Automated arteriole and venule classification using deep learning for retinal images from the UK Biobank cohort

The morphometric characteristics of the retinal vasculature are associated with future risk of many systemic and vascular diseases. However, analysis of data from large population based studies is needed to help resolve uncertainties in some of these associations. This requires automated systems that extract quantitative measures of vessel morphology from large numbers of retinal images. Associations between retinal vessel morphology and disease precursors/outcomes may be similar or opposing for arterioles and venules. Therefore, the accurate detection of the vessel type is an important element in such automated systems. This paper presents a deep learning approach for the automatic classification of arterioles and venules across the entire retinal image, including vessels located at the optic disc. This comprises of a convolutional neural network whose architecture contains six learned layers: three convolutional and three fully-connected. Complex patterns are automatically learnt from the data, which avoids the use of hand crafted features. The method is developed and evaluated using 835,914 centreline pixels derived from 100 retinal images selected from the 135,867 retinal images obtained at the UK Biobank (large population-based cohort study of middle aged and older adults) baseline examination. This is a challenging dataset in respect to image quality and hence arteriole/venule classification is required to be highly robust. The method achieves a significant increase in accuracy of 8.1% when compared to the baseline method, resulting in an arteriole/venule classification accuracy of 86.97% (per pixel basis) over the entire retinal image.

Simple tests for the diagnosis of childhood obesity: a systematic review and meta-analysis

There is a need to accurately quantify levels of adiposity in order to identify overweight and obesity in children. This systematic review aimed to identify all diagnostic accuracy studies evaluating simple tests for obesity and adiposity, including body mass index (BMI), skin-fold thickness and waist circumference, compared against high-quality reference tests. Twenty-four cohort studies including 25,807 children were included. BMI had good performance when diagnosing obesity: a sensitivity of 81.9% (95% confidence interval [CI]: 73.0 to 93.8) for a specificity of 96.0% (95% CI: 93.8 to 98.1). It was less effective at diagnosing overweight (sensitivity: 76.3%, 95% CI: 70.2 to 82.4; specificity: 92.1% 95% CI: 90.0 to 94.3). When diagnosing obesity, waist circumference had similar performance (sensitivity: 83.8%; specificity: 96.5%). Skin-fold thickness had slightly poorer performance (sensitivity: 72.5%; specificity: 93.7%). Few studies considered any other tests. There was no conclusive evidence that any test was generally superior to the others. BMI is a good simple diagnostic test for identifying childhood adiposity. It identifies most genuinely obese and adipose children while misclassifying only a small number as obese. There was no conclusive evidence that any test should be preferred to BMI, and the extra complexity of skin-fold thickness tests does not appear to improve diagnostic accuracy.

Cross-sectional study of ethnic differences in physical fitness among children of South Asian, black African-Caribbean and white European origin: the Child Heart and Health Study in England (CHASE)

OBJECTIVE

Little is known about levels of physical fitness in children from different ethnic groups in the UK. We therefore studied physical fitness in UK children (aged 9-10 years) of South Asian, black African-Caribbean and white European origin.

DESIGN

Cross-sectional study.

SETTING

Primary schools in the UK.

PARTICIPANTS

1625 children (aged 9-10 years) of South Asian, black African-Caribbean and white European origin in the UK studied between 2006 and 2007.

OUTCOME MEASURES

A step test assessed submaximal physical fitness from which estimated VO2 max was derived. Ethnic differences in estimated VO2 max were estimated using multilevel linear regression allowing for clustering at school level and adjusting for age, sex and month as fixed effects.

RESULTS

The study response rate was 63%. In adjusted analyses, boys had higher levels of estimated VO2 max than girls (mean difference 3.06 mL O2/min/kg, 95% CI 2.66 to 3.47, p<0.0001). Levels of estimated VO2 max were lower in South Asians than those in white Europeans (mean difference -0.79 mL O2/min/kg, 95% CI -1.41 to -0.18, p=0.01); levels of estimated VO2 max in black African-Caribbeans were higher than those in white Europeans (mean difference 0.60 mL O2/min/kg, 95% CI 0.02 to 1.17, p=0.04); these patterns were similar in boys and girls. The lower estimated VO2 max in South Asians, compared to white Europeans, was consistent among Indian, Pakistani and Bangladeshi children and was attenuated by 78% after adjustment for objectively measured physical activity (average daily steps).

