Please use the archived list on the right to look at past peer-reviewed articles.
Bitton,E., Keech,A., Jones,L., Simpson,T. Subjective and objective variation of the tear film pre- and post-sleep. Optometry and Vision Science 2008;85,8:740-749. [ Show Abstract ]
PURPOSE: To date, few studies have correlated the overnight effects of the preocular tear film (POTF) with subjective symptoms. This study investigates the POTF volume and stability, bulbar hyperemia (BH), tear ferning (TF) and the participant's subjective symptoms, pre- and post-sleep. METHODS: Thirty subjects were recruited, consisting of two evenly distributed groups who were symptomatic of dry eye (DE) and those that were asymptomatic dry eye, determined using the McMonnies questionnaire. Subjects were evaluated at 10 p.m. (baseline), on waking at 7 a.m., and then hourly until 10 a.m. At each visit, tear meniscus height (TMH), various subjective factors, BH and POTF stability by non-invasive break-up time (NIBUT) were assessed. Tear collection was performed at 10 p.m, 7 and 10 a.m. for TF analysis. RESULTS: With the exception of burning, all other symptoms (comfort, dryness, clarity of vision, and grittiness) revealed an overnight change (p < 0.05) within each group, but not between the two groups (p > 0.05). Both the tear meniscus height and BH were elevated upon waking and differed significantly between test times for each group (p < 0.05), but not between groups (p > 0.05). NIBUT was lower for the DE group (p < 0.001). The non-dry eye (NDE) group did not significantly alter over time (p > 0.05), but the DE group did (p = 0.004), with a longer NIBUT in the morning. TF demonstrated a degraded pattern upon waking for both groups (p < 0.05). Most of the changes returned to baseline within an hour after waking. CONCLUSIONS: The properties of the POTF undergo a change during extended periods of eye closure and the human POTF is different upon waking to that present immediately before sleep. Most of the parameters determined rapidly revert to baseline levels once the POTF is allowed to refresh.
Caffery,B., Joyce,E., Boone,A., Slomovic,A., Simpson,T., Jones,L., Senchyna,M. Tear lipocalin and lysozyme in sjögren and non-sjogren dry eye. Optometry and Vision Science 2008;85,8:661-667. [ Show Abstract ]
PURPOSE.: To evaluate the concentration of tear lipocalin, lysozyme, and total protein in Sjogrens Syndrome (SS), non-Sjogrens keratoconjunctivitis sicca (KCS), and non-dry-eyed (NDE) individuals. METHODS.: Seventy-six subjects were recruited for this study: 25 SS subjects; 25 KCS subjects, and 26 NDE individuals. Symptoms were measured with a visual analogue scale. Tear flow was measured by the Schirmer I test without anesthesia. Tears were collected using an eye wash technique. Total tear protein was quantified using the DC Protein Assay Kit. Tear lipocalin and lysozyme were quantified via Western blotting performed on a Phast System. RESULTS.: By definition, the SS and KCS groups both had significantly lower mean Schirmer scores (5.12 ± 5.96 mm and 7.84 ± 7.35 mm) compared with the NDE group (23.83 ± 7.85 mm; p < 0.0001). There was no difference in mean Schirmer scores between SS and KCS groups (p = 0.19). The tear film of the SS group was characterized by significantly reduced (p < 0.0001) total protein and lipocalin concentrations compared with both KCS and NDE groups. No difference between the KCS and NDE groups was found in total protein (p = 0.92) or lipocalin (p = 0.19) concentration. In contrast, the concentration of tear film lysozyme was found to be statistically similar in all three groups examined. No statistically significant correlation was found in any group between mean Schirmer values compared with total protein, lipocalin or lysozyme concentration. CONCLUSION.: Our data demonstrate a biochemical distinction between the Sjogrens group compared with both KCS and control groups, in that both tear lipocalin and total tear protein were significantly reduced. Although correlations were not found between protein measurements and tear flow, a combination of tests including Schirmer I and quantitation of tear film biomarkers may allow for the identification of SS patients without the need for invasive testing. © 2008 American Academy of Optometry.
Dalton,K., Subbaraman,L. N., Rogers,R., Jones,L. Physical properties of soft contact lens solutions. Optometry and Vision Science 2008;85,2:122-128. [ Show Abstract ]
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.
