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Biomedical subjects

J M Sparrow

Publications and source records attributed to J M Sparrow.

At least 55 records · Page 3Linked to original sources
PubMed1998

Clinical evaluation of scanning laser polarimetry: I. Intraoperator reproducibility and design of a blood vessel removal algorithm.

AIMS: To evaluate the reproducibility of the retardation values (change in polarisation) obtained with the scanning-laser polarimeter in a series of normal subjects and glaucoma patients. To improve the analysis of the raw data by devising and evaluating a blood vessel removal algorithm. METHODS: Scanning laser polarimetry was performed on 10 normal subjects and 10 glaucoma patients. A series of six images was obtained from each eye. The normal subjects were re-imaged 3 months after their initial assessment. The retardation values obtained from each eye were analysed using the authors' own methods, including the use of an algorithm to remove blood vessels from the polar profiles. The reproducibility of these measurements and the performance of the blood vessel removal algorithm were assessed. RESULTS: The "individual point" coefficient of variation was approximately 12.5% for normal subjects and 17.0% for glaucoma patients. The "integral" coefficient of variation for these groups was approximately 5.5% and 9.5% respectively. The reproducibility of the measurements did not improve with an increased number of measurements. There was no difference in the reproducibility of the measurements in normal subjects over time. The blood vessel removal algorithm improved the reproducibility of the measurements when the shape of the profile was assessed. CONCLUSION: The intraoperator reproducibility of retardation values obtained with the scanning laser polarimeter is satisfactory for its use as a clinical tool. The use of a blood vessel removal algorithm improves the reproducibility of the measurements and also assists the clinician in the interpretation of the polar profiles. Furthermore, it allows the construction of normal database polar profiles, thereby enabling the identification, location and quantification of retinal nerve fibre layer damage in an "at risk" individual's polar profile.

Algorithms↗
PubMed1998

Clinical evaluation of scanning laser polarimetry: II. Polar profile shape analysis.

AIMS: To devise a method to describe and quantify the shape of polar profiles obtained with the scanning laser polarimeter and to compare this measurement with other polar profile measurements in a series of normal subjects and glaucoma patients. METHODS: Scanning laser polarimetry was performed on 54 normal subjects and 74 glaucoma patients. The retardation values obtained from one randomly chosen eye of each subject were analysed using our own methods, including the use of an algorithm to remove blood vessels from the polar profiles, an algorithm to standardise the glaucoma profiles to a normal database, and a further algorithm to evaluate the profile shape. The measurements of profile shape were compared with measurements of the absolute and standardised retinal nerve fibre layer thickness obtained with the scanning laser polarimeter. RESULTS: There was no significant difference between the mean retardation values for the normal and glaucomatous subjects in either hemiretina. However, standardisation of the glaucoma retardation values to a normal database produced significant differences at p < 1 x 10-8 in the mean retardation values for these two groups in both hemiretinas. Profile shape measurement analysis produced similar significant differences between the mean retardation values for the normal and glaucomatous subjects in both hemiretinas, although the degree of separation was greater following standardisation of the retardation values. CONCLUSION: The use of an algorithm to standardise an individual's retardation values in conjunction with a blood vessel removal algorithm enables an improvement in the ability of the scanning laser polarimeter to discriminate between normal and glaucomatous patients. The polar profile shape algorithm is independent of standardisation and significantly improves the discrimination between normal and glaucomatous patients, as well as providing additional information regarding the retinal nerve fibre layer.

Adult↗
PubMed1998

Clinical evaluation of keratometry and computerised videokeratography: intraobserver and interobserver variability on normal and astigmatic corneas.

AIMS: To evaluate intra- and interobserver variability in measurements on normal and astigmatic corneas with keratometry and computerized videokeratography. METHODS: Keratometric readings with the 10 SL/O Zeiss keratometer and topographic maps with the TMS-1 were obtained by two independent examiners on 32 normal and 33 postkeratoplasty corneas. Inter- and intraobserver coefficients of variability (COR) for measurements of steep and flat meridian power and location, in addition to the magnitude of astigmatism, were assessed. RESULTS: Compared with TMS-1, the 10 SL/O keratometer showed a superior repeatability in measuring normal corneas (intraobserver COR for keratometry and TMS-1 respectively: 0.22 and 0.30 D for steep meridian power; 0.18 and 0.44 D for flat meridian power; 0.26 and 0.40 D for astigmatism; 5 degrees and 26 degrees for steep meridian location; 5 degrees and 13 degrees for flat meridian location). Astigmatism intraobserver COR (0.20 D and 0.26 D for the two observers) and interobserver COR (0.28 D) of the keratometer for normal corneas was very good and not affected by observers' experience. Repeatability of the TMS-1 on normal corneas was found to be: (a) observer related, and (b) astigmatism related. A novice observer showed a much greater COR (1.62 D for astigmatism, 30 degrees for flat meridian location) compared with the experienced examiner (0.40 D for astigmatism, 13 degrees for flat meridian location). Higher deviation scores were observed for corneas with higher astigmatism. For the postkeratoplasty corneas, again the keratometer achieved superior reproducibility (astigmatism interobserver COR 1.12 D for keratometry, 4.06 D for TMS-1; steep meridian location interobserver COR 10 degrees for keratometry, 34 degrees for TMS-1). CONCLUSION: Keratometric readings are more reproducible than topographic data both for normal and postkeratoplasty corneas. The two instruments should not be used interchangeably especially on highly astigmatic corneas. For the TMS-1, users with the same level of experience should be employed in clinical or experimental studies.

