The effect of lens wear on refractive index of conventional hydrogel and silicone-hydrogel contact lenses: a comparative study

Purpose: The purpose of this work was to evaluate the ability of four silicone-hydrogel contact lenses (galyfilcon A, balafilcon A, lotrafilcon A and lotrafilcon B) to retain their equilibrium water content before and after wear, through measurements of refractive index and compare with that of a conventional disposable hydrogel contact lens (etafilcon A). Methods: The refractive indices of 115 contact lenses were measured using an automated refractometer (CLR 12-70, Index Instruments, Cambridge, U.K.) before and after a schedule of daily wear by 58 patients for 30 days in the case of silicone-hydrogel lenses and 15 days for the conventional contact lenses. Results: In the silicone-hydrogel contact lenses the changes on the refractive indices were not statistically significant, however after being worn the refractive index of the conventional etalfilcon A hydrogel contact lens increased significantly ( p < 0.001). Conclusion: The results presented here show that after being worn the silicone-hydrogel contact lens, show more capacity to retain or to reach their initial equilibrium water content than conventional hydrogel contact lenses. This suggests that the silicone-hydrogel contact lenses are less susceptible to spoilation over time maintaining its biocompatibility and contributing to the clinical success of lens performance.Vision and Johnson & Johnson.Bausch & Lom

Qualitative and quantitative characterization of the in vitro dehydration process of hydrogel contact lenses

PURPOSE: To investigate the in vitro dehydration process of conventional hydrogel and silicone-hydrogel contact lens materials. METHODS: Eight conventional hydrogel and five silicone-hydrogel contact lenses were dehydrated under controlled environmental conditions on an analytical balance. Data were taken at 1-min intervals and dehydration curves of cumulative dehydration (CD), valid dehydration (VD), and dehydration rate (DR) were obtained. Several quantitative descriptors of the dehydration process were obtained by further processing of the information. RESULTS: Duration of phase I (r(2) = 0.921), CD at end of phase I (r(2) = 0.971), time to achieve a DR of -1%/min (r(2) = 0.946) were strongly correlated with equilibrium water content (EWC) of the materials. For each individual sample, the VD at different time intervals can be accurately determined using a 2nd order regression equation (r(2) > 0.99 for all samples). The first 5 min of the dehydration process show a relatively uniform average CD of about -1.5%/min. After that, there was a trend towards higher average CD for the following 15 min as the EWC of the material increases (r(2) = 0.701). As a consequence, average VD for the first 5 min displayed a negative correlation with EWC (r(2) = 0.835), and a trend towards uniformization among CL materials for the following periods (r(2) = 0.014). Overall, silicone-hydrogel materials display a lower dehydration, but this seems to be primarily due to their lower EWC. CONCLUSIONS: DR curves under the conditions of the present study can be described as a three-phase process. Phase I consists of a relatively uniform DR with a duration that ranges from 10 to almost 60 min and is strongly correlated with the EWC of the polymer as it is the CD during this phase. Overall, HEMA-based hydrogels dehydrate to a greater extent and faster than silicone-hydrogel materials. There are differences in water retention between lenses of similar water content and thickness that should be further investigated

