Visual performance and optical quality with soft lenses in keratoconus patients

Purpose: To assess visual performance and ocular aberrations in keratoconic patients using toric soft contact lenses (SCL), rigid-gas-permeable (RGP) contact lenses and spectacle lens correction. Methods: Twenty-two keratoconus patients (16 RGP lens wearers and six spectacle wearers) were fitted with toric SCL. Ocular aberrations were measured with and without the patient's habitual RGP lenses and with the SCL in place. In the spectacle wearers, aberrations were measured with and without the SCL. Visual performance (high- and low-contrast visual acuity) was evaluated with the patient's habitual correction and with the SCL. Results: In the RGP lens wearers both the habitual lenses and the toric SCL significantly reduced coma, trefoil, 3rd-order, 4th-order cylinder and higher-order root-mean-square (RMS) aberrations (p≤0.015). In the spectacle wearers the toric SCL significantly reduced coma, 3rd-order and higher-order RMS aberrations (p≤0.01). The patients' habitual RGP lenses gave better low-contrast acuity (p≤0.006) compared to the toric SCL; however, no significant difference was found between lens types for high-contrast acuity (p=0.10). In the spectacle wearers no significant differences in visual performance measurements were found between the patients' spectacles and the toric SCL (p≥0.06). Conclusion: The results show that RGP lenses provided superior visual performances and greater reduction of 3rd-order aberrations compared to toric SCL in this group of keratoconic patients. In the spectacle-wearing group, visual performance with the toric SCL was found to be comparable to that measured with spectacles. Nevertheless, with the exception of spherical aberration, the toric SCL were successful in significantly reducing uncorrected higher-order aberrations. Ophthalmic & Physiological Optics © 2012 The College of Optometrists.

Analysing the European Union's responses to organized crime through different securitization lenses

In the past 30 years, organized crime (OC) has shifted from being an issue of little, or no concern, to being considered one of the key security threats facing the European Union (EU), the economic and political fabric of its society and its citizens. The purpose of this article is to understand how OC has come to be understood as one of the major security threats in the EU, by applying different lenses of Securitization Theory (ST). More specifically, the research question guiding this article is whether applying different ST approaches can lead us to draw differing conclusions as to whether OC has been successfully securitized in the EU. Building on the recent literature that argues that this theoretical framework has branched out into different approaches, this article wishes to contrast two alternative views of how a security problem comes into being, in order to verify whether different approaches can lead to diverging conclusions regarding the same phenomenon. The purpose of this exercise is to contribute to the further development of ST by pointing out that the choice in approach bears direct consequences on reaching a conclusion regarding the successful character of a securitization process. Starting from a reflection on ST, the article proceeds with applying a “linguistic approach” to the case study, which it then contrasts with a “sociological approach”. The article proposes that although the application of a “linguistic approach” seems to indicate that OC has become securitized in the EU, it also overlooks a number of elements, which the “sociological approach” renders visible and which lead us to refute the initial conclusion.

Improving the cost-effectiveness of photographic screening for diabetic macular oedema:a prospective, multi-centre, UK study

Background/aims: Retinal screening programmes in England and Scotland have similar photographic grading schemes for background (non-proliferative) and proliferative diabetic retinopathy, but diverge over maculopathy. We looked for the most cost-effective method of identifying diabetic macular oedema from retinal photographs including the role of automated grading and optical coherence tomography, a technology that directly visualises oedema. Methods: Patients from seven UK centres were recruited. The following features in at least one eye were required for enrolment: microaneurysms/dot haemorrhages or blot haemorrhages within one disc diameter, or exudates within one or two disc diameters of the centre of the macula. Subjects had optical coherence tomography and digital photography. Manual and automated grading schemes were evaluated. Costs and QALYs were modelled using microsimulation techniques. Results: 3540 patients were recruited, 3170 were analysed. For diabetic macular oedema, England's scheme had a sensitivity of 72.6% and specificity of 66.8%; Scotland 's had a sensitivity of 59.5% and specificity of 79.0%. When applying a ceiling ratio of £30 000 per quality adjusted life years (QALY) gained, Scotland's scheme was preferred. Assuming automated grading could be implemented without increasing grading costs, automation produced a greater number of QALYS for a lower cost than England's scheme, but was not cost effective, at the study's operating point, compared with Scotland's. The addition of optical coherence tomography, to each scheme, resulted in cost savings without reducing health benefits. Conclusions: Retinal screening programmes in the UK should reconsider the screening pathway to make best use of existing and new technologies.