CONCLUSIONS

South Asian children have lower levels of physical fitness than white Europeans and black African-Caribbeans in the UK. This ethnic difference in physical fitness is at least partly explained by ethnic differences in physical activity.

Fruit, vegetable and vitamin C intakes and plasma vitamin C: cross-sectional associations with insulin resistance and glycaemia in 9-10 year-old children

AIM

To examine whether low circulating vitamin C concentrations and low fruit and vegetable intakes were associated with insulin resistance and other Type 2 diabetes risk markers in childhood.

METHODS

We conducted a cross-sectional, school-based study in 2025 UK children aged 9-10 years, predominantly of white European, South-Asian and black African origin. A 24-h dietary recall was used to assess fruit, vegetable and vitamin C intakes. Height, weight and fat mass were measured and a fasting blood sample collected to measure plasma vitamin C concentrations and Type 2 diabetes risk markers.

RESULTS

In analyses adjusting for confounding variables (including socio-economic status), a one interquartile range higher plasma vitamin C concentration (30.9 μmol/l) was associated with a 9.6% (95% CI 6.5, 12.6%) lower homeostatic model assessment of insulin resistance value, 0.8% (95% CI 0.4, 1.2%) lower fasting glucose, 4.5% (95% CI 3.2, 5.9%) lower urate and 2.2% (95% CI 0.9, 3.4%) higher HDL cholesterol. HbA1c concentration was 0.6% (95% CI 0.2, 1.0%) higher. Dietary fruit, vegetable and total vitamin C intakes were not associated with any Type 2 diabetes risk markers. Lower plasma vitamin C concentrations in South-Asian and black African-Caribbean children could partly explain their higher insulin resistance.

CONCLUSIONS

Lower plasma vitamin C concentrations are associated with insulin resistance and could partly explain ethnic differences in insulin resistance. Experimental studies are needed to establish whether increasing plasma vitamin C can help prevent Type 2 diabetes at an early stage.

Predicting adult obesity from childhood obesity: a systematic review and meta-analysis

A systematic review and meta-analysis was performed to investigate the ability of simple measures of childhood obesity such as body mass index (BMI) to predict future obesity in adolescence and adulthood. Large cohort studies, which measured obesity both in childhood and in later adolescence or adulthood, using any recognized measure of obesity were sought. Study quality was assessed. Studies were pooled using diagnostic meta-analysis methods. Fifteen prospective cohort studies were included in the meta-analysis. BMI was the only measure of obesity reported in any study, with 200,777 participants followed up. Obese children and adolescents were around five times more likely to be obese in adulthood than those who were not obese. Around 55% of obese children go on to be obese in adolescence, around 80% of obese adolescents will still be obese in adulthood and around 70% will be obese over age 30. Therefore, action to reduce and prevent obesity in these adolescents is needed. However, 70% of obese adults were not obese in childhood or adolescence, so targeting obesity reduction solely at obese or overweight children needs to be considered carefully as this may not substantially reduce the overall burden of adult obesity.

Automated retinal vessel recognition and measurements on large datasets

The characteristics of the retinal vascular network have been prospectively associated with many systemic and vascular diseases. QUARTZ is a fully automated software that has been developed to localize and quantify the morphological characteristics of blood vessels in retinal images for use in epidemiological studies. This software was used to analyse a dataset containing 16,000 retinal images from the EPIC-Norfolk cohort study. The objective of this paper is to both assess the suitability of this dataset for computational analysis and to further evaluate the QUARTZ software.

