Through-focus performance with multifocal contact lenses : effect of binocularity, pupil diameter and inherent ocular aberrations

Purpose to evaluate the effects of the wearer’s pupil size and spherical aberration on visual performance with centre-near, aspheric multifocal contact lenses (MFCLs). The advantage of binocular over monocular vision was also investigated. Methods Twelve young volunteers, with an average age of 27±5 years, participated in the study. LogMAR Visual Acuity (VA) was measured under cycloplegia for a range of defocus levels (from +3.0 to -3.0D, in 0.5D steps) with no correction and with three aspheric MFCLs (Air Optix Aqua Multifocal, Ciba Vision, Duluth, GA, US) with a centre-near design, providing correction for “Low”, “Med” and “High” near demands. Measurements were performed for all combinations of the following conditions: i) artificial pupils of 6mm and 3mm diameter, ii) binocular and monocular (dominant eye) vision. Depth-of-focus (DOF) was calculated from the VA vs. defocus curves. Ocular aberrations under cycloplegia were measured using iTrace. Results VA at -3.0D defocus (simulating near performance) was statistically higher for the 3mm than for the 6mm pupil (p=0.006), and for binocular rather than for monocular vision (p<0.001). Similarly, DOF was better for the 3mm pupil (p=0.002) and for binocular viewing conditions (p<0.001, ANOVA). Both VA at –3.0D defocus and DOF increased as the “addition” of the MFCL correction increased. Finally, with the centre-near MFCLs a linear correlation was found between VA at –3.0D defocus and the wearer’s ocular spherical aberration (R2=0.20 p<0.001 for 6mm data), with the eyes exhibiting the higher positive spherical aberration experiencing lower VAs. By contrast, no correlation was found between VA and spherical aberration at 0.00D defocus (distance vision). Conclusions Both near VA and depth-of-focus improve with these MFCLs, with the effects being more pronounced for small pupils and binocular than for monocular vision. Coupling of the wearer’s ocular spherical aberration with the aberration profiles provided by MFCLs affects their functionality.

Visual performance with lenses correcting peripheral refractive errors

Purpose To design and manufacture lenses to correct peripheral refraction along the horizontal meridian and to determine whether these resulted in noticeable improvements in visual performance. Method Subjective refraction of a low myope was determined on the basis of best peripheral detection acuity along the horizontal visual field out to ±30° for both horizontal and vertical gratings. Subjective refraction was compared to objective refractions using a COAS-HD aberrometer. Special lenses were made to correct peripheral refraction, based on designs optimized with and without smoothing across a 3 mm diameter square aperture. Grating detection was retested with these lenses. Contrast thresholds of 1.25’ spots were determined across the field for the conditions of best correction, on-axis correction, and the special lenses. Results The participant had high relative peripheral hyperopia, particularly in the temporal visual field (maximum 2.9 D). There were differences > 0.5D between subjective and objective refractions at a few field angles. On-axis correction reduced peripheral detection acuity and increased peripheral contrast threshold in the peripheral visual field, relative to the best correction, by up to 0.4 and 0.5 log units, respectively. The special lenses restored most of the peripheral vision, although not all at angles to ±10°, and with the lens optimized with aperture-smoothing possibly giving better vision than the lens optimized without aperture-smoothing at some angles. Conclusion It is possible to design and manufacture lenses to give near optimum peripheral visual performance to at least ±30° along one visual field meridian. The benefit of such lenses is likely to be manifest only if a subject has a considerable relative peripheral refraction, for example of the order of 2 D.

The Relation between work motivation and project management success in case of temporary organizations : theoretical lenses

The purpose of this paper is to present theoretical lenses that explain the relation between work motivation and project management success in case of temporary organizations such as projects. This paper is a part of the larger research study that first empirically identifies the constructs of work motivation in case of temporary organizations, and then empirically determines the relation between work motivation, and project management success. In the current paper, we have briefly reviewed the theories of work motivation from the work design school. These theories are predominantly drawn from the industrial/ organizational psychology literature. Then, we have considered the recent research on Nine Schools of Project Management as a point of departure to review theory on project management success. These theoretical perspectives are drawn from project management literature. We then illustrate the points of overlap for the theories drawn from these two disciplines. This review helps us to position our research study within the industrial/ organizational psychology, and project management literature as a cross-discipline study.

