PubMed Health⌕ Search

Biomedical subjects

D B Henson

Publications and source records attributed to D B Henson.

At least 19 recordsLinked to original sources
PubMed2005

The effectiveness of the Heidelberg Retina Tomograph and laser diagnostic glaucoma scanning system (GDx) in detecting and monitoring glaucoma.

OBJECTIVES: To determine the potential of optic nerve head tomography [Heidelberg Retina Tomograph (HRT)] and scanning laser polarimetry (GDx) for identifying patients with glaucomatous visual field loss. DESIGN: Examinations were performed with the HRT, GDx and Humphrey Field Analyzer (HFA). Glaucoma was defined by the presence of a field defect. Patients within the cross-sectional groups underwent a single examination, whereas patients in the longitudinal groups were examined 6 monthly, for an average of 3.5 years. SETTING: Manchester Royal Eye Hospital, UK. PARTICIPANTS: Patients with primary open angle glaucoma (POAG) or who were at risk of developing glaucoma. INTERVENTIONS: The diagnostic accuracies of the HRT and GDx were compared; specificity was set at 95%. The rate of change was determined by linear regression. To estimate the clinical application of the instruments, the proportion of an unselected group of patients on whom the examinations could be performed was calculated. Additionally, the time taken to perform and process each examination was measured. MAIN OUTCOME MEASURES: The ability of the techniques to identify cases showing deterioration. The level of agreement and applicability of the techniques. Time taken to perform and process each examination. RESULTS: From the cross-sectional group, the maximum sensitivities of the HRT and GDx were 59% and 45%, respectively (at 95% specificity). From the two longitudinal cohorts, the level of agreement between the three instruments for identification of the development and deterioration of POAG was low. The applicability of the techniques was 80% (HRT), 88% (GDx) and 98% (HFA). The length of time to perform a full examination with each instrument was 12.3, 11.8 and 28.3 minutes, respectively. Agreement of HRT and GDx parameters between and within observers was largely good. CONCLUSIONS: There is poor agreement for detection of glaucoma between the HFA, HRT and GDx. The techniques are amenable to use in the clinical environment, but no single examination has sufficient diagnostic precision to be used in isolation; also, the imaging techniques were not universally applicable. Neither the HRT nor GDx should be viewed as a replacement for visual field examination. Further research is needed into why most patients within the longitudinal arms of the study showed very little deterioration and into determining aspects of the structure versus function relationship in glaucoma that may explain why any one technique fails to detect a proportion of cases.

Adult↗
PubMed2003

Community refinement of glaucoma referrals.

AIM: To describe a Manchester-based glaucoma referral refinement scheme designed to reduce the number of false-positive referrals to the hospital eye service. To report on the first years results of this scheme and its financial costs to the NHS. METHODS: Patients with suspected glaucoma, instead of being referred to their GP and then on to the hospital eye service, were referred to a group of specially trained community optometrists working to an agreed set of referral criteria. Those patients who did not meet the referral criteria were returned to the referring optometrist, while those who met the referral criteria were referred directly to Manchester Royal Eye Hospital. The patient's GP was informed in all cases. RESULTS: The number of suspect glaucoma cases referred to the Manchester Royal Eye Hospital was reduced by 40%. This figure is close to the percentage of false-positive referrals measured at Manchester Royal Eye Hospital prior to the onset of this study. The information accompanying referral has been improved and the scheme produces a small financial cost saving to the NHS of approximately 17 pounds sterling per patient. CONCLUSION: Community refinement of suspect glaucoma offers some important benefits over the current referral pathway.

Community Health Services↗
PubMed2003

The correlation between optic nerve head topographic measurements, peripapillary nerve fibre layer thickness, and visual field indices in glaucoma.

