SiHy Lenses Research Articles

Analysis of Deposition and Diffusion of Cholesterol in Silicone Hydrogel Contact Lenses Using Confocal Microscopy.

In this study, we investigated lipid deposition and diffusion in silicone hydrogel (Si-Hy) contact lenses using confocal microscopy. Different Si-Hy lenses were analyzed to understand the interaction patterns of cholesterol with various lens materials. The results highlight significant differences in the deposition and diffusion of lipids through the lenses, revealing that some materials, such as comfilcon A, allow lipids to diffuse more freely compared to others, such as samfilcon A, which provides a greater barrier. The study also observed different morphology and movement of lipid agglomerates across the lenses and above it surfaces. These findings contribute to the understanding of lipid-lens interaction, which is important for the development of lenses with improved comfort and functionality. The research highlights the importance of considering lipid interactions in the design and selection of Si-Hy contact lenses to enhance wearer comfort and lens performance.

Study of silicone hydrogel contact lenses’ surface reflection characteristics using confocal microscopy

The physical and chemical properties of contact lenses (CLs) differ significantly from one another. This is already covered by the FDA classification, which divides soft lenses into groups and subgroups for additional characteristics. The differences relate to both the interior and surface of the lens. Several differences in the surface characteristics of individual contact lenses have been studied and demonstrated to date. However, one of their fundamental physical properties, that is light reflection or, quantitatively, reflectance has not been compared. This paper describes the surface differences of a range of silicone-hydrogel (SiHy) lenses using reflectance confocal microscopy. It shows the relationship between the amount of light reflected from the lens surface and the material parameters. Common SiHy lens materials were used in the study, including two lenses with surface modifications. Light incident at the interface between two media (phosphate-buffered saline and lens) with different refractive indices is partially reflected. The normalized results show significant differences between the reflection signals (1 vs 0.07), and that they are not correlated with the refractive index (R2 = 0.5536). For the water content (%H2O), a general trend was observed that the higher the %H2O, the lower the reflection signal is (R2 = 0.8105). The reflection signal and surface modulus show the best correlation. (R2 = 0.9883). The proposed CLs analysis method, using reflectance confocal microscopy, provides data to differentiate between lenses with and without surface modifications.

Performance of a Silicone Hydrogel Daily Disposable Contact Lens among Wearers with Lens-related Dryness

Background: Addressing contact lens dryness continues to be a development goal of contact lens (CL) manufacturers. Objective: The objective of this study is to evaluate the clinical performance of kalifilcon A, a daily disposable silicone hydrogel (SiHy) CL, in subjects that experience dryness with their habitual planned-replacement SiHy CLs relative to a non-dry subgroup. Methods: A cohort of adapted planned-replacement SiHy CL wearers wore kalifilcon A lenses for at least 8 hours daily over two weeks. After one week of lens wear, subjects completed a survey regarding their lens wearing experience with respect to comfort and vision. Subsequently, subjects visited the clinics for the 2-week visit, during which the investigators completed a slit lamp exam and questionnaire regarding lens performance. Results: The evaluation included 180 subjects experiencing CL dryness with their habitual SiHy lenses and 213 subjects that did not. Both subgroups largely agreed with all comfort and vision attribute statements, and the dryness subgroup expressed higher levels of agreement with most comfort-related statements. Among habitual rewetting drop users, 73.9% in the dryness subgroup and 73.1% in the non-dry subgroup used drops less frequently while wearing kalifilcon A lenses. Investigators found no > Grade 2 slit-lamp findings, nor differences between subgroups. Neither subgroup showed a change in ratings between visits, except for a significantly higher proportion of improvers in the non-dry subgroup for upper lid tarsal conjunctival abnormalities. Conclusion: The kalifilcon A lens performed well among habitual planned-replacement SiHy CLs wearers. Its unique chemistry can provide a more satisfying wear experience for SiHy lens wearers experiencing CL dryness.

Characterizing the surface properties of daily disposable contact lens materials

Purpose: Using surface chemistry, a daily disposable silicone hydrogel (SiHy) contact lens with unique surface properties (verofilcon A) was developed. This novel lens material with “SMARTSURFACE” technology should provide a more wettable surface than other SiHy lens materials. This study used an in vitro model to characterize the aqueous film stability of this lens and compared with other commercial contact lenses.

