Lakshman N. Subbaraman

Kinetics of in vitro lysozyme deposition on silicone hydrogel, PMMA, and FDA groups I, II, and IV contact lens materials.

We sought to compare the kinetics of in vitro lysozyme deposition on silicone hydrogel (SH), polymethyl methacrylate (PMMA), and FDA groups I, II, and IV contact lenses. Lenses were incubated in 125I-labeled lysozyme for time periods ranging from 1 hr to 28 days, and radioactive counts were determined. SH lenses and PMMA deposited less lysozyme than conventional hydrogel lenses (p < 0.05). Lysozyme accumulation on group IV lenses reached a maximum on the seventh day and then plateaued, whereas on groups I, II, and SH lenses, deposition continued to increase across all time periods, reiterating that kinetics of lysozyme deposition is highly material dependent.

Quantity and conformation of lysozyme deposited on conventional and silicone hydrogel contact lens materials using an in vitro model.

Purpose. To determine the activity of hen egg lysozyme (HEL) deposited on conventional and silicone hydrogel contact lens materials by using an in vitro model. Methods. ACUVUE 2 (etafilcon A), PureVision (balafilcon A), ACUVUE Advance (galyfilcon A), Focus NIGHT & DAY (lotrafilcon A), O2 Optix (lotrafilcon B), Proclear (omafilcon A), and ACUVUE OASYS (senofilcon A) contact lenses were deposited in vitro in a phosphate-buffered solution (PBS) containing 2 mg/mL HEL. Lenses were briefly rinsed in PBS to remove unbound material and extracted in a mixture of acetonitrile and trifluoroacetic acid. After lyophilization, extracts were examined for lysozyme activity by micrococcal assay and total protein by Western blot. Results. In terms of total protein accumulation, ACUVUE 2 showed the most, with 1,800 &mgr;g per lens. Proclear was next, with 68 &mgr;g per lens, and Focus NIGHT & DAY showed the least, with 2 &mgr;g per lens. ACUVUE Advance, ACUVUE OASYS, and O2 Optix accumulated similar amounts of lysozyme, at approximately 6 &mgr;g per lens. Lysozyme deposited on ACUVUE 2 showed the greatest activity (91% ± 5%), and this result was statistically different from all other lens types (P<0.001). Lysozyme deposited on Focus NIGHT & DAY (24% ± 5%) and O2 Optix (23% ± 11%) showed the lowest activity. Lysozyme deposits on other lens materials showed intermediate activity (ACUVUE Advance, 60% ± 15%; ACUVUE OASYS, 51% ± 9%; PureVision, 58% ± 8%; and Proclear, 38% ± 3%). Conclusions. Silicone hydrogel lenses acquire less lysozyme deposit than conventional group II (Proclear) or group IV (ACUVUE 2) lenses do, and the levels of activity of the lysozyme are highly variable between materials.

The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee

Jones, L., Brennan, N. A., Gonzalez-Meijome, J., Lally, J., Maldonado-Codina, C., Schmidt, T. A., … Nichols, J. J. (2013). The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee. Investigative Opthalmology & Visual Science, 54(11), TFOS37. https://doi.org/10.1167/iovs.13-13215

Rewetting Drops Containing Surface Active Agents Improve the Clinical Performance of Silicone Hydrogel Contact Lenses