Dumbleton,K. A., Woods,C. A., Jones,L. W., Fonn,D. Comfort and adaptation to silicone hydrogel lenses for daily wear. Eye and Contact Lens 2008;34,4:215-223. [ Show Abstract ]
Objectives. To investigate initial comfort and adaptation of currently successful low oxygen transmissibility soft lens wearers refitted with silicone hydrogel (SH) lenses for daily wear. Methods. Fifty-five subjects were enrolled in a subject-masked 5-month clinical trial in which they wore 5 SH lenses in a randomized, crossover design. Comfort, burning, and dryness were rated on scales of 0 to 100 immediately on insertion and the time for lens settling was recorded. Symptoms were then rated at various times, using BlackBerry wireless communication devices (Research in Motion, Waterloo, Canada), during the day for 2 cycles of 2 weeks wear for each lens type. Results. Comfort immediately on insertion varied between lens types (P=0.002). All lens types were reported by the subjects to have settled within 30 to 45 sec of insertion (P=0.14) and "settled" comfort was greater than comfort immediately on insertion (P<0.001). Comfort within the first hour of wear also varied between lens types (P=0.02). Comfort during the day decreased significantly for all lenses (P=0.001), but there was no difference between lenses (P=0.19) and no effect of lens age (P=0.15). The wearing times were greater with the SH lenses than the habitual lenses worn before study commencement (P=0.001). Overall performance of the lenses after 4 weeks was high, with no difference between lenses (P=0.45). Conclusions. Initial comfort and adaptation to all SH lenses were good and no differences in the overall ratings were found between the 5 SH lenses investigated. Decreased comfort was noted later in the day with all lens types, but longer wearing times were reported with the SH lenses than previous hydroxyethyl methacrylate-based lenses. © 2008 Contact Lens Association of Ophthalmologists, Inc.
Glasier,M. -A, Keech,A., Sheardown,H., Subbaraman,L. N., Jones,L. Conformational and quantitative characterization of lysozyme extracted from galyfilcon and senofilcon silicone hydrogel contact lenses. Current eye research 2008;33,1:1-11. [ Show Abstract ]
PURPOSE: To compare two solvents for retrieval of lysozyme deposited on a silicone hydrogel (SH) contact lens material galyfilcon A (GA; Acuvue Advance). METHODS: Two buffers used were 50:50 acetonitrile/0.02% trifluoroacetic acid (buffer 1) and 50:50 acetonitrile/50 mM NaOH (buffer 2). RESULTS: Extraction efficiency from GA lenses was 74% (buffer 1) and 83% (buffer 2). Buffer 2 decreased lysozyme activity > buffer 1. Ex vivo GA lenses showed total protein deposition of 2-16 microg/lens with total lysozyme deposition of 0.3-3.9 microg/lens. CONCLUSIONS: We have developed a low acid strength extraction buffer that can be used to efficiently extract active lysozyme protein from novel siloxane-based contact lens materials.
Glasier,M. -A, Subbaraman,L. N., Senchyna,M., Jones,L. A solid-phase assay for the quantitation of total protein eluted from balafilcon, lotrafilcon, and etafilcon contact lenses. Current eye research 2008;33,8:631-640. [ Show Abstract ]
PURPOSE: To compare two variations of a membrane-based protein assay utilizing Amido black (AB) detection with a commercially available 3-(4-carboxybenzoyl) quinoline-2-carboxaldehyde (CBQCA) assay for use in the quantitation of individual tear proteins, pooled human tear proteins, and protein extracted from ex vivo lotrafilcon A, balafilcon A, and etafilcon A contact lens materials. METHODS: Ex vivo contact lens extracts, pooled human tears, and individual tear proteins (human serum albumin (HSA), bovine lactoferrin, human secretory immunoglobulin A (sIgA), human lysozyme) were subjected to three solid-phase assays: AB on polyvinylidene difluoride (AB on PVDF) and AB on nitrocellulose (AB on NC) and the CBQCA assay. Micro-bicinchonic acid (micro-BCA) assay was also employed with lens extracts to determine total protein concentration. Individual and pooled tear proteins were referenced to a micro version of the quantitative ninhydrin protein assay. RESULTS: The CBQCA demonstrated the greatest overall sensitivity and lowest intra- and inter-assay variability. AB on NC demonstrated the most accurate ability to quantify total protein in pooled human tear samples, although it also displayed the greatest protein-to-protein variation using individual tear proteins. The CBQCA assay displayed the greatest cross-reactivity with unworn balafilcon and lotrafilcon lens extracts, whereas AB on NC demonstrated the least. AB on NC measured similar amounts of total protein in extracted ex vivo lenses as the CBQCA assay if background interference was subtracted from CBQCA values. AB on PVDF measured the lowest amount of deposited protein from ex vivo lenses. CONCLUSION: Both the AB on NC and CBQCA assays can be used to measure protein in extracts of lotrafilcon, balafilcon, and etafilcon lens materials.
