Tear protein composition and contact lens wear

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Experimental and theoretical studies on six-membered ring hydrogen bond systems in crystalline drug substances

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Experimental and theoretical studies on molecular geometry and polymorphism in crystalline drug substances

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Evidence of lipid degradation during overnight contact lens wear:gas chromatography mass spectrometry as the diagnostic tool

Purpose. We investigated structural differences in the fatty acid profiles of lipids extracted from ex vivo contact lenses by using gas chromatography mass spectrometry (GCMS). Two lens materials (balafilcon A or lotrafilcon A) were worn on a daily or continuous wear schedule for 30 and 7 days. Methods. Lipids from subject-worn lenses were extracted using 1:1 chloroform: methanol and transmethylated using 5% sulfuric acid in methanol. Fatty acid methyl esters (FAMEs) were collected using hexane and water, and analyzed by GCMS (Varian 3800 GC, Saturn 2000 MS). Results. The gas chromatograms of lens extracts that were worn on a continuous wear schedule showed two predominant peaks, C16:0 and C18:0, both of which are saturated fatty acids. This was the case for balafilcon A and lotrafilcon A lenses. However, the gas chromatograms of lens extracts that were worn on a daily wear schedule showed saturated (C16:0, C18:0) and unsaturated (C16:1 and C18:1) fatty acids. Conclusions. Unsaturated fatty acids are degraded during sleep in contact lenses. Degradation occurred independently of lens material or subject-to-subject variability in lipid deposition. The consequences of lipid degradation are the production of oxidative products, which may be linked to contact lens discomfort. © 2014 The Association for Research in Vision and Ophthalmology, Inc.

Contact lens interactions with the tear film

Biochemical changes brought about by the influence of the contact lens on the tear film are conveniently split into two categories. Firstly, the lens can remove or reduce the levels of specific components in the tear film, and secondly, the lens can augment the tear film, by stimulating the influx of new components or increasing the level of existing components. The most obvious tear film components for study in this context are lipids, proteins, mucins and electrolytes. The interactions are affected by the properties of the lens, the characteristics of the individual wearer and the wear schedule. An additional complicating factor is the fact that the lens is many times thicker than the tear film and any immobilised tear components will be more extensively exposed to oxygen and UV radiation than is the case in the absence of a lens. It is arguably the lipoidal components that are most markedly affected by lens wear, since their immobilisation on the lens surface markedly increases their susceptibility to autoxidative degradation. The limited information that is available highlights the importance of subject specificity and suggests that lipid oxidation phenomena are potentially important in contributing to the 'end of day' discomfort of symptomatic contact lens patients. It is clear that tear lipids, although regarded as relatively inert for many years, are now seen as a reactive and potentially important family of compounds in the search for understanding of contact lens-induced discomfort. The influence of the lens on tear proteins shows the greatest range of complexity. Deposition and denaturation can stimulate immune response, lower molecular weight proteins can be extensively absorbed into the lens matrix and the lens can stimulate cascade or upregulation processes leading either to the generation of additional proteins and peptides or an increase in concentration of existing components. Added to this is the stimulating influence of the lens on vascular leakage leading to the influx of plasma proteins such as albumin. The evidence from studies of mucin expression in tears is not consistent and conclusive. This is in part because sample sources, lens materials and methods of analysis vary considerably, and in some cases the study population numbers are low. Expression levels show mucin and material specificity but clear patterns of behaviour are elusive. The electrolyte composition of tears is significantly different from that of other body fluids. Sodium and potassium dominate but potassium ion concentrations in tears are much higher than in serum levels. Calcium and magnesium concentrations in tears are lower than in serum but closer to interstitial fluids. The contact lens provides the potential for increased osmolarity through enhanced evaporation and differential electrolyte concentrations between the anterior and posterior tear films. Since the changes in ocular biochemistry consequent upon contact lens wear are known to be subject-dependent - as indeed is wearer response to the lens - pre-characterisation of individual participant tear chemistry in clinical studies would enhance understanding of these complex effects. © 2013 Elsevier Ltd.