Impact of contact lenses on environment

Dissertação de mestrado em Genética MolecularAs lentes de contato (LC) são mais populares do que nunca e, com o aumento da prevalência da miopia e dos números de pessoas com presbiopia, espera-se que o número de utilizadores aumente. E, por questões de conveniência e de higiene, as lentes de contato descartáveis (LCD) tornam-se a primeira escolha, estando disponíveis para diferentes modalidades de uso. No entanto, estas podem ter um impacto ambiental adverso resultante da necessidade de descartar muitas lentes e as suas embalagens. Como não existem estudos que mostram se as LC têm impacto ambiental, este estudo tem como objetivo avaliar se os microrganismos conseguem degradar/deteriorar o material das LC. Foram selecionados seis fungos unicelulares (Pichia orientalis, P. fermentans, Candida humilis, C. intermedia, C. tropicalis e Wickerhamomyces anomalus), duas bactérias (Bacillus megaterium e Brucella melitensis) e três hifomicetes aquáticos (Articulospora tetracladia, Tricladium splendans e Varicosporium elodea) para incubar com os materiais de LC Nesofilcon A (Bausch & Lomb) e Senofilcon A (Johnson & Johnson) por um período desde 40 horas a 8 meses. O impacto da presença do material das LC no crescimento de leveduras, bactérias e hifomicetes aquáticos foi avaliado e os resultados indicaram que a sua presença não afetou significativamente o crescimento. Além disso, ao final do período de incubação com leveduras (40 h), o índice de refração das LC (IR) e o conteúdo em água (CA) não se alterou quando comparados com as lentes novas. A integridade da LC após as incubações com leveduras e bactérias permaneceu intacta, porém, após 8 meses na presença de hifomicetes aquáticos, as LC apresentaram roturas na sua superfície. Para avaliar o impacto da LC no meio ambiente, a LC foi colocada no solo e num extrato do solo e o IR e o CA também foram analisados após 1, 2, 4, 6 e 8 semanas. Os resultados indicaram que os valores de IR e CA não mudaram significativamente ao longo das semanas nas duas condições testadas. As análises aos materiais das LC com Microscopia de Força Atómica (AFM) e com Espectroscopia de Infravermelho com Transformada de Fourier acoplada a um acessório de refletância total atenuada (FTIR-ATR) incubadas por 6 e 8 semanas nestas condições indicam que há um aumento na rugosidade das LC, no entanto, não há alterações na composição polimérica das lentes. Estas LC foram incubadas com bactérias e testadas quanto à sua resistência ao estiramento. Os resultados mostram que a percentagem de alongamento até quebra da LC Senofilcon A piorou em todas as condições, mas o mesmo não foi observado para LC Nesofilcon A. Concluiu-se que as LC não afetam o crescimento de leveduras, bactérias e hifomicetes aquáticos. Após inseridas durante 8 semanas no solo ou no extrato do solo não parecem degradar-se ou deteriorar-se significativamente. No entanto, a lente Senofilcon A, composta por Silicone-Hidrogel (SiHi), começou a apresentar um sinal de deterioração, o que sugere que esta LC pode contribuir para o aumento dos microplásticos no meio ambiente. Considerando que o número esperado de utilizadores de LC aumentará, particularmente as LCD diárias, as LC que terminarem nos rios ou nos aterros sanitários devem ser consideradas um problema ambiental.Contact lenses (CL) are more popular than ever and with the increase in the prevalence of myopia and people with presbyopia, it is expected that the number of users will increase. The convenience and hygiene issues make disposable contact lenses (DCL) the first choice as they are available for different wearing modalities. However, they can have a high adverse environmental impact resulting from the need to discard many lenses and their packaging. Since there aren’t studies that show if CL have an environmental impact, this study aims to evaluate if microorganisms can degrade/deteriorate CL materials. Six unicellular fungi were selected (Pichia orientalis, P. fermentans, Candida humilis, C. intermedia, C. tropicalis, and Wickerhamomyces anomalus), two bacteria (Bacillus megaterium and Brucella melitensis), and three aquatic hyphomycetes (Articulospora tetracladia, Tricladium splendans, and Varicosporium elodea) to incubate with the Nesofilcon A (Bausch&Lomb) and Senofilcon A (Johnson&Johnson) CL for a period from 40 hours to 8 months. The impact of the presence of the CL material on yeast, bacteria and aquatic hyphomycete growth was evaluated and results indicated that their presence didn’t significantly affect their growth. Also, at the end of the incubation with yeast (40 h), the CL refractive index (RI) and water content (WC) didn’tt change when compared with the new lens. The CL integrity after the incubations with yeast and bacteria remains intact, however, after 8 months in the presence of aquatic hyphomycetes, the CL presented breaks at their surface. To evaluate the impact of CL on the environment, CL were placed in soil and in a soil extract and RI and WC were analyzed after 1, 2, 4, 6 and 8 weeks. Results indicated that the RI and WC values didn’t change significantly over the weeks in both conditions tested. Analyzes of CL materials with Atomic Force Microscopy (AFM) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) incubated for 6 and 8 weeks in those conditions indicate that there is an increase in CL roughness, however, there are no changes in the polymeric composition of the CL. These CL and CL incubated with bacteria were tested for their resistance to stretch and the results show that there is an impairment of Senofilcon A in all conditions but the same was not observed for Nesofilcon A. We concluded that CL do not affect yeast, bacteria and aquatic hyphomycetes growth. After inserted during 8 weeks in soil or soil extract doesn’t seem to significantly degrade or deteriorate CL. However, Senofilcon A CL, composed of silicone-Hydrogel (SiHy), began to present a sign of deterioration, which suggests that this monthly DCL may contribute to the enhancement of microplastics in the environment. Considering that the expected number of CL users will increase, particularly the daily DCL, CL ending in the rivers or in the land field should be considered an environmental problem