Haque,S., Fonn,D., Simpson,T., Jones,L. Epithelial thickness changes from the induction of myopia with CRTH RGP contact lenses. Investigative Ophthalmology and Visual Science 2008;49,8:3345-3350. [ Show Abstract ]
PURPOSE. To investigate changes in epithelial thickness after overnight wear of CRTH rigid gas-permeable (RGP) lenses (Paragon Vision Sciences, Mesa, AZ) for the correction of hyperopia. METHODS. Twenty subjects wore a +3.50 D hyperopia-correcting CRTH lens on one eye for a single night in an attempt to induce myopia (first study). The untreated eye served as the control. Corneal and epithelial thickness was measured at nine points across the horizontal meridian by OCT. Measurements were obtained the night before lens wear, immediately after lens removal the next morning, and 1, 3, 6, and 12 hours after removal. Measurements were obtained 28 hours later, to observe recovery. Then, the attempted hyperopic corrections of +1.50 and +3.50 D were evaluated, using CRTH lenses in both eyes of 20 subjects for a single night (second study). RESULTS. All values were compared to baseline unless otherwise stated. In the first study, the treated eye's central and midperipheral epithelial thickness increased by 21.5% ± 8.6% and 13.3% ± 7.6%, respectively, after lens removal (P < 0.001). The control eye's central epithelial thickness (CET) increased by 7.1% ± 6.0% (P < 0.05). In the second study, CET increased by 17.6% ± 8.5% (P < 0.001) in the +3.50 D-treated eye and by 13.3% ± 4.8% (P < 0.001) in the +1.50 D-treated eye. Midperipheral epithelial thickening was 5.9% ± 4.7% (P < 0.05) in the +3.50 D-treated eye and 6.0% ± 6.3% (P < 0.05) in the +1.50 D-treated eye. CONCLUSIONS. CRTH lenses, designed to correct hyperopia, when worn overnight, caused an increase in CET. The amount of epithelial change seemed to differ with modified lens design. Copyright © Association for Research in Vision and Ophthalmology.
Hui,A., Boone,A., Jones,L. Uptake and release of ciprofloxacin-HCl from conventional and silicone hydrogel contact lens materials.. Eye & contact lens 2008;34,5:266-271. [ Show Abstract ]
OBJECTIVES: To investigate the uptake and release characteristics of the antibiotic ciprofloxacin-HCl in conventional and silicone hydrogel lenses, and evaluate their potential as therapeutic drug delivery devices. METHODS: Nine differing soft contact lens materials were soaked in a 0.3% ciprofloxacin-HCl solution at 34 degrees C. The uptake of the drug into the lenses was measured by the change in concentration over 24 hours using fluorescence spectrophotometry. The lenses were then placed in a buffered saline solution, and the release of the drug from the lenses was also measured using spectrophotometry. RESULTS: The release of drug varied from 0.016 +/- 0.004 mg/lens for lotrafilcon A lenses to 0.42 +/- 0.03 mg/lens for etafilcon A lenses, with an average of 0.133 mg/lens. The 3 conventional lenses used in the study released a statistically significantly different amount of drug when compared with the silicone hydrogels. The release of drug was very rapid, with drug release reaching a plateau after no more than 10 minutes for the majority of the lenses. The majority of the lenses were able to release enough drug to achieve minimum inhibitory concentration 90 for most resistant ocular pathogens. Ciprofloxacin was found to heavily precipitate on the etafilcon A lenses during the release phase at physiologic pH. CONCLUSION: While balafilcon A released the most drug from the silicone hydrogel materials, all materials released the drug too quickly to be effective as drug delivery devices.
