Lens Surface Wettability Research Articles

Videokeratoscopic assessment of silicone hydrogel contact lens wettability using a new in-vitro method

PurposeThe aim of the study was to assess the surface wettability of new-generation silicone hydrogel (SiH) contact lenses (CLs) videokeratoscopically using a new in-vitro method under office conditions. MethodVideokeratoscopic methodology was used to compare time-dependent CL wettability on an in-vitro cornea model. The model cornea was a polished chrome surface coating a Teflon form. It was prepared with a base curve of 8.7 mm and a diameter of 15 mm. Laboratory temperature and humidity were controlled. Before and after placing CLs on the on the model cornea, Bausch + Lomb Biotrue® multi-purpose solution (MPS) was dropped to simulate the pre-lens and post-lens film layer. Fanfilcon A, Senofilcon A, Samfilcon A, and Lotrafilcon B CLs with -3.00D were used, and images were taken with the videokeratoscopic method for testing. In the control group, the same procedure was performed without placing CLs. The images of CLs at 0, 60, 90, 120, 150, and 180 s were taken. Distortions and gaps seen in rings were recorded. The areas in rings were calculated in pixels using İmageJ. ResultsWhen CLs were examined, statistical differences were found among average pixel values (p < 0,001). The average pixel value was 131877.4 in the Samfilcon group, 116125.5 in the Senofilcon group, 137893.2 in the Fanfilcon group, 125578.3 in the Lotrafilcon group, and 124984.6 in the control group. No difference was found between the average values of the Lotrafilcon group and the control group. Differences were found between the average values of all other groups. DiscussionThe results obtained showed that videokeratoscopy was an effective method for in-vitro testing of CL wettability. It was found that SiH lenses displayed different performance under office conditions depending on materials and technologies used for wetting the lens surface. It was shown that lens surface wettability could be measured with a repeatable and new method when the factors affecting surface wetness and image quality were ruled out.

Development of Silicone Hydrogel Antimicrobial Contact Lenses with Mel4 Peptide Coating.

This study investigated the development of an antimicrobial coating on silicone hydrogel contact lenses that may have the capacity to reduce contact lens-related infection and inflammatory events. The purpose of this study was to develop an effective antimicrobial coating for silicone hydrogel contact lenses by attachment of Mel4 peptide. Lotrafilcon A, comfilcon A, somofilcon A, senofilcon A, and lotrafilcon B silicone hydrogel contact lenses were plasma coated with acrylic acid followed by Mel4 antimicrobial peptide immobilization by covalent coupling. Peptide immobilization was quantified by x-ray electron spectroscopy. Contact lens diameter, base curve, center thickness, and lens surface wettability were measured by captive-bubble contact-angle technique. Antimicrobial activity of the lenses was determined against Pseudomonas aeruginosa and Staphylococcus aureus by viable plate count and also after soaking with artificial tears solution for 1 day. In vivo safety and biocompatibility were determined in an animal model for 1 week. Mel4 peptide-coated silicone hydrogel contact lenses were associated with high antimicrobial inhibition (>2 log), except for lotrafilcon B and senofilcon A. Lotrafilcon B did not exhibit any activity, whereas senofilcon A showed 1.4- and 0.7-log inhibition against P. aeruginosa and S. aureus, respectively. X-ray electron spectroscopy revealed significant increases in the lens surface-bound amide nitrogen in all contact lenses except for lotrafilcon B. All contact lens parameters remained unchanged except for the base curve and center thickness for senofilcon A. Mel4 immobilization was associated with a decrease in contact angle. Mel4-coated contact lens wear was not associated with any signs or symptoms of ocular irritation in a rabbit model study. Reduced antimicrobial activity was observed with all the lenses after soaking with artificial tears solution or rabbit wear. Mel4 antimicrobial coating may be an effective option for development of antimicrobial silicone hydrogel contact lenses.

The Berkeley Dry Eye Flow Chart: A fast, functional screening instrument for contact lens-induced dryness.