Adult↗
PubMed1998

Variability in glaucomatous visual fields: implications for shared care schemes.

The purpose of this study was to establish the extent of variability in the visual fields of patients with glaucoma using a suprathreshold perimetric test strategy. The visual fields of 104 patients (126 eyes) were measured twice, on separate days, with a Henson CFA3000 central visual field analyser. All eyes had a diagnosis of glaucoma and had a minimum of three stimuli missed at 12 dB above their threshold estimate derived at the beginning of the first suprathreshold examination. The perimeter tested 132 locations within the central 25 degrees with a multiple stimulus suprathreshold strategy. Data were analysed on the basis of the difference in the number of recorded missed stimuli between the two visits. Large amounts of variability were found in the visual field results. Variability was largest when all levels of defect were included (> = 5 dB) and was found to be independent of the overall extent of loss. Results from the superior hemifield were found to be more variable than those from the inferior hemifield. The results highlight the problem of differentiating real change in visual field status from the enhanced variability seen in patients with glaucomatous visual field loss. The results from this study can be used to establish return-referral criteria for shared care schemes. The advantages of duplicate measures of the visual field are highlighted.

Glaucoma↗
PubMed1997

Prevalence of age-related maculopathy at two points in time in an elderly British population.

UNLABELLED: As the demography of Western society changes, the population prevalence of diseases such as age-related macular degeneration (AMD) is expected to rise. Despite this, there remains a paucity of quality data concerning the population prevalence of AMD, the commonest cause of blindness in the elderly. PURPOSE: To report the prevalence of AMD at two points in time in an elderly population. METHOD: A geographically defined random population sample of elderly people was defined in 1980, and studied in 1982-4. In 1990, a cohort of survivors was identified. Participants underwent full ophthalmic examination with fundus photography using the same camera on each occasion. Photographs were randomly encoded and graded by two independent masked observers using the Wisconsin Age-related Maculopathy Grading System. Disagreements were resolved by consensus. RESULTS: Eighty-eight survivors participated in the follow-up examinations. Of these, 82 subjects had gradable retinal photographs for both examination points in at least one eye. There were 158 pairs of images (initial and subsequent) available for analysis. The mean age was 80 years (range 77-90 years) at the initial examination, and 87 years (range 84-97 years) at the subsequent examination; 70.7% of subjects were female. Prevalence rates for the initial examination were: drusen 72.8%, drusen confluence 37.3%, degeneration of the retinal pigment epithelium (RPE) 51.3%, increased pigment 22.2%, exudative AMD 1.9% and geographic atrophy 1.9%. Rates at second examination were: drusen 62.7% drusen confluence 41.8%, RPE degeneration 72.8%, increased pigment 16.5%, exudative AMD 3.8% and geographic atrophy 3.2%. CONCLUSION: This 'double' prevalence study provides detailed data on AMD lesions at two points in time in a population-based group of elderly people.

Age Distribution↗
PubMed1997

Seven year follow-up of age-related maculopathy in an elderly British population.

UNLABELLED: Despite age-related macular degeneration (AMD) being the commonest cause of blindness amongst the elderly in Western society, the incidence of new lesions is poorly documented and the natural history of existing disease remains ill understood. PURPOSE: To document in an elderly population the incidence of new AMD lesions and the progression of pre-existing AMD over time. METHOD: Baseline ophthalmic examinations were performed on a geographically defined random population sample of elderly people in 1982-4, and retinal photographs taken. The present study re-examined and re-photographed survivors after approximately 7 years using the same fundus camera. Photographs were randomly encoded, and independently graded for AMD features by two masked observers using the Wisconsin AMD grading system. Disagreements were resolved by review to reach a consensus. RESULTS: Eighty-two of the 88 participating survivors had photographs of gradable quality on both occasions in at least one eye. Mean age at follow-up was 87 years (range 84-97 years) and 70.7% of subjects were female. Paired photographs were available on 158 eyes, and showed important differences in drusen type, drusen area and characteristics of the retinal pigment epithelium (RPE) between initial and subsequent examinations. The 7 year incidence (and regression) of lesions was: drusen 30.6% (20.0%), RPE degeneration 54.5% (8.8%), increased pigment 11.6% (64.7%), subretinal haemorrhage 1.3%, subretinal scar/fibrin 1.3% and geographic study 1.3%. CONCLUSION: These unique population-based results provide new insight into the natural history of AMD in an elderly population.

