Graeme Young - Academia.edu (original) (raw)

Papers by Graeme Young

Clinical & experimental optometry, Jan 23, 2018

Digital eye strain, an emerging public health issue, is a condition characterised by visual distu... more Digital eye strain, an emerging public health issue, is a condition characterised by visual disturbance and/or ocular discomfort related to the use of digital devices and resulting from a range of stresses on the ocular environment. This review aims to provide an overview of the extensive literature on digital eye strain research with particular reference to the clinical management of symptoms. As many as 90 per cent of digital device users experience symptoms of digital eye strain. Many studies suggest that the following factors are associated with digital eye strain: uncorrected refractive error (including presbyopia), accommodative and vergence anomalies, altered blinking pattern (reduced rate and incomplete blinking), excessive exposure to intense light, closer working distance, and smaller font size. Since a symptom may be caused by one or more factors, a holistic approach should be adopted. The following management strategies have been suggested: (i) appropriate correction of ...

Contact lens & anterior eye : the journal of the British Contact Lens Association, Jan 10, 2017

To calculate theoretical fitting success rates (SR) for a range of typical soft contact lens (SCL... more To calculate theoretical fitting success rates (SR) for a range of typical soft contact lens (SCL) designs using a mathematical model. A spreadsheet mathematical model was used to calculate fitting SR for various SCL designs. Designs were evaluated using ocular topography data from 163 subjects. The model calculated SR based on acceptable edge strain (within range 0-6%) and horizontal diameter overlap (range 0.2-1.2mm). Where lenses had multiple base curves (BCs), eyes unsuccessful with the steeper BC were tested with the flatter BC and aggregate SR calculated. Calculations were based on typical, current, hydrogel and silicone hydrogel SCLs and allowed for appropriate on-eye shrinkage (1.0-2.3%). Theoretical results were compared with those from actual clinical trials. Theoretical success rates for one-BC lenses ranged from 60.7% (95% CI 7.2%) to 90.2% (95% CI 3.7%). With two-BC designs, most combinations showed a SR increase with a second BC (84.0%-90.2%). However, one of the two-B...

Optometry and vision science : official publication of the American Academy of Optometry, Apr 18, 2017

To evaluate the inter-relationship of soft contact lens base curve radius (BC), diameter, and len... more To evaluate the inter-relationship of soft contact lens base curve radius (BC), diameter, and lens fit using a mathematical model. A spreadsheet mathematical model was used to evaluate theoretical fitting characteristics for various combinations of soft lens BC and diameter. The designs were evaluated using ocular topography data collected from 163 UK subjects. The model evaluated lens tightness (edge strain) and on-eye diameter (horizontal corneal overlap) and assumed that acceptable values fell within the range 0 to 6% and 0.2 to 1.2 mm, respectively. Analyses were undertaken of various trends relating to soft lens fit, including (1) the effect of BC and diameter on fitting success; (2) the effect of lens asphericity, BC, and sag on lens diameter on the eye; and (3) the effect of lens diameter on lens tightness. The highest overall success rate (90.2%) was achieved with an 8.60/14.2 mm (BC/diameter) design. Using this design on the sample population, the median edge strain value w...

Contact Lens and Anterior Eye, 2016

To determine the first-year retention rate for patients fitted with contact lenses (CLs) and iden... more To determine the first-year retention rate for patients fitted with contact lenses (CLs) and identify factors associated with retention and dropout. This multi-site study was a retrospective chart review of the status of neophyte CL wearers fitted in representative UK eye care practices. Consecutive records for 524 patients at 29 sites were reviewed. Mean age at dispensing was 34 years (range 8-79), 68% were under 45 years and 61% female. Soft CLs were fitted to 98% of patients. After 12 months, 388 were still CL wearers, a retention rate of 74% (95% CI: 70.1-77.6). Of the 136 lapsed, 25% discontinued during the first month and 47% within 60 days. The main reasons cited for discontinuation included poor distance vision (26%; of whom, 37% were toric and 51% multifocal), poor near vision (16%), discomfort (14%) and handling problems (15%). In 32% of cases, the reasons for discontinuation were unknown. For 71% of dropouts, no alternative lens or management strategy had been tried. Significant factors associated with retention in univariate analysis were: age (younger), sphere power (higher), lens type (sphere vs multifocal) and purchase frequency (regular). Multivariate analysis showed lens sphere power, purchase frequency and lens material to be significant factors. There was a wide variation in retention rates between sites (40-100%). During the first year of CL wear, the overall retention rate for neophyte CL wearers was 74% (spherical CLs 79%, torics 73%, multifocals 57%), with many lapsing during the first 2 months. Factors associated with retention and dropout in these patients include: lens power, material and type, and purchase frequency. While handling and comfort are the most commonly cited performance-related reasons for discontinuing in new spherical lens wearers, visual problems are the most common among new wearers of toric and, in particular, multifocal CLs.

