Soft Contact Lens Surface Research Articles

Dynamic Aspects of Pre-Soft Contact Lens Tear Film and Their Relation to Dry Eye: Basic Science and Clinical Relevance.

Soft contact lens (SCL) perturbs the intimate connection between the pre-lens tear film (PLTF) and the ocular surface in various ways, i.e., (i) decrease in tear meniscus radius and aqueous tear thickness, (ii) attenuation of tear film lipid layer spread, (iii) limited wettability of SCL surface, (iv) increased friction with eyelid wiper, etc. This often results in SCL-related dry eye (SCLRDE) manifested as PLTF instability and contact lens discomfort (CLD). In this review, the individual contributions of factors (i-iv) to PLTF breakup patterns (BUP) and CLD are considered via the tear film-oriented diagnosis framework adopted by the Asia Dry Eye Society from a clinical and basic science perspective. It is shown that SCLRDE (due to aqueous deficiency, increased evaporation, or decreased wettability) and BUP of PLTF classify within the same types as the ones observed for the precorneal tear film. The analysis of PLTF dynamics reveals that the inclusion of SCL enhances the manifestation of BUP associated with (i) decreased thickness of PLTF aqueous layer and (ii) limited SCL wettability as shown by the rapid expansion of BUP area. PLTF thinness and instability result in increased blink-related friction and lid wiper epitheliopathy as major contributor to CLD.

New drug delivery system in ophthalmology: results studying the surface structure of soft contact lenses from various polymer

The development of an ophthalmic therapeutic system includes research on the spatial structure of soft contact lens polymers and the study of the processes of saturation and release of medicinal substances from them. This allows you to determine the methods of saturation of contact lenses with medicinal agents and will open up new opportunities in the treatment of ophthalmological diseases. The purpose of this preliminary fragment of large-scale research was to study the surface structure of soft contact lenses made of various polymers. The following polymers were used in the work: Nelfilcon A, Hilafilcon B, Nezofilcon A, Etafilcon A, Lotrafilcon B. The following pharmaceutical substances were used: Brimonidine Tartrate, Betaxolol Hydrochloride, Pyridoxine Hydrochloride. The surface structure of soft contact lenses was studied using atomic force microscopy. Each material under study has a different surface character, which together with the differences in pore properties determines its individuality. Based on this, it should be assumed that the surface of soft contact lenses affects the possibility of their potential use as a means of delivering drug agent molecules to the eye tissues. In all cases of soft contact saturation, the highest absorption capacity was demonstrated by Hilafilcon B and Etafilcon A with a similar surface.

땀에 의한 소프트렌즈의 파라미터 및 표면의 변화양상 분석

땀에 의한 소프트렌즈의 파라미터 및 표면의 변화양상 분석

A polymer-based technique to remove pollutants from soft contact lenses

PurposeTo demonstrate an alternative to the rinse and rub (RR) method for cleaning pollutants from the exterior surface of soft contact lenses. This proposed technique is termed Polymer on Polymer Pollutant Removal (PoPPR), which utilizes the elastic properties of polydimethylsiloxane (PDMS) to physically remove contaminants from contact lens surfaces through non-adhesive unpeeling. MethodsThree different ratios of setting agent to polymer PDMS (1:30, 1:40, and 1:50) were evaluated using the PoPPR method against the control method of RR with a commercial multi-purpose lens cleaning solution. Three simulated pollutants of different sizes: pollen (25−40 μm), microbeads (1−5 μm), and nanoparticles (5−10 nm), were used to test the effectiveness of both cleaning methods. The fraction of pollutants removed from each contact lens was recorded and evaluated for significance. ResultsPDMS 1:40 was found to be the optimal ratio for lens cleaning using the PoPPR method. For larger particles (>10 μm), no difference was observed between conventional RR and proposed PoPPR method (p > 0.05). However, the new PoPPR technique was significantly better at removing small PM2.5 particles (<2.5 μm) compared to the RR method, specifically for microbeads (p = 0.006) and nanoparticles (p < 0.001). ConclusionThis proof-of-concept work demonstrates that the PoPPR method of cleaning contact lenses is as effective as the conventional cleaning method for larger particles such as pollen. The PoPPR method is more effective at removing extremely fine particulate pollutants, including microplastics and nanoparticles. This method offers a potentially more efficient cleaning protocol that could enhance the safety, health, and comfort of contact lens users, especially those living in regions with significant air pollution.

