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At least 1,117 records · Page 62Linked to original sources

PubMed1999

Neural networks for visual field analysis: how do they compare with other algorithms?

PURPOSE: To compare the performance of a neural network in identifying visual field defects with the performance of other available algorithms. METHODS: A feed-forward neural network with a single hidden layer was trained to recognize visual field defects previously collected in a longitudinal follow-up glaucoma study, and then tested on fields taken from the same study but not used in the training. The receiver operating characteristics of the network then were compared with the previously determined performance of other algorithms on the same data set. RESULTS: At a specificity greater than 90%, the neural network was more sensitive than any of the available algorithms (although only the global indices were available for comparison, as the cluster and cross-meridional algorithms did not achieve such high specificity at their current settings). At a lower specificity (80-85%), the neural network was unable to attain the high sensitivity of the cluster or cross-meridional algorithms; in fact, the cluster algorithm from the Low-Tension Glaucoma study was significantly more sensitive. CONCLUSION: The receiver operating characteristics of a feed-forward neural network designed to detect visual field defects were explored. At a very high specificity (90-95%) a neural network performed better than the global indices. However, at a lower specificity (78%-88%), the neural network performed worse than cluster and cross-meridional algorithms.

Algorithms↗

PubMed1992

Visual field and grating acuity development in low-risk preterm infants during the first 2 1/2 years after term.

The effect of early visual experience on visual field size and grating acuity development was studied longitudinally in 36 appropriate for gestational age (AGA) and 26 small for gestational age (SGA) low-risk preterm infants. These were selected out of 194 very low birth weight (VLBW) infants (birthweight less than 1500 g) born in 1985 and 1986. Criteria for inclusion as low-risk were the absence of neurological, respiratory, circulatory and alimentary problems in the neonatal period; no retinopathy of prematurity and no evidence of abnormality on the neonatal cranial ultrasound scans. Binocular field sizes were assessed using kinetic arc perimetry. Binocular grating acuity was tested by means of the prototype version of the acuity card procedure. Results were compared with norms obtained in control fullterms in earlier studies. Infants were tested at 6 weeks, 6, 6, 9 and 12 months of age from the expected term date. Twenty-two of these infants were retested at 2 1/2 years of corrected age. Visual field size and visual acuity estimates of (both AGA and SGA) low-risk, VLBW preterms and control fullterms overlapped at all test ages, except for a slight but significantly faster development of the upper and the lower visual field at 6 weeks corrected age in the preterm group. These results indicate that for clinical purposes visual experience before the expected term date has not only no measurable effect on the normal development of behavioural acuity, but also no accelerating effect on the development of peripheral vision.

Child, Preschool↗

PubMed1986

[Planimetric studies of the behavior of the visual field following glaucoma operations].

This article presents the results of functional investigation of the central and peripheral visual fields of 30 patients 3 years after glaucoma surgery. The authors studied the relationship between intraocular pressure and the site of the visual field, and also between vision and the quality of the central visual field. The results of the investigation support the demand for early surgery in glaucoma cases. Patients should be advised and informed thoroughly, because in 36 percent of all cases the cataract grows postoperatively.

Adult↗

PubMed1978

Visual field defects, cup-disc ratio and fluorescein angiography in glaucomatous optic atrophy.

Fluorescein angiography was carried out in 150 glaucoma subjects. Among them 94 subjects were selected to evaluate the correlation between functional loss and the findings of fluorescein angiography in the optic disc. The intensity of fluorescence was assessed in the superficial reticular capillaries and radial epipapillary capillaries. Functional loss was estimated by the visual field defects and cup-disc ratio. A marked decrease in the capillaries was seen in accordance with the increase in the cup-disc ratio. Also, the intensity of fluorescence in the optic disc paralleled the change in the visual field: the greater the deterioration in the visual field, the fewer the capillaries in the optic nerve head and vice versa. The fluorograms of 94 subjects were placed in one out of six groups, i.e. (1) normal, (2) arcuate scotoma, (3) superior or inferior nasal defects, (4) superior or inferior defects, (5) central residue or (6) temporal residue. The common factors correlating the fluorescein angiography in the glaucomatous optic disc with visual field loss were explored in 94 subjects, and it was possible to predict the visual field change from the capillary distribution in the glaucomatous optic disc.

Fluorescein Angiography↗

PubMed2004

Seeing without the occipito-parietal cortex: Simultagnosia as a shrinkage of the attentional visual field.

Following bi-parietal lesions patient AT showed a severe inability to relocate her attention within a visual field which perimetry proved to be near-normal. An experimental approach with tasks testing visuo-spatial attention demonstrated a shrinkage of A.T.'s attentional visual field. With her visual attention narrowed to a kind of functional tunnel vision, the patient exhibited simultanagnosia (Wolpert, 1924), a symptom previously described in 1909 by Balint under the label of Psychic paralysis of "Gaze". In striking contrast AT showed an efficient and effortless perception of complex natural scenes, which, according to recent work in normal subjects, necessitate few if any attentional resources.

