Diabetes and contact lens wear

The literature suggests that diabetic patients may have altered tear chemistry and tear secretion as well as structural and functional changes to the corneal epithelium, endothelium and nerves. These factors, together with a reported increased incidence of corneal infection, suggest that diabetic patients may be particularly susceptible to developing ocular complications during contact lens wear. Reports of contact lens-induced complications in diabetic patients do exist, although a number of these reports concern patients with advanced diabetic eye disease using lenses on an extended wear basis. Over the past decade or so, there have been published studies documenting the response of the diabetic eye to more modern contact lens modalities. The results of these studies suggest that contact lenses can be a viable mode of refractive correction for diabetic patients. Furthermore, new research suggests that the measurement of tear glucose concentration could, in future, be used to monitor metabolic control non-invasively in diabetic patients. This could be carried out using contact lenses manufactured from hydrogel polymers embedded with glucose-sensing agents or nanoscale digital electronic technology. The purpose of this paper is to review the literature on the anterior ocular manifestations of diabetes, particularly that pertaining to contact lens wear. © 2012 The Authors. Clinical and Experimental Optometry © 2012 Optometrists Association Australia.

Function of lipids - their fate in contact lens wear:an interpretive review

Lipids play a vital role in the body at many interfaces. Examples include the lubrication of articulating joints by synovial fluid, the coating of the lung by pulmonary surfactant and the functions of the tear film in the protection of the anterior eye. The role of the lipids is similar at each site - acting as boundary lubricants and reducing surface and interfacial tension. This review focuses on how and why contact lens wear can disrupt the normal function of lipids within the tear film and explains how the otherwise advantageous presence and function of tear lipids can become disadvantageous, causing problems for the wearer. Because the contact lens is some ten times thicker than the tear film, lipids deposited on the anterior surface become immobilised, reducing lipid turnover and thus leading to prolonged exposure to oxygen and light with consequent generation of degradation products. These degraded lipids reduce lens wettability and have additionally been linked to problems of contact lens discomfort and intolerance. Lipid problems are influenced by the thickness of the lens, the material, surface modification, mode of wear and ultimately the subject. The most influential of these variables is frequently the subject. © 2012.

Determining which factors influence the optimum multifocal contact lens correction for presbyopia

Presbyopia is a consequence of ageing and is therefore increasing inprevalence due to an increase in the ageing population. Of the many methods available to manage presbyopia, the use of contact lenses is indeed a tried and tested reversible option for those wishing to be spectacle free. Contact lens options to correct presbyopia include multifocal contact lenses and monovision.Several options have been available for many years with available guides to help choose multifocal contact lenses. However there is no comprehensive way to help the practitioner selecting the best option for an individual. An examination of the simplest way of predicting the most suitable multifocal lens for a patient will only enhance and add to the current evidence available. The purpose of the study was to determine the current use of presbyopic correction modalities in an optometric practice population in the UK and to evaluate and compare the optical performance of four silicone hydrogel soft multifocal contact lenses and to compare multifocal performance with contact lens monovision. The presbyopic practice cohort principal forms of refractive correction were distance spectacles (with near and intermediate vision providedby a variety of other forms of correction), varifocal spectacles and unaided distance with reading spectacles, with few patients wearing contact lenses as their primary correction modality. The results of the multifocal contact lens randomised controlled trial showed that there were only minor differences in corneal physiology between the lens options. Visual acuity differences were observed for distance targets, but only for low contrast letters and under mesopic lighting conditions. At closer distances between 20cm and 67cm, the defocus curves demonstrated that there were significant differences in acuity between lens designs (p < 0.001) and there was an interaction between the lens design and the level of defocus (p < 0.001). None of the lenses showed a clear near addition, perhaps due to their more aspheric rather than zoned design. As expected, stereoacuity was reduced with monovision compared with the multifocal contact lens designs, although there were some differences between the multifocal lens designs (p < 0.05). Reading speed did not differ between lens designs (F = 1.082, p = 0.368), whereas there was a significant difference in critical print size (F = 7.543, p < 0.001). Glare was quantified with a novel halometer and halo size was found to significantly differ between lenses(F = 4.101, p = 0.004). The rating of iPhone image clarity was significantly different between presbyopic corrections (p = 0.002) as was the Near Acuity Visual Questionnaire (NAVQ) rating of near performance (F = 3.730, p = 0.007).The pupil size did not alter with contact lens design (F = 1.614, p = 0.175), but was larger in the dominant eye (F = 5.489, p = 0.025). Pupil decentration relative to the optical axis did not alter with contact lens design (F = 0.777, p =0.542), but was also greater in the dominant eye (F = 9.917, p = 0.003). It was interesting to note that there was no difference in spherical aberrations induced between the contact lens designs (p > 0.05), with eye dominance (p > 0.05) oroptical component (ocular, corneal or internal: p > 0.05). In terms of subjective patient lens preference, 10 patients preferred monovision,12 Biofinity multifocal lens, 7 Purevision 2 for Presbyopia, 4 AirOptix multifocal and 2 Oasys multifocal contact lenses. However, there were no differences in demographic factors relating to lifestyle or personality, or physiological characteristics such as pupil size or ocular aberrations as measured at baseline,which would allow a practitioner to identify which lens modality the patient would prefer. In terms of the performance of patients with their preferred lens, it emerged that Biofinity multifocal lens preferring patients had a better high contrast acuity under photopic conditions, maintained their reading speed at smaller print sizes and subjectively rated iPhone clarity as better with this lens compared with the other lens designs trialled. Patients who preferred monovision had a lower acuity across a range of distances and a larger area of glare than those patients preferring other lens designs that was unexplained by the clinical metrics measured. However, it seemed that a complex interaction of aberrations may drive lens preference. New clinical tests or more diverse lens designs which may allow practitioners to prescribe patients the presbyopic contact lens option that will work best for them first time remains a hope for the future.