Lu,F., Simpson,T., Sorbara,L., Fonn,D. Malleability of the ocular surface in response to mechanical stress induced by orthokeratology contact lenses. Cornea 2008;27,2:133-141. [ Show Abstract ]
PURPOSE: To determine the malleability of the ocular surface by examining the acute effects of local mechanical stress on optical performance, corneal shape, and corneal/epithelial thickness after corneal refractive therapy for myopia and hyperopia (CRT and CRTH). METHODS: Twenty ametropes (spherical equivalent: -2.08 ± 2.31 D) wore CRT and CRTH lenses in a random order on 1 eye (randomly selected). The lenses were worn for 15, 30, and 60 minutes (randomly ordered, with each period taking place on a different day). Refractive error, aberrations, corneal topography, and corneal/epithelial thickness (using OCT) were measured before and after lens wear. The measurements were performed on the control eyes at the 60-minute visit only. RESULTS: With both CRT and CRTH lens wear, significant changes occurred in many parameters from the 15-minute time point. The refractive error and defocus decreased after CRT lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P 0.05). CONCLUSIONS: CRT lenses for myopia and hyperopia induce significant structural and optical changes in as little as 15 minutes. The cornea, particularly the epithelium, is remarkably malleable, with rapid steepening and flattening possible in little time. © 2008 Lippincott Williams & Wilkins, Inc.
Luensmann,D., Jones,L. Albumin adsorption to contact lens materials: A review. Contact Lens and Anterior Eye 2008;31,4:179-187. [ Show Abstract ]
During contact lens wear, tear film components such as lipids, mucins and proteins tend to deposit on and within the lens material and may cause discomfort, reduced vision and inflammatory reactions. The tear film protein that has attracted most interest when studying contact lens deposition is the small (14 kDa), positively charged protein lysozyme. Albumin, which is a much larger protein (66 kDa) with an overall net negative charge is also of interest, and shows very different adsorption patterns to lysozyme. The concentration of albumin in the tear film is relatively low compared to the concentration in blood serum, but this value increases markedly under various conditions, including when the eye is closed, during contact lens wear and in various dry eye states. Gaining an understanding of the manner in which albumin deposits on biomaterials is of importance for contact lens wear, as well as for other medical applications where HEMA-based materials are used for implants, artificial blood vessels or drug delivery devices. This review paper summarizes the impact of individual material compositions, water content, hydrophobicity and electrostatic attraction on the adsorption behavior of the protein albumin.
Schulze,M. M., Hutchings,N., Simpson,T. L. The use of fractal analysis and photometry to estimate the accuracy of bulbar redness grading scales. Investigative Ophthalmology and Visual Science 2008;49,4:1398-1406. [ Show Abstract ]
Purpose. To use physical attributes of redness to determine the accuracy of four bulbar redness grading scales, and to cross- calibrate the scales based on these physical measures. Methods. Two image-processing metrics, fractal dimension (D) and percentage of pixel coverage (% PC), as well as photometric chromaticity were selected as physical measures, to describe and compare grades of bulbar redness among the McMonnies/Chapman-Davies scale, the Efron Scale, the Institute for Eye Research scale, and a validated scale developed at the Centre for Contact Lens Research. Two sets of images were prepared by using image processing: The first included multiple segments covering the largest possible region of interest (ROI) within the bulbar conjunctiva in the original images; the second contained modified scale images that were matched in size and resolution across scales, and a single, equally-sized ROI. To measure photometric chromaticity, the original scale images were displayed on a computer monitor, and multiple conjunctival segments were analyzed. Pearson correlation coefficients between each set of image metrics and the reference image grades were calculated to determine the accuracy of the scales. Results. Correlations were high between reference image grades and all sets of objective metrics (all Pearson's r ≥ 0.88, P ≤ 0.05); each physical attribute pointed to a different scale as being most accurate. Independent of the physical attribute used, there were wide discrepancies between scale grades, with almost no overlap when cross-calibrating and comparing the scales. Conclusions. Despite the generally strong linear associations between the physical characteristics of reference images in each scale, the scales themselves are not inherently accurate and are too different to allow for cross-calibration. Copyright © Association for Research in Vision and Ophthalmology.
Simpson,T. L., Situ,P., Jones,L. W., Fonn,D. Dry eye symptoms assessed by four questionnaires. Optometry and Vision Science 2008;85,8:E692-E699. [ Show Abstract ]
PURPOSE.: To establish the relationships between commonly used questionnaires including Dry Eye Questionnaire, McMonnies Questionnaire, and Ocular Surface Disease Index, and to test the construct and face validity of the simple Subjective Evaluation of Symptom of Dryness. METHODS.: Ninety-seven non-contact lens wearing subjects were enrolled in the study and classified into either a "dry" and "non-dry" group using a single score from an initially applied subjective evaluation of symptom of dryness. The four questionnaires were then completed in a random order. The unidimensionality and accuracy of the responses was assessed using Rasch and receiver (or relative) operating characteristics curve analysis and the characteristics of and association between symptoms were compared using non-parametric statistics. RESULTS.: The responses from the Dry Eye Questionnaire, McMonnies Questionnaire, and Ocular Surface Disease Index met the Rasch analysis criterion of unidimensionality. Each test separated the symptomatic and asymptomatic groups well [all receiver (or relative) operating characteristics area-under-the-curve statistics at least 0.88] and there were significant associations between the results from each questionnaire (all Spearman ρ at least 0.64). CONCLUSIONS.: The results illustrate that different questionnaire-based instruments examining symptoms in controls and symptomatic subjects derive unidimensional data that are similar inasmuch as the overall scores are highly correlated. The data also point to the utility of a quick, three-question screening tool in dry eye research. © 2008 American Academy of Optometry.