AIMS: To establish whether the structural parameters provided by the Heidelberg retina tomograph (HRT) and the laser diagnostics glaucoma scanning system (GDx) can be used to reflect functional damage in the visual field. METHODS: 62 patients with primary open angle glaucoma underwent examination with the HRT, GDx, and Humphrey field analyser. The relations between the topographic parameters, retinal nerve fibre parameters, and visual field indices were analysed by scatter plot and linear regression. RESULTS: Among the topographic parameters generated by the HRT, rim area had the best correlation with visual field indices. The "number," maximum modulation, and ellipse modulation generated by the GDx also had correlations with visual field indices. The correlations were better for the sectoral parameters than the global parameters. However, great interindividual variation was found in the association. CONCLUSION: Although relations were found between some topographic parameters, RNFL parameters, and visual field indices, great interindividual variation limits the prediction of one parameter from the other. Therefore, both structural and functional aspects should be evaluated in order to obtain full characterisation of the glaucomatous damage for clinical judgment and treatment.

Adult↗
PubMed2001

A clinical evaluation of random dot stereoacuity cards in infants.

PURPOSE: To clinically evaluate the random dot stereoacuity cards developed by Birch and Salomao on a population of infants within the first 12 months of life and to generate baseline normative data. METHODS: Random dot stereoacuity cards were constructed using vectographic vertical bar stimuli with cross disparities ranging from 45 to 1735 seconds of arc (1.65 to 3.2 log seconds of arc). Wearing polarising goggles, infants were assessed using a two-alternative forced choice preferential looking staircase procedure. Success rate and stereoacuity values for performance as a function of age were evaluated. RESULTS: One hundred and seventy-seven tests were completed on 41 infants with ages ranging from 5 to 56 weeks. The random dot stereoacuity procedure was successful in 128 (72.3%) infants, success being dependent upon age. At 0-8 weeks of age, none of the infants produced a fixation preferance towards even the coarsest stereogram. The success rate increased to 50% at 9-16 weeks, 97% at 17-24 weeks, 93% at 25-36 weeks, dropping to 69% at 37-56 weeks due to increasing intolerance to the goggles. Stereopsis was not demonstrable in infants under 8 weeks of age. By 9-16 weeks the mean stereoacuity level was 2.91 log seconds of arc, further increasing to 2.53 at 17-24 weeks, reducing slightly to 2.65 at 25-36 weeks. At 37-56 weeks the mean stereoacuity value was recorded as 2.53 log seconds of arc. CONCLUSION: Our results indicate that the infant random dot stereoacuity cards provide a simple, quick and portable test for the clinical assessment of stereopsis in infants aged between 17 and 36 weeks, and should prove to be a useful clinical tool to monitor infants at risk of binocular vision disorders.

Age Factors↗
PubMed2001

Macular pigment and risk for age-related macular degeneration in subjects from a Northern European population.

PURPOSE: Age and advanced disease in the fellow eye are the two most important risk factors for age-related macular degeneration (AMD). In this study, the authors investigated the relationship between these variables and the optical density of macular pigment (MP) in a group of subjects from a northern European population. METHODS: The optical density of MP was measured psychophysically in 46 subjects ranging in age from 21 to 81 years with healthy maculae and in 9 healthy eyes known to be at high-risk of AMD because of advanced disease in the fellow eye. Each eye in the latter group was matched with a control eye on the basis of variables believed to be associated with the optical density of MP (iris color, gender, smoking habits, age, and lens density). RESULTS: There was an age-related decline in the optical density of macular pigment among volunteers with no ocular disease (right eye: r(2) = 0.29, P = 0.0006; left eye: r(2) = 0.29, P < 0.0001). Healthy eyes predisposed to AMD had significantly less MP than healthy eyes at no such risk (Wilcoxon's signed rank test: P = 0.015). CONCLUSIONS: The two most important risk factors for AMD are associated with a relative absence of MP. These findings are consistent with the hypothesis that supplemental lutein and zeaxanthin may delay, avert, or modify the course of this disease.

Adult↗
PubMed2000

Quantitative comparison of static perimetric strategies in early glaucoma: test-retest variability.