Childhood obesity as a predictor of morbidity in adulthood: a systematic review and meta-analysis

Obese children are at higher risk of being obese as adults, and adult obesity is associated with an increased risk of morbidity. This systematic review and meta-analysis investigates the ability of childhood body mass index (BMI) to predict obesity-related morbidities in adulthood. Thirty-seven studies were included. High childhood BMI was associated with an increased incidence of adult diabetes (OR 1.70; 95% CI 1.30-2.22), coronary heart disease (CHD) (OR 1.20; 95% CI 1.10-1.31) and a range of cancers, but not stroke or breast cancer. The accuracy of childhood BMI when predicting any adult morbidity was low. Only 31% of future diabetes and 22% of future hypertension and CHD occurred in children aged 12 or over classified as being overweight or obese. Only 20% of all adult cancers occurred in children classified as being overweight or obese. Childhood obesity is associated with moderately increased risks of adult obesity-related morbidity, but the increase in risk is not large enough for childhood BMI to be a good predictor of the incidence of adult morbidities. This is because the majority of adult obesity-related morbidity occurs in adults who were of healthy weight in childhood. Therefore, targeting obesity reduction solely at obese or overweight children may not substantially reduce the overall burden of obesity-related disease in adulthood.

An approach to localize the retinal blood vessels using bit planes and centerline detection

The change in morphology, diameter, branching pattern or tortuosity of retinal blood vessels is an important indicator of various clinical disorders of the eye and the body. This paper reports an automated method for segmentation of blood vessels in retinal images. A unique combination of techniques for vessel centerlines detection and morphological bit plane slicing is presented to extract the blood vessel tree from the retinal images. The centerlines are extracted by using the first order derivative of a Gaussian filter in four orientations and then evaluation of derivative signs and average derivative values is performed. Mathematical morphology has emerged as a proficient technique for quantifying the blood vessels in the retina. The shape and orientation map of blood vessels is obtained by applying a multidirectional morphological top-hat operator with a linear structuring element followed by bit plane slicing of the vessel enhanced grayscale image. The centerlines are combined with these maps to obtain the segmented vessel tree. The methodology is tested on three publicly available databases DRIVE, STARE and MESSIDOR. The results demonstrate that the performance of the proposed algorithm is comparable with state of the art techniques in terms of accuracy, sensitivity and specificity.

Blood vessel segmentation methodologies in retinal images--a survey

Retinal vessel segmentation algorithms are a fundamental component of automatic retinal disease screening systems. This work examines the blood vessel segmentation methodologies in two dimensional retinal images acquired from a fundus camera and a survey of techniques is presented. The aim of this paper is to review, analyze and categorize the retinal vessel extraction algorithms, techniques and methodologies, giving a brief description, highlighting the key points and the performance measures. We intend to give the reader a framework for the existing research; to introduce the range of retinal vessel segmentation algorithms; to discuss the current trends and future directions and summarize the open problems. The performance of algorithms is compared and analyzed on two publicly available databases (DRIVE and STARE) of retinal images using a number of measures which include accuracy, true positive rate, false positive rate, sensitivity, specificity and area under receiver operating characteristic (ROC) curve.

Physical activity, obesity and cardiometabolic risk factors in 9- to 10-year-old UK children of white European, South Asian and black African-Caribbean origin: the Child Heart And health Study in England (CHASE)

AIMS/HYPOTHESIS

Physical inactivity is implicated in unfavourable patterns of obesity and cardiometabolic risk in childhood. However, few studies have quantified these associations using objective physical activity measurements in children from different ethnic groups. We examined these associations in UK children of South Asian, black African-Caribbean and white European origin.

METHODS

This was a cross-sectional study of 2,049 primary school children in three UK cities, who had standardised anthropometric measurements, provided fasting blood samples and wore activity monitors for up to 7 days. Data were analysed using multilevel linear regression and allowing for measurement error.