Simpson,T., Fonn,D. Optical coherence tomography of the anterior segment. Ocular Surface 2008;6,3:117-127. [ Show Abstract ]
Perhaps no diagnostic technology has emerged as rapidly in ophthalmology as optical coherence tomography (OCT). A single clinical device for this noninvasive imaging technique was first released in 1996, and now at least ten clinical devices are available. Although the first clinical anterior segment OCT was marketed only 2 years ago, a substantial amount of work has been done using modified retinal imagers or prototype laboratory-based imagers. In this review, we discuss OCT imaging primarily of the cornea. We also highlight previous and current publications on nonclinical and clinical uses of the device to illustrate how anterior segment OCT can be used to understand corneal structure and function in health and disease. © 2008 Ethis Communications, Inc.
Situ,P., Simpson,T. L., Fonn,D., Jones,L. W. Conjunctival and corneal pneumatic sensitivity is associated with signs and symptoms of ocular dryness. Investigative Ophthalmology and Visual Science 2008;49,7:2971-2976. [ Show Abstract ]
PURPOSE: To investigate the relationships of dry eye symptoms and corneal and conjunctival sensitivity to pneumatic stimulation, tear film stability, and clinical ocular surface characteristics in symptomatic and asymptomatic subjects. METHODS: Ninety-seven subjects were enrolled and grouped by a questionnaire-based single score for symptoms of ocular dryness (none to trace, non-dry group; mild to severe, symptomatic group); 43 were symptomatic and 54 were non-dry. Corneal (K) and conjunctival (C) sensitivities were measured with a computer-controlled Belmonte pneumatic (room temperature) stimulus. Symptoms were assessed according to the Ocular Surface Disease Index (OSDI). Ocular surface staining with fluorescein (FL) and lissamine green (LG), noninvasive tear film break-up time (NIBUT), and the phenol red thread test (PRT) were assessed. RESULTS: The symptomatic group showed lower K and C thresholds (P < 0.01), greater corneal FL and conjunctival LG staining, and shorter NIBUT than did the non-dry eye group (all others P < 0.05). The OSDI scores were higher in the symptomatic group (P < 0.001). K and C thresholds and NIBUT were inversely correlated with the OSDI and corneal and conjunctival staining (all P < 0.05). The K and C threshold and NIBUT (all P < 0.01) correlated positively. Step-wise multiple regression analysis showed that ocular surface sensitivity and NIBUT were significant predictors of the OSDI. CONCLUSIONS: Ocular irritation assessed with the OSDI is associated with ocular surface hyperesthesia to cooling, corneal epitheliopathy, and tear film instability. Although cause and effect are unclear, the analysis showed that altered corneal and conjunctival sensory processing and tear film attributes are essential aspects of what characterizes dry eye.
Situ,P., Simpson,T. L., Jones,L. W., Fonn,D. Conjunctival and corneal hyperesthesia in subjects with dryness symptoms. Optometry and Vision Science 2008;85,9:867-872. [ Show Abstract ]
PURPOSE.: To compare conjunctival and corneal sensitivity in noncontact lens wearing subjects with and without symptoms of ocular dryness, stratified by age and gender. METHODS.: Ninety-seven subjects were enrolled, 54 of whom were asymptomatic and 43 of whom were symptomatic of ocular dryness. A single score for the symptom of dryness was used to classify nondry eye (scores of none to trace) and dry eye symptomatic (scores of mild to severe) groups. The subjects were further stratified into "younger" (19 to 49 years) and "older" age groups (50 to 80 years). Conjunctival and corneal sensitivity of the right eye was measured at the central cornea and temporal conjunctiva, using a computer-controlled pneumatic esthesiometer with stimulus temperature set at 20°C. The ascending method of limits was used to determine the thresholds. RESULTS.: Conjunctival and corneal thresholds were significantly lower in the dry eye symptomatic than in the nondry eye group (both p 0.05). Conjunctival threshold in the nondry eye women was lower than the men (p 0.05). CONCLUSIONS.: Conjunctival and corneal sensitivity to pneumatic cool stimulation is increased in subjects with symptoms of ocular dryness. This hyperesthesia seems to be more significant in the conjunctiva. © 2008 American Academy of Optometry.