Centre For Health Research Faculty of Health Institute of Health and Biomedical Innovation, 2004

ABSTRACT A number of clinical techniques are available to assess the visual and optical performan... more ABSTRACT 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 assist researchers 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 post-operative visual satisfaction.

Journal of The British Contact Lens Association, 1985

The author reviews the early use of rigid contact lenses for prolonged periods. The literature sh... more The author reviews the early use of rigid contact lenses for prolonged periods. The literature shows that extended wear has been employed throughout the history of contact lenses and, far from being a rarity, has been practiced frequently; either by accident or intent. It is also seen that, from an early stage, special categories of patient began to emerge who were particularly suited to extended wear. These included therapeutic cases, aphakics, children and patients with special occupational requirements.

Investigative Ophthalmology Visual Science, Jan 5, 2013

PURPOSE. To evaluate factors affecting corneoscleral profile (CSP) using anterior segment optical... more PURPOSE. To evaluate factors affecting corneoscleral profile (CSP) using anterior segment optical coherence tomography (AS-OCT) in combination with conventional videokeratoscopy. METHODS. OCT data were collected from 204 subjects of mean age 34.9 years (SD: 615.2 years, range 18-65) using the Zeiss Visante AS-OCT and Medmont M300 corneal topographer. Measurements of corneal diameter (CD), corneal sagittal height (CS), iris diameter (ID), corneoscleral junction angle (CSJ), and scleral radius (SR) were extracted from multiple OCT images. Horizontal visible iris diameter (HVID) and vertical palpebral aperture (PA) were measured using a slit lamp graticule. Subject body height was also measured. Associations were then sought between CSP variables and age, height, ethnicity, sex, and refractive error. RESULTS. Significant correlations were found between age and ocular topography variables of HVID, PA, CSJ, SR, and ID (P < 0.0001), while height correlated with HVID, CD, and ID, and power vector terms with vertical plane keratometry, CD, and CS. Significant differences were noted between ethnicities with respect to CD (P ¼ 0.0046), horizontal and vertical CS (P ¼ 0.0068 and P ¼ 0.0095), and horizontal ID (P ¼ 0.0010). The same variables, with the exception of vertical CS, also varied with sex; horizontal CD (P ¼ 0.0018), horizontal CS (P ¼ 0.0018), and ID (P ¼ 0.0012). Age accounted for the greatest variance in topography variables (36%). CONCLUSIONS. Age is the main factor influencing CSP; this should be taken into consideration in contact lens design, IOL selection, and in the optimization of surgical procedures. Ocular topography also varied with height, sex, ethnicity, and refractive error.

Ophthalmic Physiological Optics the Journal of the British College of Ophthalmic Opticians, Nov 1, 2002

Discontinuation from contact lens wear has been identified as a contributing factor in the lack o... more Discontinuation from contact lens wear has been identified as a contributing factor in the lack of growth of contact lens use in Europe. The purpose of this study was to determine the proportion of lapsed contact lens wearers that can be refitted successfully with contact lenses and to evaluate the reasons for discontinuation from contact lens wear. This was a multi-site clinical study involving 15 UK investigators and 236 lapsed contact lens wearers who had previously tried contact lenses and discontinued. The reasons for discontinuation were assessed by subjects, who were then refitted with contact lenses. Investigators subsequently evaluated factors associated with their initial discontinuation. Short-term success was defined as the successful completion of 1 month of contact lens wear with absence of complications that would prevent further wear. Subjects were interviewed by telephone 6 months after being refitted to determine whether they were still wearing contact lenses. Those who were not wearing lenses were questioned about the reasons for discontinuation and their likelihood of resuming lens wear. A majority of subjects (51%) cited discomfort as the principal reason for having previously given up contact lens wear. Problems with vision were the second most common reason (13%), either with reading (6%) or general vision (7%). The most common type of discomfort was dryness (40%). In almost all cases (97%), the investigator&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s assessment of the reasons for discontinuation agreed with the subject&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s own assessment but investigators also cited product-related and practitioner-related factors as contributing to previous failure. The short-term success rate for refitting lapsed wearers was found to be 77% (Cl: 70-82%). The highest short-term success rates were for 2-weekly/monthly soft spherical lenses (91%) and daily disposable lenses (89%). Lower success rates were found for soft toric (69%) and soft bifocal (53%) lenses. At the 6-month stage, 73% of those who continued in lenses after the 1-month visit were still wearing contact lenses and a further 18% indicated that they were either &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;very likely&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; or &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;likely&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; to resume lens wear. A high proportion of lapsed contact lens wearers can be successfully refitted with contact lenses. The prime reason for previous discontinuation from contact lenses is discomfort and, in particular, dryness-related discomfort. In many cases, previous contact lens failure is product or practitioner-related rather than because of patient-specific problems. Once refitted with contact lenses, lapsed wearers cite vision problems rather than discomfort as the most common reason for discontinuing. This finding suggests that recent advances in contact lens material, design, replacement frequencies and care systems have improved the prospects for avoiding lens-related discomfort and for continuing contact lens wear.

