Biomedical subjects
Publications and source records attributed to A Heijl.
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PURPOSE: We developed a new family of test algorithms. This is an evaluation in normal subjects. METHODS: One eye in each of twenty normal subjects, with a mean age of 37 years (range 26 to 59), was tested twice with each of the SITA, Full Threshold and Fastpac strategies of the Humphrey perimeter at 3 separate visits. Actual test times and number of stimulus exposures were compared. Test-retest variability and levels of threshold estimates were also calculated and compared between strategies. RESULTS: In all subjects test times were shortest with SITA, 6.14 minutes in average, which was 50% as compared to Full Threshold (p<0.001) with an average of 12.27 minutes, and a reduction of 16% as compared to Fastpac (mean 7.28 minutes, p<0.0001). SITA required 287 stimulus exposures on the average, significantly fewer (p<0.0001) than corresponding numbers with Full Threshold (mean of 404), and significantly more (p<0.0001) than with Fastpac (average 240). SITA results showed significantly lower test-retest variability than results obtained with Fastpac (p=0.0002), and just as low as those of the Full Threshold strategy (p=0.0979). Threshold values obtained with SITA were slightly higher than those produced by the other two strategies. CONCLUSIONS: The results confirm those of previously reported simulated tests, that improved test algorithms using advanced visual field models and mathematical analyses performed in real time may effectively shorten computerized perimetry tests, while achieving the same or better test quality than today's standard methods.
PURPOSE: To study the influence of age, gender, intraocular pressure and refraction on optic disc topography in normal subjects. METHODS: We studied both eyes of 225 healthy subjects between 20 and 80 years of age using raster tomography (Glaucoma-Scope, Ophthalmic Imaging Systems, Sacramento CA, USA) and scanning laser tomography (Heidelberg Engineering, Heidelberg, Germany). We chose to study cup area and maximum cup depth, two variables that are minimally influenced by the operator. RESULTS: Raster and scanning laser tomography results were strongly correlated. Cup area was independent of age, gender and refraction. It was weakly associated with IOP, but this association was significant only when the cup area was measured with scanning laser tomography. Maximum cup depth was independent of age, gender and IOP. It was larger in hypermetropic eyes, although this trend was significant only when maximum cup depth was measured with raster tomography. CONCLUSION: Our results indicate that optic nerve head topography does not change significantly with age in normal subjects. This information has important implications for follow-up of pathological changes in optic nerve head topography.
PURPOSE: To evaluate the performance of the new perimetric threshold strategy SITA relative to older methods. METHOD: Thirty-two patients with either glaucoma or ocular hypertension performed two threshold visual field tests with each of three threshold strategies, SITA, Humphrey Full Threshold, and Fastpac. Testing was distributed over three visits, and testing order was balanced between strategies to control for order effects. RESULTS: SITA tests consumed 54% of the time taken by Full Threshold tests on average, and 85% of Fastpac tests; SITA's test times were significantly shorter than those of Full Threshold (p<0.0001) and Fastpac (p=0.0008). Test-retest threshold variability did not differ significantly between strategies. Intertest variability of the pattern deviation analysis was lowest in SITA (p<0.01) relative to both Full Threshold and Fastpac. Both SITA and Fastpac showed higher than expected average sensitivities relative to Full Threshold. SITA and Fastpac showed approximately the same amount of visual field loss. There was a significant relationship between Mean Deviation and the SITA function used to shorten stimulus sequences at points where measurement errors are small (p<0.0001). CONCLUSION: Our results suggest that SITA matches the precision of older thresholding methods, consuming considerably and significantly less test time. This indicates that SITA could replace Full Threshold as the standard clinical test used in glaucoma management, without decreasing the quality of test results.
