3D high spatial resolution visualisation and quantification of interconnectivity in polymer films.

A porous network acts as transport paths for drugs through films for controlled drug release. The interconnectivity of the network strongly influences the transport properties. It is therefore important to quantify the interconnectivity and correlate it to transport properties for control and design of new films. This work presents a novel method for 3D visualisation and analysis of interconnectivity. High spatial resolution 3D data on porous polymer films for controlled drug release has been acquired using a focused ion beam (FIB) combined with a scanning electron microscope (SEM). The data analysis method enables visualisation of pore paths starting at a chosen inlet pore, dividing them into groups by length, enabling a more detailed quantification and visualisation. The method also enables identification of central features of the porous network by quantification of channels where pore paths coincide. The method was applied to FIB-SEM data of three leached ethyl cellulose (EC)/hydroxypropyl cellulose (HPC) films with different weight percentages. The results from the analysis were consistent with the experimentally measured release properties of the films. The interconnectivity and porosity increase with increasing amount of HPC. The bottleneck effect was strong in the leached film with lowest porosity.

A new generation of algorithms for computerized threshold perimetry, SITA.

PURPOSE: The purpose of this work was to develop a new family of test algorithms for computerized static threshold perimetry which significantly reduces test time without any reduction of data quality. METHODS: A comprehensive visual field model constructed from available knowledge of normal and glaucomatous visual fields is continuously updated during testing. The model produces threshold estimates and also estimates of the certainty to which the threshold is known at each point. Testing is interrupted at each test location at predetermined levels of threshold certainty. New time-saving methods are employed for estimation of false answers, and test pacing is optimized. After completion of the test, all threshold estimates are re-computed, taking into account the complete body of patient responses. Computer simulations were used to optimize the different parameters of the new algorithms, to evaluate the relative importance of those parameters, and to evaluate the performance of the algorithm as a whole in comparison with a standard algorithm. RESULTS: Simulated test results obtained with this algorithm were slightly more accurate than those of the Humphrey Full Threshold test algorithm. The number of simulated stimuli presented was reduced by an average of 29% in normal fields and 26% in glaucomatous fields. Actual clinical test time should be further reduced, since the influence of the improved timing algorithm was not included in the simulations. CONCLUSIONS: We applied new methods which take available knowledge of visual field physiology and pathophysiology into account, and employ modern computer-intensive mathematical methods for real time estimates of threshold values and threshold error estimates. In this way it was possible to design a family of testing algorithms which significantly reduced perimetric test time without any loss of quality in results.

An improved method to estimate frequency of false positive answers in computerized perimetry.

Reliability of patient performance in static computerized perimetry is important for evaluation of results. False positive answers tend to falsely increase measured threshold sensitivity. The frequency of false positive responses is traditionally measured by adding extra questions, catch trials, to the test. Catch trials are few and limited because of time constraints, leading to inexact estimates. We developed an improved method for estimation of false positive answers by using information already available in current ordinary computerized visual field testing, without increasing test time. We here describe the method and evaluate it in a prospectively collected material of 49 glaucoma eyes of 49 patients. The results show that the new method reduces measurement errors considerably and significantly as compared with the traditional catch trials method. Test-retest change was only half with the new method as compared to the traditional method of catch trials. Furthermore, it can reduce test time by eliminating the need to use catch trials to estimate the frequency of false positive responses.

Spatial analyses of glaucomatous visual fields; a comparison with traditional visual field indices.

Interpretation of numeric automated threshold visual field results is often difficult. A large amount of data is obtained for every single field tested. Various approaches to summarize this data have been suggested, most commonly the mean and standard deviation of departures from age-corrected normal threshold values. These visual field indices differ substantially from subjective field interpretation where spatial relationships are important. We have previously devised two methods for automated field interpretation which take spatial information into account--regional up-down comparisons and arcuate cluster analysis. We now studied the merits of using these new spatial methods and compared them to traditional visual field indices for discrimination between normal and glaucomatous field results. Central static 30 degree field results in 101 eyes of 101 normal subjects and 101 eyes of 101 patients with glaucoma were discriminated using logistic regression analysis. The best field classification was obtained with a spatial visual field model combining up-down differences and arcuate clusters. The advantages of the spatial model were confirmed in an independent material of 163 eyes of 163 normal subjects and 76 eyes of 76 patients with glaucoma where eyes with large field defects had been removed. In this material the spatial model gave 87% sensitivity and 83% specificity while the best non-spatial model gave 82% sensitivity and 80% specificity. Visual field interpretation in glaucoma may be significantly enhanced if detection is focused on circumscribed field loss rather than on averages of differential light sensitivities and similar indices which do not take spatial relationships into consideration.

Effect of mouthrinsing with a sodium fluoride solution in children with different caries experience.

The present study was designed to investigate the pattern of the caries inhibiting effect of school fluoride mouthrinse programs in children of different baseline caries experience. In Phase I, 170 children 10 and 11 years of age were randomly assigned to a test group who rinsed with a 0.5% NaF solution once every 2 weeks for 3 years or to a control group who rinsed with distilled water. In Phase II, the dental records of 345 children were used. Here, the test group had rinsed weekly with a 0.2% NaF solution, while the control group consisted of children 3 years older who were not included in the program during the ages under study (10-11 to 13-14). The statistical analysis of the data was performed as linear regression of caries increments on baseline scores. The analyses included all tooth surfaces, as well as separate studies of proximal and free smooth surfaces, respectively. It was shown that caries increments increased as the baseline scores increased. The slope of the regression lines indicated that the fluoride mouthrinses were more effective in high caries groups than in low caries groups. The results are in agreement with earlier findings concerning the interaction between factors in the caries process.