Purpose. The purpose of this study was to investigate the impact of using a rewetting drop (RWD) containing surface active agents (OPTI-FREE RepleniSH; Alcon, Fort Worth, TX) on the clinical performance and protein deposition when using a continuous-wear (CW) silicone hydrogel (SH) contact lens. Methods. Subjects wore lotrafilcon A SH lenses on a 30-day CW basis for two consecutive 1-month periods while inserting either 0.9% unpreserved unit-dose saline (control) or multidose OPTI-FREE® RepleniSH™ (test RWD). Subjective comfort and symptoms were assessed after 2 and 4 weeks with each product. After 1 month of wear with each product, lenses were collected and analyzed in the laboratory for total protein, total lysozyme, and percentage of denatured lysozyme. Results. Symptoms of dryness and comfort varied across the day regardless of drop type (p < 0.001) with dryness being maximal on waking, least in the middle of the day, and increased towards the evening. The test RWD provided greater comfort on insertion (p = 0.02), better visual quality (p < 0.01), and less mucous discharge on waking (p = 0.02) than the control product. Lysozyme deposition was significantly reduced after the use of the test RWD as compared to saline (0.73 ± 0.5 &mgr;g/lens vs. 1.14 ± 0.7 &mgr;g/lens; p < 0.001) as was total protein deposition (1.17 ± 0.7 &mgr;g/lens vs. 1.86 ± 0.8 &mgr;g/lens; p < 0.001). Lysozyme denaturation was also reduced with the use of the test RWD compared with the control (76 ± 10% vs. 85 ± 7%; p < 0.01). Conclusions. The use of a RWD containing surface active agents provided greater subjective satisfaction, reduced lysozyme and total protein deposition, and reduced denatured lysozyme than a RWD containing saline alone.

Physical properties of soft contact lens solutions.

Purpose. To investigate the physical properties of commercially available soft contact lens solutions. Methods. The pH, osmolality, surface tension (ST), and viscosity of various soft contact lens solutions were measured at room temperature. Viscosity measurements were also taken at 34°C. The solutions examined were Opti-Free Express (OFX), Opti-Free RepleniSH (OFR), Complete Moisture Plus (COM), UltraCare (UC), ReNu MultiPlus, Sensitive Eyes, AOSept (AO), Clear Care, SoloCare Aqua, and SoftWear saline. The peroxide solutions were measured before and after neutralization. Results. The pH of most solutions was close to neutral (range 7.00–7.36), except for OFX and neutralized AO and Clear Care. The osmolality values of most solutions were in the 275 to 310 mOsm/kg range. OFX exhibited a significantly lower osmolality (225 mOsm/kg; p < 0.001), whereas UC was significantly higher (329 mOsm/kg; p < 0.001). Neutralized AO and SoftWear saline had ST values of approximately 67 mN/m. OFX, OFR, and SoloCare Aqua exhibited low ST values in the 30 to 35 mN/m range. The remaining solutions exhibited intermediate ST values of approximately 40 mN/m. These three groupings were significantly different (p < 0.001). The average viscosity of most solutions at room temperature was between 0.95 and 1.26 cP, except for COM (3.02 cP; p < 0.001). At 34°C, the average viscosity of most solutions was between 0.70 and 0.83 cP, except for COM, which had a viscosity of 1.92 cP (p < 0.001). The un-neutralized peroxide solutions had very different pH and osmolality values from all the solutions that would directly contact the eye (p < 0.001). Their viscosity and ST values were similar (p = NS). Conclusions. This study detailed many physical properties of soft lens solutions that are not readily available and indicated that certain properties vary significantly among these products.

Localization of Lysozyme Sorption to Conventional and Silicone Hydrogel Contact Lenses Using Confocal Microscopy

