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Biomedical subjects

A Heijl

Publications and source records attributed to A Heijl.

At least 19 recordsLinked to original sources
PubMed1992

Glaucoma Hemifield Test. Automated visual field evaluation.

We have developed an algorithm, the Glaucoma Hemifield Test (GHT), for automated evaluation of single static threshold visual field test results in glaucoma. The GHT uses empirically determined limits of normality for up-down differences in the Statpac probability maps of the Humphrey Field Analyzer to detect localized visual field loss. It is also constructed to detect field loss that is symmetric around the horizontal meridian. Analysis is done in five corresponding pairs of sectors that are based on the normal anatomy of the retinal nerve fiber layer. Deviations from the age-corrected normal threshold in the most sensitive portions of the visual field are used to detect general reductions of sensitivity or abnormally high sensitivities. The GHT provides brief visual field evaluations printed on the field chart as plain text. The aim of this article is to describe the fundamentals of the analysis program and to provide clinical examples.

Adult↗
PubMed1992

Evaluation of methods for automated Hemifield analysis in perimetry.

A new aid to perimetric analysis, the Glaucoma Hemifield Test, primarily evaluates up-down differences in automated static visual field tests. We analyzed the visual fields of 163 eyes of 163 normal subjects and 77 eyes of 77 patients with glaucoma diagnosed on bases other than perimetry using the Glaucoma Hemifield Test and a similar, previously developed, hemifield analysis method. The performance of the Glaucoma Hemifield Test was compared with that of the earlier method and the differences in test design were evaluated individually. The Glaucoma Hemifield Test allowed significantly improved separation between the normal group and the group with glaucoma than did the earlier method. This improvement was due to an increase in sensitivity, and was associated with the use of test point significances instead of threshold values, and a large normal database alone in the determination of normal limits.

Adult↗
PubMed1992

Weighting according to location in computer-assisted glaucoma visual field analysis.

In recent years several aids for automated interpretation of visual field data have been suggested. We believed that incorporation of thorough knowledge of normal visual field variability would allow improvements in the performance of such aids since more attention would be paid to field results in areas with low physiological variability. Two visual field models for classification of fields in glaucoma based on comparisons of sensitivity values in the upper and lower hemifields and on analysis of test point clusters with diminished sensitivity were compared. Both models were constructed using logistic regression analysis in 101 normal eyes and 101 eyes with glaucoma. The first, more traditional model assumed Gaussian distributions of deviations from age-corrected normal thresholds and constant variability across the field (non-weighted model). The second model took into account empirically determined variability of pointwise threshold results and of cluster volumes in various visual field regions (weighted model). The two models were subsequently tested on an independent material of 163 normal eyes and 76 eyes with glaucoma. The weighted model gave significantly better classification of the fields in both materials. Accounting for physiological threshold variability can offer significant advantages in the construction of perimetric analysis aids for detection of glaucoma.

Adult↗
PubMed1992

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.

Adult↗
PubMed1989

Test-retest variability in glaucomatous visual fields.

We measured test-retest variations in computerized visual fields from glaucomatous eyes. Fifty-one patients were tested four times within a four-week period; the severity of disease varied from incipient to advanced. We determined the dependence of threshold variability on defect depth and test point location. In areas of the visual field initially found to have moderate loss of sensitivity, variation in follow-up measurements ranged from normal sensitivity to absolute defect, with little dependence on distance from fixation. Conversely, large changes were considerably more unusual in locations initially showing normal or near-normal sensitivities, and variability was lowest in the most central portion of the field. Our findings suggest that differentiation between true progression and random variation will be facilitated if these factors are taken into account, as well as if comparisons are based on more than two tests. The complex nature of interest variation in glaucoma makes it natural to approach this problem with the help of computer-assisted analyses.

Adult↗
PubMed1989

The effect of perimetric experience in normal subjects.

