Lipid-based eye drop formulations for the management of evaporative dry eyes.

Dry eye disease is a progressive prevalent ocular surface disorder that arises from various factors and is characterized by insufficient quality and/or quantity of tears. The underlying pathophysiology is intricate and can progress to chronic, difficult-to-treat conditions. Multiple strategies and therapeutic approaches are utilized in its management that target one or more etiopathological components of dry eyes, which may include aqueous tear deficiency or evaporative dry eyes. The primary focus of this paper is on treatment alternatives that utilize lipids for the treatment of evaporative dry eyes. This may arise from either abnormal lipid production or inadequate lipid spreading caused by meibomian gland dysfunction. The hypothesis behind the development of these lipid-containing eye drops is that if they can imitate the lipid layer, they may be able to help in the management of the signs and symptoms of evaporative dry eyes. The lipids used in commercial formulations for dry eyes are mineral oil, castor oil, phospholipids, omega-3 fatty acid, and medium-chain triglycerides. The literature suggests the potential of lipid-containing eye drops to alleviate some of the signs and symptoms and enhance the quality of life for individuals suffering from evaporative dry eyes.

Biochemistry of human tear film: A review.

The precorneal tear film is a complex mixture of proteins, lipids, metabolites, and electrolytes with different structures and functionalities. Sustainable production of each tear component is vital to the health of the ocular surface. Abnormalities in the tear film components may reflect alterations in the health of the ocular surface or the presence of systemic disease. Despite all the research performed over the recent two decades, our knowledge of the tear film molecular profile in healthy individuals is scant and incomplete. The reported studies have mostly investigated small sample size populations in incomparably varying age groups and ethnic backgrounds. The methods used for detection and measurement of various tear compounds have been widely disparate making the comparison of results difficult. All these in addition to certain environmental factors are known to influence the resultant data. Therefore, studying normal human tear profile would require involvement of a wide range of sample population, factoring in age, race, gender, geographical and environmental parameters. Establishing a normal human tear profile may open the path to fast and simple diagnosis of disease, which in turn may lead to improved prognosis of treatments via early detection of disease.

Development of an enzymatic method for the evaluation of protein deposition on contact lenses.

The aim of this study was to evaluate a new digestion method to quantify protein deposition on contact lenses. Four silicone hydrogel and one hydrogel contact lens material were incubated in lactoferrin, lysozyme, immunoglobulin A, and bovine serum albumin solutions at approximate physiological concentrations and temperature. Immobilized trypsin was used to digest the protein deposits from the contact lens surfaces. The total protein absorbed to lenses was extracted and digested using sequencing grade trypsin. The tryptic peptides were quantified using selected reaction monitoring mass spectrometry. The concentration of surface protein deposits was either lower than or the same as the total protein for all lens types and proteins. Immobilised trypsin can digest protein deposits from the surface of contact lenses. This ability to analyse the amount of protein at a contact lens surface may help in elucidating the effect of surface deposition on clinical outcomes during lens wear.

A method for studying lipid adsorption to silicone hydrogel contact lenses.

The aim of this study was to develop an experimental methodology to measure lipid deposition with contact lenses. Contact lenses were incubated in a lipid solution. The amount and types of adsorbed lipids were assessed using mass spectrometry and confocal microscopy. The recovery of lipids from lenses varied with lipid and lens type. Most non-polar and polar lipids were desorbed from lenses during the first 5 min of extraction. Fluorescently labelled phosphatidylcholine bound within the matrix of Senofilcon A lenses but to the surface of Lotrafilcon B lenses, whereas fluorescently labelled cholesteryl ester was found throughout both lenses. The efficacy of extraction of lipids from contact lenses varies for different lipid classes and different lens materials. Differences in the amount and time of lipid desorption probably resulted from the strength of the bond between lipid and lens polymer and the depth of adsorption of lipid in the polymer.

Profiling of non-polar lipids in tears of contact lens wearers during the day.

PURPOSE: This study explored whether the non-polar lipids in the human tear fluid lipidome show diurnal variation with and without contact lens wear. It also addressed the relationship between changes in ocular comfort during the day with the level of non-polar lipids. METHODS: Tear samples were collected in the morning and evening with and without contact lenses using fine glass capillary tubes and were analysed by chip-based nano-electrospray ionization tandem mass spectrometric techniques. Tear levels of cholesteryl esters (CE), wax esters (WE) and triacylglycerides (TAG) were quantified. RESULTS: TAG 48:0, 52:0 and WE 26:0/16:0, and 27:0/17:0 increased from morning to evening. TAG 52:2, WE 21:0/16:0, 21:0/18:1 and 28:0/18:1 decreased during the day when no lenses were worn. CE 21:0 was the only non-polar lipid that increased from morning to evening in contact lens wear. WE 21:0/16:0 and 27:0/17:0 were lower in the morning in contact lens wear compared to no lens wear (p ≤ 0.05). The level of non-polar lipids did not correlate with ocular comfort at the end of the day. CONCLUSION: Even though the level of some of non-polar lipid species changed from morning to evening the total level of major tear non-polar lipids remained unchanged during the day with and without contact lens wear. The effect of change in the quantity and structure of lipid species on tear stability and ocular comfort warrants more investigation.

CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears.

Contact lens materials have undergone significant changes over the past 20 years, particularly with respect to the introduction of silicone hydrogel materials. Whilst this development addressed hypoxic issues, other important areas relating to contact lens success, notably comfort, require further research. Contact lens wettability remains a crucially important part of biocompatibility. Contact lenses can be made more wettable by incorporation of surfactants into blister packs, internal wetting agents, surface treatments or care solutions. However, there remains no clear association between contact lens wettability and comfort, making it challenging to determine the potential for these approaches to be of significant clinical benefit. Most contact lenses are used on a daily wear, reusable basis, which requires them to be disinfected when not worn. The ideal disinfecting solution would also improve comfort during wear. However, balancing these requirements with other factors, including biocompatibility, remains a challenge. Soft lens materials invariably take up and subsequently release certain components of disinfecting solutions onto the ocular surface. This may affect tear film stability and the normal ocular microbiome, and further research is needed in this area to determine whether this has any affect on comfort. Finally, contact lens materials sorb components of the tear film, and these interactions are complex and may change the biochemistry of the tear film, which in turn may affect their comfort. In conclusion, the interaction between lens materials, tear film and disinfection solution plays an important role in the biocompatibility of lenses. However, the exact role and whether this can be altered to improve biocompatibility and comfort during wear remains debatable. This report summarises the best available evidence to examine this complex relationship and the opportunities for practitioners to enhance in-eye comfort of contemporary lenses, along with providing suggestions for areas of study that may provide further information on this topic.

Differences in Tear Film Biochemistry of Symptomatic and Asymptomatic Lens Wearers.

SIGNIFICANCE: The concentration of selected proteins and inflammatory mediators in tears of symptomatic and asymptomatic contact lens wearers were quantified. The level of leukotriene B4 was higher in the symptomatic group. This may suggest that inflammation can be the cause of discomfort sensation at the end of day. PURPOSE: The present study aims to quantify the concentration of selected tear lipids and proteins in symptomatic and asymptomatic contact lens wearers. METHODS: Unstimulated evening tears were collected using glass capillary tubes from 45 healthy, adapted contact lens wearers. Twenty-two had self-described symptoms of dryness and discomfort with contact lenses and 23 were asymptomatic. Tear proteins were assayed using selected reaction monitoring mass spectrometry. Enzyme immunoassay kits were used to measure prostaglandins, leukotriene B4, and cysteinyl leukotrienes. Ocular comfort was rated on a scale of 1 to 100 at the time of tear collection. RESULTS: The average evening comfort level was above 70 for the asymptomatic (83.96 ± 9.51, mean ± SE) and equal or below 70 for the symptomatic group (57.28 ± 12.38) (P < .001). LTB4 was significantly higher in symptomatic than asymptomatic contact lens wearers (0.32 ± 0.06 ng/µL vs. 0.17 ± 0.04 ng/µL, respectively; P = .03). Lysozyme was slightly but not significantly lower in symptomatic subjects (symptomatic 0.58 ± 0.10 mg/mL vs. asymptomatic 1.73 ± 0.46 mg/mL; P = .10). The levels of lactoferrin, lipocalin 1, proline-rich 4, prolactin-induced protein, prostaglandins, and cysteinyl leukotrienes were unchanged (P > .1) between symptomatic and asymptomatic subjects. CONCLUSIONS: The LTB4 concentration was significantly higher in symptomatic contact lens wearers compared to the asymptomatic group, and this may partly mediate the discomfort response during lens wear in the symptomatic lens wearers. No other differences were found in the level of tear factors of interest between the two groups.

Relation between Ocular Comfort, Arachidonic Acid Mediators, and Histamine.