Subjective and objective performance of the Lenstec KH-3500 "accommodative" intraocular lens

Aim: To determine whether eyes implanted with the Lenstec KH-3500 "accommodative" intraocular lenses (IOLs) have improved subjective and objective focusing performance compared to a standard monofocal IOLs. Methods: 28 participants were implanted monocularly with a KH-3500 " accommodative" IOL and 20 controls with a Softec1 IOL. Outcome measures of refraction, visual acuity, subjective amplitude of accommodation, objective accommodative stimulus response curve, aberrometry, and Scheimpflug imaging were taken at ∼3 weeks and repeated after 6 months. Results: Best corrected acuity with the KH-3500 was 0.06 (SD 0.13) logMAR at distance and 0.58 (0.20) logMAR at near. Accommodation was 0.39 (0.53) D measured objectively and 3.1 (1.6) D subjectively. Higher order aberrations were 0.87 (0.85) μm and lower order were 0.24 (0.39) μm. Posterior subcapsular light scatter was 0.95% (1.37%) greater than IOL clarity. In comparison, all control group measures were similar except objective (0.17 (0.13) D; p = 0.032) and subjective (2.0 (0.9) D; p = 0.009) amplitude of accommodation. Six months following surgery, posterior subcapsular scatter had increased (p<0.01) in the KH-3500 implanted subjects and near word acuity had decreased (p<0.05). Conclusions: The objective accommodating effects of the KH-3500 IOL appear to be limited, although the subjective and objective accommodative range is significantly increased compared to control subjects implanted with conventional IOLs. However, this "accommodative" ability of the lens appears to have decreased by 6 months post-surgery.

Adverse events and discontinuations during 18 months of silicone hydrogel contact lens wear

PURPOSE. To report differences in the incidence of adverse events and discontinuations found in a group of neophyte contact wearers using two different silicone hydrogel contact lenses on a daily- and continuous-wear basis during an 18-month period. METHODS. Sixty-one subjects were initially examined, and 53 were eligible to participate in the study. Eligible subjects were randomly assigned to wear one of two silicone hydrogel materials: lotrafilcon A or balafilcon A lenses on a daily- or continuous-wear basis. After an initial screening, subjects were monitored weekly for the first month and then after 3, 6, 12, and 18 months. The incidence of adverse events, including corneal infiltrative events, superior epithelial arcuate lesions, and contact lens-induced papillary conjunctivitis, and discontinuations in each of the four contact lens groups were recorded. RESULTS. Twenty-two adverse events were found. A higher incidence of adverse events was found in subjects wearing lotrafilcon A lenses than in those wearing balafilcon A lenses (χ = 4.40, P=0.04). There were fewer adverse events in subjects wearing lenses on a daily-wear basis than in those wearing lenses on a continuous-wear basis (χ = 5.98, P=0.01). Eight subjects discontinued from the study as a result of recurrent corneal infiltrative events (one), vision problems (two), excessive ocular discomfort (one), relocation (one), noncompliance with the study protocol (one), and being lost to follow-up (two). No significant differences were found in the number of discontinuations between the two lens types (χ = 0.66, P=0.42) and wearing regimens (χ = 0.08, P=0.78). CONCLUSIONS. Lotrafilcon A lenses were associated with a higher incidence of adverse events than balafilcon A lenses were, and this difference is attributed to the difference in the incidence of corneal infiltrative events. Subjects wearing lenses on a daily-wear basis had fewer adverse events than did subjects wearing lenses on a continuous-wear basis. Both lens types and wearing regimens showed a similar incidence of discontinuations. © 2007 Lippincott Williams & Wilkins, Inc.

Tear analysis and lens-tear interactions:Part I. Protein fingerprinting with microfluidic technology

The purpose of this work is to establish the application of a fully automated microfluidic chip based protein separation assay in tear analysis. It is rapid, requires small sample volumes and is vastly superior to, and more convenient than, comparable conventional gel electrophoresis assays. The protein sizing chip technology was applied to three specific fields of analysis. Firstly tear samples were collected regularly from subjects establishing the baseline effects of tear stimulation, tear state and patient health. Secondly tear samples were taken from lens wearing eyes and thirdly the use of microfluidic technology was assessed as a means to investigate a novel area of tear analysis, which we have termed the 'tear envelope'. Utilising the Agilent 2100 Bioanalyzer in combination with the Protein 200 Plus LabChip kit, these studies investigated tear proteins in the range of 14-200 kDa. Particular attention was paid to the relative concentrations of lysozyme, tear lipocalin, secretory IgA (sIgA), IgG and lactoferrin, together with the overall tear electropherogram 'fingerprint'. Furthermore, whilst lens-tear interaction studies are generally thought of as an investigation into the effects of tears components on the contact lens material, i.e. deposition studies, this report addresses the reverse phenomenon-the effect of the lens, and particularly the newly inserted lens, on the tear fluid composition and dynamics. The use of microfluidic technology provides a significant advance in tear studies and should prove invaluable in tear diagnostics and contact lens performance analysis.

