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.

The development of biomaterials for contact lens applications:effects of wear modality on materials design

The successful design of polymers for contact lens applications depends on the ability to provide a balance of properties appropriate to the ocular environment. Principal relevant aspects of the anterior eye are the tear film, eyelid and cornea, which govern the requirements for surface properties, modulus and oxygen permeability, respectively. Permeability requirements and the developing view of the needs of the cornea, in terms of oxygen consumption and the particular roles of fluorine and silicon in the design of silicone hydrogels, which have proved to be the most successful family of materials for this demanding application, are discussed. The contact lens field is complicated by the fact that contact lenses are used in a range of wear modalities, the extremes of which can conveniently be classified as lenses that are disposed of at the end of a single period of daily wear and those used for 30. days of successive day-and-night periods, frequently referred to as extended or continuous wear. As silicone hydrogels developed, in the decade following their launch there has been a progressive trend in properties taking both modulus and water content closer to those of conventional hydrogels. This is particularly evident in the family of daily disposable contact lenses that have appeared since 2008.

Effect of third-order aberrations on dynamic accommodation

We investigate the potential for the third-order aberrations coma and trefoil to provide a signed cue to accommodation. It is first demonstrated theoretically (with some assumptions) that the point spread function is insensitive to the sign of spherical defocus in the presence of odd-order aberrations. In an experimental investigation, the accommodation response to a sinusoidal change in vergence (1–3 D, 0.2 Hz) of a monochromatic stimulus was obtained with a dynamic infrared optometer. Measurements were obtained in 10 young visually normal individuals with and without custom contact lenses that induced low and high values of r.m.s. trefoil (0.25, 1.03 μm) and coma (0.34, 0.94 μm). Despite variation between subjects, we did not find any statistically significant increase or decrease in the accommodative gain for low levels of trefoil and coma, although effects approached or reached significance for the high levels of trefoil and coma. Theoretical and experimental results indicate that the presence of Zernike third-order aberrations on the eye does not seem to play a crucial role in the dynamics of the accommodation response.

Influence of presbyopic corrections on driving-related eye and head movements

Purpose: To investigate whether wearing different presbyopic vision corrections alters the pattern of eye and head movements when viewing and responding to driving-related traffic scenes. Methods: Participants included 20 presbyopes (mean age: 56.1 ± 5.7 years) who had no experience of wearing presbyopic vision corrections, apart from single vision (SV) reading spectacles. Each participant wore five different vision corrections: distance SV lenses, progressive addition spectacle lenses (PAL), bifocal spectacle lenses (BIF), monovision (MV) and multifocal contact lenses (MTF CL). For each visual condition, participants were required to view videotape recordings of traffic scenes, track a reference vehicle, and identify a series of peripherally presented targets. Digital numerical display panels were also included as near visual stimuli (simulating the visual displays of a vehicle speedometer and radio). Eye and head movements were measured, and the accuracy of target recognition was also recorded. Results: The path length of eye movements while viewing and responding to driving-related traffic scenes was significantly longer when wearing BIF and PAL than MV and MTF CL (both p ≤ 0.013). The path length of head movements was greater with SV, BIF, and PAL than MV and MTF CL (all p < 0.001). Target recognition and brake response times were not significantly affected by vision correction, whereas target recognition was less accurate when the near stimulus was located at eccentricities inferiorly and to the left, rather than directly below the primary position of gaze (p = 0.008), regardless of vision correction. Conclusions: Different presbyopic vision corrections alter eye and head movement patterns. The longer path length of eye and head movements and greater number of saccades associated with the spectacle presbyopic corrections may affect some aspects of driving performance.