PURPOSE: Contact lenses are associated with discomfort during wear. This may be the result of stimulation of the ocular surface and production of pro-inflammatory mediators which are then released into the tears. This study examined changes in the concentration in tears of arachidonic acid metabolites (AAM) prostaglandins, cysteinyl leukotrienes, and resolvin-D1, as well as histamine in a general contact lens population in the morning and evening. METHOD: Tears were collected twice a day (morning and evening) for up to 10 days on two different occasions (with and without contact lens wear) from 30 experienced contact lens wearers for analysis of AAM and a separate group (N = 33) for analysis of histamine. Ocular comfort was rated subjectively on an ordinal scale at each time of tear collection. Tears were analyzed using commercial immunoassay-based kits. Statistical analysis was performed using linear mixed model test. RESULTS: Ocular comfort decreased from morning to evening with and without contact lenses (p = 0.001), and the difference in comfort in the evening was greater with contact lens wear (80.9 ± 16.2 vs. 75.5 ± 16.8; p = 0.008). The total concentration of PGs (10.7 ± 10.8 ng/ml), cysteinyl leukotrienes (8.7 ± 0.38 ng/ml), resolvin-D1 (1.6 ± 0.5 ng/ml), or histamine 13.8 ± 10.4 ng/ml) did not change during the day or during contact lens wear (p > 0.05). CONCLUSIONS: Prostaglandins, cysteinyl leukotrienes, resolvin-D1, or histamine concentrations did not alter in relation to changes in comfort of the eye during the day or during contact lens wear. These results suggest that release of these mediators is not responsible for contact lens discomfort.

Contact Lens-Induced Discomfort and Inflammatory Mediator Changes in Tears.

PURPOSE: Studies indicate that contact lens (CL) discontinuation mostly occurs because of dryness and discomfort symptoms. This study aimed to investigate relationships between changes in the concentration of tear inflammatory mediators with subjective comfort ratings with CL wear and no contact lens wear between morning and evening. METHOD: Forty-five subjects collected tears twice daily in the morning and in the evening with or without lenses. Comfort was rated subjectively on a scale from 1 to 100 (where 100 was extremely comfortable) just before each tear collection. Tear samples were assayed for complement components (C3 and C3a), leukotriene B4 (LTB4), secretory phospholipase A2 (sPLA2), secretory immunoglobulin A (sIgA), and bradykinin using commercially available immuno-based assay kits. RESULTS: Comfort ratings showed a statistically significant decline from morning to evening both with CL (89.0±10.1 AM vs. 76.7±15.2 PM; P<0.001) and without CL (89.1±10.2 AM vs. 84.2±12.6 PM; P<0.005) wear. The decline was steeper with lens wear (P<0.001). Bradykinin and sPLA2 levels did not change between morning and evening or with CL wear (P>0.05). Leukotriene B4 levels were slightly higher in CL (CL 43.4±12.6 pg/ml vs. No CL 39.4±13.4 pg/mL; P=0.034), whereas the concentration of LTB4, C3, C3a, and sIgA dropped by the end of the day in the presence or absence of lens wear (P<0.001). For most mediators, tear levels were not correlated with comfort ratings in any of the conditions. Leukotriene B4 had a higher concentration in the evening, and when measured as a ratio to sIgA, there was a trend for increased concentration of this mediator during CL wear. CONCLUSION: Although specific mediators showed changes from morning to evening with and without lens wear, most of these were not correlated with subjective comfort ratings in lens wear. The only mediator that showed an increase in concentration during the day and during lens wear was LTB4, and further studies on this mediator are warranted.

Evaluation of Protamine as a Disinfectant for Contact Lenses.

PURPOSE: To investigate the ability of protamine, alone or in combination with other antimicrobial agents, to kill bacteria and fungi associated with contact lens-related keratitis. METHODS: The International Organization for Standardization 14729:2001 procedure was used to test the antimicrobial activity of solutions of protamine (23-228 µM) with and without polyhexamethylene biguanide (PHMB) and ethylenediamine tetra-acetic acid (EDTA). The recommended ISO panel of microbes along with six clinical isolates was tested. The effect of increasing sodium chloride concentration on the antimicrobial activity was also assessed. The cytotoxicity of the final protamine/EDTA/PHMB solution was measured using ISO 10993-5 standard assays. RESULTS: Protamine gave a dose-dependent antimicrobial effect, with the highest effect for most strains being at 228 µM (≥6 log reductions of viable bacteria and ≥1 log reduction of viable fungi). Addition of EDTA and PHMB increased the antimicrobial effect for all strains except Pseudomonas aeruginosa ATCC6538, which had optimum activity (≥6 log inhibition) even in protamine alone. The optimum antimicrobial activity of all microbes was achieved in 0.2% sodium chloride, but even in 0.8% sodium chloride, the activity met or exceeded the ISO standard (>3 log reductions for bacteria and >1 log reduction for fungi). None of the formulations was cytotoxic to mammalian cells. CONCLUSIONS: This study highlights the potential for protamine to be used for the development of effective multipurpose disinfection solutions. Further investigations such as stability, compatibility with contact lenses, and in vivo toxicity are warranted.