Interaction of silicone hydrogel contact lenses with lipids – a chronological review

Silicone hydrogel (Si-Hy) contact lenses are a common form of correction of refractive errors and are prescribed by eye care professionals around the world. Si-Hy lenses perform in a complex environment, which is the surface of the eye and the tear film. Therefore, they are exposed to various factors, such as lipid deposits. The aims of this paper are to review available scientific reports on the study of Si-Hy lens interactions with lipids and search for further research objectives. A total of 57 publications were identified and reviewed, from 2003 to 2020. In general, Si-Hy lenses are more likely to accumulate lipid deposits than traditional hydrogel lenses, although there are significant differences between Si-Hy lens materials that may result from different methods used in the studies. The review includes studies on various aspects of interactions between lenses and lipids, such as those concerning the effectiveness of lipids removal from lenses by care solutions. The conclusion points out future research directions, such as measurements of lipid diffusion in Si-Hy lens' matrices.

Kinetic Deposition of Polar and Non-polar Lipids on Silicone Hydrogel Contact Lenses

ABSTRACT Purpose: This study investigated kinetic lipid uptake to four silicone hydrogel (SiHy) lenses over a period of four weeks, using an in-vitro radiolabel method. Methods: Four contemporary monthly replacement SiHy lenses (lotrafilcon B, senofilcon C, comfilcon A, samfilcon A) were incubated in three different solutions: 1) An artificial tear solution (ATS) containing 14C-labeled phosphatidylcholine (PC), 2) an ATS containing 14C-cholesteryl oleate (CO) and 3) an ATS containing four 14C-radiolabeled lipids (PC, phosphatidylethanolamine, CO, and cholesterol (total lipid)). After 16 hours, lipids were extracted twice from the lenses with chloroform:methanol and the radioactive counts determined the lipid quantities to simulate 1 day of wear. OPTI-FREE PureMoist (Alcon) was used to clean and disinfect the remaining lenses daily and the lipid quantities were further determined after 2 weeks and 4 weeks. Results: The amount of total lipid increased for all lenses over time (p < .01). After four weeks, total lipid accumulated was 20.26 ± 0.15 µg/lens for senofilcon C, which was significantly higher (p < .01) than all other lens materials (samfilcon A – 17.84 ± 0.21; comfilcon A – 16.65 ± 0.12; lotrafilcon B – 7.41 ± 0.56 µg/lens). CO was highest on lotrafilcon B (1.26 ± 0.13 µg/lens) and senofilcon C attracted the most PC (3.95 ± 0.12 µg/lens) compared to the other materials. Conclusion: The amount of both polar and non-polar lipid deposition on monthly replacement SiHy lenses increased over 4 weeks, with significant differences being seen between lens materials.

Latanoprost uptake and release from commercial contact lenses

This study investigated the potential of delivering an anti-glaucoma drug using commercial silicone hydrogel (SiHy) contact lenses. The moderately hydrophobic drug latanoprost was rapidly loaded in 4 min by swelling contact lenses in a solution of the drug in n-propanol. A fraction of the drug was radiolabeled, thus allowing measurement of the uptake and subsequent release of drug into artificial tear fluid. Three questions were addressed: (1) how much drug can be loaded into each type of lens, (2) how fast is drug release, and (3) how are these values related to the contact lens chemistry. The results showed that much more latanoprost could be loaded into SiHy lenses than a conventional contact lens of poly(hydroxyethyl methacrylate). The drug uptake correlated with the amount of swelling in n-propanol, with Galyfilcon lenses having the greatest swelling and highest drug uptake. The drug release from the SiHy lenses occurred over days, whereas the conventional lens released nearly all drug in a burst over a few hours. To examine correlations between lens chemistry, drug chemistry and uptake, and solvent chemistry, the Hansen solubility parameters were calculated using estimates of contact lens chemistry. These results showed that drug uptake in SiHy lenses correlated with favorable solubility parameter interactions between the n-propanol and the lens material, but did not correlate with interactions between the drug and the lens materials.