PURPOSE: The aim of this study is to describe and compare test-retest variability of threshold-related suprathreshold and threshold examination strategies. METHODS: Threshold-related suprathreshold and FASTPAC threshold central visual field examinations were performed twice (test and retest) within a 4-week period on 322 subjects with early to moderate primary open-angle glaucoma and glaucoma suspects. For both strategies, defects were quantified by a count, or score, of the number of defective locations within the field as a whole and by hemifield, thereby providing a simple measure of defect extent. This quantification was obtained for the suprathreshold strategy at three suprathreshold increments (5, 8, and 12 dB) and for the full threshold strategy at two levels of pattern deviation probability, although absolute full threshold defect depth was not considered. Mean test-retest score differences and spread of score differences were used to describe variability. An index of relative variability was used to compare the two visual field examination strategies. RESULTS: Marked degrees of defect extent variability were found to exist in both suprathreshold and FASTPAC examination strategies. In general, the suprathreshold strategy exhibited lower test-retest variability of defect extent than the FASTPAC strategy. Suprathreshold test variability was dependent on the suprathreshold increment. FASTPAC examination variability was independent of defect depth when analyzed on the basis of pattern deviation probability values and was also found to be independent of the area of visual field loss. CONCLUSIONS: Suprathreshold examination techniques may provide a reliable perimetric alternative to thresholding strategies for monitoring individuals with early and moderate glaucoma, although they may not be suitable for individuals with advanced glaucomatous visual field loss.

Glaucoma, Open-Angle↗
PubMed2000

Response variability in the visual field: comparison of optic neuritis, glaucoma, ocular hypertension, and normal eyes.

PURPOSE: To compare the relationship between sensitivity and response variability in the visual field of normal eyes and eyes with optic neuritis (ON), glaucoma (POAG), and ocular hypertension (OHT). METHODS: Frequency-of-seeing (FOS) data were collected from four visual field locations in one eye of 71 subjects (12 ON, 25 POAG, 11 OHT, and 23 normal), using a constant stimulus method on an Henson 4000 perimeter (Tinsley Instruments, Croydon, UK). At each location, at least 20 stimuli (subtending 0.5 degrees) were presented for 200 ms at six or more intensities above and below the estimated threshold. The mean and SD of the probit fitted cumulative Normal function were used to estimate sensitivity and response variability. Cluster regression analysis was carried out to determine whether there were differences in the sensitivity-log (variability) relationship between the four groups. RESULTS: Variability was found to increase with decreased sensitivity for all four groups. The combined data from the four groups was well represented (R2 = 0.57) by the function log(e)(SD) = A.sensitivity (dB) + B, where the constants A and B were -0.081 (SE, +/-0.005) and 3.27 (SE, +/-0.15), respectively. Including other statistically significant covariates (false-negative errors, P = 0.004) and factors (diagnosis, P = 0.005) into the model increased the proportion of explained variance to 62% (R2 = 0.62). Stimulus eccentricity (P = 0.34), patient age (P = 0.33), fixation loss rate (P = 0.10), and false-positive rate (P = 0.66) did not reach statistical significance as additional predictors of response variability. CONCLUSIONS: The relationship between response variability and sensitivity is similar for ON, POAG, OHT, and normal eyes. These results provide supporting evidence for the hypothesis that response variability is dependent on functional ganglion cell density.

Cell Count↗
PubMed1999

The effect of six weeks topical nasal betamethasone drops on the hypothalamo-pituitary-adrenal axis and bone turnover in patients with nasal polyposis.

Betamethasone topical nasal drops may have systemic corticosteroid activity and cause suppression of the hypothalamo-pituitary-adrenal (HPA) axis and impairment of bone turnover. The aim of this study was to assess the effect of a standard 6-week regime of betamethasone topical nasal drops on the HPA axis (using a physiological dose (1 microg) ACTH test) and on bone turnover (using markers of bone turnover, urinary deoxypyridinoline and serum bone specific alkaline phosphatase). Eleven patients with nasal polyposis were included in a prospective cohort study. Plasma cortisol was lower after betamethasone treatment at all time intervals (P < 0. 0001). There was no change in urinary deoxypyridinoline corrected for creatinine or bone specific alkaline phosphatase. Six weeks' treatment with recommended doses of betamethasone suppresses the HPA axis, but has no significant effect upon markers of bone turnover. Topical betamethasone in subjects with nasal polyps should be viewed as systemic corticosteroid administration and the long and short-term sequelae should be borne in mind.