Effect of presbyopic vision corrections on perceptions of driving difficulty

Objectives: As the population ages, more people will be wearing presbyopic vision corrections when driving. However, little is known about the impact of these vision corrections on driving performance. This study aimed to determine the subjective driving difficulties experienced when wearing a range of common presbyopic contact lens and spectacle corrections.----- Methods: A questionnaire was developed and piloted that included a series of items regarding difficulties experienced while driving under daytime and night-time conditions (rated on five-point and seven-point Likert scales). Participants included 255 presbyopic patients recruited through local optometry practices. Participants were categorized into five age-matched groups; including those wearing no vision correction for driving (n = 50), bifocal spectacles (n = 54), progressive spectacles (n = 50), monovision contact lenses (n = 53), and multifocal contact lenses (n = 48).----- Results: Overall, ratings of satisfaction during daytime driving were relatively high for all correction types. However, multifocal contact lens wearers were significantly less satisfied with aspects of their vision during night-time than daytime driving, particularly regarding disturbances from glare and haloes. Progressive spectacle lens wearers noticed more distortion of peripheral vision, whereas bifocal spectacle wearers reported more difficulties with tasks requiring changes of focus and those who wore no optical correction for driving reported problems with intermediate and near tasks. Overall, satisfaction was significantly higher for progressive spectacles than bifocal spectacles for driving.----- Conclusions: Subjective visual experiences of different presbyopic vision corrections when driving vary depending on the vision tasks and lighting level. Eye-care practitioners should be aware of the driving-related difficulties experienced with each vision correction type and the need to select corrective types that match the driving needs of their patients.

Assessment of tear film surface quality using dynamic-area high-speed videokeratoscopy

A new method for noninvasive assessment of tear film surface quality (TFSQ) is proposed. The method is based on high-speed videokeratoscopy in which the corneal area for the analysis is dynamically estimated in a manner that removes videokeratoscopy interference from the shadows of eyelashes but not that related to the poor quality of the precorneal tear film that is of interest. The separation between the two types of seemingly similar videokeratoscopy interference is achieved by region-based classification in which the overall noise is first separated from the useful signal (unaltered videokeratoscopy pattern), followed by a dedicated interference classification algorithm that distinguishes between the two considered interferences. The proposed technique provides a much wider corneal area for the analysis of TFSQ than the previously reported techniques. A preliminary study with the proposed technique, carried out for a range of anterior eye conditions, showed an effective behavior in terms of noise to signal separation, interference classification, as well as consistent TFSQ results. Subsequently, the method proved to be able to not only discriminate between the bare eye and the lens on eye conditions but also to have the potential to discriminate between the two types of contact lenses.

Influence of presbyopic corrections on driving-related eye and head movements

Purpose: To investigate whether wearing different presbyopic refractive corrections alters the pattern of eye and head movements when searching for dynamic targets in driving-related traffic scenes. Methods: Eye and head movements of 20 presbyopes (mean age = 56.2 ± 5.7 years), who had no experience of wearing presbyopic corrections or were unadapted wearers were recorded using the faceLABTM eye and head tracker, while wearing five different corrections: single vision lenses (SV), progressive addition lenses (PALs), bifocal spectacles (BIF), monovision and multifocal contact lenses (MTF CLs) in random order (within-subjects comparison). Recorded traffic scenes of suburban roads and expressways with edited targets were viewed as dynamic stimuli. Results: The magnitude of eye and head movements was significantly greater for SV, BIF and PALs than monovision and MTF CLs (p < 0.001). In addition, BIF wear led to more eye movements than PAL wear (p = 0.017), while PAL wear resulted in greater head movements than SV wear (p = 0.018). The ratio of eye to head movement was smaller for PALs than all other groups (p < 0.001). The number of saccades made to fixate a target was significantly higher for BIF and PALs than monovision or MTF CLs (p < 0.05). Conclusions: Different presbyopic corrections can alter eye and head movement patterns. Wearing spectacles such as BIF and PALs produced relatively greater eye and head movements and saccades when viewing dynamic targets. The impact of these changes in eye and head movement patterns may have implications for driving performance under real world driving conditions.