Faculty of Health Institute of Health and Biomedical Innovation, Feb 1, 1988

An attempt was made to derive a model for predicting the extent of hydrogel lens dehydration in v... more An attempt was made to derive a model for predicting the extent of hydrogel lens dehydration in vivo (delta Wv) by using a contact lens refractometer to (1) measure the water content (W) of eight lenses ranging from 36.5 to 85.8% water before and after 90 min lens wear by six subjects; and (2) measure the rate of dehydration of the same lenses in vitro (delta Wt), in a controlled, randomized, double-masked experiment. A significant correlation was demonstrated between W and the rate of change of delta Wt (the dehydration rate, D), whereby lenses of higher water content dehydrate at a slower rate. No correlation was found between W and delta Wv or between D and delta Wv, thus precluding the development of a predictive model. Possible reasons for this failure, and directions for further research, are discussed.

Contact Lens Anterior Eye the Journal of the British Contact Lens Association, 2014

Please cite this article in press as: Hickson-Curran S, et al. The use of daily disposable lenses... more Please cite this article in press as: Hickson-Curran S, et al. The use of daily disposable lenses in problematic reusable contact lens wearers.

Eye & Contact Lens: Science & Clinical Practice, 2015

The diameters of soft contact lenses are conventionally measured at room temperature (RT), howeve... more The diameters of soft contact lenses are conventionally measured at room temperature (RT), however, all soft lenses shrink when raised to eye temperature (ET). The purpose of this study was to evaluate RT to ET shrinkage in a representative sample of contemporary spherical soft contact lenses. Twenty-four reusable and daily disposable lens types (10 hydrogel and 14 silicone hydrogel) in three powers were measured for total diameter at RT (20°C±1°C) and ET (34°C±1°C). Lens diameter measurements were undertaken after equilibration in ISO saline in a temperature controlled lens analyzer (Optimec Ltd, Malvern, UK). Theoretical changes in base curve radii were also calculated. All lens types reduced in diameter when raised to ET. The largest mean changes with silicone hydrogel and hydrogel lenses were with Avaria (Δ0.33 mm) and SofLens Daily Disposable (Δ0.69 mm), respectively. The smallest mean changes for silicone hydrogel and hydrogel lenses were with 1-DAY ACUVUE TruEye (Δ0.04 mm) and SofLens 38 (Δ0.11 mm), respectively. There was, however, a wide range in change between the different lenses tested. This study has identified the levels of shrinkage in current soft contact lenses. In many cases, these shrinkage levels can be expected to have significant effects on clinical performance.

$Research paper thumbnail of Monovision vs. soft diffractive bifocal contact lenses: A crossover study$

International Contact Lens Clinic, 1990

The relative clinical performance of monovision and the Hydron@ ECHELON@ soft diffractive bifocal... more The relative clinical performance of monovision and the Hydron@ ECHELON@ soft diffractive bifocal contact lens were evaluated in a 1-month, two-period, open-label crossover study. Wearers' subjective impressions were also elicited. Monovision provided superior low contrast acuity and the bifocal better stereopsis. No difference was found for high-contrast visual acuity or physiological signs. Although monovision was subjectively preferred for reading, no difference was found for other subjective variabks. These included visual quality ratings at far and intermediate viewing distances, under dimly lit conditions, when driving at night, and for overall preference. Similiar patient acceptance can be expected for both mod&es. The results of this study refkct a significant improvement in performance of the diffractive bifocal lens over previous simultaneous vision bifocal contact lens damage.

Current eye research, 1989

A wide-field color-coded infra-red imaging device was applied to the measurement of i) the temper... more A wide-field color-coded infra-red imaging device was applied to the measurement of i) the temperature profile across the ocular surface and ii) the temporal stability of central corneal temperature, on 21 subjects. The thermographs showed a pattern of ellipsoidal isotherms (major axis horizontal) approximately concentric about a temperature apex (coldest point) which was slightly inferior to the geometric center of the cornea (GCC). The GCC had a mean temperature (+/- SD) of 34.3 +/- 0.7 degrees C (range 32.8 to 35.4 degrees C). Temperature increased towards the periphery of the cornea with the limbus being 0.45 degrees C warmer than the GCC (p less than 0.0001). Following a blink, the GCC cooled at a mean (+/- SD) rate of 0.033 +/- 0.024 degrees C/s (p less than 0.0001) over the first 15s. Subjects whose corneas cooled more slowly following a blink demonstrated a greater capacity to avoid blinking for a prolonged period (p less than 0.05). This improved method of measuring ocular ...