Contact Lens-Induced Discomfort and Protein Changes in Tears.

PURPOSE: Ocular discomfort is among the main causes of contact lens wear discontinuation. This study investigated the association between subjective ocular comfort ratings and diurnal changes in tear protein concentrations with and without contact lens wear. METHODS: The study was a prospective, open-label, single-group two-staged investigation. Basal tears were collected from 30 experienced contact lens wearers twice a day (morning and evening) using a noninvasive method without lens wear (stage 1) and during wear of Etafilcon A contact lenses (stage 2) for 7 to 10 days. Subjects rated their ocular comfort on a scale of 1 to 100 (with 100 as extremely comfortable) at each time of tear collection. Tears were analyzed using liquid quadrupole mass spectrometry in conjunction with selected reaction monitoring (SRM) method. RESULTS: End-of-day comfort was reduced when wearing lenses (87.8 ± 14.3 AM vs. 79.2 ± 16.6 PM) compared to no lens wear (88.3 ± 12.6 AM vs. 84.7 ± 13.3 PM) (AM vs. PM, p < 0.05). A greater reduction in comfort over the day was seen during lens wear (p < 0.01). The concentration of prolactin-induced protein increased from morning to evening in both stages (mean ± SD; 0.08 ± 0.04 mg/ml, AM vs. 0.09 ± 0.05 mg/ml, PM, p < 0.05). There was no change in the concentration of lactoferrin (1.20 ± 0.77 mg/ml), lysozyme (2.11 ± 1.50 mg/ml), lipocalin 1 (1.75 ± 0.99 mg/ml), or proline-rich protein 4 (0.80 ± 0.49 mg/ml). The prolactin-induced protein concentration was negatively associated with discomfort levels in tears (p < 0.05, r = -0.29). CONCLUSIONS: Only the absolute concentration of prolactin-induced protein correlated with subjective comfort ratings. Taking into consideration that prolactin-induced protein can be associated with disruption in water transport in lacrimal glands, our findings may indicate that changes to aqueous secretion are associated with contact lens discomfort.

Method development for quantification of five tear proteins using selected reaction monitoring (SRM) mass spectrometry.

PURPOSE: To establish the use of selected reaction monitoring (SRM) mass spectrometry for quantification of tear proteins. METHODS: Tear samples were collected on multiple occasions (7-10 days) from healthy subjects with contact lens wear (CL = 3) and without contact lens wear (NCL = 4). Tear proteins were denatured using 8M urea, reduced with iodoacetamide, precipitated by acetone, and digested using trypsin. Internal standards were included by adding isotopically-labelled standards of known concentrations to the samples. Lactoferrin, lysozyme, prolactin-induced protein, lipocalin 1, and proline-rich protein 4 were quantified using liquid chromatography-triple quadruple mass spectrometry in conjunction with selected reaction monitoring. RESULTS: The limits of quantification for the selected peptides were below 50 pg/µL. The recovery of peptides from spiked digested tears was greater than or equal to 56% and the coefficient of variation values were less than or equal to 16%. The concentration of lactoferrin (1.20 ± 0.77 µg/µL), lysozyme (2.11 ± 1.50 µg/µL), and lipocalin-1 (1.75 ± 0.99 µg/µL) were consistent with previous ELISA studies. Tear levels of prolactin-induced protein (0.09 ± 0.06 µg/µL) and proline-rich 4 (0.80 ± 0.50 µg/µL) are reported here for the first time. CONCLUSIONS: The SRM method can be used for simultaneous detection and quantification of selected proteins in low volumes of human tear samples (2.5 µL per sample) without prior purification of each protein component or need for antibodies.

Bacterial adhesion to unworn and worn silicone hydrogel lenses.