Randomized crossover trial of silicone hydrogel presbyopic contact lenses

PURPOSE: To assess the performance of four commercially available silicone hydrogel multifocal monthly contact lens designs against monovision. METHODS: A double-masked randomized crossover trial of Air Optix Aqua multifocal, PureVision 2 for Presbyopia, Acuvue OASYS for Presbyopia, Biofinity multifocal, and monovision with Biofinity contact lenses was conducted on 35 presbyopes (54.3 ± 6.2 years). After 4 weeks of wear, visual performance was quantified by high- and low-contrast visual acuity under photopic and mesopic conditions, reading speed, defocus curves, stereopsis, halometry, aberrometry, Near Activity Visual Questionnaire rating, and subjective quality of vision scoring. Bulbar, limbal, and palpebral hyperemia and corneal staining were graded to monitor the impact of each contact lens on ocular physiology. RESULTS: High-contrast photopic visual acuity (p = 0.102), reading speed (F = 1.082, p = 0.368), and aberrometry (F = 0.855, p = 0.493) were not significantly different between presbyopic lens options. Defocus curve profiles (p <0.001), stereopsis (p <0.001), halometry (F = 4.101, p = 0.004), Near Activity Visual Questionnaire (F = 3.730, p = 0.007), quality of vision (p = 0.002), bulbar hyperemia (p = 0.020), and palpebral hyperemia (p = 0.012) differed significantly between lens types, with the Biofinity multifocal lens design principal (center-distance lens was fitted to the dominant eye and a center-near lens to the nondominant eye) typically outperforming the other lenses. CONCLUSIONS: Although ocular aberration variation between individuals largely masks the differences in optics between current multifocal contact lens designs, certain design strategies can outperform monovision, even in early presbyopes.

Photographic Plate Libraries at European Astronomical Observatories

ACM Computing Classification System (1998): J.2.

Potsdam Library of Astronomical Photographic Plates

ACM Computing Classification System (1998): J.2.

Software Tools for Digitization of Astronomical Photographic Plates

ACM Computing Classification System (1998): J.2.

Technology for Scanning Astronomical Photographic Plates

ACM Computing Classification System (1998): J.2.

Weighted ICP Algorithm for Alignment of Stars from Scanned Astronomical Photographic Plates

ACM Computing Classification System (1998): I.2.8, I.2.10, I.5.1, J.2.

Evaluating techniques to improve visual performance with and assessment of premium intraocular lenses