Administration, Intranasal↗
PubMed1999

Diffuse loss of sensitivity in early glaucoma.

PURPOSE: To establish whether there is significant diffuse loss of sensitivity in a population of patients with early glaucoma. METHODS: The differential light sensitivities at the 10 most sensitive locations from within the central 24 degrees of program 30-2 of the Humphrey Field Analyzer (Humphrey Instruments, San Leandro, CA) were compared in 38 pairs of age-matched subjects, one of each pair with early primary open-angle glaucoma (POAG) and the other with normal eyes. All subjects had had experience with automated perimetry and had clear media, visual acuity of 20/25 or better, and one or fewer false-positive or false-negative responses to catch trials. RESULTS: The mean difference in age between the subjects with glaucoma and normal subjects was 29 days (P = 0.44, maximum 1.42 years). The mean paired difference in pupil size was 0.16 mm (P = 0.26), and visual acuity was higher in the glaucoma-affected subjects (P = 0.044). The 10 highest sensitivity measurements in the POAG-affected subjects were found to be lower by a median of between 1.0 and 2.0 dB than those in the normal pair members (0.0001<P<0.012, sign test). In 60% of the pairs the sensitivity at the seventh most sensitive location was 2 dB or more lower in the POAG-affected eyes. CONCLUSIONS: Early glaucomatous visual field loss frequently involves a diffuse component that includes the 10 most sensitive locations. These findings suggest that purely localized visual field loss in glaucoma is rare. These observations could not be explained by factors of pupil size and media opacity.

Glaucoma, Open-Angle↗
PubMed1998

Preoperative carcinoembryonic antigen is related to tumour stage and long-term survival in colorectal cancer.

Evidence as to the value of preoperative carcinoembryonic antigen (CEA) in guiding treatment for patients with colorectal cancer is conflicting. The aim of this prospective study was to investigate the value of preoperative CEA in predicting tumour factors of proven prognostic value and long-term survival in patients undergoing surgery for colorectal cancer. Preoperative serum CEA, tumour ploidy, stage and grade were ascertained in 277 patients undergoing colorectal cancer surgery. This cohort of patients were followed up for a minimum of 5 years, or until death, in a dedicated colorectal clinic. Patients with an elevated CEA had a 5 year survival of 39%. This increased to 57% if the CEA was normal (P=0.001). The proportion of patients with a raised CEA increased with a more advanced tumour stage (P < 0.000001) and a poorly differentiated tumour grade (P < 0.005). Once stage had been controlled for, CEA was not a predictor of survival. No relationship between tumour ploidy and CEA was found. In conclusion, a raised preoperative serum CEA is likely to be associated with advanced tumour stage and poor long-term survival, compared with patients with a normal value.

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

Artificial neural network analysis of noisy visual field data in glaucoma.

This paper reports on the application of an artificial neural network to the clinical analysis of ophthalmological data. In particular a 2-dimensional Kohonen self-organising feature map (SOM) is used to analyse visual field data from glaucoma patients. Importantly, the paper addresses the problem of how the SOM can be utilised to accommodate the noise within the data. This is a particularly important problem within longitudinal assessment, where detecting significant change is the crux of the problem in clinical diagnosis. Data from 737 glaucomatous visual field records (Humphrey Visual Field Analyzer, program 24-2) are used to train a SOM with 25 nodes organised on a square grid. The SOM clusters the data organising the output map such that fields with early and advanced loss are at extreme positions, with a continuum of change in place and extent of loss represented by the intervening nodes. For each SOM node 100 variants, generated by a computer simulation modelling the variability that might be expected in a glaucomatous eye, are also classified by the network to establish the extent of noise upon classification. Field change is then measured with respect to classification of a subsequent field, outside the area defined by the original field and its variants. The significant contribution of this paper is that the spatial analysis of the field data, which is provided by the SOM, has been augmented with noise analysis enhancing the visual representation of longitudinal data and enabling quantification of significant class change.