Teichroeb,J. H., Forrest,J. A., Jones,L. W., Chan,J., Dalton,K. Quartz crystal microbalance study of protein adsorption kinetics on poly(2-hydroxyethyl methacrylate). Journal of colloid and interface science 2008;325,1:157-164. [ Show Abstract ]
The interaction of macromolecules with artificial biomaterials may lead to potentially serious complications upon implantation into a biological environment. The interaction of one of the most widely used biomaterials, polyHEMA, with lysozyme, bovine serum albumin (BSA), and lactoferrin was investigated using quartz crystal microbalance (QCM). The concentration dependence of adsorption was measured for the aforementioned proteins individually as well as for lysozyme-BSA, and lysozyme-lactoferrin combinations. An extension of Voinova's viscoelastic model to n layers was used to create thickness-time graphs for adsorption. For each of lactoferrin and lysozyme, two distinctly different timescales of adsorption could be differentiated. However, the mechanisms of adsorption appeared to differ between the two. Negative dissipation shifts were measured for low concentrations of lysozyme, trending to positive dissipation at higher concentrations. This suggested that lysozyme was adsorbed initially into the matrix, stiffening the hydrogel, and later onto the surface of polyHEMA. Additionally, trials with commercial no-rub cleaning solutions indicated little added effectiveness over buffer solutions. Mixtures of proteins showed behaviour which differed in some cases from the simple combination of single protein adsorption experiments. Crown Copyright © 2008.
Van Beek,M., Jones,L., Sheardown,H. Hyaluronic acid containing hydrogels for the reduction of protein adsorption. Biomaterials 2008;29,7:780-789. [ Show Abstract ]
Recently, new contact lens materials have been introduced which are reported to improve comfort by incorporating wetting agents either in a releasable or nonreleasable form. In the present work, model lens materials based on poly(2-hydroxyethyl methacrylate) (pHEMA) were developed which incorporate releasable or crosslinked and therefore physically entrapped hyaluronic acid (HA) of various molecular weights as a wetting agent. Crosslinked HA, despite being only present in very small amounts, resulted in consistently lower water contact angles over 4 h in comparison to controls, indicating that HA is present at the interface and was not being released over time. The presence of HA in the material was further confirmed by increases in the glass transition temperature measured by differential scanning calorimetry (DSC), and small increases in the stiffness as measured by Instron testing. This crosslinking procedure appeared to have no effect on optical transparency using 35 kDa HA, whereas small decreases in optical transparency at higher wavelengths were noted for the 169 kDa HA crosslinked material, as measured by UV spectrophotometry. Most importantly, protein adsorption results indicated that the adsorption of all proteins studied was considerably decreased by the presence of the small amount of crosslinked HA. The results provide insight into the mechanisms of comfort improvement with commercially available lens materials and suggest that HA containing materials may have significant potential for use in contact lens applications. © 2007 Elsevier Ltd. All rights reserved.
Varikooty,J., Srinivasan,S., Jones,L. Atypical manifestation of upper lid margin staining in silicone hydrogel lens wearers with symptoms of dry eye. Contact Lens and Anterior Eye 2008;31,1:44-46. [ Show Abstract ]
Purpose: To report an atypical manifestation of upper lid margin staining (ULMS) that occurred in adapted silicone hydrogel (SH) contact lens wearers who complained of ocular surface dryness. Methods: Sequential staining with sodium fluorescein (FL) and lissamine green (LG) strips was performed in 38 SH lens wearers. The "wiper area" of the upper lid was examined with the slit lamp, at 8× and 12× magnifications. Results: Four out of 38 subjects (10.5%) showed fimbriated or "feathery" extensions from the superior margin of the subtarsal fold onto the upper tarsal plate. The extent of these feathery extensions varied between subjects, with a mean (±S.D.) length of 2 ± 0.8 mm. In all cases a broad band of staining with both FL and LG was demonstrated, which extended along the entire length of the lid margin. Conclusion: The staining patterns shown on the subjects' upper lid margins and tarsal plates suggest that ULMS may include more complex variants. The putative tissue damage revealed through the staining, points to a mechanism not simply restricted to the upper lid margin. © 2007 British Contact Lens Association.