RESULTS

Overall physical activity levels showed strong inverse graded associations with adiposity markers (particularly sum of skinfold thicknesses), fasting insulin, HOMA insulin resistance, triacylglycerol and C-reactive protein; for an increase of 100 counts of physical activity per min of registered time, levels of these factors were 12.2% (95% CI 10.2-14.1%), 10.2% (95% CI 7.5-12.8%), 10.2% (95% CI 7.5-12.8%), 5.8% (95% CI 4.0-7.5%) and 19.2% (95% CI 13.9-24.2%) lower, respectively. Similar increments in physical activity levels were associated with lower diastolic blood pressure (1.0 mmHg, 95% CI 0.6-1.5 mmHg) and LDL-cholesterol (0.04 mmol/l, 95% CI 0.01-0.07 mmol/l), and higher HDL-cholesterol (0.02 mmol/l, 95% CI 0.01-0.04 mmol/l). Moreover, associations were broadly similar in strength in all ethnic groups. All associations between physical activity and cardiometabolic risk factors were reduced (albeit variably) after adjustment for adiposity.

CONCLUSIONS/INTERPRETATION

Objectively measured physical activity correlates at least as well with obesity and cardiometabolic risk factors in South Asian and African-Caribbean children as in white European children, suggesting that efforts to increase activity levels in such groups would have equally beneficial effects.

Refractive error and visual impairment in school children in Northern Ireland

AIMS

To describe the prevalence of refractive error (myopia and hyperopia) and visual impairment in a representative sample of white school children.

METHODS

The Northern Ireland Childhood Errors of Refraction study, a population-based cross-sectional study, examined 661 white 12-13-year-old and 392 white 6-7-year-old children between 2006 and 2008. Procedures included assessment of monocular logarithm of the minimum angle of resolution (logMAR), visual acuity (unaided and presenting) and binocular open-field cycloplegic (1% cyclopentolate) autorefraction. Myopia was defined as -0.50DS or more myopic spherical equivalent refraction (SER) in either eye, hyperopia as > or =+2.00DS SER in either eye if not previously classified as myopic. Visual impairment was defined as >0.30 logMAR units (equivalent to 6/12).

RESULTS

Levels of myopia were 2.8% (95% CI 1.3% to 4.3%) in younger and 17.7% (95% CI 13.2% to 22.2%) in older children: corresponding levels of hyperopia were 26% (95% CI 20% to 33%) and 14.7% (95% CI 9.9% to 19.4%). The prevalence of presenting visual impairment in the better eye was 3.6% in 12-13-year-old children compared with 1.5% in 6-7-year-old children. Almost one in four children fails to bring their spectacles to school.

CONCLUSIONS

This study is the first to provide robust population-based data on the prevalence of refractive error and visual impairment in Northern Irish school children. Strategies to improve compliance with spectacle wear are required.

Is body mass index before middle age related to coronary heart disease risk in later life? Evidence from observational studies

Objective

Although obesity beginning early in life is becoming more common, its implications for coronary heart disease (CHD) risk in later life remain uncertain. We examined the relationship of body mass index (BMI) before 30 years of age to CHD risk in later life.

Design

Systematic review of published studies relating BMI between age 2-30 years to later CHD risk. Studies were identified using Medline (1950 onwards), Embase (1980 onwards) and Web of Science (1970 onwards) databases (to November 2007).

Measurements

Relative risks (RR) of CHD associated with a 1 standard deviation (SD) increase in BMI (most based on a narrow age-range at measurement) were extracted by 2 authors independently, and combined using random-effect models.

Results

Fifteen studies provided seventeen estimates (731,337 participants, 23,894 CHD events) of the association of early BMI to later CHD outcome. BMI in early childhood (2 to 6 years, 3 estimates) showed a weak inverse association with CHD risk (RR 0.94, 95% CI 0.82-1.07). BMI in later childhood (7 to <18 years, 7 estimates) and BMI in early adult life (18-30 years, 7 estimates) were both positively related to later CHD risk (RR 1.09, 95% CI 1.00-1.20; RR 1.19, 95% CI 1.11-1.29 respectively). However, there was considerable statistical heterogeneity between study estimates. Results were unaffected by adjustment for social class and/or cigarette smoking, blood pressure and/or total cholesterol, in studies with available data. Gender and year of birth (1900-1976) had little effect on the association.