PurposeIn this article, we introduce a novel flow chart-based screening tool for the categorization of contact lens-induced dryness (CLIDE) and its impact on daily visual activities: the Berkeley Dry Eye Flow Chart (DEFC).MethodsOne hundred thirty (130) experienced soft contact lens wearers discontinued lens wear for 24 hrs, passed a baseline screening and eye health examination, completed the Ocular Surface Disease Index (OSDI) then were dispensed fresh pairs of their habitual lenses. After 6 hrs of wear, subjects were administered a battery of symptom questionnaires, and underwent non–invasive tear breakup time (NITBUT) measurement, grading of distortion in reflected topographer mires, grading of lens surface wettability, and a fluorescein examination of the ocular surface. Subjects returned after at least 48 hrs and repeated all assessments after 6 hrs of wear of a second fresh pair of habitual lenses.ResultsThe repeatability of the DEFC between visits was within 1%, and Limits of Agreement and Coefficient of Repeatability were comparable to those of the other CLIDE assessments. Higher DEFC score was significantly related to shorter pre-lens NITBUT, higher OSDI score, and higher Visual Analog Scale (VAS) ratings of average and end-of-day severity and frequency of dryness (all p < 0.001). For CLIDE as diagnosed based on DEFC score, the highest sensitivities and specificities were achieved by the OSDI and VAS ratings; pre-lens NITBUT exhibited good sensitivity but poor specificity. The optimum pre-lens NITBUT diagnostic threshold was found to be ≤ 2.0 sec for debilitating CLIDE, and the OSDI threshold was ≥ 11.4.ConclusionsThe DEFC provides a means of quickly categorizing CLIDE patients based on severity and frequency of symptoms, and on the degree to which symptoms impact daily life. The DEFC has several potential advantages as a CLIDE screening and monitoring tool, has good repeatability, and is significantly related to commonly employed clinical assessments for CLIDE.

Effects of Lens-Care Solutions on Hydrogel Lens Performance.

Lens care multipurpose solutions (MPSs) can have varying effects on contact lens (CL) surface properties and the corneal epithelium. The aim of this study was to investigate the short-term effects of newer MPS on CL comfort and dryness, prelens tear-film stability, and ocular-surface health. In vitro study was also performed to assess the effect of MPSs on CL surface properties. Acuvue 2 CLs were soaked in control solution, Clear Care (CC), or test solutions: PureMoist, Biotrue, RevitaLens (RL), or saline solution (SS). Over four visits, subjects were exposed to control solution in one eye and to test solution in the contralateral eye for 2 hours using presoaked CLs. Contact lens comfort and dryness, ocular-surface health assessment, prelens noninvasive tear breakup time, and corneal epithelial permeability measured with fluorometry were assessed. Captive-sessile bubble technique evaluated CL wettability and viscous drag in vitro. At 10 minutes, mean comfort ± SD with PureMoist (76 ± 22) was lower than CC (86 ± 15, P = .02), Biotrue (92 ± 9, P < .005), RL (90 ± 13, P < .005), and SS (90 ± 14, P < .005). No other difference in comfort or dryness was noted. RevitaLens was associated with greater corneal epithelial permeability than CC (P = .020) and increased corneal staining compared with all MPSs (P < .005 for all). RevitaLens was also associated with longer prelens noninvasive tear breakup than CC (P < .005). In vitro results agreed with clinical findings of tear-film stability as RL reduced viscous drag. Contact lens surface wettability was enhanced by all MPSs in comparison to SS. Differences of MPSs on the ocular surface were found in vivo and in vitro. RL caused the greatest corneal epithelium disruption but also associated with higher tear-film stability. The effect of MPSs on CL surface properties in vitro seems to reflect how MPSs altered prelens tear stability.

Effect of contact lens surface properties on comfort, tear stability and ocular physiology.

Retrospective analysis of different contact lens wearing groups suggests lens surface lubricity is the main factor influencing contact lens comfort. However, the examined commercially available contact lenses differ in material and design as well as surface properties. Hence this study isolates the contribution of lens surface properties using an ultra-thin coating technology. Nineteen habitual contact lens wearers (21.6±1.7years) wore formofilcon B soft monthly disposable contact lenses with and without coating technology modified surface properties for a month each in a randomised double-masked cross-over study. OBJECTIVE NON-INVASIVE: breakup time (NIKBUT), NIKBUT average and ocular redness (Jenvis grading scale) were evaluated (Keratograph 5M) after 1 week and 1 month of wear. Symptoms were assessed using the Contact Lens Dry Eye Questionnaire (CLDEQ-8); perceived vision quality and subjective lens comfort at insertion, mid-day and end of the day were rated with four Visual Analog Scales. Perceived visual quality (F=5.049,p=0.037), contact lens dry eye symptoms (F=14.408,p=0.001) and subjective lens comfort (F=28.447,p<0.001) were better for coated compared to uncoated lenses. The surface coating postponed the lens dewetting (F=8.518,p=0.009) and increased the pre-lens tear film stability (F=5.626,p=0.029), but bulbar (F=0.340,p=0.567) and limbal (F=0.110,p=0.744) redness were similar for both contact lenses. No parameter changed significantly between a weeks' and months' wear (p>0.05). Lens surface wettability and ocular redness were not correlated to changes in symptoms (p>0.05). As previously hypothesised, enhancing the physical surface properties of a soft contact lens improves subjectively rated wearer comfort, which, in turn, should result in reduced contact lens discontinuation.

