Anna Sulley

Prevalence of astigmatism in relation to soft contact lens fitting.

Purpose: To estimate the proportion of potential soft contact lens wearers requiring an astigmatic correction and to estimate the proportion of astigmats who can be accommodated with toric soft lenses of varying prescription range. Method: A database of 11,624 spectacle prescriptions was used to calculate the prevalence of astigmatism for various thresholds (0.50-2.00 DC) by eye and by patient. The coverage of various prescription ranges was estimated using a subset of the database comprising those patients with at least 0.75 D of astigmatism in at least one eye (n = 5,444). Results: The prevalence of patients showing astigmatism of 0.75 and 1.00 D or greater in at least one eye was 47.4% and 31.8% and, in both eyes, 24.1% and 15.0%, respectively. The proportion of eyes showing astigmatism greater than or equal to 0.75, 1.00, 1.50, and 2.00 D was 35.7%, 23.4%, 10.8%, 5.6%, respectively. The prevalence of astigmatism of 0.75 D or greater was almost double in myopes compared with hyperopes: 31.7% vs. 15.7%. The prevalence of with-the-rule (WTR) astigmatism was higher than against-the-rule (32.9% vs. 29.1%); the proportion was also higher for WTR in eyes with astigmatism ≥0.75 D (15.3% vs. 14.5%). We estimate that approximately one third of potential contact lens wearers require astigmatic correction. A stock range of toric soft lenses in sphere powers +6.00 to −9.00 D, three cylinder powers, and 18 axes requires nearly 3,000 prescriptions and provides coverage for 90% of astigmats. Conclusion: These findings provide an estimate of the proportion of soft contact lens patients requiring an astigmatic correction and some useful insights into the proportion of astigmats covered by toric soft lens stocks of varying range.

Conjunctival UV autofluorescence - prevalence and risk factors

PURPOSE Autofluorescence of ultraviolet (UV) light has been shown to occur in localised areas of the bulbar conjunctiva, which map to active cellular changes due to UV and environmental exposure. This study examined the presence of conjunctival UV autofluorescence in eye care practitioners (ECPs) across Europe and the Middle East and its associated risk factors. METHOD Images were captured of 307 ECPs right eyes in the Czech Republic, Germany, Greece, Kuwait, Netherlands, Sweden, Switzerland, United Arab Emirates and the United Kingdom using a Nikon D100 camera and dual flash units through UV filters. UV autofluorescence was outlined using ImageJ software and the nasal and temporal area quantified. Subjects were required to complete a questionnaire on their demographics and lifestyle including general exposure to UV and refractive correction. RESULTS Average age of the subjects was 38.5±12.2 years (range 19-68) and 39.7% were male. Sixty-two percent of eyes had some conjunctival damage as indicated by UV autofluorescence. The average area of damage was higher (p=0.005) nasally (2.95±4.52mm(2)) than temporally (2.19±4.17mm(2)). The area of UV damage was not related to age (r=0.03, p=0.674), gender (p=0.194), self-reported sun exposure lifestyle (p>0.05), geographical location (p=0174), sunglasses use (p>0.05) or UV-blocking contact lens use (p>0.05), although it was higher in those wearing contact lenses with minimal UV-blocking and no spectacles (p=0.015). The area of UV damage was also less nasally in those who wore contact lenses and spectacles compared to those with no refractive correction use (p=0.011 nasal; p=0.958 temporal). CONCLUSION UV conjunctival damage is common even in Europe, Kuwait and UAE, and among ECPs. The area of damage appears to be linked with the use of refractive correction, with greater damage nasally than temporally which may be explained by the peripheral light focusing effect.

Clinical evaluation of fitting toric soft contact lenses to current non-users

To evaluate the ease with which astigmats from three groups of current non‐wearers of toric contact lenses can be fitted with current toric soft lenses, and to determine toric lens‐wearing success.

Factors in the success of new contact lens wearers.

PURPOSE To determine the first-year retention rate for patients fitted with contact lenses (CLs) and identify factors associated with retention and dropout. METHODS This multi-site study was a retrospective chart review of the status of neophyte CL wearers fitted in representative UK eye care practices. RESULTS 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%). CONCLUSIONS 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.

Inter-relationship of soft contact lens diameter, base curve radius, and fit

PURPOSE To evaluate the inter-relationship of soft contact lens base curve radius (BC), diameter, and lens fit using a mathematical model. METHODS 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. RESULTS 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 was 3.2% (IQR: 2.1%) whereas median corneal overlap was 0.62 mm (IQR: 0.35). There was a positive correlation (r = 0.37, P < .0001) between edge strain and corneal overlap. Edge strain showed significant correlations with each of the ocular topography variables, most notably corneal asphericity (-0.62, P < .0001). Corneal overlap showed significant correlations with corneal asphericity (r = -0.42, P < .0001) and corneal diameter (r = 0.92, P < .0001). For a 0.4 mm change in BC, it is necessary to change diameter by 0.2 mm to maintain similar on-eye diameter (arclength). When changing lens diameter, a change in BC of 0.2 mm is required to maintain similar tightness of fit. CONCLUSIONS Mathematical modeling is a useful technique for large-scale evaluation of the interactions of soft contact lens design and fit. The study has given useful insights into the general performance of soft lens designs.

The Effect of Temperature on Soft Contact Lens Diameter.