Elemental Composition at Silicone Hydrogel Contact Lens Surfaces

The outermost surface composition of 11 silicone hydrogel (SiHy) lenses was measured using X-ray photoelectron spectroscopy (XPS) to understand differences in wettability and potential interactions within an ocular environment. The SiHy lenses tested included balafilcon A, lotrafilcon A, lotrafilcon B, senofilcon A, comfilcon A, and somofilcon A reusable 2-week or monthly replacement lenses and delefilcon A, samfilcon A, narafilcon A, stenfilcon A, and somofilcon A daily disposable lenses. All lenses were soaked for 24 hr in phosphate-buffered saline to remove all packaging solution and dried under vacuum overnight before analysis. X-ray photoelectron spectroscopy measurements were performed at 2 take-off angles, 55° and 75°, to evaluate changes in elemental composition as a function of depth from the surface. Detailed analysis of the XPS data revealed distinct differences in the chemical makeup of the different lens types. For all lenses, carbon, oxygen, and nitrogen were observed in varying quantities. In addition, fluorine was detected at the outermost surface region of comfilcon A (3.4%) and lotrafilcon A and B (<0.5%). The silicon content of the near-surface region analyzed varied among lens types, ranging from a low of 1.6% (lotrafilcon B) to a high of 16.5% (comfilcon A). In most instances, silicon enrichment at the outermost surface was observed, resulting from differences in lens formulation and design. Lenses differed most in their surface silicon concentration, with lotrafilcon B and delefilcon A exhibiting the lowest silicon contents and comfilcon A lens exhibiting the highest. Silicon has hydrophobic properties, which, when found at the surface, may influence the wettability of the contact lenses and their interaction with the tear film and ocular tissues. Higher surface silicon contents have been previously correlated with adverse effects, such as enhanced lipid uptake, thus underscoring the importance of monitoring their presence.

Evaluation of the impact of a new selective blue light filter and class 1 UV blocking SiHy lens (75% WC) examining contrast sensitivity and colour perception

Purpose: Changes in lifestyles and the exposure, both at work and leisure time, to smartphones, tablets, screens and led illumination, has raised concerns about the potential harmful effects of blue light. The purpose of this study is to evaluate the impact of a new blue light and UV blocking silicone hydrogel lens measuring contrast sensitivity and colour perception, under photopic and mesopic conditions, and to compare it with same material with no filters.

Mixed Model Analysis of Between-Subject Variability in Overnight Corneal Swelling and Deswelling With Silicone Hydrogel Lenses.

To model between subject variability of corneal swelling (CS) and deswelling after overnight wear of silicone hydrogel (SiHy) contact lenses. A total of 29 neophyte subjects wore 12 SiHy lenses with central transmissibility range of 31 to 211 Dk/t units on separate nights, in random order, and on one eye only. The contralateral eye served as the control. Central corneal thickness was measured using digital optical pachymetry before lens insertion, immediately after lens removal on waking, then 20, 40 minutes, 1, 2, and 3 hours later. Mixed modelling was conducted for simultaneous analysis of group and between-subject effects of CS and deswelling. The best model for overnight CS versus Dk/t was linear with a random intercept showing constant between-subject differences in CS for different Dk/t values. The best fit for corneal deswelling versus time was a curvilinear random intercept and random slope model. About 90% of the total between-subject deswelling variance in either lens or control eyes was due to the intercept variability with much less (∼10%) being due to the variability of the individual deswelling rate (slope). Subject age, sex, and ametropia were not predictors of individual corneal swelling in the swelling versus Dk/t analysis. Age, however, was a significant (inverse) predictor of the rate of corneal deswelling, only in lens-wearing eyes. A large proportion of variability in corneal swelling is because of subject-specific differences in corneal response to hypoxia. This shows that "low swellers" and "high swellers" actually do exist.