Assessment of pre-lens tear film particle velocity measurements in participants wearing daily disposable silicone hydrogel lenses

Purpose: Themeasurement of the free upward flow of particles that occur naturally in the tear-film is an in-vivo and non-invasive way to assess tear-film spread and stability after a blink, where faster movement suggests enhanced contact lens surface wettability. Method: In a double-masked, randomized, contralateral-eye design, 40 videos from 20 participants wearing stenfilcon A (SA; CooperVision) in one eye and delefilcon A (DA; Alcon) in the other for at least six-hours were analyzed. Tear-film spread over the lens surface was imaged in the morning, approximately five minutes post lens-insertion, and again after six hours of lens wear. Using a customized calibrated ImageJmacro, the upward particle velocities (UPV) of multiple reflective particles from each video were determined and averaged. The UPV is reported as Mean± SD (mm/s). Wilcoxon matched-pairs signed-ranks test was used to compare the average UPV between the two lenses at each time-point. Results: Themean participant agewas 31.9±12.3 years (19–60 years). The SA lens exhibited greater UPV than the DA lens postinsertion (2.50±0.98 vs 2.16±0.70; p=0.035). After six hours of lenswear therewere no differences in UPV between the lenses (SA: 2.23±0.58 vs DA: 2.12±0.52; p=0.218). There was a strong correlation between the post-insertion UPV of both lenses (Spearman’s rho correlation coefficient =0.83). The average UPV measurement period, across all observations, was 1.45 s, with no difference between SA and DA lenses (p=0.191). Conclusions: The higher UPV of the SA lens post-insertion is suggestive of enhanced lens surface wetting immediately following insertion. However, there was no statistical difference when UPV was measured after six hours of lens wear. The link between comfort and UPV is worthy of further study. Jalaiah Varikooty is a Clinical Scientist at the Centre for Contact Lens Research, School of Optometry and Vision Science, University of Waterloo. His research interests focus on the tear film and the ocular surface. He is currently developing novel methods to objectively measure interactions between contact lens wettability, the tear-film, ocular surface signs, and ocular discomfort.

Clinical evaluation of a new multi-purpose disinfecting solution in symptomatic wearers of silicone hydrogel contact lenses

Correspondence: Renee Garofalo Alcon Research Ltd, 6201 South Freeway, TC-44, Fort Worth, TX 76134, USA Tel +1 817 615 2712 Fax +1 817 615 4602 Email renee.garofalo@alconlabs.com Background: The purpose of this study was to evaluate the safety and efficacy of a new multi-purpose disinfecting solution containing a diblock copolymer, poly(oxyethylene)poly(oxybutylene), designed to improve the wetting properties of silicone hydrogel lenses in patients with symptoms of discomfort. Methods: This 30-day, randomized, concurrently controlled, double-masked, multi-site study involved 589 subjects at 42 investigational sites in the US. Existing symptomatic lens wearers were randomly assigned to either regimen 1 (OPTI-FREE PureMoist, Alcon Laboratories Inc,) a newly developed formulation containing the diblock copolymer), or regimen 2 (renu freshTM multi-purpose solution Bausch + Lomb, Inc). On days 0, 14 and 30, subjects assessed acceptability and comfort using seven Likert-type questions, rated the intensity of ocular symptoms (comfort, dryness, irritation, scratchiness, burning, stinging) on a visual analog scale (0–100), as well as reported lens wearing time, comfortable lens wearing time, and rewetting drop frequency. The investigators assessed slitlamp findings (including circumlimbal conjunctival lissamine green staining and corneal fluorescein staining), on-eye lens surface wettability and deposits, visual acuity, and adverse events. Results: Differences favoring regimen 1 were noted on Day 30 for the primary Likert statement “I can comfortably wear my lenses” (P = 0.047) and for comfortable lens wear time (P = 0.041). Symptoms of ocular scratchiness, ocular burning, and ocular stinging were all rated lower after 30 days of use by subjects using regimen 1 compared with those using regimen 2 (P # 0.024). Circumlimbal conjunctival staining (sum score) was significantly lower with regimen 1 (P , 0.0001). Other parameters did not show any difference between the two treatment regimens. Conclusion: This study shows that the new multi-purpose disinfecting solution is safe and effective when used by symptomatic silicone hydrogel contact lens wearers. By improving symptoms of scratchiness, burning, stinging, and comfortable wear time, and decreasing circumlimbal conjunctival staining, the new multi-purpose disinfecting solution enhances the patient’s wearing experience and helps maintain optimal lens performance.