Aged↗
PubMed1997

The Bristol Shared Care Glaucoma Study--validity of measurements and patient satisfaction.

BACKGROUND: The aims of the study were to determine (1) whether community optometrists are able to make valid measurements of visual parameters in patients with established or suspect primary open angle glaucoma and (2) patient satisfaction with follow-up by community optometrists. METHODS: A randomized study was carried out in the former county of Avon in South West England with patients allocated to follow-up by the hospital eye service or by community optometrists. The subjects were 403 patients with established or suspected primary open angle glaucoma attending Bristol Eye Hospital and meeting defined inclusion and exclusion criteria. The main outcome measures were 91) measurements of key visual parameters (intraocular pressure, visual fields and cup/disc ratio) made by hospital eye service and community optometrists, compared with a research clinic reference standard at baseline, and (2) patient satisfaction at baseline and at six months. RESULTS: Community optometrists were able to make measurements of comparable accuracy to those made in the hospital eye service. Patients were significantly more satisfied with a number of aspects of care provided by community optometrists, particularly those relating to waiting times, compared with those from the hospital eye service. CONCLUSIONS: Community optometrists are able to make measurements of key visual parameters in patients with established or suspect primary open angle glaucoma which are of comparable quality to the hospital eye service. Follow-up by community optometrists is acceptable to patients. The costs of each option are reported elsewhere.

Aged↗
PubMed1997

The Wisconsin Age-related Macular Degeneration grading system: performance in an independent centre.

INTRODUCTION: Age-related Macular Degeneration (AMD) is the commonest cause of blindness in developed nations. Despite this, the epidemiology of AMD is poorly understood. A need for the documentation of AMD prevalence and incidence at a population level has stimulated the development of a comprehensive, observer-based, photographic grading method for AMD in Wisconsin. AIM: To independently assess the performance of the Wisconsin method by self-taught graders outside its centre of inception. METHOD: The inter-observer variability and confidence limits for detection of change were assessed for two self-taught graders (ophthalmologists). Self teaching was achieved exclusively from documentation and photographs provided by the system developers in Wisconsin. 295 retinal photographs of elderly people were independently assessed for 13 features by each of the two graders. RESULTS: Weighted and unweighted kappa statistics, % exact and one step apart agreement, and confidence limits for detection of change were calculated for the graded features on a "by eye' basis, and where appropriate, on a "by retinal subfield' basis. Levels of agreement for weighted kappa were moderate to substantial for most features. 95% and 90% confidence limits for significant change beyond measurement error were determined in terms of scale increments. CONCLUSION: We conclude that the Wisconsin AMD grading system can be independently learnt from documentation and photographs alone, and that an acceptable level of performance is attainable by self-taught graders.

Aged↗
PubMed1995

Vitreous loss in planned extracapsular cataract extraction does lead to a poorer visual outcome.

Forty-six cases of vitreous loss during planned extracapsular cataract extraction salvaged by anterior vitrectomy and primary anterior chamber lens implantation were compared in a retrospective cohort study with 92 individually matched controls. The postoperative visual outcome for cases with vitreous loss was significantly poorer than that for controls even after adjustment for confounding variables. Part of this visual morbidity was explained by cystoid macular oedema and retinal detachment, but even after adjusting for these two complications visual outcome remained worse among cases than controls. There was a significantly higher incidence of clinically apparent cystoid macular oedema amongst cases compared with controls (20% versus 1%). Two retinal detachments occurred among the cases but this difference in incidence was not statistically significant.

Aged↗
PubMed1995

The cost of monitoring glaucoma patients by community optometrists.

Glaucoma patients are currently undergoing monitoring by community based optometrists as part of a randomised controlled trial of shared care. As part of this trial, the costs of monitoring these patients by community optometrists are being calculated. Data were obtained from eight practices for the 1993-1994 financial year. The average 'full' cost of a 40 min appointment was calculated as epsilon 31.56 pounds. The average number of unbooked appointments for the month of October 1994 was 16 per practice, which equated to 12, 40 min appointments. Once the number of unbooked appointments was surpassed for each practice, an average opportunity cost of epsilon 54.00 pounds was experienced per appointment. The participating optometrists were willing to accept a minimum fee of epsilon 26.03 pounds for a small number of patient assessments but this rose to epsilon 43.16 pounds for up to 100 glaucoma patients seen per annum.