Purpose: 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. Methods: 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. Results: All lens types reduced in diameter when raised to ET. The largest mean changes with silicone hydrogel and hydrogel lenses were with Avaria (&Dgr;0.33 mm) and SofLens Daily Disposable (&Dgr;0.69 mm), respectively. The smallest mean changes for silicone hydrogel and hydrogel lenses were with 1-DAY ACUVUE TruEye (&Dgr;0.04 mm) and SofLens 38 (&Dgr;0.11 mm), respectively. There was, however, a wide range in change between the different lenses tested. Conclusions: 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.

Theoretical fitting characteristics of typical soft contact lens designs

PUROSE To calculate theoretical fitting success rates (SR) for a range of typical soft contact lens (SCL) designs using a mathematical model. METHOD 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. RESULTS 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-BC combinations showed only negligible increase with a second BC (72.4%-73.0%). For designs with lower SR, the greatest contributor to failure was inadequate lens diameter. For a given design, differences in shrinkage (i.e. on-eye bulk dehydration) had a significant effect on success rate. In comparison with historical clinical data, there was a positive correlation between small lens fitting prevalence and discomfort reports (r=+0.95, P=<0.001) with a poor correlation between theoretical and actual tight/loose fittings. CONCLUSIONS Mathematical modelling is a useful method for testing SCL design combinations. The results suggest that judicious choice of additional fittings can expand the range of fitting success.

Resultant vertical prism in toric soft contact lenses.

PURPOSE Rotational stability of toric soft contact lenses (TSCLs) is achieved using a range of designs. Designs utilising prism or peripheral ballast may result in residual prism in the optic zone. This study quantifies the vertical prism in the central 6mm present in TSCLs with various stabilisation methods. METHOD Vertical prism was computed using published refractive index and vertical thickness changes in the central optic zone on a full lens thickness map. Thickness maps were measured using scanning transmission microscopy. Designs tested were reusable, silicone hydrogel and hydrogel TSCLs: SofLens(®) Toric, PureVision(®)2 for Astigmatism, PureVision(®) Toric, Biofinity(®) Toric, Avaira(®) Toric, clariti(®) toric, AIR OPTIX(®) for ASTIGMATISM and ACUVUE OASYS(®) for ASTIGMATISM; with eight parameter combinations for each lens (-6.00DS to +3.00DS, -1.25DC, 90° and 180° axes). RESULTS All TSCL designs evaluated had vertical prism in the optic zone except one which had virtually none (0.01Δ). Mean prism ranged from 0.52Δ to 1.15Δ, with three designs having prism that varied with sphere power. Vertical prism in ACUVUE OASYS(®) for ASTIGMATISM was significantly lower than all other TSCLs tested. CONCLUSIONS TSCL designs utilising prism-ballast and peri-ballast for stabilisation have vertical prism in the central optic zone. In monocular astigmats fitted with a TSCL or those wearing a mix of toric designs, vertical prism imbalance could create or exacerbate disturbances in binocular vision function. Practitioners should be aware of this potential effect when selecting which TSCL designs to prescribe, particularly for monocular astigmats with pre-existing binocular vision anomalies, and when managing complaints of asthenopia in monocular astigmats.

Management of digital eye strain: Management of digital eye strain

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 refractive error, including astigmatism and presbyopia; (ii) management of vergence anomalies, with the aim of inducing or leaving a small amount of heterophoria (~1.5Δ Exo); (iii) blinking exercise/training to maintain normal blinking pattern; (iv) use of lubricating eye drops (artificial tears) to help alleviate dry eye‐related symptoms; (v) contact lenses with enhanced comfort, particularly at end‐of‐day and in challenging environments; (vi) prescription of colour filters in all vision correction options, especially blue light‐absorbing filters; and (vii) management of accommodative anomalies. Prevention is the main strategy for management of digital eye strain, which involves: (i) ensuring an ergonomic work environment and practice (through patient education and the implementation of ergonomic workplace policies); and (ii) visual examination and eye care to treat visual disorders. Special consideration is needed for people at a high risk of digital eye strain, such as computer workers and contact lens wearers.

Retention Rates in New Contact Lens Wearers

Purpose: To determine the retention rate (RR) for neophyte patients fitted with contact lenses (CLs) and to identify factors associated with retention and dropout. Method: This multisite, sponsor-masked registry study evaluated the 1-year status of neophyte CL wearers fitted in a representative range of UK practices. A total of 26 UK investigational sites each recruited up to 89 neophyte patients. The participants were requested to complete surveys at 1 month (±1 week from date of fitting), 3 months (±2 weeks), and 12 months (±3 weeks) online or through phone. Participants were contacted by email (or phone) and invited to complete an online survey that asked a range of questions regarding their CL wearing experience. Results: Of the 531 participants recruited, 65.3% (347/531) responded to at least one follow-up survey and 42.3% (225/531) responded to all three surveys. One in four patients showed discontinued CL wear by 12 months. Based on evaluable subjects at 12 months, the RR was 77.6% (194/250, 95% confidence interval: 72.0–82.3). The most common reason for discontinuation was problems with vision (41%), followed by discomfort (36%) and handling problems (25%). The factors affecting first-year RRs: sex, spherical refraction, lens usage (full time or part time), and supply method (collected or posted). Conclusions: In this prospective study, the first-year RR for neophyte CL wearers was 77.6%. This was consistent with that noted in a retrospective study: 74.0%. As with the previous study, the commonly cited reason for discontinuation was visual problems.