The impact of soft contact lens surface and optics on symptoms associated with digital eye fatigue in symptomatic soft contact lens wearers

Purpose Near work, often on digital devices, now permeates the daily life of individuals of all ages at both work and play. Sustained near work on digital devices has been found to increase symptoms of eye strain. A contact lens which reduces the accommodative demand may help reduce symptoms. The current study compared subjectively reported eye strain, dryness, overall fatigue, and quality of vision of symptomatic subjects while binocularly wearing soft, daily disposable spherical and multifocal contact lenses.

Short-Term Deposition of PM2.5 Particles on Contact Lens Surfaces: Effect on Oxygen Permeability and Refractive Index

ABSTRACTPurposes: To identify the deposition of fine (≤2.5 μm diameter) particulate matter (PM) particles (PM2.5) on contact lens surfaces and to investigate the effects of such deposition on the oxygen permeability (OP) and refractive index (RI) of contact lenses.Methods: A total of 36 contact lenses, including rigid gas permeable (RGP) lens and soft contact lens (SCL), were investigated. RGP lens (n=12) and SCL (n=12) (experimental group) were incubated in a PM2.5 solution for 24 h, after which PM2.5-treated RGP lens (n=6) and SCL (n=6) were further washed for 1 h in phosphate-buffered saline (PBS). All lenses were examined by field emission scanning electron microscopy. OP and RI of all lenses were measured.Results: Average-sized PM2.5 particles deposited on RGP contact lens and SCL surfaces after immersion in the PM2.5 solution were 3.192 ± 1.637 and 2.158 ± 1.187/100 μm2, respectively. On RGP lens surfaces, we observed both large (≥2.5 µm diameter) and small (PM2.5) particles. PM2.5 particles were deposited in diffuse patterns, primarily along the honeycomb structural border of SCL, while no PM2.5 particles were found in the honeycomb hole of SCL surfaces. Washing in PBS removed the larger PM particles from RGP lens surfaces, but left copious amounts of PM2.5 particles. In contrast, nearly all PM particles were removed from SCL surfaces after PBS washing. OP values of RGP lens and SCL appeared to be unchanged by PM2.5 deposition. RI values increased in both RGP lens and SCL groups after PM2.5 deposition. However, these increases were not statistically significant, suggesting that PM2.5 deposition itself does not cause fluctuations in contact lens RI.Conclusions: Deposition of PM2.5 particles on contact lens surfaces varies according to lens material. PM2.5 particles deposited on SCL, but only large particles on RGP surfaces were able to be removed by washing in PBS and did not appear to alter OP and RI of either lens type.

Hydrogel Contact Lens Water Content is Dependent on Tearfilm pH

Based on clinical inferences, investigators theorized in situ soft lens hydration was linked to the precorneal tearfilm pH. Forty-one myopic subjects at Fort Rucker, AL, USA were fitted with one of two types of extended-wear soft contact lenses, and were followed quarterly for a period of 33 mo. The anterior soft contact lens surface pH was measured in situ, while the in vitro lens water content was measured immediately after lens removal, using a hand-held refractometer on one lens, and a gravimetric means of hydration measurement on the other lens. The in situ pH increased logarithmically across extended wearing time, reaching an asymptote at approximately 5 d' wearing time at a pH of 7.45 ± 0.03. Lens water content was shown to similarly decrease at an inversely logarithmic rate, leveling off at 4-5 d' extended wearing time. Both means of hydration assessment correlated well with each other across days' extended wearing time (R = 0.98; p < 0.0001). A log-log dual conversion yielded significantly different linear slopes (p < 0.001), based on a multifactorial analysis of both lens types, by the pH, and by their water content. The differing ionic status of each material accentuated their varied polar attraction characteristics. Two soft lenses, identical in all patient-based parameters, could provide differing oxygen availability, as well as differing physical fits in patients of identical physical characteristics, as a result of their unique tearfilm pH differences. The in situ hydrogel lens water content is directly dependent on the precorneal tearfilm pH.