The influence of surface treatment on hydrophobicity, protein adsorption and microbial colonisation of silicone hydrogel contact lenses

Purpose: To evaluate the influence of surface treatment of silicone-hydrogel CL on lens hydrophobicity, protein adsorption and microbial colonisation by studying several silicone hydrogel contact lenses (CL) with and without surface treatment. The lenses used in this study were Balafilcon A, Lotrafilcon A, Lotrafilcon B and Galyfilcon A. A conventional hydrogel CL (Etafilcon A) was also tested. Methods: Hydrophobicity was determined through contact angle measurement using the advancing type technique on air. The type and quantity of proteins adsorbed were assessed through SDS-PAGE and fluorescence spectroscopy, respectively. Microbial colonisation was studied by removing the microbes from the lenses through sonication, and counting the colony-forming units on agar plates. Results: Regarding hydrophobicity, both surface and non-surface-treated silicone hydrogel CL were found to be hydrophobic, and the conventional hydrogel CL was found to be hydrophilic. Concerning protein adsorption, different protein profiles were observed on the several lenses tested. Nevertheless, the presence of proteins with the same molecular weight as lysozyme and lactoferrin was common to all lenses, which is probably related to their abundance in tears. In terms of total protein adsorption, silicone hydrogel CL did not exhibit any differences between themselves. However, the conventional hydrogel Etafilcon A adsorbed a larger amount of proteins. Regarding microbial colonisation, Balafilcon A exhibited the greatest amount of colonising microbes, which can be due to its superior hydrophobicity and higher electron acceptor capacity. Conclusion: This study suggests that silicone hydrogel lenses adsorb a lower amount of proteins than the conventional hydrogel lenses and that this phenomenon is independent of the presence of surface treatment. Concerning microbial colonisation, the surface treated Balafilcon A, exhibited a greater propensity, a fact that may compromise the lens wearer’s ocular health.Fundação para a Ciência e a Tecnologia (FCT

Multi-site clinical assessment of Complete Revitalens MPDS in 2981 contact lens wearers across Europe and USA

(MPDS), Complete Revitalens (RevitaLens OcuTec in the US Market), for soft contact lens care in a large “real practice” setting. Method: This is an international multi-center, open-label assessment carried out in 10 countries across Europe and in the USA. Up to 10 subjects who were currently wearing soft contact lenses for at least 1 year and using a MPS as a lens care system were included at each investigational site. Results: Data were collected from 996 European and 1985 American wearers, 75% of those patients wore silicone hydrogel contact lenses. Approximately 94% found the new MPDS “somewhat more effective” to “much more effective” in keeping contact lenses feeling clean and 88% found the new MPDS to be somewhat more effective to much more effective in keeping their lenses feeling comfortable in the evening. Over 93% reported an improvement in vision clearness in the evening after approximately 1 month while using the new MPDS. Wearers with grade 2, 3 or 4 of severity decreased by 11.3, 6.4 and 9.8% over 1 month period for redness, burning and irritation, respectively. After approximately 1 month 83% of wearers declared that they would prefer to use the new MPDS. Conclusions: Over 88% felt their lenses were somewhat to much more comfortable at the end-of-day and 94% found the new MPDS to be somewhat to much more effective in keeping their lenses feeling clean compared to their previous care system.The authors wish to thank the eye care practitioners participating in this study across Europe and USA. The D'Ellis Group for the statistical support and Rafael Guerrero and Will Heydorn from Abbott Medical Optics, Inc. for their contributions in planning and coordinating the European and American branches of the study, respectively. The authors declare no proprietary or financial interest in any of the materials mentioned in this article. This study has been sponsored by Abbott Medical Optics Inc. These results were presented to the American Academy of Optometry Boston, 12-15th, 2011