Conclusions

BMI is positively related to CHD risk from childhood onwards; the associations in young adults are consistent with those observed in middle age. Long-term control of BMI from childhood may be important to reduce the risk of CHD.

What factors are associated with physical activity in older people, assessed objectively by accelerometry?

OBJECTIVES

To assess physical activity (PA) levels measured objectively using accelerometers in community-dwelling older people and to examine the associations with health, disability, anthropometric measures and psychosocial factors.

DESIGN

Cross-sectional survey.

SETTING

Single general practice (primary care centre), United Kingdom.

PARTICIPANTS

Random selection of 560 community-dwelling older people at least 65 years old, registered with the practice. 43% (238/560) participated.

ASSESSMENT OF RISK FACTORS

Participants completed a questionnaire assessing health, disability, psychosocial factors and PA levels; underwent anthropometric assessment; and wore an accelerometer (Actigraph) for 7 days.

MAIN OUTCOME MEASURES

Average daily accelerometer step-counts and time spent in different PA levels. Associations between step-counts and other factors were examined using linear regression.

RESULTS

Average daily step-count was 6443 (95% CI 6032 to 6853). Men achieved 754 (84 to 1424) more steps daily than women. Step-count declined steadily with age. Independent predictors of average daily step-count were: age; general health; disability; diabetes; body mass index; exercise self-efficacy; and perceived exercise control. Activities associated independently with higher step-counts included number of long walks and dog-walking. Only 2.5% (6/238) of participants achieved the recommended 150 minutes weekly of at least moderate-intensity activity in > or = 10 minute bouts; 62% (147/238) achieved none.

CONCLUSIONS

This is the first population-based sample of older people with objective PA and anthropometric measures. PA levels in older people are well below recommended levels, emphasising the need to increase PA in this age group, particularly in those who are overweight/obese or have diabetes. The independent effects of exercise self-efficacy and exercise control on PA levels highlight their role as potential mediators for intervention studies.

The epidemiology of medical treatment for glaucoma and ocular hypertension in the United Kingdom: 1994 to 2003

AIMS

To study trends in the prevalence of being treated for glaucoma and ocular hypertension from 1994 to 2003, and to examine factors determining treatment in 2002.

METHODS

Computerised data (the DIN-LINK database) from 131 general practices across the United Kingdom, in which half a million patients aged 40 years or more were registered annually, were used. On average 10 000 patients were treated for glaucoma and ocular hypertension annually.

RESULTS

Prevalence of being treated for glaucoma and ocular hypertension increased from 1.7% in 1994 to 2.3% in 2003. Those aged 85 years or more were 13 times (95% CI 12.2 to 13.8) more likely to be treated than those aged 40-64 years. Men were more likely to be treated than women (OR 1.24, 95% CI 1.19 to 1.28). Subjects "hard pressed" were less likely to be treated than "wealthy achievers" (OR 0.92, 95% CI 0.86 to 0.99). While use of topical beta blocker only medications has declined since 1995, use of topical prostaglandins and combination therapies has increased. In 2003, use of prostaglandins overtook beta blocker only medications.

CONCLUSION

Prevalence of being treated for glaucoma has increased over time, and rises with age. Differences in treatment by sex and social status could be explained by use of or access to health care or by underlying prevalence of disease. Trends in treated glaucoma emphasise the shift from use of topical beta blockers to newer therapies.

British South Asians aged 13-16 years have higher fasting glucose and insulin levels than Europeans

AIM

To examine whether plasma glucose, insulin resistance and markers of adiposity differed between British adolescents of South Asian and European origin.

METHODS

School-based cross-sectional study (1998-2000), in which detailed measurements of adiposity, fasting plasma glucose and serum insulin were made in 90 South Asian and 1248 European pupils (overall 69% response rate).