Anterior ophthalmic imaging

Improvements in imaging chips and computer processing power have brought major advances in imaging of the anterior eye. Digitally captured images can be visualised immediately and can be stored and retrieved easily. Anterior ocular imaging techniques using slitlamp biomicroscopy, corneal topography, confocal microscopy, optical coherence tomography (OCT), ultrasonic biomicroscopy, computerised tomography (CT) and magnetic resonance imaging (MRI) are reviewed. Conventional photographic imaging can be used to quantify corneal topography, corneal thickness and transparency, anterior chamber depth and lateral angle and crystalline lens position, curvature, thickness and transparency. Additionally, the effects of tumours, foreign bodies and trauma can be localised, the corneal layers can be examined and the tear film thickness assessed. © 2006 The Authors.

Changes in ocular physiology, tear film characteristics, and symptomatology with 18 months silicone hydrogel contact lens wear

Purpose. The purpose of this study was to evaluate the longitudinal changes in ocular physiology, tear film characteristics, and symptomatology experienced by neophyte silicone hydrogel (SiH) contact lens wearers in a daily-wear compared with a continuous-wear modality and with the different commercially available lenses over an 18-month period. Methods. Forty-five neophyte subjects were enrolled in the study and randomly assigned to wear one of two SiH materials: lotrafilcon A or balafilcon A lenses on either a daily- (LDW; BDW) or continuous-wear (LCW; BCW) basis. Additionally, a group of noncontact lens-wearing subjects (control group) was also recruited and followed over the same study period. Objective and subjective grading of ocular physiology were carried out together with tear meniscus height (TMH) and noninvasive tear breakup time (NITBUT). Subjects also subjectively rated symptoms and judgments with lens wear. After initial screening, subsequent measurements were taken after 1, 3, 6, 12, and 18 months. Results. Subjective and objective grading of ocular physiology revealed a small increase in bulbar, limbal, and palpebral hyperemia as well as corneal staining over time with both lens materials and regimes of wear (p < 0.05). No significant changes in NITBUT or TMH were found (p > 0.05). Subjective symptoms and judgment were not material- or modality-specific. Conclusions. Daily and continuous wear of SiH contact lenses induced small but statistically significant changes in ocular physiology and symptomatology. Clinical measures of tear film characteristics were unaffected by lens wear. Both materials and regimes of wear showed similar clinical performance. Long-term SiH contact lens wear is shown to be a successful option for patients. Copyright © 2006 American Academy of Optometry.

Objective accommodative amplitude and dynamics with the 1CU accommodative intraocular lens

PURPOSE. To compare the objective accommodative amplitude and dynamics of eyes implanted with the one-compartment-unit (1CU; HumanOptics AG, Erlangen, Germany) accommodative intraocular lenses (IOLs) with that measured subjectively. METHODS. Twenty eyes with a 1CU accommodative IOL implanted were refracted and distance and near acuity measured with a logMAR (logarithm of the minimum angle of resolution) chart. The objective accommodative stimulus-response curve for static targets between 0.17 and 4.00 D accommodative demand was measured with the SRW-5000 (Shin-Nippon Commerce Inc., Tokyo, Japan) and PowerRefractor (PlusOptiX, Nürnberg, Germany) autorefractors. Continuous objective recording of dynamic accommodation was measured with the SRW-5000, with the subject viewing a target moving from 0 to 2.50 D at 0.3 Hz through a Badal lens system. Wavefront aberrometry measures (Zywave; Bausch & Lomb, Rochester, NY) were made through undilated pupils. Subjective amplitude of accommodation was measured with the RAF (Royal Air Force accommodation and vergence measurement) rule. RESULTS. Four months after implantation best-corrected acuity was -0.01 ± 0.16 logMAR at distance and 0.60 ± 0.09 logMAR at near. Objectively, the static amplitude of accommodation was 0.72 ± 0.38 D. The average dynamic amplitude of accommodation was 0.71 ± 0.47 D, with a lag behind the target of 0.50 ± 0.48 seconds. Aberrometry showed a decrease in power of the lens-eye combination from the center to the periphery in all subjects (on average, -0.38 ± 0.28 D/mm). Subjective amplitude of accommodation was 2.24 ± 0.42 D. Two years after 1CU implantation, refractive error and distance visual acuity remained relatively stable, but near visual acuity, and the subjective and objective amplitudes of accommodation decreased. CONCLUSIONS. The objective accommodating effects of the 1CU lens appear to be limited, although patients are able to track a moving target. Subjective and objective accommodation was reduced at the 2-year follow-up. The greater subjective amplitude of accommodation is likely to result from the eye's depth of focus of and the aspheric nature of the IOL. Copyright © Association for Research in Vision and Ophthalmology.