Premium Intraocular Lenses (IOLs) such as toric IOLs, multifocal IOLs (MIOLs) and accommodating IOLs (AIOLs) can provide better refractive and visual outcomes compared to standard monofocal designs, leading to greater levels of post-operative spectacle independence. The principal theme of this thesis relates to the development of new assessment techniques that can help to improve future premium IOL design. IOLs designed to correct astigmatism form the focus of the first part of the thesis. A novel toric IOL design was devised to decrease the effect of toric rotation on patient visual acuity, but found to have neither a beneficial or detrimental impact on visual acuity retention. IOL tilt, like rotation, may curtail visual performance; however current IOL tilt measurement techniques require the use of specialist equipment not readily available in most ophthalmological clinics. Thus a new idea that applied Pythagoras’s theory to digital images of IOL optic symmetricality in order to calculate tilt was proposed, and shown to be both accurate and highly repeatable. A literature review revealed little information on the relationship between IOL tilt, decentration and rotation and so this was examined. A poor correlation between these factors was found, indicating they occur independently of each other. Next, presbyopia correcting IOLs were investigated. The light distribution of different MIOLs and an AIOL was assessed using perimetry, to establish whether this could be used to inform optimal IOL design. Anticipated differences in threshold sensitivity between IOLs were not however found, thus perimetry was concluded to be ineffective in mapping retinal projection of blur. The observed difference between subjective and objective measures of accommodation, arising from the influence of pseudoaccommodative factors, was explored next to establish how much additional objective power would be required to restore the eye’s focus with AIOLs. Blur tolerance was found to be the key contributor to the ocular depth of focus, with an approximate dioptric influence of 0.60D. Our understanding of MIOLs may be limited by the need for subjective defocus curves, which are lengthy and do not permit important additional measures to be undertaken. The use of aberrometry to provide faster objective defocus curves was examined. Although subjective and objective measures related well, the peaks of the MIOL defocus curve profile were not evident with objective prediction of acuity, indicating a need for further refinement of visual quality metrics based on ocular aberrations. The experiments detailed in the thesis evaluate methods to improve visual performance with toric IOLs. They also investigate new techniques to allow more rapid post-operative assessment of premium IOLs, which could allow greater insights to be obtained into several aspects of visual quality, in order to optimise future IOL design and ultimately enhance patient satisfaction.

Clinical techniques to assess the visual and optical performance of intraocular lenses:a review

A number of clinical techniques are available to assess the visual and optical performance of the eye. This report aims to review the advantages and limitations of techniques used in previous studies of patients implanted with intraocular lenses (IOLs), whose designs are ever increasing in optical complexity. Although useful, in-vitro measurements of IOL optical quality cannot account for the wide range of biological variation in ocular anatomy and corneal optics, which will impact on the visual outcome achieved. This further highlights the need for a standardised series of visual performance tests that can be applied to a wide range of IOL designs. The conclusions of this report intend to assistresearchers in developing a comprehensive series of investigations to evaluate IOL performance. Repeatable and reproducible in-vivo assessments of visual and optical performance are desirable to further develop IOL concepts and designs, in the hope of improving current postoperative visual satisfaction. © 2013 Nova Science Publishers, Inc.

Improving the economic value of photographic screening for optical coherence tomography-detectable macular oedema:a prospective, multicentre, UK study

Objectives: To determine the best photographic surrogate markers for detecting sight-threatening macular oedema (MO) in people with diabetes attending UK national screening programmes. Design: A multicentre, prospective, observational cohort study of 3170 patients with photographic signs of diabetic retinopathy visible within the macular region [exudates within two disc diameters, microaneurysms/dot haemorrhages (M/DHs) and blot haemorrhages (BHs)] who were recruited from seven study centres. Setting: All patients were recruited and imaged at one of seven study centres in Aberdeen, Birmingham, Dundee, Dunfermline, Edinburgh, Liverpool and Oxford. Participants: Subjects with features of diabetic retinopathy visible within the macular region attending one of seven diabetic retinal screening programmes. Interventions: Alternative referral criteria for suspected MO based on photographic surrogate markers; an optical coherence tomographic examination in addition to the standard digital retinal photograph. Main outcome measures: (1) To determine the best method to detect sight-threatening MO in people with diabetes using photographic surrogate markers. (2) Sensitivity and specificity estimates to assess the costs and consequences of using alternative strategies. (3) Modelled long-term costs and quality-adjusted life-years (QALYs). Results: Prevalence of MO was strongly related to the presence of lesions and was roughly five times higher in subjects with exudates or BHs or more than two M/DHs within one disc diameter. Having worse visual acuity was associated with about a fivefold higher prevalence of MO. Current manual screening grading schemes that ignore visual acuity or the presence of M/DHs could be improved by taking these into account. Health service costs increase substantially with more sensitive/less specific strategies. A fully automated strategy, using the automated detection of patterns of photographic surrogate markers, is superior to all current manual grading schemes for detecting MO in people with diabetes. The addition of optical coherence tomography (OCT) to each strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. Conclusions: Compared with all current manual grading schemes, for the same sensitivity, a fully automated strategy, using the automated detection of patterns of photographic surrogate markers, achieves a higher specificity for detecting MO in people with diabetes, especially if visual acuity is included in the automated strategy. Overall, costs to the health service are likely to increase if more sensitive referral strategies are adopted over more specific screening strategies for MO, for only very small gains in QALYs. The addition of OCT to each screening strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. © Queen's Printer and Controller of HMSO 2013.