RESULTS

Compared with Europeans, South Asian subjects had higher mean fasting insulin levels (percentage mean difference 17.2%, 95% confidence interval 7.2-26.1%, P = 0.001), a higher mean fasting glucose (mean difference 0.19 mmol/l, 95% confidence interval 0.08-0.29 mmol/l, P = 0.0005) and a higher prevalence of impaired fasting glucose (> or = 6.1 mmol/l) (5.6% vs. 1.5%, odds ratio 3.9, 95% confidence interval 1.4-10.9, P = 0.004). Although South Asian children tended to have slightly higher indices of adiposity than Europeans (other than body mass index), the differences in glucose and insulin levels persisted after adjustment for adiposity and for pubertal status.

CONCLUSIONS

The predisposition to Type 2 diabetes observed in South Asian adults is apparent before adult life. Establishing the contributions of the childhood and fetal environments and of genetic factors to the development of these ethnic differences is an important priority. Prevention of Type 2 diabetes in British South Asians needs to begin before adult life.

How big is the burden of visual loss caused by age related macular degeneration in the United Kingdom?

AIMS

To predict the burden of blindness, partial sight, and visual impairment (binocular visual acuity 6/18 or less) due to late stage age related macular degeneration (AMD) in the ageing population of the United Kingdom.

METHODS

A systematic review, followed by a request for data, was used to establish a pooled prevalence of AMD and corresponding visual loss. Prevalence figures were applied to the UK population. Using UK population trends, the future burden of AMD over the coming decade was established.

RESULTS

Pooled data from six studies showed that the prevalence of visual loss caused by AMD increased exponentially from the age of 70-85 years of age, with 3.5% (95% CI 3.0 to 4.1) having visual impairment beyond the age of 75 years. The authors estimate that there are currently 214 000 (95% CI 151 000 to 310 000) with visual impairment caused by AMD (suitable for registration). This number is expected to increase to 239 000 (95% CI 168 000 to 346 000) by the year 2011. Currently there are 172 000 (95% CI 106 000 to 279 000) and 245 000 (95% CI 163 000 to 364 000) with geographical and neovascular AMD, respectively.

CONCLUSIONS

Estimates of visual impairment agree with official statistics for the number registered partially sighted or blind, caused by AMD, and are well below other figures often cited. Although these estimates are associated with wide confidence intervals (CI) and a number of caveats, they represent the best available data, which can be used to guide health and social care provision for older people in the UK setting. Implications for low vision services are outlined.

Nonlinear behavior of certain optic nerve head parameters and their determinants in normal subjects

OBJECTIVE

To investigate the relationship between the absolute area of certain optic disc parameters and a number of ocular dimensional characteristics and demographic factors in young, healthy subjects.

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred twenty-one subjects, aged 16.5 to 35.4 years participated, encompassing a wide range of refractive error from +4 diopters (D) to -25.75 D. One eye from each subject was randomly selected for examination.

MAIN OUTCOME MEASURES

Absolute size of the optic disc parameters: optic disc area (DA), neuroretinal rim area (NRA), optic cup area (CA), and peripapillary atrophy area (PA).

METHODS

Absolute sizes of optic disc parameters were determined from digitized photographic color transparencies, taking into consideration the magnification of the fundus camera and human eye. Relationships between the absolute size of the optic disc features and axial length, crystalline lens thickness, anterior chamber depth, ocular refraction, front surface keratometry, age, and gender were examined.

RESULTS

Axial length, lens thickness, front surface keratometry, and age demonstrated positive associations with all optic disc parameters, and anterior chamber depth and ocular refraction demonstrated negative associations in all cases. Multiple regression analysis revealed that the associations observed univariately for age, anterior chamber depth, lens thickness, front surface keratometry, and ocular refraction were confounded by axial length for all disc parameters. After taking logs, DA and NRA exhibit an exponential relationship with axial length, whereas PA and CA exhibit a linear relationship with axial length. DA and NRA increase by approximately 3% per millimeter increase in axial length at 20 mm and up to 40% for DA and 50% for NRA at an axial length of 35 mm. PA and CA are estimated to increase by 26% (10%-44%) and 10% (5%-16%), respectively, per millimeter increase in axial length. Females have approximately 5% smaller DA and 7% smaller NRA than males, but these effects are not statistically significant (P > 0.2). From the multiple regression analysis, females have 31% larger optic cup areas (1%-57%, P = 0.03) and 24% smaller PA (42% smaller to 5% larger P = 0.06) than males, but these effects are of borderline statistical significance at 5%.