The impact of daily disposable soft contact lens wear on tear film surface quality over a three month period

PurposeTo study the changes in Tear Film Surface Quality (TFSQ) on a Silicon Hydrogel (SiHy) and a Hydrogel (Hy) daily contact lens (CL), during a follow‐up period of three months.MethodsForty‐six subjects aged 25.5 ± 4.3 (mean ± standard deviation) years with a refractive error limited to ±4.50 spherical and ±0.75 cylindrical dioptres were recruited. Based on a pre‐clinical analysis which took into account visual acuity (VA), comfort, and fitting, 31 subjects were fitted with SiHy and 13 with Hy lenses. TFSQ was studied based on measurements of the first and the mean non‐invasive keratography tear break up time (F/M–NIKBUT). All measurements were acquired at baseline, post four hours (4 h) and three months (3 m) of CL lens wear. Ocular Surface Disease Index (OSDI) questionnaire was also completed.ResultsThe results of the OSDI questionnaire showed an average improvement of 3.09 and 4.16 units for 3 m visit for SiHy and Hy lens, respectively. Nevertheless, this improvement was not statistically significant (p = 0.144 and p = 0.215). For F‐NIKBUT, there was no significant difference between 4h and 3m measurements (p=0.490 and p = 0.588 for SiHy and Hy lens, respectively). For M‐NIKBUT, there was no significant difference for SiHy and Hy groups between baseline and 4 h (p = 0.052 and p = 0.110, respectively). However, there was a significant difference between baseline and 3 m for SiHy group (p = 0.009) but not for the Hy group (p = 0.376). Lastly, no significant differences were observed between 4 h and 3 m M‐NIKBUT measurements for both lenses (p = 0.746 and p = 0.273 for SiHy and Hy lens, respectively).ConclusionsThe results indicate that estimates of 4 h of lens wear NIKBUT can be used to predict those at a 3 m visit. Also, Hy lens appeared to have less impact on TFSQ than the SiHy lens.

Oxygen, water, and sodium chloride transport in soft contact lenses materials.

Oxygen permeability, diffusion coefficient of the sodium ions and water flux and permeability in different conventional hydrogel (Hy) and silicone-hydrogel (Si-Hy) contact lenses have been measured experimentally. The results showed that oxygen permeability and transmissibility requirements of the lens have been addressed through the use of siloxane containing hydrogels. In general, oxygen and sodium chloride permeability values increased with the water content of the lens but there was a percolation phenomenon from a given value of water uptake mainly in the Si-Hy lenses which appeared to be related with the differences between free water and bound water contents. The increase of ion permeability with water content did not follow a unique trend indicating a possible dependence of the chemical structure of the polymer and character ionic and non-ionic of the lens. Indeed, the salt permeability values for silicone hydrogel contact lenses were one order of magnitude below those of conventional hydrogel contact lenses, which can be explained by a diffusion of sodium ions occurring only through the hydrophilic channels. The increase of the ionic permeability in Si-Hy materials may be due to the confinement of ions in nanoscale water channels involving possible decreased degrees of freedom for diffusion of both water and ions. In general, ionic lenses presented values of ionic permeability and diffusivity higher than most non-ionic lenses. The tortuosity of the ionic lenses is lower than the non-ionic Si-Hy lenses. Frequency 55 and PureVision exhibited the highest water permeability and flux values and, these parameters were greater for ionic Si-Hy lenses than for ionic conventional hydrogel lenses. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2218-2231, 2017.

Visualization of a hyaluronan network on the surface of silicone-hydrogel materials.

Biotrue multipurpose solution (MPS) is a bioinspired disinfecting and conditioning solution that includes hyaluronic acid (HA) as a natural wetting agent. Previous studies demonstrated that HA sorbed from Biotrue MPS on both conventional and silicone hydrogel (SiHy) contact lens materials; an in vitro simulated-wear test validated the presence of HA on the lens surfaces for as long as 20 hours. In this study, the morphology and distribution of HA sorbed from both Biotrue and pure HA solution on SiHy contact lens surfaces was examined. Atomic force microscopy imaging was used to illustrate the topography of fresh SiHy contact lens materials before and after incubation with 0.1% (w/v) HA solution. The distribution, as well as fine details of the HA network, were resolved by first staining HA with Gram’s safranin, then imaging with confocal laser-scanning microscopy and differential interference-contrast microscopy. In this approach, SiHy materials take up the dye (safranin) nonspecifically, such that the resultant safranin–HA complex appears dim against the fluorescent lens background. Balafilcon A was chosen as the representative of glassy SiHy lenses that require postpolymerization plasma treatment to increase wettability. Senofilcon A and samfilcon A were chosen as representatives of SiHy materials fabricated with an internal wetting agent. A confluent and dim HA–safranin network was observed adhered to balafilcon A, senofilcon A, and samfilcon A lens surfaces incubated with either 0.1% (w/v) HA solution or Biotrue MPS. Therefore, the conditioning function provided by Biotrue MPS may be in part explained by the presence of the HA humectant layer that readily sorbs on the various types of SiHy contact lens materials.

