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Biomedical subjects

B Parkin

Publications and source records attributed to B Parkin.

10 recordsLinked to original sources
PubMed2004

Effect of video display on the grading of diabetic retinopathy.

PURPOSE: Digital images are increasingly being used in ophthalmology. These may be viewed either on thin-film transistor (TFT) or on cathode-ray tube (CRT) displays. However, there is little data showing which is superior. In this study, we compared the performance of CRT and TFT displays for grading of both compressed and uncompressed images of diabetic retinopathy. METHODS: A total of 49 35 mm transparencies of diabetic retinopathy were scanned and compressed. The images comprised 17 with no retinopathy, eight with background, five with preproliferative, and 19 with proliferative retinopathy. Four levels of compression were used: 0, 70, 80, and 90%. A total of 196 randomised images were presented to two masked graders using both TFT and CRT displays under uniform lighting conditions, 2 months apart. The grade of retinopathy was assessed. Statistical analysis of grading accuracy was performed using receiver operator characteristic curves of sensitivity and specificity and the Stuart-Maxwell test for paired, nonparametric data. RESULTS: Both displays showed high sensitivity and specificity for the detection of any retinopathy. For the specific grade of retinopathy, the CRT performed slightly better with a sensitivity of 0.80 for uncompressed images, compared with 0.75 using the TFT. Compression reduced these sensitivities to 0.73 on the CRT and 0.63 on the TFT. Grading of uncompressed images magnified to four times their original size was more accurate on the TFT. CONCLUSIONS: Grading on both displays met sensitivity and specificity criteria proposed by Diabetes UK (formerly British Diabetic Association) for screening of diabetic retinopathy. The CRT generally performed slightly better than the TFT in relation to the detection of the specific grade of retinopathy.

Computer Peripherals↗
PubMed2001

Axenfeld anomaly and retinal changes in Ramon syndrome: follow-up of two sibs.

Two siblings with Ramon syndrome (MIM 266270) were found at follow-up to have anterior and posterior segment ocular abnormalities, including Axenfeld anomaly, retinopathy, and pale anomalous optic discs. These features were not described in the original report on this family. A recent report of another family with Ramon syndrome describes pigmentary retinopathy and optic disc pallor. It may be concluded that ocular abnormalities are another feature of this syndrome with anterior chamber abnormalities present at birth and retinopathy developing later.

Adult↗
PubMed2001

A comparison of stereoscopic and monoscopic evaluation of optic disc topography using a digital optic disc stereo camera.

AIMS: To compare stereophotographic and monophotographic optic disc assessments made using a digital optic disc stereo camera. METHODS: Stereo digital optic disc photographs of 150 selected patients who had presented to a glaucoma clinic were assessed by two masked observers on separate occasions using (1) the stereophotographs and a stereoviewer, (2) a single image from the same stereopair. Results were analysed for both right and left eyes separately. 95% tolerance limits for change (TC) and intraclass correlation coefficients (ICC) were calculated and a multivariate analysis using a general linear model for repeated measures was performed. RESULTS: A total of 201 optic disc images of 150 patients (84 females, 108 left eyes) were analysed. Mean age of patients was 64 years. The results for right eyes are as follows (similar results were obtained for left eyes). Intraobserver (stereoscopic compared to monoscopic) measurements of: horizontal cup:disc ratios (CDR), ICC = 0.5995 and 0.7269, TC = 34% and 27%; vertical CDR, ICC = 0.8298 and 0.817, TC = 25% and 27%; area CDR, ICC = 0.7757 and 0.8259, TC = 28% and 25%; circumference CDR, ICC = 0.7618 and 0.8103, TC = 28% and 25%. Interobserver measurements of: horizontal CDR, ICC stereoscopic (SS) = 0.7287; monoscopic (MS) = 0.5030; TC SS = 30%; MS = 32%; vertical CDR, ICC SS = 0.8439; MS = 0.7106; TC SS = 25%; MS = 31%; area CDR, ICC SS = 0.8392; MS = 0.6276; TC SS = 26%; MS = 32%; circumference CDR, ICC SS = 0.8433; MS = 0.6438, TC SS = 26%; MS = 31%. Systematic bias between observers and between methods was within acceptable limits. CONCLUSIONS: This study using a digital stereo camera indicates that there may be little benefit of stereoscopic imaging over monoscopic imaging despite demonstrating small but inconsistent differences between both observers and methods.

Adult↗
PubMed2000

Aspirin and warfarin therapy in oculoplastic surgery.