Optometry and vision science : official publication of the American Academy of Optometry, 2014

To provide comparative ocular topography data from a substantial population of East Asian and whi... more To provide comparative ocular topography data from a substantial population of East Asian and white eyes. This study evaluated 675 subjects from three ethnic groups: white (n = 255), Chinese (n = 299), and Japanese (n = 121) at investigational sites in four locations: Wenzhou, China; Melbourne, Australia; Tokyo, Japan; and Jacksonville, USA. Subjects underwent the same measurements of ocular topography using identical equipment and protocols. A videokeratoscope (Medmont E300) was used to measure apical corneal radius, simulated K-reading (K), corneal shape factor (CSF), and corneal sagittal height at 10 mm in the two principal meridians. Digital photography was also used to measure ocular parameters including horizontal visible iris diameter (HVID), vertical palpebral aperture (PA), the intercanthal angle (ICA), and upper and lower lid angles. Mean HVID measurements were significantly smaller for the Chinese and Japanese groups than whites: 11.26, 11.10, and 11.75 mm, respectively. ...

Optometry and Vision Science, 1996

Optometry and Vision Science, 2014

To evaluate the effect of varying lens and ocular topography parameters on soft contact lens (SCL... more To evaluate the effect of varying lens and ocular topography parameters on soft contact lens (SCL) fit, using a novel computer spreadsheet model. Although SCLs are worn by more than 100 million ametropes, the factors governing their fitting characteristics are poorly understood. A spreadsheet-based computer model used a novel ellipto-conical corneal model coupled with population data on corneoscleral topography obtained in a previous clinical study. The model calculated lens edge strain (circumferential elongation) as a predictor of lens tightness. The following parameters were systematically varied: corneal curvature, corneal diameter, corneal shape factor, corneoscleral junction angle, lens base curve (BC), and diameter. The ellipto-conical corneal model showed closer concordance with actual measurements of corneal sagittal height than a simple elliptical model (limits of agreement, ±0.20 vs. ±0.25 mm; p = 0.0015). For an eye with average ocular parameters wearing a typical SCL design (BC, 8.60; diameter, 14.2 mm), the model calculated an edge strain of 2.7%. For the same SCL, the tightest fit (8.5% strain) was found with the eye showing the combination of smallest, flattest, most aspheric cornea. Conversely, the loosest fitting (-2.6%) was found with the eye showing the combination of largest, steepest, least aspheric cornea. A change in BC of 0.4 mm typically resulted in changes in edge strain of less than 2.5%, whereas a change in diameter of 0.5 mm resulted in a change of less than 2%. Using the typical SCL design and average corneal model, wide variations in corneoscleral junction angle did not critically affect lens fit. More extreme combinations of SCL and ocular parameters resulted in edge strain likely to result in a tight (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;6%) or loose fit (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0%). A novel ellipto-conical corneal model in conjunction with spreadsheet mathematical modeling proved to be a useful tool for attempting to understand the factors governing SCL fit.

Optometry and Vision Science, 1992

A 12-month clinical trial involving 88 subjects was undertaken to compare the clinical performanc... more A 12-month clinical trial involving 88 subjects was undertaken to compare the clinical performance of rigid gas-permeable contact lens extended wear (EWRGP) with that of RGP daily wear (DWRGP) lenses and soft lens extended wear (SLEW) with medium water content lenses. Withdrawals from the EWRGP group tended to result from lens-related problems, whereas the SLEW withdrawals generally resulted from adverse effects on corneal physiology. Changes in spherical refractive error during the 1-year study were small (less than 1.00 D) and similar for both gas-permeable lens-wearing groups. Most of the SLEW group (58%) showed an increase in myopia and the mean increase was 0.38 D, which represented a significant difference from the EWRGP group. The EWRGP group showed a mean flattening in corneal curvature of 0.11 and 0.15 mm in the flattest and steepest corneal meridians, respectively. A positive correlation was noted between change in corneal curvature and baseline corneal astigmatism, which suggests corneal molding as a result of lid pressure as the most likely cause. The DWRGP and SLEW groups showed small, nonsignificant changes in corneal curvature. Most of the EWRGP subjects (69%) who completed the study showed increased corneal distortion. This compares with 30 and 17% with the DWRGP and SLEW groups, respectively. Likely corneal edema was a major contributory factor. For most of the slitlamp variables monitored, there were no significant differences between the groups. However, microcystic changes were detected in both EWRGP (35%) and SLEW subjects but not in the DWRGP group. Corneal staining was noted in all groups but was more prevalent among the EWRGP group. The findings of this study are discussed in relation to the clinical management of RGP extended wear.

International Contact Lens Clinic, 1996

Journal of The British Contact Lens Association, 1992