PURPOSE: To describe and evaluate the new rapid SITA Fast computerized perimetric threshold strategy. METHOD: Computer simulations of visual fields were used to develop a new rapid threshold strategy, SITA Fast. In a clinical evaluation 30 patients were examined twice with each of the Full Threshold, Fastpac and SITA Fast strategies. RESULTS: SITA Fast had significantly shorter test time using on average 34% of the test time when compared to the Full Threshold strategy (p<0.0001) and 53% compared to Fastpac (p<0.0001). Reproducibility, calculated as the average Root Mean Square Error, was 1.84 dB in SITA tests, and 1.99 dB and 2.02 dB with Full Threshold and Fastpac, respectively. Both SITA Fast and Fastpac showed slightly higher sensitivities on average than theoretically expected. Sensitivity differences were larger in eyes with large differences in test time. Defects detected by SITA Fast were often deep and more localised than those detected by the Full Threshold and the Fastpac strategies. CONCLUSION: SITA Fast tests were considerably shorter than Fastpac tests. The low test-retest variability found in the SITA Fast tests implies that it may be a sensitive test for detection of field progression.
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The aim of this follow-up study has been to assess retinopathy and change of treatment to insulin therapy as risk factors for mortality in diabetic patients participating in a control and screening programme for retinopathy. A total of 3220 diabetic patients, 483 with an age at diagnosis <30 years, and 2737 with an age at diagnosis > or = 30 years, were included. Retinopathy was graded on fundus photographs using the Wisconsin Scale, and the visual acuity was assessed. The average HbA1c value was calculated for each patient for the previous 8 years to estimate long-term glycaemic control. Mortality data were obtained from death certificates. Two hundred and sixty-three diabetic patients (8.2%) died during the mean follow-up time of 3.4 years, 13 (2.7%) of those with younger-onset (<30 years) and 250 (9.1%) of those with older-onset (> or = 30 years) diabetes. Of them, 148 (56.3%) died from cardiovascular and 23 (8.7%) from cerebrovascular disorders. After adjusting for differences in age and sex, more severe retinopathy and the use of antihypertensive drugs were associated with a decreased overall survival rate as well as an increased mortality from cardiovascular and cerebrovascular diseases. A statistically significant association between HbA1c values in the highest quartile, i.e. > or =8.4%, and cardiovascular and all cause mortality did not remain when retinopathy was entered into the multivariate analyses. Duration of diabetes, but not change of treatment to insulin therapy, was associated with higher cardiovascular mortality in patients whose diabetes was diagnosed after the age of 30 years. We conclude that severe retinopathy, use of antihypertensive drugs, and poor glycaemic control predicted death from cardiovascular disease in diabetic patients participating in an ophthalmological screening programme.
PURPOSE: The purpose of the study is to compare the efficacy and safety profile of 2.0% dorzolamide (three times daily) and 0.5% timolol (twice daily) for up to 6 months in patients with glaucoma or ocular hypertension associated with pseudoexfoliation. The additive effects of dorzolamide and timolol in patients requiring add-on therapy also was evaluated. METHODS: This was a double-masked, randomized, parallel comparison study at 15 Scandinavian sites. One hundred eighty-four patients with pseudoexfoliation and either glaucoma or ocular hypertension who were 21 to 85 years of age were studied. The treatment groups were 2.0% dorzolamide three times daily and 0.5% timolol maleate twice daily. RESULTS: At 6 months, the mean percent reduction in intraocular pressure of 2% dorzolamide and 0.5% timolol was 24% and 29%, respectively, at morning peak and 21% and 23%, respectively, at afternoon trough. The additional intraocular pressure-lowering effect of adding 2.0% dorzolamide twice daily to patients receiving timolol was 14% and 15%, at peak and trough, respectively. There were no differences between treatment groups in the incidence of clinical adverse experiences, and dorzolamide was not associated with the systemic adverse effects typically ascribed to the use of oral carbonic anhydrase inhibitors. CONCLUSION: Two percent dorzolamide (three times daily) was effective and well tolerated in patients with glaucoma or ocular hypertension associated with pseudoexfoliation over the course of 6 months; 0.5% timolol (twice daily) had a greater level of intraocular pressure-lowering activity than did dorzolamide, although the difference between the two treatments became less pronounced during the study period. Finally, 2.0% dorzolamide (twice daily) produced additional lowering of intraocular pressure when given with 0.5% timolol (twice daily).
