Dendritic immune cell densities in the central cornea associated with soft contact lens types and lens care solution types: a pilot study.

BACKGROUND: The purpose of this study was to assess whether differences in central corneal dendritic immune cell densities associated with combinations of soft contact lenses and lens care solutions could be detected by in vivo confocal microscopy. METHODS: Participants were adults naïve to contact lens wear (n = 10) or who wore soft contact lenses habitually on a daily-wear schedule (n = 38) or on a study-assigned schedule for 30 days with daily disposable silicone hydrogel lenses (n = 15). Central corneas were scanned using an in vivo confocal microscope. Cell densities were compared among groups by demographic parameters, lens materials, and lens care solutions (polyhexamethylene biguanide [PHMB], polyquaternium-1 and myristamidopropyl dimethylamine [PQ/MAPD], peroxide, or blister pack solution [for daily disposable lenses]). RESULTS: Among lens wearers, no associations were observed between immune cell densities and age, gender, or years of lens-wearing experience. Mean cell density was significantly lower (P < 0.01) in nonwearers (29 ± 23 cells/mm(2), n = 10) than in lens wearers (64 ± 71 cells/mm(2), n = 53). Mean cell density was lower (P = 0.21) with traditional polymer lenses (47 ± 44 cells/mm(2), n = 12) than with silicone hydrogel lenses (69 ± 77 cells/mm(2), n = 41). Lowest to highest mean density of immune cells among lens wearers was as follows: PQ/MAPD solution (49 ± 28 cells/mm(2)), blister pack solution (63 ± 81 cells/mm(2)), PHMB solution (66 ± 44 cells/mm(2)), and peroxide solution (85 ± 112 cells/mm(2)). CONCLUSION: In this pilot study, in vivo confocal microscopy was useful for detecting an elevated immune response associated with soft contact lenses, and for identifying lens-related and solution-related immune responses that merit further research.

Temperature-induced transitions in the structure and interfacial rheology of human meibum.

Meibomian lipids are the primary component of the lipid layer of the tear film. Composed primarily of a mixture of lipids, meibum exhibits a range of melt temperatures. Compositional changes that occur with disease may alter the temperature at which meibum melts. Here we explore how the mechanical properties and structure of meibum from healthy subjects depend on temperature. Interfacial films of meibum were highly viscoelastic at 17°C, but as the films were heated to 30°C the surface moduli decreased by more than two orders of magnitude. Brewster angle microscopy revealed the presence of micron-scale inhomogeneities in meibum films at higher temperatures. Crystalline structure was probed by small angle x-ray scattering of bulk meibum, which showed evidence of a majority crystalline structure in all samples with lamellar spacing of 49 Å that melted at 34°C. A minority structure was observed in some samples with d-spacing at 110 Å that persisted up to 40°C. The melting of crystalline phases accompanied by a reduction in interfacial viscosity and elasticity has implications in meibum behavior in the tear film. If the melt temperature of meibum was altered significantly from disease-induced compositional changes, the resultant change in viscosity could alter secretion of lipids from meibomian glands, or tear-film stabilization properties of the lipid layer.

A preliminary study of silicone hydrogel lens material and care solution bioincompatibilities.

PURPOSE: The study purpose was to evaluate corneal barrier function and staining relative to potential bioincompatibilities. METHODS: This was a randomized double-masked study (n = 25 subjects). Three lens material-care solution combinations were tested: (1) lotrafilcon B/polyhexamethylene biguanide (PHMB)-based multipurpose (MPS) solution (MPS-1); (2) lotrafilcon B/polyquaternium-1 and myristamidopropyl dimethylamine-based solution (MPS-2); and (3) lotrafilcon B and another PHMB-based solution (MPS-3). Saline served as the control. New lenses were soaked in the preserved solutions or saline and then worn for 2 hours before corneal measurements. Barrier function was characterized by the fluorescein penetration rate, corneal amount, both measured with an objective scanning fluorometer. The dye penetration rate ratio, test to control; amount ratio, test to control, and corneal staining were evaluated. RESULTS: The mean rate ratios (± SD) for the combinations were 2.98 (± 3.04), 1.23 (± 1.01), and 1.83 (± 1.77) for MPS-1, MPS-2, and MPS-3 solutions, respectively. Significant ratio differences were found across regimens (P = 0.007); for MPS-1 compared with baseline (P = 0.031) and for MPS-1 compared with MPS-2 (P = 0.007). The statistical results for staining were similar. CONCLUSIONS: Use of an objective quantitative physiological method suggests that significant differences in lens solution bioincompatibilities occur that mirror corneal staining data relative to corneal compromise.