Power profiles of multifocal contact lenses and their interpretation

Purpose Many contact lens (CL) manufacturers produce simultaneous-image lenses in which power varies either smoothly or discontinuously with zonal radius. We present in vitro measurements of some recent CLs and discuss how power profiles might be approximated in terms of nominal distance corrections, near additions, and on-eye visual performance. Methods Fully hydrated soft, simultaneous-image CLs from four manufacturers (Air Optix AQUA, Alcon; PureVision multifocal, Bausch & Lomb; Acuvue OASYS for Presbyopia, Vistakon; Biofinity multifocal- ‘‘D’’ design, Cooper Vision) were measured with a Phase focus Lens Profiler (Phase Focus Ltd., Sheffield,UK) in a wet cell and powerswere corrected to powers in air. All lenses had zero labeled power for distance. Results Sagittal power profiles revealed that the ‘‘low’’ add PureVision and Air Optix lenses exhibit smooth (parabolic) profiles, corresponding to negative spherical aberration. The ‘‘mid’’ and ‘‘high’’ add PureVision and Air Optix lenses have biaspheric designs, leading to different rates of power change for the central and peripheral portions. All OASYS lenses display a series of concentric zones, separated by abrupt discontinuities; individual profiles can be constrained between two parabolically decreasing curves, each giving a valid description of the power changes over alternate annular zones. Biofinity lenses have constant power over the central circular region of radius 1.5 mm, followed by an annular zone where the power increases approximately linearly, the gradient increasing with the add power, and finally an outer zone showing a slow, linear increase in power with a gradient being almost independent of the add power. Conclusions The variation in power across the simultaneous-image lenses produces enhanced depth of focus. The throughfocusnature of the image, which influences the ‘‘best focus’’ (distance correction) and the reading addition, will vary with several factors, including lens centration, the wearer’s pupil diameter, and ocular aberrations, particularly spherical aberration; visual performance with some designs may show greater sensitivity to these factors.

An international survey of daily disposable contact lens prescribing

Purpose The aim was to determine the extent of daily disposable contact lens prescribing worldwide and to characterise the associated demographics and fitting patterns. Methods Up to 1,000 survey forms were sent to contact lens fitters in up to 40 countries between January and March every year for five consecutive years (2007 to 2011). Practitioners were asked to record data relating to the first 10 contact lens fits or refits performed after receiving the survey form. Survey data collected since 1996 were also analysed for seven nations to assess daily disposable lens fitting trends since that time. Results Data were collected in relation to 97,289 soft lens fits, of which 23,445 (24.1 per cent) were with daily disposable lenses and 73,170 (75.9 per cent) were with reusable lenses. Daily disposable lens prescribing ranged from 0.6 per cent of all soft lenses in Nepal to 66.2 per cent in Qatar. Compared with reusable lens fittings, daily disposable lens fittings can be characterised as follows: older age (30.0 ± 12.5 versus 29.3 ± 12.3 years for reusable lenses); males are over-represented; a greater proportion of new fits versus refits; 85.9 per cent hydrogel; lower proportion of toric and presbyopia designs and a higher proportion of part-time wear. There has been a continuous increase in daily disposable lens prescribing between 1996 and 2011. The proportion of daily disposable lens fits (as a function of all soft lens fits) is positively related to the gross domestic product at purchasing power parity per capita (r2 = 0.55, F = 46.8, p < 0.0001). Conclusions The greater convenience and other benefits of daily disposable lenses have resulted in this modality capturing significant market share. The contact lens field appears to be heading toward a true single-use-only, disposable lens market.

Determinants of the frequency of contact lens wear

Objectives To characterize and discover the determinants of the frequency of wear (FOW) of contact lenses. Methods Survey forms were sent to contact lens fitters in up to 40 countries between January and March every year for 5 consecutive years (2007–2011). Practitioners were asked to record data relating to the first 10 contact lens fits or refits performed after receiving the survey form. Only data for daily wear lens fits were analyzed. Results Data were collected in relation to 74,510 and 9,014 soft and rigid lens fits, respectively. Overall, FOW was 5.9±1.7 days per week (DPW). When considering the proportion of lenses worn between one to seven DPW, the distribution for rigid lenses is skewed toward full-time wear (7 DPW), whereas the distribution for soft daily disposable lenses is perhaps bimodal, with large and small peaks at seven and two DPW, respectively. There is a significant variation in FOW among nations (P<0.0001), ranging from 6.8±1.0 DPW in Greece to 5.1±2.5 DPW in Kuwait. For soft lenses, FOW increases with decreasing age. Females (6.0±1.6 DPW) wear lenses more frequently than males (5.8±1.7 DPW) (P=0.0002). FOW is greater among those wearing presbyopic corrections (6.1±1.4 DPW) compared with spherical (5.9±1.7 DPW) and toric (5.9±1.6 DPW) designs (P<0.0001). FOW with hydrogel peroxide systems (6.4±1.1 DPW) was greater than that with multipurpose systems (6.2±1.3 DPW) (P<0.0001). Conclusions Numerous demographic and contact lens–related factors impact FOW. There may be a future trend toward a lower FOW associated with the increasing popularity of daily disposable lenses.

Why fit contact lenses? Part 1 - clinical reasons

There are probably two main reasons why some practitioners do not bother fitting contact lenses – that it is not profitable and it is clinically too difficult. Although this article will concentrate on clinical issues rather than questions of profitability, I feel that the belief that contact lens fitting is not as profitable as prescribing spectacles is unfounded.