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.
We describe a new method for analysis of change in glaucomatous visual fields with the object to differentiate between changes caused by glaucoma from those caused by cataract. New pattern deviation change probability maps were developed from a prospectively collected glaucoma material and designed to be sensitive to changes in localized field loss, but to be unaffected by media-induced perimetric change. We compared the new change probability maps with the commercially available total deviation change probability maps in series of Humphrey perimetric tests in a glaucoma material of 43 eyes of 35 patients, who had undergone cataract surgery. When using the total deviation maps, considerable differences were seen between fields obtained before and after cataract surgery. Much smaller differences were seen when using the new change probability maps, that almost eliminated the common and disturbing effect of increasing cataract. This new tool could be of considerable help in differentiation between progressive glaucomatous visual field loss and deterioration caused by increasing media opacities.
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.
PURPOSE: Certain individuals need earlier perimetric experience before producing normal fields on automated static threshold perimetry. Mid-peripheral depressions and an unaffected central field are typical findings in such cases. We have devised a learner's index, to detect defect patterns that may be due to such perimetric inexperience. METHODS: The central visual field was partitioned into 5 concentric zones and averages of deviations from the age-corrected normal threshold values were studied in each zone. The third test session in 74 randomly selected normal subjects provided an experienced reference material. Visual field results typical of normal individuals lacking perimetric experience were represented by the first field test obtained from each of 7 subjects ('learners') from the same group, who showed significant learning during three test sessions. A linear discriminant function, learner's index, was constructed that discriminates between typically experienced and typically inexperienced field results in normals. RESULTS: Average deviation from age-corrected normal threshold increased with increasing eccentricity in the learner's initial fields. Clinical examples illustrate the intended use of the new index. CONCLUSIONS: The learner's index highlights those first field tests from eyes with normal visual fields, that deviate significantly from a normal experienced result in the direction of a learner's result. Patients showing significant learner's index are candidates for repeated visual field testing.
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OBJECTIVE: To study prospectively the effects of perimetric learning in glaucoma patients. PATIENTS AND METHODS: Twenty-five patients with newly detected glaucoma underwent repeated perimetric testing using the 30-2 full threshold program with the Humphrey perimeter. Each patient was tested five times at about 1-week intervals. No patient had undergone perimetry before entering the study. RESULTS: In most patients, visual field results improved with repeated testing. Improvements were obvious in 21 of the 37 glaucomatous eyes. Means of mean deviation values improved significantly, by 2.81 dB (P < .001, analysis of variance), between the first and the second test session, and no significant differences were shown between tests 2 and 5. Fields with moderate field loss improved more than fields with milder or more severe loss. Learning effects were more pronounced peripherally than centrally, and better points improved more than more disturbed ones. CONCLUSIONS: The effects of perimetric learning were large and common, and are clinically important. Baselines for perimetric follow-up of patients with glaucoma should consist of more than one test. To avoid misleading conclusions, studies using perimetry to assess the effects of glaucoma treatment should take learning effects into consideration.
We studied different structural optic disc parameters and their ability to discriminate between normal and glaucoma eyes using computerized raster tomography. Two hundred and seventy-six eyes of 138 normal subjects and 146 eyes of 102 glaucoma patients were examined with a raster tomographic imaging system (The Glaucoma-ScopeTM, Ophthalmic Imaging Systems, Sacramento, CA). Glaucoma eyes were classified into four groups according to their perimetric mean deviation values. Minimum rim width within the 60 degrees and 90 degrees sectors across the vertical meridian, vertical and horizontal cup-disc ratio, rim and cup area were calculated for each optic disc. Receiver operating characteristics curves were set up for comparisons of the different parameters. Representing localised changes of the optic disc, minimum rim width 60 degrees and 90 degrees showed the best separating characteristics with sensitivity values of 91% at a fixed specificity of 90%, followed by vertical cup-disc ratio. Global indices like cup and rim area and horizontal cup-disc ratio showed the poorest separation. These differences were particularly obvious in the group with mild to moderate glaucomatous visual field defects. Thus, global parameters were less likely to detect early focal glaucomatous optic nerve head changes, than parameters representing localised changes.
