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1.  A comparison of stereoscopic and monoscopic evaluation of optic disc topography using a digital optic disc stereo camera 
The British Journal of Ophthalmology  2001;85(11):1347-1351.
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.

PMCID: PMC1723792  PMID: 11673304
2.  Aspirin and warfarin therapy in oculoplastic surgery 
The British Journal of Ophthalmology  2000;84(12):1426-1427.
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.

PMCID: PMC1723338  PMID: 11090488
3.  Bacterial keratitis in the critically ill 
The British Journal of Ophthalmology  1997;81(12):1060-1063.
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.

PMCID: PMC1722071  PMID: 9497465
4.  Stochastic Models of Soil Denitrification 
Soil denitrification is a highly variable process that appears to be lognormally distributed. This variability is manifested by large sample coefficients of variation for replicate estimates of soil core denitrification rates. Deterministic models for soil denitrification have been proposed in the past, but none of these models predicts the approximate lognormality exhibited by natural denitrification rate estimates. In this study, probabilistic (stochastic) models were developed to understand how positively skewed distributions for field denitrification rate estimates result from the combined influences of variables known to affect denitrification. Three stochastic models were developed to describe the distribution of measured soil core denitrification rates. The driving variables used for all the models were denitrification enzyme activity and CO2 production rates. The three models were distinguished by the functional relationships combining these driving variables. The functional relationships used were (i) a second-order model (model 1), (ii) a second-order model with a threshold (model 2), and (iii) a second-order saturation model (model 3). The parameters of the models were estimated by using 12 separate data sets (24 replicates per set), and their abilities to predict denitrification rate distributions were evaluated by using three additional independent data sets of 180 replicates each. Model 2 was the best because it produced distributions of denitrification rate which were not significantly different (P > 0.1) from distributions of measured denitrification rates. The generality of this model is unknown, but it accurately predicted the mean denitrification rates and accounted for the stochastic nature of this variable at the site studied. The approach used in this study may be applicable to other areas of ecological research in which accounting for the high spatial variability of microbiological processes is of interest.
PMCID: PMC184056  PMID: 16347838

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