Why GP lenses are on the decline

Current contact lens prescribing data speaks for itself: GP lenses represented 5 percent or less of fits in 13 of the 27 countries examined in the February 2009 article "International Contact Lens Prescribing in 2008" by Morgan et al. GP lens fitting is becoming a specialist activity undertaken by a minority of practitioners. I believe the question is no longer: "Are GP lenses on the decline?" but rather: "Why are GP lenses on the decline?" So, here I'll try to answer the latter question.

Book review: 'Contact lenses: The Story', by T. Bowden. Bower House Publications, Kent 2009.

This book had to be written. Congratulations to British dispensing optician Timothy Bowden for his dogged determination in researching, writing and essentially self-publishing this hefty tome. How does one tackle the monumental task of tracking the complex history of the development of the contact lens, from the production of the first human artificial glass eyes by Ludwig Müller-Uri in Germany in 1835 to the sophisticated, high-technology, multi-billion dollar contact lens industry of today? The superficial answer may seem simple: do it chronologically, but it is much more difficult than that. Multiple contemporaneous and seemingly unconnected events often converged to result in ideas that elevated contact lens technology to the next level and many developments revolved around the deliberate and sometimes accidental activities of a long list of enthusiasts, inventors, entrepreneurs, businessmen, technicians, scientists, engineers, polymer scientists, opticians, optometrists and ophthalmologists.

RGP lenses 2010 : the last decade and the next decade

The results of the annual survey on international contact lens fits have become available again, which presents a great opportunity to distill the RGP lens data to see what the status of RGP lenses is today as well as to revisit the last decade of RGP lens fitting and to look ahead to the next decade.

Why fit contact lenses?

Contrary to what many practitioners believe, current generation contact lenses are easy to fit, are well tolerated, provide superior vision, are physiologically compatible with the anterior ocular structures, cause few serious complications and are cost effective. These factors will be explored with examples of advancements that have occurred in contact lens practice over the past two decades. Consideration will also be given to the role of optometrists, the contact lens industry and educational institutions in promoting contact lenses as an alternative form of vision correction.

The role of RGPs in modern practice

Has the 1998 prediction of a well-known contact lens researcher – that rigid contact lenses will be obsolete by the year 2010 – come to fruition? This Eulogy to RGPs will demonstrate why it has. A recent survey of international contact lens prescribing trends shows that rigid lenses constituted less than 5% of all contact lenses prescribed in 16 out of 27 nations surveyed. This compares with rigid lenses representing 100% of all lenses prescribed 1965 and about 40% in 1990). With the wide range of sophisticated soft lens materials available today, including super-permeable silicone hydrogels, and designs capable of correcting astigmatism and presbyopia, there is now no need to fit cosmetic patients with rigid lenses, with the associated intractable problems of rigid lens-induced ptosis, 3 and 9 o’clock, staining, lens binding, corneal warpage and adaptation discomfort. Orthokeratology is largely a fringe application of marginal efficacy, and the notion that rigid lenses arrest myopia progression is flawed. That last bastion of rigid lens practice – fitting patients with severely distorted corneas as in keratoconus – is about to crumble in view of a number of demonstrations by independent research groups of the efficacy of custom-designed wavefront-corrected soft contact lenses for the correction of keratoconus. It is concluded that rigid contact lenses now have no place in modern contact lens practice.

The changing performance of multifocal contact lenses compared to monovision.

Purpose:Multifocal contact lenses (MCLs) have been available for decades. A review of the literature suggests that while, historically, these lenses have been partially successful, they have struggled to compete with monovision (MV). More recent publications suggest that there has been an improvement in the performance of these lenses. This study set out to investigate whether the apparent improved lens performance reported in the literature is reflected in clinical practice. Methods:Data collected over the last 5yrs via the International Contact Lens Prescribing Survey Consortium was reviewed for patients over the age of 45yrs. The published reports of clinical trials were reviewed to assess lens performance over the time period. Results:Data review was of 16,680 presbyopic lens fits in 38 countries. The results are that 29% were fit with MCLs, 8% MV and 63% single vision (SV). A previous survey conducted in Australia during 1988-89 reported that 9% of presbyopes were fit with MCLs, 29% MV and 63% SV. The results from our survey for Australia alone were 28% (MV 13%) vs 9% (MV 29%) suggesting an increase in usage of MCLs from 1988-89 to 2010. A review of the literature indicates the reported level of visual acuities with MCLs in comparison to MV has remained equivalent over this time period, yet preference has switch from MV to MCLs. Conclusions:There is evidence that currently more MCLs than MV are being fit to presbyopes, compared to 1988-89. This increased use is likely due to the improved visual performance of these lenses, which is not demonstrated with acuity measures but reported by wearers, suggesting that patient-based subjective ratings are currently the best way to measure visual performance.