Driving-related eye and head movements are changed by the type of presbyopic correction

Purpose: To investigate whether wearing different presbyopic vision corrections alters the pattern of eye and head movements when viewing dynamic driving-related traffic scenes. Methods: Participants included 20 presbyopes (mean age: 56±5.7 years) who had no experience of wearing presbyopic vision corrections (i.e. all were single vision wearers). Eye and head movements were recorded while wearing five different vision corrections: single vision lenses (SV), progressive addition spectacle lenses (PALs), bifocal spectacle lenses (BIF), monovision (MV) and multifocal contact lenses (MTF CL) in random order. Videotape recordings of traffic scenes of suburban roads and expressways (with edited targets) were presented as dynamic driving-related stimuli and digital numeric display panels included as near visual stimuli (simulating speedometer and radio). Eye and head movements were recorded using the faceLAB™ system and the accuracy of target identification was also recorded. Results: The magnitude of eye movements while viewing the driving-related traffic scenes was greater when wearing BIF and PALs than MV and MTF CL (p≤0.013). The magnitude of head movements was greater when wearing SV, BIF and PALs than MV and MTF CL (p<0.0001) and the number of saccades was significantly higher for BIF and PALs than MV (p≤0.043). Target recognition accuracy was poorer for all vision corrections when the near stimulus was located at eccentricities inferiorly and to the left, rather than directly below the primary position of gaze (p=0.008), and PALs gave better performance than MTF CL (p=0.043). Conclusions: Different presbyopic vision corrections alter eye and head movement patterns. In particular, the larger magnitude of eye and head movements and greater number of saccades associated with the spectacle presbyopic corrections, may impact on driving performance.

The effect of presbyiopic vision corrections on nighttime driving performance

Purpose. To investigate the effect of various presbyopic vision corrections on nighttime driving performance on a closed-road driving circuit. Methods. Participants were 11 presbyopes (mean age, 57.3 ± 5.8 years), with a mean best sphere distance refractive error of R+0.23±1.53 DS and L+0.20±1.50 DS, whose only experience of wearing presbyopic vision correction was reading spectacles. The study involved a repeated-measures design by which a participant's nighttime driving performance was assessed on a closed-road circuit while wearing each of four power-matched vision corrections. These included single-vision distance lenses (SV), progressive-addition spectacle lenses (PAL), monovision contact lenses (MV), and multifocal contact lenses (MTF CL) worn in a randomized order. Measures included low-contrast road hazard detection and avoidance, road sign and near target recognition, lane-keeping, driving time, and legibility distance for street signs. Eye movement data (fixation duration and number of fixations) were also recorded. Results. Street sign legibility distances were shorter when wearing MV and MTF CL than SV and PAL (P < 0.001), and participants drove more slowly with MTF CL than with PALs (P = 0.048). Wearing SV resulted in more errors (P < 0.001) and in more (P = 0.002) and longer (P < 0.001) fixations when responding to near targets. Fixation duration was also longer when viewing distant signs with MTF CL than with PAL (P = 0.031). Conclusions. Presbyopic vision corrections worn by naive, unadapted wearers affected nighttime driving. Overall, spectacle corrections (PAL and SV) performed well for distance driving tasks, but SV negatively affected viewing near dashboard targets. MTF CL resulted in the shortest legibility distance for street signs and longer fixation times.

Professor Emeritus Leo G Carney Optometry's quiet achiever

Perhaps more than any other sub-discipline in optometry and vision science, the academic field of cornea and contact lenses is populated by an assortment of extroverted and flamboyant characters who constantly travel the world, entertaining clinicians with dazzling audiovisual presentations, informing them about the latest advances in the field and generally promoting their own scientific agendas. The antithesis of this is Leo Carney (Figure 1), a highly accomplished researcher, teacher, mentor and administrator, who has quietly and with great dignity carved out an impressive career in academic optometry. Indeed, Leo Carney is optometry's quintessential ‘quiet achiever’