CONCLUSIONS

Of the ocular biometric factors considered, axial length seems to be the most important predictor of the absolute area of the optic disc parameters. No association exists between any disc parameter and age in this sample of subjects less than 40 years of age. Females exhibited smaller values for DA, NRA, and PA than did males, differences that were not statistically significant, and larger CA (P = 0.03).

Use of contact lenses by firefighters: Part 2. Clinical evaluation

Contact lenses can be worn in a variety of environmental conditions and do not increase the wearers risk of injury. In many situations they offer significant corneal protection. Currently firefighters are prohibited from using contact lenses. To evaluate whether contact lenses are a safe form of visual correction 50 firefighters were fitted, and examined after 1, 4 and 10 months of contact lens wear. Twenty-nine were fitted with soft contact lenses, and 21 with rigid gas permeable contact lenses. Statistically significant increase in lid sulcus hyperaemia was found in both the SCL and RGPCL groups (P < 0.01, P = 0.02, respectively), as well as an increase in hyperaemia of the vertical quadrant of the bulbar conjunctivae (P = 0.01, P = 0.02, respectively). In addition the RGPCL group showed a statistically significant increase in hyperaemia of the lateral portion of the bulbar conjunctivae (P < 0.01), consistent with exposure epitheliopathy. The SCL group showed statistically significant increase in corneal staining in the vertical quadrant for all visits (P = 0.02, P = 0.01, P = 0.02 for all visits, respectively), indicative of lens dehydration. These findings although clinically significant are not unique to firefighting, and are found within a "normal" population of contact lens wearers. In conjunction with questionnaire data (Owen et all, 1996) we conclude that soft contact lenses can be worn safely by firefighters without additional risk.

Use of contact lenses by firefighters. Part 1: Questionnaire data

The use of contact lenses by firefighters is currently prohibited. However, many firefighters may benefit from this form of visual correction, without predisposing themselves to additional risk. Visual benefits gained by contact lens wear may increase a firefighter's safety. To determine if it is safe to allow firefighters to use contact lenses 29 were fitted with soft contact lenses and 21 with rigid gas permeable contact lenses. Questionnaires were completed prior to fitting, after 1, 4 and 10 months of contact lens wear. Both soft contact lens (SCL) wearers, and rigid gas permeable contact lens (RGPCL) wearers showed a statistically significantly reduction in the frequency with which they experience irritable foreign bodies and irritant fumes in the eyes, compared to not wearing contact lenses. Firefighters felt that their performance on the fireground had been improved by the use of contact lenses. SCL wearers also benefited from a reduction in the frequency with which they experienced watery eyes and ocular discomfort. There were significantly fewer problems encountered with SCL wearers than RGPCL wearers. The frequency with which firefighters experienced lenses falling out, lens displacement, watery eyes, ocular discomfort, and operational difficulties was significantly less for the SCL group than the RGPCL group. SCL appear to offer considerable benefits for firefighters with refractive error, but their use cannot be sanctioned without assessment of their effect on the ocular adnexa.