Convective loading and release of latanoprost in silicone hydrogel contact lenses

Event Abstract Back to Event Convective loading and release of latanoprost in silicone hydrogel contact lenses William Pitt1, Ryan R. Horne1 and Kevin E. Judd1 1 Brigham Young University, Chemical Engineering Department, United States Statement of Purpose: We investigated the feasibility loading silicone hydrogel (SiHy) contact lenses with a hydrophobic anti-glaucoma drug, latanoprost, by swelling the lenses in a n-propanol solution of drug. Subsequent release into artificial tear solution (ATS) was measured. This study compares the loading and release of latanoprost in Acuvue Advance® (Johnson & Johnson Vision Care, Jacksonville, FL), Air Optix® (Alcon, Fort Worth, Texas) and Total Dailies 1® (Alcon). Methods: A 0.125 g/L n-propanol solution of radiolabeled latanoprost was made by dissolving latanoprost in n-propanol to which was added 5 µL of ethanol which contained 10 µCi of radioactive latanoprost. The loading procedure was performed at 25°C by removing a contact lens from its blister pack, rinsing with double-distilled water (DDH2O), blotting dry, immersing the contact lens in a loading solution for 240 seconds, immediately removing and washing the lens in 3 rinses for 5 seconds each in ~15 mL of DDH2O, and in ~5 mL of DDH2O for 15 minutes to allow for the lens to shrink to original size. The lens was moved either to a latanoprost extraction step or to ATS. Latanoprost extraction, a series of 2 soaks of 1 hr each in 2 mL n-propanol at 35°C, quantitated the radiolabeled latanoprost loaded into the lens, as described previously [1]. To simulating wear in ATS, the lens is immersed in 3 mL of ATS and swirled at 35°C. The lens was moved to fresh ATS after 1, 2, 4, and 6 days. A sample of ATS was taken for quantitation right before transferring the lens. Results: Latanoprost was successfully loaded into SiHy lenses. The drug showed 1st order release into artificial tears over a span of 2-3 days by which time the latanoprost was mostly depleted. For the same loading conditions, the amount of drug loaded and initial release rate were functions of the type of silicone hydrogel (see Figure 1). Of the lenses tested, Acuvue Advance® (galyfilcon A) accepted the most latanoprost and released at the fastest rates (p<0.05), followed by Air Optix® (lotrafilcon B) and Total Dailies 1® (delefilcon A) which released at similar rates. When normalized to the amount loaded, the kinetics of release of latanoprost were highly comparable for the different silicone hydrogels. Caption to Figure 1. Cumulative release of latanoprost per lens into ATS from different contact lenses . Error bars show the 95% CI, n=3. Conclusions: Literature reports of loading times for hydrophobic drugs are usually hours or days, [2] but this method allows for rapid loading of the drug latanoprost on the order of minutes. Despite a loading time of only 4 minutes, release is on the order of 2-4 days for the given conditions. We postulate that the hydrophobic character of SiHy contact lenses enables favorable interaction with the hydrophobic moieties of latanoprost, enhancing uptake during the loading process when latanoprost-solvating n-propanol in the polymer matrix is displaced by water, in which latanoprost is only minimally soluble. Loading and release was less for latanoprost than our previous findings for DMPC [1], which is consistent with latanoprost being less hydrophobic than DMPC. The amount of loading was higher in galyfilcon A which has 47% water content as compared to that of lotrafilcon B and delefilcon A, both having 33% water content. The higher loading is roughly correlated with the increase in water content of the polymer. Additional correlations of the silicone hydrogel chemistries and their potential effect on loading will also be presented. Funding for this study was provided by Brigham Young University.