Objective analysis of contact lens fit

Purpose: To assess the validity and repeatability of objective compared to subjective contact lens fit analysis. Methods: Thirty-five subjects (aged 22.0. ±. 3.0 years) wore two different soft contact lens designs. Four lens fit variables: centration, horizontal lag, post-blink movement in up-gaze and push-up recovery speed were assessed subjectively (four observers) and objectively from slit-lamp biomicroscopy captured images and video. The analysis was repeated a week later. Results: The average of the four experienced observers was compared to objective measures, but centration, movement on blink, lag and push-up recovery speed all varied significantly between them (p 0.05). The 95% confidence interval of subjective repeatability was better than objective assessment (±0.128. mm versus ±0.168. mm, p = 0.417), but utilised only 78% of the objective range. Vertical centration assessed objectively showed a slight inferior decentration (0.371. ±. 0.381. mm) with good inter- and intrasession repeatability (p > 0.05). Movement-on-blink was lower estimated subjectively than measured objectively (0.269. ±. 0.179. mm versus 0.352. ±. 0.355. mm; p = 0.035), but had better repeatability (±0.124. mm versus ±0.314. mm 95% confidence interval) unless correcting for the smaller range (47%). Horizontal lag was lower estimated subjectively (0.562. ±. 0.259. mm) than measured objectively (0.708. ±. 0.374. mm, p <. 0.001), had poorer repeatability (±0.132. mm versus ±0.089. mm 95% confidence interval) and had a smaller range (63%). Subjective categorisation of push-up speed of recovery showed reasonable differentiation relative to objective measurement (p <. 0.001). Conclusions: The objective image analysis allows an accurate, reliable and repeatable assessment of soft contact lens fit characteristics, being a useful tool for research and optimisation of lens fit in clinical practice

Characterization of materials for commercial and new nanophotonic soft contact lenses by optomagnetic spectroscopy

Industrija proizvodnje i tržište tražnje kontaktnih sočiva su pokazali visok nivo dinamičnosti u proteklih nekoliko decenija, i evoluirali su u dinamičkim promenama u kojima nauka i svakodnevna praksa stalno uzajamno interaguju. Ovaj rad predstavlja uporedno ispitivanje karakteristika osnovnog (komercijalnog) materijala i nanofotoničnog materijala koji su dobijeni inkorporacijom nanomaterijala (fulerena) i njegovih derivata u osnovni materijal za meka kontaktna sočiva. Osnovni materijal za kontaktna sočiva sintetisan je od monomera 2-hidroksietil metakrilata (HEMA), a fuleren i njegovi derivati su korišćeni zbog svojih dobrih transmisionih karakteristika u ultra-ljubičastom, vidljivom i infra-crvenom spektru. Za potrebe karakterizacije materijala za meka kontaktna sočiva korišćena je Optomagnetna spektroskopija (OMS). OMS se zasniva na konvolucionom spektru dobijenom kao razlika digitalne slike difuzno reflektovane bele svetlosti i reflektovane polarizovane bele svetlosti za plavi i crveni kanal. Ova istraživanja imaju značaj kako za optiku kontaknih sočiva tako i njihovu praktičnu biomedicinsku primenu.The contact lens industry and market have displayed a high level of dynamism in the past few decades, and have evolved into a rapidly changing field in which science and everyday practice constantly interact. This work presents the comparative research of characteristics of the basic (commercial) material and nanophotonic materials which were obtained by incorporation of fullerene nanoparticles and its derivate in basic material for soft contact lenses. Basic contact lens material was sintetized of monomer 2-hydroxyethyl methacrylate (HEMA), and fullerene and its derivates were used due to their good transmission characteristics in ultraviolet, visible and near infra-red spectrum. For the purposes of characterization of materials for soft contact lenses Optomagnetic Spectroscopy (OMS) was used. OMS is based on difference between diffusely reflected white light and reflected polarized white light. This research contributes to applied optical science and biomedical application industry

End-of-day dryness, corneal sensitivity and blink rate in contact lens wearers

Purpose: To study the relationship among the variables intensity ofthe end-of-day (EOD) dryness, corneal sensitivity and blink rate in soft contact lens (CL) wearers. Methods: Thirty-eight soft CL wearers (25 women and 13 men; mean age 27.1 ± 7.2 years) were enrolled. EOD dryness was assessed using a scale of 0–5 (0, none to 5, very intense). Mechanical and thermal (heat and cold) sensitivity were measured using a Belmonte’s gas esthesiometer. The blink rate was recorded using a video camera while subjects were wearing a hydrogel CL and watching a film for 90 min in a controlled environmental chamber. Results: A significant inverse correlation was found between EOD dryness and mechanical sensitivity (r: −0.39; p = 0.02); however, there were no significant correlations between EOD dryness and thermal sensitivity. A significant (r: 0.56; p < 0.001) correlation also was observed between EOD dryness and blink rate, but no correlations were found between blink rate and mechanical or thermal sensitivity. Conclusions: CL wearers with higher corneal sensitivity to mechanical stimulation reported more EOD dryness with habitual CL wear. Moreover, subjects reporting more EOD dryness had an increased blink rates during wear of a standard CL type. The increased blink rate could act to improve the ocular surface environment and relieve symptom