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.

Biofilm formation of Achromobacter xylosoxidans on contact lens

Achromobacter spp. may contaminate lenses, lens cases, and contact lens solutions and cause ocular infections. The aim of this study was to investigate the possibility of isolated strain of Achromobacter xylosoxidans to form biofilm on the surface of soft contact lenses (CL), to quantify the production of the formed biofilm, and compare it with the reference strains (Pseudomonas aeruginosa, Staphylococcus aureus, and Haemophilus influenzae). Bacterial strain isolated from one contact lens case was identified as A. xylosoxidans using Vitek2 Automated System. Biofilm forming capacity of isolated strain of A. xylosoxidans and reference strains of P. aeruginosa, S. aureus, and H. influenzae on soft CL were analyzed by commonly used microtitre plate method. Our results showed that isolated strain of A. xylosoxidans was capable to form biofilm on the surface of soft contact lens. A. xylosoxidans was strong biofilm producer while all examined reference strains were moderate biofilm producers. A. xylosoxidans appears to be superior biofilm producer on soft CL compared to reference strains.

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.

Soft Contact Lens Surface Profile by Atomic Force Microscopy

This study was designed to qualitatively and quantitatively characterize the surface morphology of four unworn conventional hydrogel contact lenses (omafilcon, hioxifilcon, nelfilcon A, and ocufilcon B) and two silicone-hydrogel contact lenses (senofilcon A and comfilcon A) without surface treatment. Surface roughness was assessed using atomic force microscopy in Tapping Mode to determine the representative roughness parameters mean surface roughness (Ra), mean square roughness (Rms), kurtosis (Rku), and skewness (Rsk). To date, these last two parameters have not been used to characterize contact lens surfaces. Rku provides information on the distribution of spikes above and below the mean line, and Rsk provides information about the asymmetric roughness of surfaces. The surface topography of the lenses was also mapped in detail. In all the lenses, higher Ra and Rms values were obtained when larger surface areas were examined. The daily replacement contact lenses (nelfilcon A and ocufilcon B) showed the highest Ra and Rms values but according to their Rku scores, their surface profiles were less spiky than the remaining lenses. On the contrary, the lowest Ra and Rms values were recorded for comfilcon A and omafilcon A, which also exhibited the spikiest surface profiles. All the materials except the hioxifilcon showed a predominance of peaks (Rsk >0) over troughs. The shape parameters Rku and Rsk are useful for characterizing contact lens surfaces, because they provide different yet complementary information to that offered by Ra and Rms. Precise knowledge of the shape profile of a contact lens surface will give an idea of its susceptibility to deposit formation or colonization by microorganisms.

Adsorption of Actives in Ophthalmological Drugs for Over-The-Counter on Soft Contact Lens Surfaces

The adsorption of various kinds of ionic/nonionic actives, added in ophthalmological drugs (artificial tear, contact lens wetting solution, eye-drops, and eyewash) for over-the-counter (marketable drugs with no need of any medical prescription) , on soft contact lens (SCL) surfaces has been studied as a function of hydrophobicity of the actives. The common logarithm of the 1-octanol/water partitioning coefficient (AC_log P) has been used in order to normalize the hydrophobicity of the actives employed in this study. No significant adsorption occurs for relatively hydrophilic actives, whereas the adsorption rate is gradually increased with an increase in the hydrophobicity of the actives. This suggests that the adsorption is predominantly governed by the hydrophobic interaction of the actives with the SCL surfaces, although an electrostatic interaction plays an additional role for the adsorption. The most effective adsorption occurs in the following active-lens combinations: cationic actives--the anionic and hydrated lens IV (methacrylic acid-based SCL); anionic actives---the nonionic and hydrated lens II (N-vinyl pyrrolidone-based SCL); and nonionic actives--the anionic and less-hydrated lens III (containing hydrophobic silicone monomers).