Diagnosis, Computer-Assisted↗
PubMed1996

Visual field test simulation and error in threshold estimation.

AIM: To establish, via computer simulation, the effects of patient response variability and staircase starting level upon the accuracy and repeatability of static full threshold visual field tests. METHOD: Patient response variability, defined by the standard deviation of the frequency of seeing versus stimulus intensity curve, is varied from 0.5 to 20 dB (in steps of 0.5 dB) with staircase starting levels ranging from 30 dB below to 30 dB above the patient's threshold (in steps of 10 dB). Fifty two threshold estimates are derived for each condition and the error of each estimate calculated (difference between the true threshold and the threshold estimate derived from the staircase procedure). The mean and standard deviation of the errors are then determined for each condition. The results from a simulated quadrantic defect (response variability set to typical values for a patient with glaucoma) are presented using two different algorithms. The first corresponds with that normally used when performing a full threshold examination while the second uses results from an earlier simulated full threshold examination for the staircase starting values. RESULTS: The mean error in threshold estimates was found to be biased towards the staircase starting level. The extent of the bias was dependent upon patient response variability. The standard deviation of the error increased both with response variability and staircase starting level. With the routinely used full threshold strategy the quadrantic defect was found to have a large mean error in estimated threshold values and an increase in the standard deviation of the error along the edge of the defect. When results from an earlier full threshold test are used as staircase starting values this error and increased standard deviation largely disappeared. CONCLUSION: The staircase procedure widely used in threshold perimetry increased the error and the variability of threshold estimates along the edges of defects. Using earlier data, when available, overcomes this problem and reduces examination time.

Computer Simulation↗
PubMed1996

Spatial classification of glaucomatous visual field loss.

AIMS: To develop and describe an objective classification system for the spatial patterns of visual field loss found in glaucoma. METHODS: The 560 Humphrey visual field analyser (program 24-2) records were used to train an artificial neural network (ANN). The type of network used, a Kohonen self organising feature map (SOM), was configured to organise the visual field defects into 25 classes of superior visual field loss and 25 classes of inferior visual field loss. Each group of 25 classes was arranged in a 5 by 5 map. RESULTS: The SOM successfully classified the defects on the basis of the patterns of loss. The maps show a continuum of change as one moves across them with early loss at one corner and advanced loss at the opposite corner. CONCLUSIONS: ANNs can classify visual field data on the basis of the pattern of loss. Once trained the ANN can be used to classify longitudinal visual field data which may prove valuable in monitoring visual field loss.

Glaucoma↗
PubMed1996

Influence of fixation accuracy on threshold variability in patients with open angle glaucoma.

PURPOSE: To evaluate the contribution that fixation errors make to the overall variability of perimetric responses in patients with glaucoma. METHODS: Frequency of seeing curves were established, with and without fixation error correction, at two locations in each of 14 patients with glaucoma and good visual acuity. One location corresponded to a relatively normal region of the visual field, whereas the second corresponded to a region in which there was a sensitivity deficit. All patients had an acuity of better than 20/63 (except one whose acuity was 20/100). The locations of the first and fourth Purkinje images of a collimated infrared source were used to give a measure of eye position, during each stimulus presentation (accuracy 10 minutes of arc). RESULTS: Considerable variation was found in patient fixation accuracy. In the worst case, fixation was within 30 minutes of the target in only 7% of presentations whereas in the best, it was within this range in more than 60%. No relationship was found between accuracy of fixation and extent of loss. The gradient of the frequency of seeing curve was found to be shallow at regions of reduced sensitivity, a finding that supports the recognized relationship between variability and sensitivity deficit. A recalculation of the frequency of seeing curves, using only those responses in which the patient's fixation was within a specified range ( < 60 minutes of arc), did not show a meaningful reduction in variability at either location. CONCLUSIONS: It is concluded that fixation errors, though contributing to variability, are not the major cause of the increased variability seen at locations with reduced sensitivity.

Aged↗