Impact of Cosmetics on the Physical Dimension and Optical Performance of Silicone Hydrogel Contact Lenses.

To evaluate the impact of cosmetics on silicone hydrogel (SiHy) contact lens shape, lens power, and optical performance. In this in vitro experiment, 7 SiHy materials were coated with 9 marketed brands of cosmetics, including hand creams (HCs) (3), eye makeup removers (MRs) (3), and mascaras (3). Diameter, sagittal depth, and base curve were determined using the Chiltern (Optimec Limited), whereas lens power and optical performance were assessed using the Contest Plus (Rotlex). Six replicates were used for each lens and cosmetic combination. Measurements were repeated after a cleaning cycle using a one-step hydrogen peroxide solution. Makeup removers had the greatest impact on diameter, sagittal depth, and base curve, resulting in changes of up to 0.5, 0.15, and 0.77 mm, respectively. The HCs and mascaras had little impact on these parameters; however, differences were observed between lens types. Optical performance was reduced with all mascaras, and a decrease of greater than 2 units on a 0 to 10 scale (10=uniform power distribution) was seen for 5 lens types exposed to waterproof mascara (P<0.01). Most HCs and MRs had minimal impact on image quality. Lens power did not change with any of the cosmetics (± 0.25 diopter; P>0.05). Lens cleaning resulted in some recovery of the lens parameters, and efficiency varied between cosmetics. Some eye MRs and waterproof mascaras changed the shape and optical performance of some SiHy lenses. Further research is needed to understand the clinical implications for SiHy lens wearers using cosmetics.

Impact of Cosmetics on the Surface Properties of Silicone Hydrogel Contact Lenses.

This study evaluated the impact of various cosmetics on the surface properties of silicone hydrogel (SiHy) contact lens materials. In this in vitro experiment, 7 SiHy contact lens materials were coated with 1 of 9 cosmetics, including common hand creams (3), eye makeup removers (3), and mascaras (3). Dark-field microscopy images were taken to determine pixel brightness (PB) after cosmetic exposure, which describes the visible surface deposition (n=6 for each lens type), with a higher PB indicating increased deposition. The sessile drop technique was used to determine the advancing contact angle (CA). Measurements were repeated for both methods after a single peroxide-based cleaning cycle. Pixel brightness was significantly higher for mascara-coated lenses compared with the other cosmetic products (P<0.01). The peroxide-based lens care solution removed most deposits from the nonwaterproof mascara for 4 lens types, whereas deposits remained relatively unchanged for 1 waterproof mascara (P>0.05). Hand creams and makeup remover had minimal impact on PB. Changes in CA measurements after cosmetic application were highly lens dependent. Hand creams caused primarily a decrease in CA for 5 of the 7 lens types, whereas 1 of the waterproof mascaras caused a significant increase of 30 to 50° for 3 lens types. Some mascara-lens combinations resulted in increased CA and PB, which could have an impact on in vivo lens performance. Nonwaterproof mascara was mostly removed after a cleaning cycle. Further research is needed to understand the clinical implications for SiHy lens wearers using cosmetics.

Ex vivo analysis of cholesterol deposition for commercially available silicone hydrogel contact lenses using a fluorometric enzymatic assay.

Lipid deposition on silicone hydrogel (SiHy) lenses, which are believed to be caused by their hydrophobic surface, can lead to discomfort, reduced vision, and inflammatory reactions. This study used a highly specific and sensitive fluorometric enzymatic assay for ex vivo cholesterol analysis of seven types of SiHy lenses: balafilcon A, comfilcon A, enfilcon A, enhanced-lotrafilcon A, enhanced-lotrafilcon B, galyfilcon A, and senofilcon A. Cholesterol sorption was assessed in 140 previously worn SiHy lenses from 8 clinical trials conducted in the United States and Australia between 2006 and 2008. Patients wore the lenses for 2 to 4 weeks. Unworn negative control lenses for each lens material were obtained directly from the manufacturer. Lipids were isolated from the lenses using a two-step chloroform: methanol extraction method, and total cholesterol was quantified using a fluorometric enzymatic assay. Nonparametric Mann Whitney statistical analysis was performed to determine the differences in total cholesterol sorption between lens-specific data sets. Enhanced-lotrafilcon A and enhanced-lotrafilcon B contact lenses showed significantly lower median total cholesterol sorption (median±quartile, 0.30±0.2 μg/lens and 0.09±0.1 μg/lens, respectively) than all other types of lenses that were tested (P<0.0001). By contrast, enfilcon A (3.96±0.8 μg/lens) and galyfilcon A (3.75±1.1 μg/lens) showed the highest median total cholesterol sorption of all tested lenses. Cholesterol deposition in SiHy contact lenses seems to be lens polymer dependent. Enhanced-lotrafilcon A and enhanced-lotrafilcon B both sorbed the lowest amount of cholesterol compared with the other five types of SiHy lenses that were tested in this study.