PURPOSE: The objective of this study was to determine the bacterial adhesion to various silicone hydrogel lens materials and to determine whether lens wear modulated adhesion. METHODS: Bacterial adhesion (total and viable cells) of Staphylococcus aureus (31, 38, and ATCC 6538) and Pseudomonas aeruginosa (6294, 6206, and GSU-3) to 10 commercially available different unworn and worn silicone hydrogel lenses was measured. Results of adhesion were correlated to polymer and surface properties of contact lenses. RESULTS: S. aureus adhesion to unworn lenses ranged from 2.8 × 10 to 4.4 × 10 colony forming units per lens. The highest adhesion was to lotrafilcon A lenses, and the lowest adhesion was to asmofilcon A lenses. P. aeruginosa adhesion to unworn lenses ranged from 8.9 × 10 to 3.2 × 10 colony forming units per lens. The highest adhesion was to comfilcon A lenses, and the lowest adhesion was to asmofilcon A and balafilcon A lenses. Lens wear altered bacterial adhesion, but the effect was specific to lens and strain type. Adhesion of bacteria, regardless of genera/species or lens wear, was generally correlated with the hydrophobicity of the lens; the less hydrophobic the lens surface, the greater the adhesion. CONCLUSIONS: P. aeruginosa adhered in higher numbers to lenses in comparison with S. aureus strains, regardless of the lens type or lens wear. The effect of lens wear was specific to strain and lens. Hydrophobicity of the silicone hydrogel lens surface influenced the adhesion of bacterial cells.

Importance of rub and rinse in use of multipurpose contact lens solution.

PURPOSE: The introduction of contact lens multipurpose disinfection solution (MPDS) that can be used in conjunction with a "no-rub" regimen has simplified lens care requirements. Once adhered to a surface, microorganisms can become less susceptible to disinfection. The aim of the study was to evaluate the effect of various regimen steps on the efficacy of MPDS when used with silicone hydrogel and conventional lenses. METHODS: Commercially available MPDSs containing polyquad or polyhexamethylene biguanide were used in conjunction with two types of silicone hydrogel (lotrafilcon B and galyfilcon A) and one type of conventional soft contact lenses (etafilcon A). Challenge microorganisms included Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, Serratia marcescens ATCC 13880, Fusarium solani ATCC 36031, Candida albicans ATCC 10231, or Acanthamoeba polyphaga Ros. The effect of regimen steps "rub and rinse," "rinse-only," or "no rub and no rinse" on the disinfection efficacy of test MPDSs was examined using the ISO 14729 Regimen Test procedure. RESULTS: Overall, the greatest efficacy of MPDSs was observed when "rub and rinse" was performed before disinfection with each of the microorganisms tested, regardless of lens type. "No rub and no rinse" steps resulted in a greater load of microorganisms remaining on lenses compared with the other regimens (p < 0.05). When "rinse-only" was performed before disinfection, the MPDS containing polyquad performed generally better (p < 0.05) than MPDSs containing polyhexamethylene biguanide against bacteria. Significantly, less microorganisms were recovered from galyfilcon A than from other lenses (p < 0.05) when MPDSs were used with "rinse-only" step. CONCLUSIONS: This study has demonstrated that "rub and rinse" is the most effective regimen and should be recommended in conjunction with all multipurpose lens care solutions and all contact lens types, particularly with silicone hydrogel lenses.

Soft contact lens disinfection solution efficacy: clinical Fusarium isolates vs. ATCC 36031.

PURPOSE: To compare the disinfecting efficacy of five soft contact lens multipurpose disinfection solutions (MPDS) against Fusarium solani clinical isolates and the ISO standard ATCC 36031 strain. METHODS: Three commercially available and two recalled MPDS were tested using the ISO/CD 14,729 stand-alone test for contact lens care products against 10 ocular isolates of F. solani and the ATCC 36031 strain. The effect of filtering the fungal suspension before incubating in MPDS was also tested. An average log reduction in colony forming units at the manufacturer's minimum recommended disinfection time was determined and compared with criteria for stand-alone disinfection products for each MPDS against each strain. RESULTS: No difference between filtered and unfiltered fungal suspensions was observed for the ISO standard, whereas in one MPDS the representative clinical isolate showed significantly increased resistance when unfiltered. All but one solution met the stand-alone criteria of 1.0-log reduction of colony forming units against the recommended ISO standard strain ATCC 36031. However, there was wide variation in the ability of MPDS to meet the ISO disinfection criteria when tested against clinical isolates. Among the commercially available MPDS, the two polyquaternium-based solutions showed a higher disinfecting efficacy than the biguanide-based solution. The two recalled solutions showed a lower disinfecting efficacy than the polyquaternium-based solutions. Further, the clinical isolates were significantly more resistant to disinfection than was the recommended ISO strain. CONCLUSIONS: The effect of filtering the fungal suspension to remove hyphae seems to be relevant in the clinical isolate tested, but not in the ISO strain. Clinical isolates were significantly more resistant to disinfection than the recommended ISO strain in the presence of both the commercially available and the recalled MPDS. The use of clinical isolates in stand-alone disinfection testing is indicated. Because there were significant differences in increased resistance exhibited by clinical isolates and in a mixed (unfiltered) culture the use of a single laboratory strain may be insufficient to provide assurance that the disinfection solution will be effective against clinical isolates.