Correcting anterior corneal aberration and variability of lens movements in keratoconic eyes with back-surface customized soft contact lenses

Customized contact lenses are limited in their correction performance, especially on irregular corneas, owing to decentration and rotation of the lenses. To overcome this limitation, we proposed to customize the back surface of soft contact lenses to match the anterior irregular corneal surface. These lenses were designed to correct anterior corneal aberrations and to improve lens stability. Although in keratoconic eyes the anterior corneal aberrations were effectively corrected, significant residual aberrations were observed. The internal optics, especially the posterior surface of the cornea, was the main source of these residual aberrations. Compared with conventional soft contact lenses, lens stability, on average over three eyes, was improved by a factor of 2 for horizontal and vertical decentrations and a factor of 5 in rotational orientation with the back-surface customized lenses.

Friction studies of hydrogel contact lenses using AFM: non-crosslinked polymers of low friction at the surface

The surface of soft contact lenses made of crosslinked poly(2-hydroxyethyl methacrylate), pHEMA, has been investigated with atomic force microscopy in contact mode. The friction force and adhesive force measurements were able to differentiate the non-crosslinked pHEMA chains from the surface of the crosslinked pHEMA networks. These non-crosslinked pHEMA chains at the surface were anchored to the crosslinked pHEMA network, most likely by entanglement and their surfaces were about 2–4 nm higher than the surrounding surface in a dehydrated state. In saline solution, the surface friction and adhesive force of the contact lens were significantly reduced compared to those measured for the surface-dehydrated contact lens.

Videokeratography for quantitative surface analysis of used soft contact lenses

The greater utilization of soft contact lenses calls for the development of new and objective methods of evaluating the optical performance of the different lens types, in situ. We used videokeratography to examine the surface topography of soft contact lenses that had been worn for more than 1 year on 27 eyes of 23 patients, and compared the resulting color-coded maps and topographic indices as well as contact lens-corrected visual acuities, with those obtained with new replacement lenses on the same eyes. Visual inspection of the color-coded maps revealed differences in the surface characteristics of the used and new lenses. Comparison of quantitative indices including the SAI (Surface Asymmetry Index), IAI (Irregular Astigmatism Index), SRI (Surface Regularity Index), and SDP (Standard Deviation of Powers) showed that asymmetry, surface irregularity, potential visual acuity (derived from the SRI), and corneal power distribution were significantly poorer with the used lenses than with the new ( P = 0.0001). The videokeratoscope is useful for evaluating the soft contact lens surface in situ, as an indicator of optical quality; it also permits the objective evaluation of lens cleaning techniques.

Characterization of lacrymal component accumulation on worn soft contact lens surfaces by atomic force microscopy

The purpose of this study was to investigate lacrymal component accumulation on a soft contact lens (SCL) surface after various periods of continuous wear, using the recently developed atomic force microscopy (AFM). AFM allowed high resolution images of unworn and worn SCL, and presented two main advantages. 1. The SCL are analysed under nearly physiological conditions without being dried or destroyed. So the same SCL was analysed at various times during a long wearing period. To identify the deposited tear proteins, a qualitative analysis of solubilized deposit by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) on 4–15% gradient minigels was performed as well. We present typical images which emphasize the importance of the coating by lacrymal components. AFM analysis of worn SCL showed the deposition on the surfaces of a uniform lacrymal component coating (named deposit type I) with a progressive accumulation of numerous discrete granules (named deposit type II). SDS-PAGE of extracted deposits revealed the main tear proteins as: IgA, lactoferrin, tear lipocalin and lysozyme and the unknown protein of molecular weight 30,000. There is no clear difference in the protein patterns of the two types of deposits. Furthermore, a particular mode of use of AFM is described to illustrate the potential of this technique as a local tool for measuring protein coating thickness. Thus, for analysis of protein deposits on SCL surfaces, SDS-PAGE on minigels and AFM were easy and rapid to perform. When associated, these two techniques could find use in a wide range of worn SCL evaluation and most generally in biocompatibility evaluation studies.