Two groups of normal subjects were submitted to repeated automated static threshold perimetry. Perimetric results were strongly affected by the level of experience in some subjects; in the majority, however, the effect of experience was small. Initial field tests often showed high numbers of depressed points. Sensitivity increased with perimetric training, particularly between the first sessions. Those subjects who improved most started low, gradually approaching normal levels with experience. Learning effects were more pronounced peripherally than paracentrally and "untrained" fields characteristically showed concentric contraction with numerous points with low sensitivity peripherally. An important practical conclusion is to allow repeated testing of all inexperienced patients in whom initial fields do not agree with clinical findings. A chart showing a concentrically narrowed field should be viewed with particular suspicion. Furthermore, a single initial field may constitute an inadequate baseline for clinical follow-up.

Adult↗
PubMed1989

A clinical study of perimetric probability maps.

Perimetric probability maps depict visual field results in terms of the frequency with which the measured findings are seen in a normal population. We tested clinically the importance of the model of the normal visual field used to calculate such maps. Forty-one eyes of 41 normal subjects and 58 eyes of 46 glaucomatous patients were studied. Probability maps were calculated by means of two different models of the normal visual field. The first model assumed gaussian threshold distributions with constant variability across the field. The second used empirically determined nongaussian location-dependent threshold distributions. Probability maps using the empiric model allowed better separation between glaucomatous and normal eyes, and the number of significant points in normal subjects was in better agreement with the theoretically expected number. The gaussian model yielded an unacceptably high frequency of significant points in normal fields, particularly in the midperiphery. The clinical usefulness of perimetric probability maps depends critically on the choice of normal visual field model.

Adult↗
PubMed1989

Visual field interpretation with empiric probability maps.

Automated visual field charts may be difficult to interpret partly because of the magnitude and complex nature of normal threshold variability. We devised two types of empiric probability maps in which this variability is taken into account and the significances of measured threshold values are displayed. These maps are highly sensitive to nonobvious but significant paracentral field loss but will at the same time deemphasize false-positive patterns commonly found more peripherally. They also frequently show field defects before these are obvious in conventional threshold printouts. In addition, they differentiate between generalized loss of sensitivity and localized field defects.

Cataract↗
PubMed1989

Effect of IOP on the visual field in ocuLar hypertension and glaucoma.

The traditional opinion that increased intraocular pressure is the cause of glaucoma is controversial, probably mainly because of the fact that firm evidence for the value of pressure reduction is largely lacking. The present article reviews results from short term studies of visual fields before and after pressure reduction. It also reviews published and unpublished preliminary results from studies addressing the problem of whether the long term visual field prognosis, in glaucoma and in ocular hypertension, is affected by pressure lowering therapy. There is no convincing agreement among results from modern studies using computerized perimetry indicating that acute lowering of the ocular tension results in an improvement of the glaucomatous visual field. Long-term result are equally conflicting, and often negative. We have noted from a preliminary analysis of our own masked, prospective study of patients with 'high risk' ocular hypertension, that the same results may be interpreted in quite different ways. The results of available studies certainly indicate that pressure reduction does not automatically lead to clear and positive effects on the visual field. The studies have often been small, however, and have usually not had the power of detecting small effects of treatment. Also, pressure reduction has usually not been dramatic and many treated patients have maintained 'elevated' pressure levels. Patients with very high pressures have not been included, and the effect of pressure reduction in this situation has therefore not been investigated at all. More controlled, prospective therapeutic studies are necessary and ethical. It seems particularly important to study the long-term effects of non-pharmacologically induced pressure reduction in patients with manifest field loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Glaucoma↗
PubMed1989

Computerized perimetry in glaucoma management.

The present article discusses the role of computerized perimetry in the management of patients with suspect and manifest glaucoma. The value of visual field examination is compared to that of inspection and photography of the optic disc and to some extent to retinal nerve fibre layer photography. Computerized perimetry is related to standard manual visual field examination. Guidelines are offered for the choice of test programs and for the interpretation of results.

Computers↗
PubMed1989

Lack of diffuse loss of differential light sensitivity in early glaucoma.