The effect of contact lens wear on dynamic ocular surface temperature

Aim: To determine the dynamic emitted temperature changes of the anterior eye during and immediately after wearing different materials and modalities of soft contact lenses. Method: A dynamic, non-contact infrared camera (Thermo-Tracer TH7102MX, NEC San-ei) was used to record the ocular surface temperature (OST) in 48 subjects (mean age 21.7 ± 1.9 years) wearing: lotrafilcon-A contact lenses on a daily wear (LDW; n = 8) or continuous wear (LCW; n = 8) basis; balafilcon-A contact lenses on a daily wear (BDW; n = 8) or continuous wear (BCW; n = 8) basis; etafilcon-A contact lenses on a daily disposable regimen (EDW; n = 8); and no lenses (controls; n = 8). OST was measured continuously five times, for 8 s after a blink, following a minimum of 2 h wear and immediately following lens removal. Absolute temperature, changes in temperature post-blink and the dynamics of temperature changes were calculated. Results: OST immediately following contact lens wear was significantly greater compared to non-lens wearers (37.1 ± 1.7 °C versus 35.0 ± 1.1 °C; p < 0.005), predominantly in the LCW group (38.6 ± 1.0 °C; p < 0.0001). Lens surface temperature was highly correlated (r = 0.97) to, but lower than OST (by -0.62 ± 0.3 °C). There was no difference with modality of wear (DW 37.5 ± 1.6 °C versus CW 37.8 ± 1.9 °C; p = 0.63), but significant differences were found between etafilcon A and silicone hydrogel lens materials (35.3 ± 1.1 °C versus 37.5 ± 1.5 °C; p < 0.0005). Ocular surface cooling following a blink was not significantly affected by contact lens wear with (p = 0.07) or without (p = 0.47) lenses in situ. Conclusions: Ocular surface temperature is greater with hydrogel and greater still with silicone hydrogel contact lenses in situ, regardless of modality of wear. The effect is likely to be due to the thermal transmission properties of a contact lens. © 2004 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Customer loyalty among daily disposable contact lens wearers

Background: Optometric practices offer contact lenses as cash sale items or as part of monthly payment plans. With the contact lens market becoming increasingly competitive, patients are opting to purchase lenses from supermarkets and Internet suppliers. Monthly payment plans are often implemented to improve loyalty. This study aimed to compare behavioural loyalty between monthly payment plan members and non-members. Methods: BBR Optometry Ltd offers a monthly payment plan (Eyelife™) to their contact lens wearers. A retrospective audit of 38 Eyelife™ members (mean. ±. SD: 42.7. ±. 15.0 years) and 30 non-members (mean. ±. SD: 40.8. ±. 16.7 years) was conducted. Revenue and profits generated, service uptake and product sales between the two groups were compared over a fixed period of 18 months. Results: Eyelife™ members generated significantly higher professional fee revenue ( P<. 0.001), £153.96 compared to £83.50, and profits ( P<. 0.001). Eyelife™ members had a higher uptake of eye examinations ( P<. 0.001). The 2 groups demonstrated no significant difference in spectacle sales by volume ( P= 0.790) or value ( P= 0.369). There were also no significant differences in contact lens revenue ( P= 0.337), although Eyelife™ members did receive a discount. The Eyelife™ group incurred higher contact lens costs ( P= 0.037), due to a greater volume of contact lens purchases, 986 units compared to 582. Conclusions: Monthly payment plans improve loyalty among contact lens wearers, particularly service uptake and volume of lens purchases. Additionally the greater professional fees generated, render monthly payment plans an attractive business model and practice builder.

BCLA Pioneers Lecture - evidence basis for patient selection:how to predict contact lens success

Editorial

Analysis of femtosecond laser surface patterning on bulk single-crystalline diamond

Preliminary work is reported on 2-D and 3-D microstructures written directly with a Yb:YAG 1026 nm femtosecond (fs) laser on bulk chemical vapour deposition (CVD) single-crystalline diamond. Smooth graphitic lines and other structures were written on the surface of a CVD diamond sample with a thickness of 0.7mm under low laser fluences. This capability opens up the opportunity for making electronic devices and micro-electromechanical structures on diamond substrates. The fabrication process was optimised through testing a range of laser energies at a 100 kHz repetition rate with sub-500fs pulses. These graphitic lines and structures have been characterised using optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Using these analysis techniques, the formation of sp2 and sp3 bonds is explored and the ratio between sp2 and sp3 bonds after fs laser patterning is quantified. We present the early findings from this study and characterise the relationship between the graphitic line formation and the different fs laser exposure conditions. © 2012 Taylor & Francis.