To study the frequency of diabetic retinopathy in relation to age at diagnosis, treatment, duration of diabetes and glycemic control as measured by means of HbA1c levels, we performed a cross-sectional, registered-based study in the Helsingborg area of southern Sweden, comprising 2232 diabetic patients. Of the known diabetic population < 75 years old, approximately 70% were estimated to be included. We graded retinopathy according to the alternative classification of the Wisconsin study. With an age at diagnosis < 30 years (19% of patients) the prevalence of retinopathy was 64%, whereas with an age at diagnosis > or = 30 years the prevalence of retinopathy was 57% in insulin-treated, and 26% in non-insulin treated patients. Levels of glycated hemoglobin and duration of diabetes were associated with retinopathy in the group with younger onset. In the older-onset group, there was a relationship between retinopathy and duration of diabetes and insulin treatment; glycated hemoglobin had a relationship which was of borderline significance with any retinopathy, but clearly significant with the pooled group: severe non-proliferative, proliferative retinopathy and/or macular edema. Hyperglycemia and duration of diabetes were thus associated with retinopathy in both younger- and older-onset diabetes, but hyperglycemia less so in the older-onset group.
To study the progression of retinopathy in patients with mild diabetes mellitus, we examined, in a cohort study, 347 patients treated with diet alone at baseline. The patients participated in an ophthalmological screening and control programme, and diet-treated patients who were examined between January 1990 and July 1992 were included in the study and followed until October 1995. Mean follow-up was 3.4 +/- 1.1 years. The alternative classification of the Wisconsin study was used to classify retinopathy, and the mean HbA1c values for the study period, to estimate the level of glycaemic control. At baseline, 314 of the patients (90.5%) had no retinopathy, and 33 (9.5%) had mild non-proliferative diabetic retinopathy. In 296 patients there was no retinopathy progression, in 27 patients there was progression by 1 level in the retinopathy scale, and in 24 patients by 2 levels or more. In 2 patients there was progression to proliferative diabetic retinopathy. The mean HbA1c (%) was 6.5 +/- 1.3. Higher HbA1c correlated to increased progression (r = 0.16; p = 0.005), and in a multivariate analysis, HbA1c remained associated with a progression of retinopathy by 2 levels or more, with a relative risk of 1.4 per percent increase in HbA1c (95% CI 1.1-2.0; p = 0.02). Furthermore, the presence of any retinopathy at baseline was associated with progression with a relative risk of 1.7 (95% confidence interval 1.1-2.8; (p = 0.02). These data indicate that even slightly elevated levels of HbA1c might be associated with a risk of retinopathy progression.
We studied the incidence of blindness and visual impairment in patients who were enrolled in a photographic control- and screening program for diabetic retinopathy. The study cohort consisted of 2133 patients examined between January 1990 and December 1992 and followed until October 1st 1995. The occurrence of blindness (visual acuity < or = 0.1) and moderate visual impairment (visual acuity 0.2-0.4) was assessed. The Wisconsin scale was used to grade retinopathy. The mean HbA1c value for the last 8 years was used to represent long-term glycaemic control. Average follow-up time was 2.9 years. Seven patients were blind and 24 had visual impairment caused by retinopathy at the entry of the study. Six patients went blind due to retinopathy during the study period, corresponding to an incidence of 1.0 per 1000 person-years (95% confidence interval 0.4-2.1), and 28 became visually impaired, corresponding to an incidence of 4.6 per 1000 person-years (95% confidence interval 3.0-6.6). Multivariate analysis showed a statistically significant association between blindness/visual impairment and old age, long duration of diabetes, and poor glycaemic control. HbA1c values in the highest quartile, i.e. > or = 8.5%, were associated with a 65% increase in risk of blindness/visual impairment (95% confidence interval 14-130%). Retinopathy was the major cause of blindness and visual impairment in patients with diabetes. The study revealed a low incidence of blindness, which is in line with recent reports. Control of hyperglycaemia may be of value for the prevention of visual loss.