Purpose: To investigate the distribution profile of hen egg lysozyme (HEL) through poly-2-hydroxyethyl methacrylate (pHEMA)-based lens materials and silicone hydrogel (SH) lens materials using confocal laser scanning microscopy (CLSM). Methods: Five silicone SH materials (balafilcon A, lotrafilcon A, lotrafilcon B, galyfilcon A, senofilcon A) and four pHEMA-based materials (alphafilcon A, etafilcon A, omafilcon A, vifilcon A) were incubated in 1.9 mg/ml protein solution for 24 hours. The protein solution consisted of HEL, which was conjugated with either fluorescein isothiocyanate (FITC) or lucifer yellow VS dilithium salt (LY). CLSM (Zeiss LSM 510 META) identified the location of the fluorescently labeled protein by using 1 μ m depth scans through the lens. In a second experiment, lenses were incubated with 2% 125 I labeled HEL to determine the amount of deposited protein on each lens. Both techniques were combined to describe the individual HEL profiles. Results: After the incubation in fluorescently labeled HEL, all pHEMA-based materials and the SH material balafilcon A accumulated protein throughout the entire lens material, while, for the SH lenses lotrafilcon A and lotrafilcon B, HEL was primarily detected on the lens surface alone. Differences in protein uptake pattern due solely to the two conjugated dyes were most apparent for the SH materials galyfilcon A and senofilcon A; HEL was detected throughout these lenses when conjugated with LY but accumulated primarily on the surface when conjugated with FITC. Conclusion: CLSM in combination with a radiolabel technique can describe both the location and degree of protein deposition on different contact lens materials.

Influence of Protein Deposition on Bacterial Adhesion to Contact Lenses

Purpose. The aim of the study is to determine the adhesion of Gram positive and Gram negative bacteria onto conventional hydrogel (CH) and silicone hydrogel (SH) contact lens materials with and without lysozyme, lactoferrin, and albumin coating. Methods. Four lens types (three SH—balafilcon A, lotrafilcon B, and senofilcon A; one CH—etafilcon A) were coated with lysozyme, lactoferrin, or albumin (uncoated lenses acted as controls) and then incubated in Staphylococcus aureus (Saur 31) or either of two strains of Pseudomonas aeruginosa (Paer 6294 and 6206) for 24 h at 37°C. The total counts of the adhered bacteria were determined using the 3H-thymidine method and viable counts by counting the number of colony-forming units on agar media. Results. All three strains adhered significantly lower to uncoated etafilcon A lenses compared with uncoated SH lenses (p < 0.05). Lysozyme coating on all four lens types increased binding (total and viable counts) of Saur 31 (p < 0.05). However, lysozyme coating did not influence P. aeruginosa adhesion (p > 0.05). Lactoferrin coating on lenses increased binding (total and viable counts) of Saur 31 (p < 0.05). Lactoferrin-coated lenses showed significantly higher total counts (p < 0.05) but significantly lower viable counts (p < 0.05) of adhered P. aeruginosa strains. There was a significant difference between the total and viable counts (p < 0.05) that were bound to lactoferrin-coated lenses. Albumin coating of lenses increased binding (total and viable counts) of all three strains (p < 0.05). Conclusions. Lysozyme deposited on contact lenses does not possess antibacterial activity against certain bacterial strains, whereas lactoferrin possess an antibacterial effect against strains of P. aeruginosa.

Protein deposition and clinical symptoms in daily wear of etafilcon lenses.

Purpose. To determine the relationship between clinical signs and symptoms and protein deposition over 8 h of wear of etafilcon A lenses in symptomatic and asymptomatic contact lens wearers. Methods. Thirty adapted soft contact lens wearers (16 symptomatic and 14 asymptomatic) were fitted with etafilcon A lenses. In vivo wettability, non-invasive tear break-up time, and subjective symptoms (vision, comfort, and dryness) were assessed at baseline and after 2, 4, 6, and 8 h. After 2, 4, 6, and 8 h time points, lenses were collected, and total protein, total lysozyme, and active lysozyme deposition were assessed. Results. There was a significant reduction (p = 0.032) in the non-invasive tear break-up time at 8 h in both groups. In the symptomatic group, there was a significant reduction in subjective comfort and dryness ratings at 6 and 8 h measurement with respect to baseline (p < 0.05). There was a significant increase in total lysozyme and total protein deposition (p = 0.027) across all time points in both groups; most of the lysozyme remained active (>94% at 8 h). Pearsons correlations between subjective symptoms and protein deposition showed poor correlations for total protein/lysozyme and any subjective factor (r < 0.3; p > 0.05), and only weak correlations between dryness and % active lysozyme (r = 0.3 to 0.5 for all time points). However, stronger correlations were found between active lysozyme and subjective comfort (r = 0.6 to 0.7; p < 0.001). Conclusions. In addition to investigating total protein deposited on contact lenses, it is of significant clinical relevance to determine the conformational state of the deposited protein.