Precorneal residence time of artificial tears measured in dry eye subjects.

PURPOSE: The purpose of this investigation was to measure the precorneal residence time of saline and five marketed artificial tears in dry eye subjects using fluorometry. METHODS: FITC-dextran, 70 kDa molecular weight, was admixed under sterile conditions (0.1% wt/vol) into buffered saline and the marketed artificial tear formulations of varying viscosity. Precorneal residence time (RT) was measured directly in 16 mild to moderate dry eye subjects, classified by sub-type, in a six-way cross-over, masked and randomized study. FITC-dextran tracer decay with a scanning fluorometer was used to estimate the gross RT (i.e., the time in minutes for the signal to return to baseline). RESULTS: All subjects were classified as having non-inflammatory meibomian gland dysfunction except one, who had a mixture of aqueous deficiency and meibomian gland dysfunction. In two separate determinations, the saline RTs were 19.1 +/- 7.4 and 17.6 +/- 8.2 min. The RTs for the formulations varied to some degree by viscosity, with two higher viscosity formulations demonstrating the longest RTs of 36 to 41 min, approximately twice that of saline (p < 0.001 for both 0.4% polyethylene glycol/0.3% propylene glycol, and 1.0% carboxymethylcellulose). An oil emulsion, low viscosity carboxymethylcellulose and moderate viscosity hydroxypropylmethylcellulose-containing formulation were not statistically different from saline (RTs of 18, 22 and 24 min, p values = 0.983, 0.818 and 0.099, respectively). CONCLUSIONS: More than two-fold RT differences were found for the higher viscosity, more muco-adhesive formulations compared to saline. However, other formulations provided RTs close to saline, suggesting that RT is influenced by factors other than simple viscosity. Future studies should examine the interplay of spreading characteristics, pseudoplasticity and muco-adhesion relative to RT to determine the individual and cumulative effects on formulation retention.

Biocide uptake in contact lenses and loss of fungicidal activity during storage of contact lenses.

PURPOSE: With recent outbreaks of Fusarium keratitis related to contact lens wear, studies were conducted to determine the biocide uptake during lens storage, and the resulting effect on antifungal activity of related products. METHODS: ACUVUE 2 (etafilcon A) soft, hydrophilic contact lenses (group IV) were soaked from 1 hour to 7 days in OPTI-FREE Express and OPTI-FREE RepleniSH multipurpose disinfecting solutions with POLYQUAD (polyquaternium-1) and ALDOX (myristamidopropyl dimethylamine) biocides and multipurpose solutions, Bausch & Lomb ReNu with MoistureLoc (Alexidine), ReNu MultiPlus (polyhexamethylene biguanide [PHMB]), and AMO Complete MoisturePLUS (PHMB). Storage solutions were tested to evaluate the effect of preservative uptake on the residual biocide activity against Fusarium solani. RESULTS: Approximately 30% to 60% of the PHMB and Alexidine were depleted by 6 hours, with comparable loss of antimicrobial activity. Decreasing activity was noted with corresponding decreases in active concentration throughout the course of the evaluation. The POLYQUAD systems retained nearly 100% of the biocide and fungicidal activity and maintained their concentration in the solution. CONCLUSIONS: OPTI-FREE Express and OPTI-FREE RepleniSH multipurpose disinfecting solutions maintained fungicidal efficacy after storage of lenses. The Alexidine- and PHMB-based multipurpose solutions tested showed significant uptake of preservative into group IV lenses, resulting in a decrease in the residual activity of the storage solution. The POLYQUAD systems showed a low uptake of biocide and maintained fungicidal efficacy against F. solani.