Wettability conundrum: Discrepancies of soft contact lens performance in vitro and in vivo

The recognition and appreciation of soft contact lenses as simple, efficient and aesthetically gratifying vision-correction devices is ever growing, especially among younger population. Stable thin tear film uniformly spread over corrective lens surface is essential for acute vision, and also for comfortable and safe contact lens wear. The significant efforts have been invested by the contact lens industry to develop soft lens surface that is completely wet by tear aqueous in the ocular environment. Number of the publications dedicated to the wettability properties of the soft hydrogel lenses is on the steady rise. However, the clinical results show that no unambiguous correlation emerges when lens surface wettability in vitro is judged against tear film stability evaluated in vivo. This paper assesses and compares the modern techniques used for evaluation of soft contact lens surface wettability and reports some findings regarding relations between lens surface wettability in vitro and in vivo.

Contact Lenses Wettability In Vitro: Effect of Surface-Active Ingredients

To investigate the release of surface-active agents (surfactants) from unworn soft contact lenses (SCLs) and their influence on the lens surface wettability in vitro. Surface tension (ST) of blister pack solutions was measured by pendant-drop technique. STs at the air-aqueous interface and contact angles (CAs) of four conventional and seven silicone hydrogel SCLs were evaluated in a dynamic-cycling regime using a modified captive-bubble tensiometer-goniometer. Measurements were performed immediately after removal from blister packs, and after soaking in a glass vial filled with a surfactant-free solution, which was replaced daily for 1 week. Lens surface wettability was expressed as adhesion energy according to Young equation. STs of all blister pack solutions were lower than the reference ST of pure water (72.5 mN/m), indicating the presence of surfactants. When lenses were depleted of surfactants by soaking, the STs for all studied lenses and advancing CAs of selected lenses increased (p < 0.001). Receding CAs of all studied lenses were 12 degrees +/- 5 degrees and were not affected by the presence of surfactants. For most of the conventional lenses, the surface wettability was largely dependent on surfactants, and reduced significantly after surfactant depletion. In contrast, most silicone hydrogel lenses exhibited stable and self-sustained surface wettability in vitro. The manufacturer-added surfactants affected wetting properties of all studied SCLs, although to different degrees.

Role of hypo-osmotic saline drops in ocular comfort during contact lens wear

To determine whether hypo-osmotic saline drops can improve contact lens associated discomfort and dryness by decreasing contact lens osmolality. Fifteen symptomatic subjects wore Lotrafilcon A lenses bilaterally for 6h on two different days. According to randomisation, hypo-osmotic (280mmol/kg) or hyper-osmotic (380mmol/kg) saline drops were applied four times during each day and ocular symptoms, tear film and contact lens parameters, and contact lens osmolality were assessed. Sixty percent of the subjects preferred the hypo-osmotic saline drops, compared to 33%, who preferred the hyper-osmotic ones. Subjects experienced significantly less dryness and lens awareness with hypo-osmotic saline drops compared to hyper-osmotic ones (p<0.05). Using the hypo-osmotic drops, there was a trend for decreased contact lens osmolality from 379 to 343mmol/kg (p=0.06). There were no differences in lipid layer, non-invasive tear film break-up time, lens surface wettability, lens water content after wear, lens movement on eye or ocular staining and indentation between saline drops (all p>0.05). Interestingly, the difference in contact lens osmolality between drops did not reflect the osmolality difference between the two saline drops. Hypo-osmotic saline drops were preferred by a greater number of subjects and contact lens osmolality tended to be lower with the use of hypo-osmotic saline. Hypo-osmotic drops have the potential to decrease contact lens osmolality which in turn may help improve ocular comfort. This has possible impact on the practitioners' choice of the lens rewetting drop recommended and the design of future lens rewetting drops.

Dynamic wettability of pHEMA‐based hydrogel contact lenses

Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film.