Test-retest variability of frequency-doubling perimetry and conventional perimetry in glaucoma patients and normal subjects.
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PURPOSE: To compare the test-retest variability characteristics of frequency-doubling perimetry, a new perimetric test, with those of conventional perimetry in glaucoma patients and normal control subjects. METHODS: The study sample contained 64 patients and 47 normal subjects aged 66.16+/-11.86 and 64.26+/-7.99 years (mean +/- SD), respectively. All subjects underwent frequency-doubling perimetry (using the threshold mode) and conventional perimetry (using program 30-2 of the Humphrey Field Analyzer; Humphrey Instruments, San Leandro, CA) in one randomly selected eye. Each test was repeated at 1-week intervals for five tests with each technique over 4 weeks. Empirical 5th and 95th percentiles of the distribution of threshold deviations at retest were determined for all combinations of single tests and mean of two tests, stratified by threshold deviation. The influence of visual field eccentricity and overall visual field loss on variability also were examined. RESULTS: Mean test time with frequency-doubling perimetry in patients and normal control subjects was 5.90 and 5.25 minutes, respectively, and with conventional perimetry was 17.20 and 14.01 minutes, respectively. In patients, there was a significant correlation between the results of the two techniques, in the full field and in quadrants, whereas in normal subjects there was no such correlation. In patients, the retest variability of conventional perimetry in locations with 20-dB loss was 120% (single tests) and 127% (mean tests) higher compared with that in locations with 0-dB loss. Comparative figures for frequency-doubling perimetry were 40% and 47%, respectively. Variability also increased more with threshold deviation in normal subjects tested with conventional perimetry. In both patients and normal subjects, variability increased with visual field eccentricity in conventional perimetry, but not in frequency-doubling perimetry. Both techniques showed an increase in variability with overall visual field damage. CONCLUSIONS: Frequency-doubling perimetry has different test-retest variability characteristics than conventional perimetry and may have potential for monitoring glaucomatous field damage. (+info)
Between-algorithm, between-individual differences in normal perimetric sensitivity: full threshold, FASTPAC, and SITA. Swedish Interactive Threshold algorithm.
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PURPOSE: To determine the between-algorithm differences in perimetric sensitivity for the Swedish Interactive Threshold algorithm (SITA) Standard, SITA Fast, FASTPAC, and Full Threshold algorithms; to determine the between-subject, between-algorithm differences in the magnitude of the normal variation in sensitivity. METHODS: The sample comprised 50 normal subjects (mean age, 52.9 +/- 18.5 years) experienced in automated perimetry. One randomly assigned eye was examined at three visits with Program 30-2 of the Humphrey Field Analyzer (HFA). The first visit was a familiarization session. A two-period crossover design with order randomization within visits was used over the second and third visits. SITA Standard, SITA Fast, and HFA 640 Full Threshold were administered during one visit. FASTPAC and HFA 750 Full Threshold were administered during the remaining visit. RESULTS: Group mean Mean Sensitivity was 0.8 dB higher for SITA Standard than for Full Threshold (P < 0.001) and 1.3 dB higher for SITA Fast than for Full Threshold (P < 0.001). A similar trend was found between SITA and FASTPAC. The group mean Mean Sensitivity for SITA Fast was 0.5 dB higher than for SITA Standard (P < 0.001). The pointwise between-algorithm difference in sensitivity was similar for all algorithms. The pointwise between-algorithm, between-subject variability was lower for SITA. The examination durations for SITA Fast and SITA Standard were half those for FASTPAC and Full Threshold; SITA Fast was 41% that of SITA Standard (P < 0.001). CONCLUSIONS: SITA produced marginally higher mean mean sensitivity compared with that of existing algorithms and markedly reduced examination duration. The reduced between-subject variability of SITA should result in narrower confidence limits for definition of normality. (+info)
Looking behind a pathological blind spot in human retina.
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Recent work suggests that dichoptic lateral interactions occur in the region of the visual field of one eye that corresponds to the physiological blind spot in the other eye (Tripathy, S. P., & Levi, D. M. (1994). The two-dimensional shape of spatial interaction zones in the parafovea. Vision Research, 34, 1127-1138.) Here we ask whether dichoptic lateral interactions occur in the region of the visual field of one eye that corresponds to a pathological blind spot, a retinal coloboma in the other eye. To address this question we had the observer report the orientation of a letter 'T' presented within this region in the presence of flanking 'T's presented to the other eye around the coloboma. A large drop in performance was seen due to the flanks, showing the existence of dichoptic lateral interactions in this monocular region. The presence of these dichoptic interactions in a region lacking direct retinal afferents from one eye is consistent with the proposition that long-range horizontal connections of the primary visual cortex mediate these interactions. (+info)
Does visual sensitivity improve between 5 and 8 years? A study of automated visual field examination.
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In 74 normal subjects (62 children aged 5-8 years and 12 adults), we tested the widely-held belief that visual sensitivity improves substantially during childhood. Maturation of the retino-striate pathways is generally invoked to account for age-related changes in visual sensitivity. We evaluated the extent to which attentional factors unduly emphasized the effect of age on the purely physiological mechanisms. After a specially-designed familiarization procedure, sensitivity was fully evaluated at two locations in the superior temporal field using a bracketing technique (Octopus 2000R). False-positive (FP) and false-negative (FN) catch-trials were interspersed with the sequence of stimuli. Analyses demonstrated that: (1) age affected sensitivity; and (2) the general level of attentiveness varied not only with age, but also among subjects in the same age group. We then estimated the extent to which improved visual sensitivity may reflect a concomitant evolution of vigilance. Firstly, controlled variance analyses indicated that factors for evaluating attentiveness (rate of FN responses, slope of the psychometric function at the median, and goodness of fit) were indeed much better predictors than age of the sensitivity measured. Secondly and more significantly, the grouping of subjects into homogeneous subgroups, on the basis of their attentional performance, showed that children as young as 5 years may have a visual sensitivity that is only marginally lower than that of adults. (+info)
Models for the description of angioscotomas.