Wavefront aberrations and the depth of focus of the human eye

The depth of focus (DOF) can be defined as the variation in image distance of a lens or an optical system which can be tolerated without incurring an objectionable lack of sharpness of focus. The DOF of the human eye serves a mechanism of blur tolerance. As long as the target image remains within the depth of focus in the image space, the eye will still perceive the image as being clear. A large DOF is especially important for presbyopic patients with partial or complete loss of accommodation (presbyopia), since this helps them to obtain an acceptable retinal image when viewing a target moving through a range of near to intermediate distances. The aim of this research was to investigate the DOF of the human eye and its association with the natural wavefront aberrations, and how higher order aberrations (HOAs) can be used to expand the DOF, in particular by inducing spherical aberrations ( 0 4 Z and 0 6 Z ). The depth of focus of the human eye can be measured using a variety of subjective and objective methods. Subjective measurements based on a Badal optical system have been widely adopted, through which the retinal image size can be kept constant. In such measurements, the subject.s tested eye is normally cyclopleged. Objective methods without the need of cycloplegia are also used, where the eye.s accommodative response is continuously monitored. Generally, the DOF measured by subjective methods are slightly larger than those measured objectively. In recent years, methods have also been developed to estimate DOF from retinal image quality metrics (IQMs) derived from the ocular wavefront aberrations. In such methods, the DOF is defined as the range of defocus error that degrades the retinal image quality calculated from the IQMs to a certain level of the possible maximum value. In this study, the effect of different amounts of HOAs on the DOF was theoretically evaluated by modelling and comparing the DOF of subjects from four different clinical groups, including young emmetropes (20 subjects), young myopes (19 subjects), presbyopes (32 subjects) and keratoconics (35 subjects). A novel IQM-based through-focus algorithm was developed to theoretically predict the DOF of subjects with their natural HOAs. Additional primary spherical aberration ( 0 4 Z ) was also induced in the wavefronts of myopes and presbyopes to simulate the effect of myopic refractive correction (e.g. LASIK) and presbyopic correction (e.g. progressive power IOL) on the subject.s DOF. Larger amounts of HOAs were found to lead to greater values of predicted DOF. The introduction of primary spherical aberration was found to provide moderate increase of DOF while slightly deteriorating the image quality at the same time. The predicted DOF was also affected by the IQMs and the threshold level adopted. We then investigated the influence of the chosen threshold level of the IQMs on the predicted DOF, and how it relates to the subjectively measured DOF. The subjective DOF was measured in a group of 17 normal subjects, and we used through-focus visual Strehl ratio based on optical transfer function (VSOTF) derived from their wavefront aberrations as the IQM to estimate the DOF. The results allowed comparison of the subjective DOF with the estimated DOF and determination of a threshold level for DOF estimation. Significant correlation was found between the subject.s estimated threshold level for the estimated DOF and HOA RMS (Pearson.s r=0.88, p<0.001). The linear correlation can be used to estimate the threshold level for each individual subject, subsequently leading to a method for estimating individual.s DOF from a single measurement of their wavefront aberrations. A subsequent study was conducted to investigate the DOF of keratoconic subjects. Significant increases of the level of HOAs, including spherical aberration, coma and trefoil, can be observed in keratoconic eyes. This population of subjects provides an opportunity to study the influence of these HOAs on DOF. It was also expected that the asymmetric aberrations (coma and trefoil) in the keratoconic eye could interact with defocus to cause regional blur of the target. A dual-Badal-channel optical system with a star-pattern target was used to measure the subjective DOF in 10 keratoconic eyes and compared to those from a group of 10 normal subjects. The DOF measured in keratoconic eyes was significantly larger than that in normal eyes. However there was not a strong correlation between the large amount of HOA RMS and DOF in keratoconic eyes. Among all HOA terms, spherical aberration was found to be the only HOA that helped to significantly increase the DOF in the studied keratoconic subjects. Through the first three studies, a comprehensive understanding of DOF and its association to the HOAs in the human eye had been achieved. An adaptive optics system was then designed and constructed. The system was capable of measuring and altering the wavefront aberrations in the subject.s eye and measuring the resulting DOF under the influence of different combination of HOAs. Using the AO system, we investigated the concept of extending the DOF through optimized combinations of 0 4 Z and 0 6 Z . Systematic introduction of a targeted amount of both 0 4 Z and 0 6 Z was found to significantly improve the DOF of healthy subjects. The use of wavefront combinations of 0 4 Z and 0 6 Z with opposite signs can further expand the DOF, rather than using 0 4 Z or 0 6 Z alone. The optimal wavefront combinations to expand the DOF were estimated using the ratio of increase in DOF and loss of retinal image quality defined by VSOTF. In the experiment, the optimal combinations of 0 4 Z and 0 6 Z were found to provide a better balance of DOF expansion and relatively smaller decreases in VA. Therefore, the optimal combinations of 0 4 Z and 0 6 Z provides a more efficient method to expand the DOF rather than 0 4 Z or 0 6 Z alone. This PhD research has shown that there is a positive correlation between the DOF and the eye.s wavefront aberrations. More aberrated eyes generally have a larger DOF. The association of DOF and the natural HOAs in normal subjects can be quantified, which allows the estimation of DOF directly from the ocular wavefront aberration. Among the Zernike HOA terms, spherical aberrations ( 0 4 Z and 0 6 Z ) were found to improve the DOF. Certain combinations of 0 4 Z and 0 6 Z provide a more effective method to expand DOF than using 0 4 Z or 0 6 Z alone, and this could be useful in the optimal design of presbyopic optical corrections such as multifocal contact lenses, intraocular lenses and laser corneal surgeries.