The design of contact lens based ocular drug delivery systems for single-day use:part (I) structural factors, surrogate ophthalmic dyes and passive diffusion studies

The poor retention and efficacy of instilled drops as a means of delivering drugs to the ophthalmic environment is well-recognised. The potential value of contact lenses as a means of ophthalmic drug delivery, and consequent improvement of pre-corneal retention is one obvious route to the development of a more effective ocular delivery system. Furthermore, the increasing availability and clinical use of daily disposable contact lenses provides the platform for the development of viable single-day use drug delivery devices based on existing materials and lenses. In order to provide a basis for the effective design of such devices, a systematic understanding of the factors affecting the interaction of individual drugs with the lens matrix is required. Because a large number of potential structural variables are involved, it is necessary to achieve some rationalisation of the parameters and physicochemical properties (such as molecular weight, charge, partition coefficients) that influence drug interactions. Ophthalmic dyes and structurally related compounds based on the same core structure were used to investigate these various factors and the way in which they can be used in concert to design effective release systems for structurally different drugs. Initial studies of passive diffusional release form a necessary precursor to the investigation of the features of the ocular environment that over-ride this simple behaviour. Commercially available contact lenses of differing structural classifications were used to study factors affecting the uptake of the surrogate actives and their release under 'passive' conditions. The interaction between active and lens material shows considerable and complex structure dependence, which is not simply related to equilibrium water content. The structure of the polymer matrix itself was found to have the dominant controlling influence on active uptake; hydrophobic interaction with the ophthalmic dye playing a major role. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Effect of methane concentration in hydrogen plasma on hydrogen impurity incorporation in thick large-grained polycrystalline diamond films

We investigate the impact of methane concentration in hydrogen plasma on the growth of large-grained polycrystalline diamond (PCD) films and its hydrogen impurity incorporation. The diamond samples were produced using high CH4 concentration in H2 plasma and high power up to 4350 W and high pressure (either 105 or 110 Torr) in a microwave plasma chemical vapor deposition (MPCVD) system. The thickness of the free-standing diamond films varies from 165 µm to 430 µm. Scanning electron microscopy (SEM), micro-Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology, crystalline and optical quality of the diamond samples, and bonded hydrogen impurity in the diamond films, respectively. Under the conditions employed here, when methane concentration in the gas phase increases from 3.75% to 7.5%, the growth rate of the PCD films rises from around 3.0 µm/h up to 8.5 µm/h, and the optical active bonded hydrogen impurity content also increases more than one times, especially the two CVD diamond specific H related infrared absorption peaks at 2818 and 2828 cm−1 rise strongly; while the crystalline and optical quality of the MCD films decreases significantly, namely structural defects and non-diamond carbon phase content also increases a lot with increasing of methane concentration. Based on the results, the relationship between methane concentration and diamond growth rate and hydrogen impurity incorporation including the form of bonded infrared active hydrogen impurity in CVD diamonds was analyzed and discussed. The effect of substrate temperature on diamond growth was also briefly discussed. The experimental findings indicate that bonded hydrogen impurity in CVD diamond films mainly comes from methane rather than hydrogen in the gas source, and thus can provide experimental evidence for the theoretical study of the standard methyl species dominated growth mechanism of CVD diamonds grown with methane/hydrogen mixtures.