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To describe small scotomas in visual field examinations several statistical models are proposed and applied to the evaluation of angioscotoma in 13 ophthalmologically normal subjects. A special perimetric grid is used where thresholds can be estimated along a line of narrow-spaced test points which crosses the predicted location of the retinal vessel. A two-stage analysis employs single estimations to fit a threshold curve by means of a special parametric description of the luminance difference sensitivity threshold as a function of stimulus position. An alternative model incorporates the threshold as a function of position into the probabilistic description of the binary response (stimulus seen/not seen). (+info)
Angioscotoma detection with fundus-oriented perimetry. A study with dark and bright stimuli of different sizes.
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Fundus-oriented perimetry (FOP) was used to evaluate the effectiveness of different-sized bright and dark stimuli in detecting and quantitatively measuring angioscotoma. The foveolas and optic disks of digitized fundus images were aligned with their psychophysical counterparts to construct individual grids of perimetric stimuli. Each grid included a linear set of test point locations crossing a retinal vessel. Angioscotomas immediately became visible in nine of 13 healthy normal volunteers tested with FOP. Additional mathematical processing of local loss of differential light sensitivity (dls) disclosed an angioscotoma for at least one stimulus condition in all persons tested. The angioscomas were usually deeper for small (12) targets than for large (32') ones. On the other hand, the overall noise at dls thresholds was generally higher for small than for large stimuli regardless of whether the stimuli were bright or dark. No noteworthy differences were found in detection rates or signal-to-noise ratios under different stimulus conditions (dark/bright/small/large). FOP permits the individual arrangement of stimuli for specific morphological conditions and is thus capable of detecting even minute visual field defects such as angioscotomas. (+info)
Preperimetric glaucoma diagnosis by confocal scanning laser tomography of the optic disc.
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AIM: To evaluate the ability of confocal scanning laser tomography of the optic nerve head to detect glaucomatous optic nerve damage in ocular hypertensive eyes without visual field defects. METHODS: The study included 50 normal subjects, 61 glaucoma patients with glaucomatous changes in the optic disc and visual field, and 102 "preperimetric" patients with increased intraocular pressure, normal visual fields, and glaucomatous appearance of the optic disc as evaluated on colour stereo optic disc photographs. For all individuals, confocal scanning laser tomographs of the optic nerve head were taken using the Heidelberg retina tomograph (HRT; software 2.01). RESULTS: Almost all investigated HRT variables varied significantly (p < 0.05) between the normal eyes and preperimetric glaucoma eyes with pronounced overlap between the two study groups. Corresponding to the overlap, sensitivity and specificity values were relatively low when HRT variables were taken to differentiate between normal and preperimetric glaucoma eyes. At a given specificity of 95% highest sensitivities were found for the variables "rim area in the superior disc sector" (24.8%), "nerve fibre layer thickness in the inferior disc sector" (26.5%), and "rim volume in the superior disc sector" (25.5%). A multivariate approach increased sensitivity to 42.2% at a given specificity of 95%. For the glaucoma group highest sensitivity values were reached by rim volume in the superior disc sector (73.8%) and rim area (72.1%); the multivariate approach reached 83.6%. CONCLUSIONS: Owing to pronounced overlapping between the groups, confocal scanning laser tomography of the optic nerve head has relatively low diagnostic power to differentiate between normal eyes and preperimetric glaucoma eyes. One of the reasons may be the biological interindividual variability of quantitative optic disc variables. (+info)
Measurement of retinal nerve fibre layer by scanning laser polarimetry and high pass resolution perimetry in normal tension glaucoma with relatively high or low intraocular pressure.
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AIMS: To determine whether any differences may exist in the relation between the neural capacity as determined by high pass resolution perimetry and the thickness of the retinal nerve fibre layer (RNFL) in patients having normal tension glaucoma (NTG) with a relatively high intraocular pressure (IOP) between 16 and 21 mm Hg (HNTG) v those with a lower IOP below 15 mm Hg (LNTG). METHODS: Scanning laser polarimetry and high pass resolution perimetry were performed in 20 eyes of 20 patients with HNTG and 21 eyes of 21 patients with LNTG. The correlation between total and regional thickness of the peripapillary RNFL and the corresponding total and regional neural capacity with linear regression analysis were evaluated. RESULTS: Overall, although the total RNFL thickness was not significantly correlated with the total neural capacity, the RNFL thickness in each of the superior and inferior quadrants was significantly correlated with the corresponding regional neural capacity (r = 0.44, p = 0.0045; r = 0.39, p = 0.0126 for each). The RNFL thickness in each of the superior and inferior quadrants in the HNTG group was significantly correlated with the corresponding regional neural capacity (r = 0.52, p = 0.0196; r = 0.49, p = 0.0286 for each). No significant correlation between neural capacity and the RNFL thickness was observed either globally or regionally in the LNTG group. CONCLUSION: The degree of the correlation between neural capacity as determined by high pass resolution perimetry and thickness of the RNFL as measured by scanning laser polarimetry appeared to differ in NTG patients with an IOP higher than 15 mm Hg v those with a lower IOP. (+info)