Characterization of materials for commercial and new nanophotonic soft contact lenses by optomagnetic spectroscopy

Industrija proizvodnje i tržište tražnje kontaktnih sočiva su pokazali visok nivo dinamičnosti u proteklih nekoliko decenija, i evoluirali su u dinamičkim promenama u kojima nauka i svakodnevna praksa stalno uzajamno interaguju. Ovaj rad predstavlja uporedno ispitivanje karakteristika osnovnog (komercijalnog) materijala i nanofotoničnog materijala koji su dobijeni inkorporacijom nanomaterijala (fulerena) i njegovih derivata u osnovni materijal za meka kontaktna sočiva. Osnovni materijal za kontaktna sočiva sintetisan je od monomera 2-hidroksietil metakrilata (HEMA), a fuleren i njegovi derivati su korišćeni zbog svojih dobrih transmisionih karakteristika u ultra-ljubičastom, vidljivom i infra-crvenom spektru. Za potrebe karakterizacije materijala za meka kontaktna sočiva korišćena je Optomagnetna spektroskopija (OMS). OMS se zasniva na konvolucionom spektru dobijenom kao razlika digitalne slike difuzno reflektovane bele svetlosti i reflektovane polarizovane bele svetlosti za plavi i crveni kanal. Ova istraživanja imaju značaj kako za optiku kontaknih sočiva tako i njihovu praktičnu biomedicinsku primenu.The contact lens industry and market have displayed a high level of dynamism in the past few decades, and have evolved into a rapidly changing field in which science and everyday practice constantly interact. This work presents the comparative research of characteristics of the basic (commercial) material and nanophotonic materials which were obtained by incorporation of fullerene nanoparticles and its derivate in basic material for soft contact lenses. Basic contact lens material was sintetized of monomer 2-hydroxyethyl methacrylate (HEMA), and fullerene and its derivates were used due to their good transmission characteristics in ultraviolet, visible and near infra-red spectrum. For the purposes of characterization of materials for soft contact lenses Optomagnetic Spectroscopy (OMS) was used. OMS is based on difference between diffusely reflected white light and reflected polarized white light. This research contributes to applied optical science and biomedical application industry

Nanoparticle-laden contact lens for controlled ocular delivery of prednisolone : formulation optimization using statistical experimental design

Human eye is one of the most accessible organs in the body, nonetheless, its physiology and associated precorneal factors such as nasolacrimal drainage, blinking, tear film, tear turnover, and induced lacrimation has significantly decreased the residence time of any foreign substances including pharmaceutical dosage forms. Soft contact lenses are promising delivery devices that can sustain the drug release and prolong residence time by acting as a geometric barrier to drug diffusion to tear fluid. This study investigates experimental parameters such as composition of polymer mixtures, stabilizer and the amount of active pharmaceutical ingredient on the preparation of a polymeric drug delivery system for the topical ocular administration of Prednisolone. To achieve this goal, prednisolone-loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles were prepared by single emulsion solvent evaporation method. Prednisolone was quantified using a validated high performance liquid chromatography (HPLC) method. Nanoparticle size was mostly affected by the amount of co-polymer (PLGA) used whereas drug load was mostly affected by amount of prednisolone (API) used. Longer homogenization time along with higher amount of API yielded the smallest size nanoparticles. The nanoparticles prepared had an average particle size of 347.1 ± 11.9 nm with a polydispersity index of 0.081. The nanoparticles were then incorporated in the contact lens mixture before preparing them. Clear and transparent contact lenses were successfully prepared. When the nanoparticle (NP)-loaded contact lenses were compared with control contact lenses (unloaded NP contact lenses), a decrease in hydration by 2% (31.2% ± 1.25% hydration for the 0.2 g loaded NP contact lenses) and light transmission by 8% (unloaded NP contact lenses 94.5% NP 0.2 g incorporated contact lenses 86.23%). The wettability of the contact lenses remained within the desired value (<90 °C) even upon incorporation of the NP. NP alone and NP-loaded contact lenses both displayed a slow in vitro drug release of drug over 24 h; where 42.3% and 10.8% prednisolone release were achieved, respectively. Contact lenses can be used as a medicated device to sustain ocular drug delivery and improve patient compliance; nonetheless, patients and healthcare professionals' acceptability and perceptions of the new formulations entail further investigations