We studied the differential light sensitivity in 83 patients who were prospectively followed with computerized threshold preimetry and optic disc pathography because of suspect glaucoma. Eyes with media opacities were excluded from the analysis. Fourteen eyes developed progressive optic disc cupping and/or localized visual field loss. In this glaucoma group light sensitivity in the 10 best points in the visual field did not deviate more from estimated age-corrected standard values than in the remaining groups of 115 eyes with increased intraocular pressure and 18 normotensive eyes. The results do not support the concept that diffuse loss of differential light sensitivity should be common in early glaucoma.

Follow-Up Studies↗
PubMed1989

Normal visual fields as assessed by computerized static threshold perimetry in patients with untreated primary hypothyroidism.

In this prospective study, 25 consecutive patients with untreated primary hypothyroidism were tested with a highly sensitive perimetric technique, since a high prevalence of visual field defects has been described in this condition. All patients had clinical hypothyroidism, a serum TSH value greater than 20 mU/l (reference range 0.4-4.0) and decreased/low normal serum total T4 concentration. Visual fields were tested with fully automated threshold-measuring computerized perimetry of the central 30 degrees field. Interpretation of fields included computer-assisted analysis provided by a perimetric statistical programme package. In 23 patients, conventional inspection and computer-assisted analysis showed no visual field defects. Two patients were excluded from the latter analysis: one patient who did not respond adequately at computerized perimetry and in whom manual field tests were entirely normal: one patient who had low sensitivity values in the uppermost parts of both visual fields owing to markedly swollen upper eye lids. In conclusion, although pituitary hyperplasia has been well documented in primary hypothyroidism, the present prospective study clearly indicates that visual field defects are not a common finding in patients with this disease.

Adult↗
PubMed1989

Diagnosis of early glaucoma with flicker comparisons of serial disc photographs.

We evaluated flicker comparison, a technique for detecting differences in serial fundus photographs. Serial optic disc photographs and computerized threshold visual fields were obtained every 3 months for an average of 40 months in 131 eyes of 81 patients with elevated intraocular pressure and normal visual fields. Two serial monophotographs were projected, optically aligned, and superimposed; analysis was done by alternately viewing first one and then the other image. We found flicker analysis of serial disc photographs to provide results which were closely correlated with those of computerized threshold perimetry. Thus, of those 12 eyes which developed field defects, eight showed definite change and two showed highly suspected change in optic disc configuration. Only two eyes showed a definite alteration in optic disc anatomy without the development of field loss, and field defects appeared in only one of 109 eyes in which there was no change or suspected change on flicker comparison. The flicker method was more sensitive than conventional nonflickered comparisons, but changes could usually be seen also with conventional inspection once they had been detected by the flicker method. Our findings suggest that flicker analysis may offer a considerable improvement over current standard methods of analyzing serial photography and may be a useful complement to routine perimetry. However, this method requires special equipment; requires that the photographs be similarly centered; and is time-consuming. Alignment of photographs by means of computerized image analysis techniques could make the method clinically practicable.

Diagnosis, Differential↗
PubMed1988

Evaluation of adaptive spatial enhancement in suprathreshold visual field screening.

Sixty-three normal subjects and 94 abnormal patients, most of whom had glaucoma, were tested in the central visual field using a threshold-related, eccentricity-compensated, spatially adaptive suprathreshold screening program and a full-threshold program on the Humphrey field analyzer. The initial stimulus locations on the screening test were identical to those of the threshold test; additional screening stimuli were presented surrounding each missed initial stimulus. Surprisingly, this spatial enhancement strategy did not improve sensitivity or specificity rates of the screening beyond that achieved by considering the initial stimulus locations alone. Points missed during screening often showed a depressed sensitivity rate (measured threshold greater than 6 dB below the age-corrected normal reference value) in the same area of the threshold field. This was true in fields from abnormal and normal subjects. This finding of persistent shallow defects in the same test session among otherwise normal persons has disturbing implications for the importance of "confirmed" defects in the diagnosis of disease.

Adolescent↗