Crossover evaluation of silicone hydrogel daily disposable contact lenses

PURPOSE: To assess the surface tear breakup time and clinical performance of three daily disposable silicone hydrogel contact lenses over 16 hours of wear. METHODS: Thirty-nine patients (mean [±SD] age, 22.1 [±3.5] years) bilaterally wore (narafilcon A, filcon II-3, and delefilcon A) contact lenses in a prospective, randomized, masked, 1-week crossover clinical trial. Tear film was assessed by the tear meniscus height (TMH), ocular/contact lens surface temperature dynamics, and lens surface noninvasive breakup time at 8, 12, and 16 hours of wear. Clinical performance and ocular physiology were assessed by subjective questionnaire, by high-/low-contrast logMAR (logarithm of the minimum angle of resolution) acuity, and through bulbar and limbal hyperemia grading. Corneal and conjunctival staining were assessed after lens removal. RESULTS: Delefilcon A demonstrated a longer noninvasive breakup time (13.4 [±4.4] seconds) than filcon II-3 (11.6 [±3.7] seconds; p < 0.001) and narafilcon A (12.3 [±3.7] seconds; p < 0.001). A greater TMH (0.35 [±0.11] mm) was shown by delefilcon A than filcon II-3 (0.32 [±0.10] seconds; p = 0.016). Delefilcon A showed less corneal staining after 16 hours of lens wear (0.7 [±0.6] Efron grade) than filcon II-3 (1.1 [±0.7]; p < 0.001) and narafilcon A (0.9 [±0.7]; p = 0.031). Time was not a significant factor for prelens tear film stability (F = 0.594, p = 0.555) or TMH (F = 0.632, p = 0.534). Lens brand did not affect temperature (F = 1.220, p = 0.308), but it decreased toward the end of the day (F = 19.497, p < 0.001). Comfort, quality of vision, visual acuity and contrast acuity, and limbal grading were similar between the lens brands but decreased with time during the day (p < 0.05). CONCLUSIONS: The tear breakup time over the contact lens surface differed between lens types and may have a role in protecting the ocular surface.

The measurement of intraocular pressure over positive soft contact lenses by rebound tonometry

Purpose - To investigate if the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over disposable hydrogel (etafilcon A) contact lenses (CL) is affected by the positive power of the CLs. Methods - The experimental group comprised 26 subjects, (8 male, 18 female). IOP measurements were undertaken on the subjects’ right eyes in random order using a Rebound Tonometer (ICare). The CLs had powers of +2.00 D and +6.00 D. Measurements were taken over each contact lens and also before and after the CLs had been worn. Results - The IOP measure obtained with both CLs was significantly lower compared to the value without CLs (t test; p < 0.001) but no significant difference was found between the two powers of CLs. Conclusions - Rebound tonometry over positive hydrogel CLs leads to a certain degree of IOP underestimation. This result did not change for the two positive lenses used in the experiment, despite their large difference in power and therefore in lens thickness. Optometrists should bear this in mind when measuring IOP with the rebound tonometer over plus power contact lenses.