BACKGROUND/AIMS: There are no nationally agreed guidelines on preoperative management of patients who are on aspirin or warfarin therapy. There is considerable evidence that complication rates in anticoagulated patients are low whereas there are higher rates of thromboembolic complications in those whose therapy is manipulated. This survey aimed to establish oculoplastic specialist and non-specialist ophthalmic surgeons' current management practice of patients before oculoplastic surgery who are taking aspirin or warfarin and to assess the rate of complications in these patients. METHOD: An anonymous postal questionnaire survey of all ophthalmic consultants and specialist registrars in the Wessex region along with oculoplastic specialists in the Southern region. RESULTS: The overall response rate was 92%. Preoperative management was influenced both by type of operation and by type of surgeon. A statistically significant higher proportion of surgeons would consider altering warfarin compared with aspirin treatment. For all procedures, non-specialists are unlikely to stop aspirin therapy, and are less likely to stop warfarin before all procedures apart from dacrocystorhinostomy. A significant proportion of surgeons (18%) would allow insufficient time for the coagulation status of the patient to change after altering treatment. A considerable proportion of surgeons (54%) reported that they had seen complications as a result either of stopping or continuing anticoagulation therapy. CONCLUSIONS: In this survey, at least half the surgeons questioned would consider stopping warfarin before oculoplastic procedures. Over half of all surgeons have seen complications related to aspirin or warfarin, some of which were serious. A suggested approach to minimising patient risk is given.

Anticoagulants↗
PubMed1997

Bacterial keratitis in the critically ill.

BACKGROUND: In the 4 year period (1988-91 there were nine cases of bacterial keratitis in five critically ill patients on an intensive care unit ('unit A'), all except one due to Pseudomonas aeruginosa. Many of these patients had serious ocular complications requiring surgery and all surviving patients were left with significant visual deficits. One further case of keratitis due to P aeruginosa occurred on unit A in April 1993. The problem of keratitis in ventilated patients is not unique to this unit as a further four cases in three patients from additional units in this area have been treated. METHODS: Predisposing factors in unit A were established through subsequent investigations. It was found, in particular, that all the ocular infections were preceded by colonisation of the respiratory tract with the pathogenic organism. Recommendations concerning eye care and tracheal suctioning were adopted by unit A in 1991. RESULTS: In the subsequent 4 years (1991-5), the frequency of isolation of pseudomonas from the respiratory tract per patient treated in unit A remained relatively high at 3.8% (153/4032). However, the conjunctival pseudomonas isolation rate has decreased significantly (p < 0.001) from 0.8% (19/2430) to 0.05% (2/4032). CONCLUSIONS: Ventilated patients may be at risk from inoculation of pathogens into the eyes. The principal risk factor for bacterial keratitis in this series was corneal exposure secondary to conjunctival chemosis or lid damage. The adoption of simple preventative measures on unit A had a significant impact on the incidence of eye infections due to pseudomonas, despite the high proportion of patients whose respiratory tracts were colonised with the same organism. There is a need for additional research into the most effective method of eye care for ventilated patients in order to reduce the frequency of this avoidable condition.

Critical Care↗
PubMedDate not supplied

Global form perception: interactions between luminance and texture information.

PURPOSE: This experiment reports the independence of first- and second-order processing mechanisms in form perception. METHODS: Symmetrical dot patterns were created using either luminance-increment dots (luminance above background), or texture-defined dots (average luminance equal to background). The proportion of luminance increment or texture dots defining each pattern was varied among fields of noise dots of the same type to determine symmetry detection thresholds. RESULTS: Differences in detection thresholds were found between luminance- and texture-defined patterns. Further, symmetry detection thresholds for luminance-increment dot patterns were resistant to noise defined by dots of opposite contrast polarity (luminance-decrement dots) or texture, while texture-defined patterns were resistant to neither texture nor luminance-decrement noise. CONCLUSIONS: These data suggest that symmetry perception, along with other types of form perception, use both first- and second-order processing mechanisms. The data are compatible with a second-order system that includes a negative half-wave rectifying non-linearity.

Contrast Sensitivity↗
PubMedDate not supplied

Phosphoglucomutase polymorphism detected by isoelectric focusing: gene frequencies, evolution and linkage.

Four alleles at the phosphoglucomutase (PGM1) locus in man have been recently demonstrated by isoelectric focusing, and in this study gene frequencies have been estimated for four populations, and significant differences have been indicated between the results. Pedigree analysis of the PGM1 and rhesus loci confirm a weak linkage in males, but none in females. An examination of PGM1 phenotypes in a range of primates shows that a proportion possess a band focusing at the same isoelectric point as human PGM1+1. We propose that all the human and primate alleles may have evolved from a common ancestral PGM1+1 locus.

Animals↗