Community Health Services↗
PubMed1995

The Bristol Shared Care Glaucoma Study: study design.

The purpose of this study was the evaluation of community based optometric monitoring of stable glaucoma patients and glaucoma suspects compared to the routine Hospital Eye Services (HES) monitoring. Four hundred and five subjects were recruited from routine outpatient clinics at the Bristol Eye Hospital. All eligible participants were seen in the routine hospital clinic and then within two months were given a 'Gold Standard Assessment' (GSA) by an independent research team. Participants then visited one of 12 glaucoma-trained optometrists, for a standard battery of tests. Randomisation resulted in 204 subjects being allocated to community care, with reviews on a six monthly basis, with 201 who remained a control group within the hospital. Referral criteria were established to enable optometric detection of apparent glaucomatous progression. A questionnaire was used to assess patient satisfaction with both care types. Additionally a cost analysis exercise was performed.

Community Health Services↗
PubMed1994

The sight test fee: effect on ophthalmology referrals and rate of glaucoma detection.

OBJECTIVE: To assess changes, if any, in the numbers of referrals and outcome of glaucoma referrals to the hospital eye service since the introduction of the sight test fee on 1 April 1989. DESIGN: Review of referral records and clinical notes. SETTING: Referrals to the Bristol Eye Hospital. SUBJECTS: 51,919 patients referred to the Bristol Eye Hospital between 1984 and 1992. 9438 case notes of patients referred between 1987 and 1991 were examined in detail. MAIN OUTCOME MEASURES: Numbers of referrals; rate of adult true positive glaucoma referrals. RESULTS: Referrals to the Bristol Eye Hospital were between 13.7% and 19.0% fewer than expected after the introduction of the sight test fee. True positive glaucoma referrals were reduced by the same proportion. CONCLUSIONS: The numbers of patients being identified as requiring treatment or follow up for potentially blinding glaucoma have declined by nearly one fifth since the introduction of the sight test fee. An increased prevalence of preventable blindness may result.

Adult↗
PubMed1993

Cataract and survival in an elderly nondiabetic population.

Follow-up ranging between 6 and 8 years of the survival of a cohort of 473 elderly nondiabetic subjects randomly selected from a small English town showed an age- and sex-adjusted association between nuclear cataract at the time of baseline examination and decreased survival (P = .002). Comparing those with and without nuclear cataract, the adjusted relative hazard for death was 1.52 (95% confidence interval, 1.15 to 1.99). This effect remained virtually unchanged when also adjusted for whether the subject reported ever having been a smoker.

Aged↗
PubMed1993

The prevalence of diabetic retinopathy and maculopathy and their risk factors in the non-insulin-treated diabetic patients of an English town.

A total population study of the ocular status of all known non-insulin-treated diabetic patients resident in the English town of Melton Mowbray has been conducted. The population prevalence of non-insulin-treated diabetes in the town was 6.7/1000. There were 215 patients in the target population, with 65% of the resident survivors participating in the study. Further data on ocular status were gathered from hospital records, bringing the total percentage for whom some information on ocular status was available to 74%. Corrected Snellen acuity was 6/12 or better in 76% of patients and the over-all prevalence rate for any diabetic retinopathy was 52%, for proliferative retinopathy was 4%, and for maculopathy requiring treatment was 10%. In a multivariate analysis, risk factors for retinopathy and/or maculopathy included longer diabetic duration, female sex, higher blood pressure, the use of anti-hypertensive drugs and cigarette smoking.

Adult↗
PubMed1993

Estimation of the thickness of the crystalline lens from on-axis and off-axis Scheimpflug photographs.

Measurement of human lens biometry directly from Scheimpflug images of the anterior ocular segment may be impossible when pupil size precludes an adequate Scheimpflug view of the posterior lens surface. The authors describe a simple and accurate geometric method of overcoming this problem by estimating the true lens thickness from pairs of on-axis and off-axis Scheimpflug images. The method is validated and the variability of the estimate is quantified. This new method has utility in the study of lens biometry in subjects with large lenses whose pupils cannot be adequately dilated.

Anthropometry↗
PubMed1992

Factors related to the final visual outcome of 425 patients with traumatic hyphema.

A retrospective study of the visual outcome of 425 in-patients with traumatic hyphaema has been conducted. A multivariate analysis demonstrated that after adjusting for age, sex and pre-existing poor vision, the size of hyphaema on presentation and the presence of retinal damage were significant predictors of a worse final visual outcome (p = 0.00003 and 0.00001 respectively). Topical steroid and/or cycloplegic medication, and the occurrence of secondary haemorrhage did not influence the final visual outcome after adjustment for the other variables. These data illustrate, in an unselected sequential population of patients, the role of these factors in terms of final visual outcome following hyphaema from blunt ocular trauma.

Eye Injuries↗