Structural design of contact lens-based drug delivery systems; in vitro and in vivo studies of ocular triggering mechanisms

This study identifies and investigates the potential use of in-eye trigger mechanisms to supplement the widely available information on release of ophthalmic drugs from contact lenses under passive release conditions. Ophthalmic dyes and surrogates have been successfully employed to investigate how these factors can be drawn together to make a successful system. The storage of a drug-containing lens in a pH lower than that of the ocular environment can be used to establish an equilibrium that favours retention of the drug in the lens prior to ocular insertion. Although release under passive conditions does not result in complete dye elution, the use of mechanical agitation techniques which mimic the eyelid blink action in conjunction with ocular tear chemistry promotes further release. In this way differentiation between passive and triggered in vitro release characteristics can be established. Investigation of the role of individual tear proteins revealed significant differences in their ability to alter the equilibrium between matrix-held and eluate-held dye or drug. These individual experiments were then investigated in vivo using ophthalmic dyes. Complete elution was found to be achievable in-eye; this demonstrated the importance of that fraction of the drug retained under passive conditions and the triggering effect of in-eye conditions on the release process. Understanding both the structure-property relationship between drug and material and in-eye trigger mechanisms, using ophthalmic dyes as a surrogate, provides the basis of knowledge necessary to design ocular drug delivery vehicles for in-eye release in a controllable manner.

Microlocal Approach to Tensor Tomography and Boundary and Lens Rigidity

2000 Mathematics Subject Classification: 53C24, 53C65, 53C21.

How should initial fit inform soft contact lens prescribing

Purpose: To investigate how initial HEMA and silicone-hydrogel (SiHy) contact lens fit on insertion, which informs prescribing decisions, reflect end of day fit. Methods: Thirty participants (aged 22.9. ±. 4.9 years) were fitted contralaterally with HEMA and SiHy contact lenses. Corneal topography and tear break-up time were assessed pre-lens wear. Centration, lag, post-blink movement during up-gaze and push-up recovery speed were recorded after 5,10,20. min and 8. h of contact lens wear by a digital slit-lamp biomicroscope camera, along with reported comfort. Lens fit metrics were analysed using bespoke software. Results: Comfort and centration were similar with the HEMA and SiHy lenses (p > 0.05), but comfort decreased with time (p <. 0.01) whereas centration remained stable (F = 0.036, p = 0.991). Movement-on-blink and lag were greater with the HEMA than the SiHy lens (p <. 0.01), but movement-on-blink decreased with time after insertion (F = 22.423, p <. 0.001) whereas lag remained stable (F = 1.967, p = 0.129). Push-up recovery speed was similar with the HEMA and the SiHy lens 5-20. min after insertion (p > 0.05), but was slower with SiHy after 8. h wear (p = 0.016). Lens movement on blink and push-up recovery speed was predictive of the movement after 8. h of wear after 10-20. min SiHy wear, but after 5 to 20. min of HEMA lens wear. Conclusions: A HEMA or SiHy contact lens with poor movement on blink/push-up after at least 10. min after insertion should be rejected.

Generation of 49-fs pulses directly from distributed Kerr-lens mode-locked Yb:YAG thin-disk oscillator

The concept of distributed Kerr-lens mode-locking and a thin-disk Yb:YAG oscillator based on this concept are presented. The described oscillator directly generates pulses with a duration of 49 fs and spectral width of 33 nm

Editorial

The year so far has been a slow start for many businesses, but at least we have not seen the collapse of as many businesses that we were seeing around two years ago. We are, however, still well and truly in the midst of a global recession. Interest rates are still at an all time low, UK house prices seem to be showing little signs of increase (except in London where everyone still seems to want to live!) and for the ardent shopper there are bargains to be had everywhere. It seems strange that prices on the high street do not seem to have increased in over ten years. Mobile phones, DVD players even furniture seems to be cheaper than they used to be. Whist much of this is down to cheaper manufacturing and the rest could probably be explained by competition within the market place. Does this mean that quality suffered too? Now that we live in a world when if a television is not working it is thrown away and replaced. There was a time when you would take it to some odd looking man that your father would know who could fix it for you. (I remember our local television fix-it man, with his thick rimmed bifocal spectacles and a poor comb-over; he had cardboard boxes full of resistors and electrical wires on the floor of his front room that smelt of soldering irons!) Is this consumerism at an extreme or has this move to disposability made us a better society? Before you think these are just ramblings there is a point to this. According to latest global figures of contact lens sales the vast majority of contact lenses fitted around the world are daily, fortnightly or monthly disposable hydrogel lenses. Certainly in the UK over 90% of lenses are disposable (with daily disposables being the most popular, having a market share of over 50%). This begs the question – is this a good thing? Maybe more importantly, do our patients benefit? I think it is worth reminding ourselves why we went down the disposability route with contact lenses in the first place, and unlike electrical goods it was not just so we did not have to take them for repair! There are the obvious advantages of overcoming problems of breakage and tearing of lenses and the lens deterioration with age. The lenses are less likely to be contaminated and the disinfection is either easier or not required at all (in the case of daily disposable lenses). Probably the landmark paper in the field was the work more commonly known as the ‘Gothenburg Study’. The paper, entitled ‘Strategies for minimizing the Ocular Effects of Extended Contact Lens Wear’ published in the American Journal of Optometry in 1987 (volume 64, pages 781-789) by Holden, B.A., Swarbrick, H.A., Sweeney, D.F., Ho, A., Efron, N., Vannas, A., Nilsson, K.T. They suggested that contact lens induced ocular effects were minimised by: •More frequently removed contact lenses •More regularly replaced contact lenses •A lens that was more mobile on the eye (to allow better removal of debris) •Better flow of oxygen through the lens All of these issues seem to be solved with disposability, except the oxygen issue which has been solved with the advent of silicone hydrogel materials. Newer issues have arisen and most can be solved in practice by the eye care practitioner. The emphasis now seems to be on making lenses more comfortable. The problems of contact lens related dry eyes symptoms seem to be ever present and maybe this would explain why in the UK we have a pretty constant contact lens wearing population of just over three million but every year we have over a million dropouts! That means we must be attracting a million new wearers every year (well done to the marketing departments!) but we are also losing a million wearers every year. We certainly are not losing them all to the refractive surgery clinics. We know that almost anyone can now wear a contact lens and we know that some lenses will solve problems of sharper vision, some will aid comfort, and some will be useful for patients with dry eyes. So if we still have so many dropouts then we must be doing something wrong! I think the take home message has to be ‘must try harder’! I must end with an apology for two errors in my editorial of issue 1 earlier this year. Firstly there was a typo in the first sentence; I meant to state that it was 40 years not 30 years since the first commercial soft lens was available in the UK. The second error was one that I was unaware of until colleagues Geoff Wilson (Birmingham, UK) and Tim Bowden (London, UK) wrote to me to explain that soft lenses were actually available in the UK before 1971 (please see their ‘Letters to the Editor’ in this issue). I am grateful to both of them for correcting the mistake.

Visual and quality outcomes following bilateral implantation of a trifocal intraocular lens

Purpose: To examine visual outcomes following bilateral implantation of the FineVision trifocal intraocular lens (IOL; PhysIOL, Liège, Belgium). Methods: 26 patients undergoing routine cataract surgery were implanted bilaterally with the FineVision Trifocal IOL and followed up post-operatively for 3 months. The FineVision optic features a combination of 2 diffractive structures, resulting in distance, intermediate (+1.75 D add) and near vision (+3.50 D add) zones. Apodization of the optic surface increases far vision dominance with pupil aperture. Data collected at the 3 month visit included uncorrected and corrected distance (CDVA) and near vision; subjective refraction; defocus curve testing (photopic and mesopic); contrast sensitivity (CSV-1000); halometry glare testing and a questionnaire (NAVQ) to gauge near vision function and patient satisfaction. Results: The cohort comprised 15 males and 11 females, aged 52.5–82.4 years (mean 70.6 ± 8.2 years). Mean post-operative UDVA was 0.22 ± 0.14 logMAR, with a mean spherical equivalent refraction of +0.02 ± 0.35 D. Mean CDVA was 0.13 ± 0.10 logMAR monocularly, and 0.09 ± 0.07 logMAR binocularly. Defocus curve testing showed an extensive range of clear vision in both photopic and mesopic conditions. Patients showed high levels of satisfaction with their near vision (mean ± 0.9 ± 0.6, where 0 = completely satisfied, and 4 = completely unsatisfied) and demonstrated good spectacle independence. Conclusion: The FineVision IOL can be considered in patients seeking spectacle dependence following cataract surgery, and provide good patient satisfaction with uncorrected vision.

Fitting an MSD (Mini Scleral Design) rigid contact lens in advanced keratoconus with INTACS

Keratoconus is a bilateral degenerative disease characterized by a non-inflammatory, progressive central corneal ectasia (typically asymmetric) and decreased vision. In its early stages it may be managed with spectacles and soft contact lenses but more commonly it is managed with rigid contact lenses. In advanced stages, when contact lenses can no longer be fit, have become intolerable, or corneal damage is severe, a penetrating keratoplasty is commonly performed. Alternative surgical techniques, such as the use of intra-stromal corneal ring segments (INTACS) have been developed to try and improve the fit of rigid contact lenses in keratoconic patients and avoid penetrating keratoplasties. This case report follows through the fitting of rigid contact lenses in an advanced keratoconic cornea after an INTACS procedure and discusses clinical findings, treatment options, and the use of mini-scleral and scleral lens designs as they relate to the challenges encountered in managing such a patient. Mini-scleral and scleral lenses are relatively easy to fit, and can be of benefit to many patients, including advanced keratoconic patients, post-INTAC patients and post-penetrating keratoplasty patients. © 2011 British Contact Lens Association.