Factors that Influence In Vitro Cholesterol Deposition on Contact Lenses

The purpose of this study was to analyze the impact that incubation time, lipid concentration, and solution replenishment have on silicone hydrogel (SiHy) and conventional hydrogel (CH) contact lens cholesterol deposition via in vitro radiochemical experiments. Four SiHy (senofilcon A, lotrafilcon B, comfilcon A, balafilcon A) and two CH (etafilcon A and omafilcon A) contact lenses were incubated in an artificial tear solution (ATS) that contained major tear film proteins, lipids, salts, salts, and a trace amount of radioactive C-cholesterol. Lenses were incubated for various incubation times (1, 3, 7, 14, or 28 days), with three concentrations of lipid (0.5×, 1×, 2× tear film concentration) and with or without solution replenishment to assess each variable's impact on cholesterol deposition. After incubation, the lenses were extracted using 2:1 chloroform:methanol, extracts were analyzed in a beta counter and masses (micrograms per lens) were extrapolated from standard curves. Within the SiHy materials, balafilcon A deposited the greatest amount of cholesterol (p < 0.001) and lotrafilcon B the lowest (p < 0.001). The CH lens materials showed significantly lower uptake amounts than any of the SiHy lens materials (p < 0.001). The uptake of cholesterol ranged from 0.01 ± 0.01 μg/lens to 3.22 ± 0.34 μg/lens for all lens materials. Kinetic uptake of cholesterol was shown to be continuous throughout the 28 days of incubation without plateau (p < 0.001), and varying the lipid concentration did impact the resulting cholesterol deposition (p < 0.001). Replenishing the ATS every other day also affected cholesterol deposition throughout the experiment. Overall, the deposition pattern was 2× > replenishing > 1× > 0.5×. Overall, SiHy lenses deposit significantly more cholesterol than CH lens materials, and the mass of lipid deposited is dependent on the contact lens material, length of incubation, concentration of lipids in the ATS, and the replenishment of ATS.

Quantitation of cholesterol and phospholipid sorption on silicone hydrogel contact lenses

The introduction of silicone hydrogel (SiHy) contact lenses to the consumer marketplace necessitates study of the susceptibility of these lenses to spontaneous deposition by hydrophobic lipid components of ocular tears. The use of radioisotopes to measure lipid sorption on SiHy contact lenses gives precise and accurate results but requires institutional infrastructure and compels efficient lipid removal from the lens. This study compares three methods of quantitating phospholipid and cholesterol sorption on SiHy lenses using radiolabeled cholesterol and phosphatidylcholine that were sorbed on lenses from an artificial tear fluid. A triple extraction technique using n-propanol gives the most reliable results. Comparison of sorption on SiHy lenses shows that balafilcon A and senofilcon A lenses sorb similar amounts, while lotrafilcon B lenses sorb comparatively less.

Biocompatibility in the Development of Silicone-Hydrogel Lenses

In response to patient demands for extended contact lens wearing times, the contact lens industry has developed novel silicone-hydrogel (SiHy) lens materials that combine the enhanced oxygen permeability of silicone polymers with the water-based comfort of conventional hydrogels. In the past 12 years since the successful launch of these SiHy lenses, much has been learned about their ability to provide the biocompatibility necessary to sustain ocular health and comfort. A review of the unique physiologic requirements for a successful extended wear lens and how the first and current SiHy lenses address them is provided.