Topographic Evaluation of Toric Soft Contact Lens Correction

The anterior surface of the eye provides the greatest refracting surface to the optical system of the eye because of the large difference in refractive index between air and tissue. When a contact lens is placed on the eye, its anterior surface becomes the greatest refracting surface. Toric soft contact lenses have been designed to neutralize ocular astigmatism. We observed that topographic analysis of toric soft contact lenses on an astigmatic eye demonstrated residual astigmatism on the anterior surface of soft toric contact lenses. In this paper we show toric soft contact lens surface astigmatism by videokeratoscopy and interpret the origins of the astigmatism.

Contact lens surface deposits increase the adhesion of Pseudomonas aeruginosa

Soft contact lenses are bathed with tear components during wear and surface deposits accumulate. This report shows that Pseudomonas aeruginosa adheres to the surface of worn extended wear contact lenses in direct proportion to the amount of lens surface deposits as determined by the Rudko method (P less than .05). More hydrophobic bacteria adhered 10 times greater than bacteria which were relatively hydrophilic (P less than .005). The effect upon bacterial adhesion of enzyme and surfactant cleaning of worn extended wear contact lenses was investigated by two independent methods: one involving a high inoculum and the other a low inoculum of Pseudomonas. Treatment of worn lenses with commercially available enzymes such as papain and pork pancreatin as well as treatment with neuraminidase, mannosidase, glucosidase and alkylcarboxylic acid for as long as 48 hours failed to reduce subsequent bacterial adhesion in both the high and low inoculum experiments. We conclude that soft contact lens surface deposits are a major determinant in the adhesion of Pseudomonas aeruginosa to the worn lens surface and that enzyme cleaning of worn lenses does not significantly reduce bacterial adhesion.

The contribution of bacterial surface hydrophobicity to the process of adherence ofPseudomonas aeruginosato hydrophilic contact lenses

Ten isolates of Pseudomonas aeruginosa obtained from the corneas of patients with Pseudomonas keratitis adhered to soft contact lenses in significantly greater numbers than did six isolates from other body sites (P less than .05). However, there was no predominant serotype among the 10 corneal isolates tested. Isolates grown statically in broth at 37 degrees C formed a pellicle and adhered two times as much to contact lenses as did isolates grown in broth while shaking which did not form a pellicle (P less than .01). The more adherent isolates (grown at 37 degrees C) were shown to be more hydrophobic than the less adherent bacteria (grown at 26 degrees C) by their propensity to accumulate at the interface between hexadecane and saline and their movement into polyethylene glycol from dextran. These corneal isolates agglutinated erythrocytes, a process that was inhibited by dilute solutions (as low as 0.01%) of three commonly used surfactants. These same surfactants inhibited the adherence of Pseudomonas aeruginosa to soft contact lens surfaces by as much as 52%. It is concluded that hydrophobic interactions may significantly contribute to the ability of Pseudomonas aeruginosa to adhere to contact lenses.

Protein adsorption on hydrogels: II. Reversible and irreversible interactions between lysozyme and soft contact lens surfaces

Lysozyme was adsorbed on spin cast and lathe cut soft contact lenses of poly-2-hydroxyethylmethacrylate (PHEMA) and on poly-HEMA-methacrylic acid (PHEMA/MAA). The in vitro adsorption process was followed by ATR-FTIR. Lysozyme adsorbs both, reversibly and irreversibly, on the surfaces. While the reversible bound lysozyme experiences only minor changes in its secondary structure, conformational changes occur for the irreversibly adsorbed protein. The type and extent of structural changes depend on the degree of protein coverage on the lens surface, as well as the chemical structure and surface morphology of the lenses. PHEMA/MAA lenses adsorbed thirty times more lysozyme than either of the PHEMA lenses. Fabrication processes appear to induce different adsorption behaviour, PHEMA lathe cut lenses adsorb twice the amount of protein compared with PHEMA spin cast lenses.