An early assessment of silicone hydrogel safety : pearls and pitfalls, and current status

The contact lens industry has evolved and now provides many choices, including continuous wear, overnight orthokeratology, frequent-replacement lenses, daily-disposable lenses, and many alternatives in systems of care and maintenance. Epidemiologic studies to date have shown that how a lens is worn, particularly if worn overnight, can increase the risk of microbial keratitis. However, the risk of silicone hydrogel contact lenses worn on a continuous-wear basis has been evaluated only recently. This article summarizes the recent research data on extended-wear silicone hydrogel lenses and discusses the challenges of early evaluations of silicone hydrogel lens safety. Finally, the relevance of this information is discussed to practitioners and contact lens wearers making choices about the risks and benefits of different products and how they are used.

The visual and functional impacts of astigmatism and its clinical management

Purpose: To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism. Recent findings: The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options. Conclusion: Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.

The influence of a novel simulated learning environment upon student clinical subjective refraction performance: A pilot study

Background: Optometry students are taught the process of subjective refraction through lectures and laboratory based practicals before progressing to supervised clinical practice. Simulated learning environments (SLEs) are an emerging technology that are used in a range of health disciplines, however, there is limited evidence regarding the effectiveness of clinical simulators as an educational tool. Methods: Forty optometry students (20 fourth year and 20 fifth year) were assessed twice by a qualified optometrist (two examinations separated by 4-8 weeks) while completing a monocular non-cycloplegic subjective refraction on the same patient with an unknown refractive error simulated using contact lenses. Half of the students were granted access to an online SLE, The Brien Holden Vision Institute (BHVI®) Virtual Refractor, and the remaining students formed a control group. The primary outcome measures at each visit were; accuracy of the clinical refraction compared to a qualified optometrist and relative to the Optometry Council of Australia and New Zealand (OCANZ) subjective refraction examination criteria. Secondary measures of interest included descriptors of student SLE engagement, student self-reported confidence levels and correlations between performance in the simulated and real world clinical environment. Results: Eighty percent of students in the intervention group interacted with the SLE (for an average of 100 minutes); however, there was no correlation between measures of student engagement with the BHVI® Virtual Refractor and speed or accuracy of clinical subjective refractions. Fifth year students were typically more confident and refracted more accurately and quickly than fourth year students. A year group by experimental group interaction (p = 0.03) was observed for accuracy of the spherical component of refraction, and post hoc analysis revealed that less experienced students exhibited greater gains in clinical accuracy following exposure to the SLE intervention. Conclusions: Short-term exposure to a SLE can positively influence clinical subjective refraction outcomes for less experienced optometry students and may be of benefit in increasing the skills of novice refractionists to levels appropriate for commencing supervised clinical interactions.