Dynamic wettability properties of a soft contact lens hydrogel.

The wettability of poly[2-hydroxyethyl methacrylate-co-methacrylic acid] (pHEMA-MAA) soft contact lenses was investigated in the absence and presence of block copolymer surfactants and lysozyme using the sessile drop method. The advancing dynamic contact angles (Thetaw/a) values are reported for water as a function of sequential wetting and drying cycles. The Thetaw/a values for the pHEMA-MAA in the absence of surfactant and lysozyme increased from approximately 20 degrees to 100 degrees as the number of cycles increased from two to ten, and they were independent of the pHEMA-MAA bulk water content. The change from the highly hydrophilic to hydrophobic pHEMA-MAA surface could not be reversed using the sequential wetting and drying cycles even under repeated exposures to saline solution. The effect of block copolymer surfactants with different molecular weights (MW) and hydrophilic-lipophilic balance (HLB) values on the pHEMA-MAA wettability were also studied. Low Theta(w/a) values were observed for pHEMA-MAA hydrogels that were treated with T1304 (MW 10500, HLB 14) and T904 (MW 6700, HLB 15). The surface tension data indicated that these surfactants were incompletely desorbed from the pHEMA-MAA and that the rate of desorption was slow in the timescale of the cycling experiments. Comparatively, poor wettability was observed for pHEMA-MAA surfaces presoaked in T304 (MW 1650, HLB 16) and T1107 (MW 15000, HLB 24) as Thetaw/a values greater than 90 degrees were measured for these surfactants. The surface tension data indicated that the rate of desorption of T304 and T1107 from the pHEMA-MAA was rapid and that they had a low affinity to the pHEMA-MAA. High contact angles were observed for the pHEMA-MAA hydrogels treated with lysozyme and also for the T1107 presoaked pHEMA-MAA that was also treated with lysozyme. Zero wetting angles throughout the sequential cycling were observed for the T1304 pre-treated pHEMA-MAA that had been treated with lysozyme. These results suggested that the adsorbed lysozyme on the pHEMA-MAA hydrogel had no significant influence on its wetting properties when the hydrogel was pre-treated with T1304.

A novel method to evaluate residence time in humans using a nonpenetrating fluorescent tracer.

PURPOSE: The purpose of these investigations was to develop an improved method for measuring precorneal residence time (RT) and to demonstrate its efficacy with novel formulations. METHODS: A biomicroscope was adapted for use as a clinical fluorometer. Using a nonpenetrating fluorescent probe (FITC-dextran, 70,000-73,000 molecular weight [MW]), RT was estimated as the time to return to baseline (gross RT) and from parameters derived from least-squares regression fits to the decay data (area under the curve [AUC], elimination rate, and time for 50% of the signal to be eliminated [T(50)]). One rabbit and two human studies were conducted. The studies were randomized, double-masked, and controlled. Repeatability in humans was examined in 15 subjects (six determinations per subject, n = 90 total). RESULTS: The FITC-dextran tracer did not penetrate into corneal tissue. The rabbit gross RTs were 14.5, 15.0, and 16.0 minutes for three low-viscosity solutions (eta = 2.7-7.7 mPa/sec) and 22.5 minutes for a more viscous solution (eta = 357 mPa/sec). For a high-viscosity (eta approximately equal 30,000 mPa/sec) gel in humans, the method demonstrated approximately a twofold increase in gross RT and AUC compared with buffered saline. Repeatability of the method appeared acceptable, with intersubject variability the most significant factor affecting precision. CONCLUSIONS: The new method is safe and convenient and offers comprehensive RT data. Furthermore, it appears to differentiate among formulations. However, as with other tear-influenced parameters, there is significant variability. Thus, sufficient sample sizes are necessary for meaningful comparative investigations.