A new computer assisted objective method for quantifying vascular changes of the bulbar conjunctivae

A novel computer software method was used to quantify the conjunctival plexus on the scleral background for measurement of the vascular surface area from photographs. A previously described method was used (Palmer, J. R., Owen, C. G., Ford, A. M., Jacobson, R. E. and Woodward, E. G. (1996). Optimal photographic imaging of the bulbar conjunctival vasculature. Ophthal. Physiol. Opt. 16, 144-149) to optimise photographic imaging of the bulbar conjuctival vasculature by increasing the information content in the image. Repeatability of this technique was evaluated. Twenty subjects (20 eyes) free from ophthalmological and systemic abnormality were examined on two separate occasions. The maximum 95% confidence limits for repeatability are +8.58/-3.95%. For 10 consecutive estimates of vascularity the maximum 95% confidence interval lie between +/- 6.54%. To evaluate the technique the lateral-bulbar conjunctivaein 10 soft (SCL) and 10 rigid gas permeable contact lens (RGPCL) wearers during the first 10 months of contact lens wear, were assessed and compared with subjective grading of hyperaemia. The new method showed sufficient sensitivity in detecting increased hyperaemia in the RGPCL wearing group and demonstrated statistically significant change. Subjective graded assessment of vascularity (using established classifications) detected increased hyperaemia, however, this was not statistically significant. Conjunctival vasculature is a dynamic structure and a source of valuable quantitative information where the ocular environment is varied, or where the ocular surface is affected by disease. Hence it is worthy of further investigation. A simple inexpensive method of computer assisted determination of vascularity is described.

Colour vision requirements of firefighters

To perform their job safely firefighters must be able to identify colours on industrial gas cylinders, portable fire extinguishers, road traffic signals and several pieces of firefighting equipment. Although good colour vision is necessary we believe that the existing colour vision standard, which bars entry to the fire service to applicants who fail more than two plates of the Ishihara test, is unnecessarily stringent. We have identified and quantified the colour coded information encountered by firefighters. Colours were plotted on the CIE chromaticity diagram (1931) and isochromatic zones, which document the colour confusions of colour deficient observers, superimposed. This novel technique established possible colour confusions in different types of colour deficiency. Analysis of the results showed that red/green dichromats (protanopes and deuteranopes), severe deuteranomalous trichromats who fail the Farnsworth D15 test, and protanomalous trichromats are unsuitable for firefighting work. However, people with slight deuteranomalous trichromatism who pass the D15 test, are not disadvantaged and can be employed safely as firefighters. A new colour vision standard and a new testing procedure is recommended.

Optimal photographic imaging of the bulbar conjunctival vasculature

A method for imaging the conjunctiva to yield greater contrast between the vasculature and the scleral background, by optimisation of the imaging system, is described. A simple modification to the image capture system, based on first principles calculations, is shown to give images with much improved information content. This will enhance the assessment of hyperaemic changes induced by foreign materials, indicating the degree of biocompatibility, e.g. with contact lenses and ophthalmic medications. Observation of vascular abnormalities associated with pathological conditions may assist in their diagnosis and monitor progressive changes.

Prevalence of spectacle and contact lens wear in the UK fire service

Despite the fact that firefighting has been shown to be a visually demanding occupation, the present visual standards for firefighters prohibit the use of spectacles or contact lenses operationally. To determine the proportion of the UK fire service currently using spectacles and contact lenses, and how many may benefit from optical correction, a questionnaire was distributed. This contained 30 questions and was sent to 1550 firefighters. The data from 1064 returned questionnaires have been analysed. The results show that approximately 20% of those serving in the fire service have used an optical correction at some time in their lives. When not working, approximately 6% of firefighters wear spectacles for distance vision and 15% wear them for reading. Only 0.4% of firefighters use contact lenses. Half of this contact lens wearing group use their lenses while on operational duty. In total, approximately 2% of firefighters use an optical correction for operational duties. The results indicate that a high visual standard at the time of entry into an occupation cannot guarantee good vision throughout an individual's career. In addition, an estimated 11,000 firefighters in the UK, who have spectacles or contact lenses, do not use them for operational duties. The present visual standards prevent this group of firefighters from obtaining their optimal visual performance at work.

Crevice corrosion products of dental amalgam

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products [Sn4(OH)6Cl2, SnO, and Cu2O] and a new product, CuCl, which formed on high-copper, gamma 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion.