion or regulating IOP. It is important to note that exogenous application of Ap₄A to cells or animal models can significantly modify pathophysiological conditions and thus is an attractive therapeutic molecule. The ocular location where Ap₄A actions have not been fully elucidated is in the retina. Although some analogues show interesting actions on pathological situations such as retinal detachment, little is known about the real effect of this dinucleotide, this being one of the challenges that require pursuing in the near future.

Impact of Contact Lens Material, Design, and Fitting on Discomfort

OBJECTIVE

To review the effect of contact lens (CL) material, design, and fitting characteristics on CL discomfort.

METHODS

A PubMed search identified publications describing subjective comfort and CL material, fitting, and design parameters. The review included clinical signs associated with discomfort that may be a consequence of these parameters.

RESULTS

Reduced lens movement or more CL tightness were associated with improved comfort. Increased lens-induced paralimbal conjunctival staining and indentation, considered as quasi-indicators of CL fitting or edge design, were also associated with better comfort. No recent studies have evaluated varying CL design parameters and subjective comfort. Silicone hydrogel CLs are no different in comfort compared with hydrogel CLs. Lower equilibrium water content is associated with improved comfort in hydrogel CL wear. Coefficient of friction shows promise as a material factor potentially associated with comfort. Lid wiper epitheliopathy and lid-parallel conjunctival folds have been linked with comfort in established wearers.

CONCLUSIONS

Recent studies have confirmed the association between more mobile CLs and more discomfort, whereas closer conformity of the CL to the bulbar conjunctiva improved subjective comfort. There is no evidence to support the perceived comfort difference between silicone hydrogel and hydrogel CL. There has been limited progress in understanding the impact of varying specific CL design parameters. Although specific clinical signs may be predictive of discomfort, their role in the natural history of discomfort remains unclear. A better understanding of the relationship between coefficient of friction and comfort and strategies to improve lubricity may hold promise for limiting CL discomfort.