Kinetics of Lysozyme Activity Recovered from Conventional and Silicone Hydrogel Contact Lens Materials

We determined the activity of lysozyme recovered from various conventional and silicone hydrogel (SH) contact lens materials as a function of time, using an in vitro model. Polymacon, omafilcon, etafilcon, vifilcon, lotrafilcon A, lotrafilcon B, balafilcon A, galyfilcon A and senofilcon A contact lenses (n = 5) were incubated in lysozyme solution for time periods ranging from 1 h to 28 days. Following the specified incubation period, the lysozyme deposited on the lenses was extracted and the sample extracts were assessed for lysozyme activity and total lysozyme. We found no significant difference (NSD) between omafilcon and polymacon lens materials for the initial 3 days (P > 0.05); however, there was a significant difference between the two lenses from 5 to 28 days (P < 0.05). There was NSD (P > 0.05) between etafilcon and vifilcon lens materials at all time-points and significant differences were seen between various SH lens materials at different time points. After 28 days, lysozyme deposited on etafilcon (90 ± 3%) and vifilcon (91.4 ± 3%) exhibited the greatest activity. Lysozyme deposited on polymacon (17.8 ± 4%), lotrafilcon A (23.4 ± 4%) and lotrafilcon B (24 ± 5%) exhibited the lowest activity. Lysozyme deposited on omafilcon, galyfilcon, senofilcon and balafilcon exhibited 38 ± 3%, 62.3 ± 8%, 47 ± 6% and 61 ± 7% of activity, respectively. The reduction in activity of lysozyme deposited on contact lens materials is time-dependent and the rate of reduction varies between lens materials. This variation in activity recovered from lenses could be due to the differences in surface/bulk material properties or the location of lysozyme on these lenses.

Kinetics of in Vitro Lactoferrin Deposition on Silicone Hydrogel and FDA Group II and Group IV Hydrogel Contact Lens Materials

The aim of this study was to compare the kinetics of lactoferrin deposition on silicone hydrogel (SH) and conventional FDA group II and group IV hydrogel contact lens materials. Seven lens materials, two conventional (etafilcon A, FDA group IV; omafilcon A, FDA group II) and five SH (lotrafilcon A, lotrafilcon B, balafilcon A, galyfilcon A and senofilcon A), were incubated in 1 ml 125I-labeled lactoferrin solution for time periods ranging from 1 h to 28 days. At the end of specified incubation periods radioactive counts were determined on the lenses using an Automatic Gamma Counter. There was a gradual increase in lactoferrin deposition on all the lenses across all time points. At the end of 28 days the amount of lactoferrin/lens in μg was 11.3 ± 1.9 for etafilcon A, 6.8 ± 2.0 for omafilcon A, 2.1 ± 0.9 for lotrafilcon A, 3.1 ± 1.0 for lotrafilcon B, 11.8 ± 2.9 for balafilcon A, 5.4 ± 1.1 for galyfilcon A and 5.6 ± 0.6 for senofilcon A. After 28 days, etafilcon A and balafilcon A deposited lactoferrin to the greatest degree (P < 0.05), but these were not different from each other (P = 0.48), while lotrafilcon A and B deposited the least (P < 0.05 vs. other lenses; P = 0.57 with each other). Galyfilcon A, senofilcon A and omafilcon A (P < 0.05 compared with other lenses; P > 0.05 with each other) deposited intermediate levels of lactoferrin. We concluded that radiochemical analysis is a sensitive and effective technique to determine the small quantities of lactoferrin deposited on SH lenses. The kinetics of lactoferrin deposition on contact lens materials depend on the chemical structure of the lens material.