Adult↗

PubMed1997

Screening for glaucomatous visual field loss with frequency-doubling perimetry.

PURPOSE: To conduct a preliminary evaluation of the efficacy of the frequency-doubling contrast test as a means of screening for glaucomatous visual field loss. METHODS: Contrast thresholds for frequency-doubled stimuli were obtained under four test conditions: superior hemifield, inferior hemifield, and central (5 degrees radius) targets using a method of adjustment (MOA); superior hemifield, inferior hemifield, and central targets using a modified binary search (MOBS); four quadrant stimuli and the central target using MOBS; and 16 stimuli (four per quadrant) and the central target using MOBS. One eye each of 36 patients with early (12), moderate (12), and advanced (12) glaucomatous visual field loss was tested, as was one eye each of 36 age-matched normal control subjects. RESULTS: For hemifield stimuli, the MOBS test procedure had better test-retest reliability, lower individual variation, and greater separation of the normal population and the population with glaucoma than did the MOA procedure. The use of progressively smaller, more localized stimuli produced successively better separation of glaucomatous and age-matched normal control eyes. Area under the Receiver Operating Characteristic curve was 0.81 for hemifield stimuli (sensitivity and specificity, 70% to 75%), 0.91 for quadrant stimuli (sensitivity and specificity, 83% to 85%), and 0.965 for the 16 stimuli (sensitivity 93%, specificity 100%). Test time was approximately 1.3 minutes for hemifields, 1.5 minutes for quadrants, and 5 minutes for the 16 targets. CONCLUSIONS: Preliminary results indicate that the frequency-doubled contrast test provides a quick, efficient means of screening for glaucomatous visual field loss. Test time is relatively short, test-retest reliability is good, and sensitivity and specificity for detection of glaucomatous visual field loss is very good. The use of the MOBS staircase procedure and small, localized stimuli result in the best performance for screening purposes. An expanded normative database and the use of more rapid suprathreshold screening strategies should enhance further the efficacy of this test.

Adult↗

PubMed2006

Prevalence and causes of visual field loss as determined by frequency doubling perimetry in urban and rural adult Chinese.

PURPOSE: To determine prevalence and causes of visual field loss (VFL) as determined by frequency doubling perimetry in elderly Chinese individuals. DESIGN: Population-based, cross-sectional cohort study. METHODS: The Beijing Eye Study included 4439 of 5324 subjects (83.4%) who were invited to participate with an age of 40+ years. Visual field was assessed by frequency doubling threshold perimetry. Main outcome measure was an abnormal visual field defined as at least one test location of reduced sensitivity. RESULTS: Of the 4439 people who were examined, 4350 subjects (98.0%; 8617 eyes) provided measurement data by frequency doubling perimetry. In subjects aged 40 to 49 years, the most frequent cause for VFL was degenerative myopia followed by glaucoma, other optic nerve diseases, and cataract. In the subjects aged 60 to 69 years, the most frequent cause for VFL was cataract, followed by glaucoma and degenerative myopia. In the subjects aged 70+ years, the most frequent cause for VFL was glaucoma, followed by cataract and degenerative myopia. VFL was associated significantly with age (P < .001), myopic refractive error (P < .001), rural region (P = .001), low level of education (P = .01), degree of nuclear cataract (P < .001), and intraocular pressure (P < .001). CONCLUSION: In contrast to Western countries, age-related macular degeneration and diabetic retinopathy play a minor role as a cause for VFL in China.

Adult↗

PubMed1999

Risk factors for visual field damage progression in normal-tension glaucoma eyes.

BACKGROUND: This study was carried out to evaluate intraocular or systemic factors associated with the visual field damage progression in eyes with normal-tension glaucoma (NTG). PATIENTS AND METHODS: Forty-seven NTG eyes with a minimum follow-up of 5 years were enrolled into the retrospective study. A stepwise regression analysis was performed to correlate the visual field damage progression, expressed as the mean deviation (MD) change per year, with several independent clinical factors including age, history of disc hemorrhage, initial MD, mean intraocular pressure (IOP), peak IOP, diurnal fluctuation of IOP, presence of a beta zone of peripapillary atrophy, and use of Ca(2+)-channel blockers. RESULTS: Statistical analysis revealed that non-use of Ca(2+)-channel blockers (P = 0.01), peripapillary atrophy (P = 0.03) and disc hemorrhage (P = 0.04) were associated with visual loss progression. CONCLUSIONS: Risk factors unrelated to IOP were suggested to be associated with progression of visual field loss. Systemic use of Ca(2+)-channel blockers has a favorable effect on visual field prognosis in NTG eyes.

Adult↗

PubMed2007

Further evidence that Whorfian effects are stronger in the right visual field than the left.

The Whorf hypothesis holds that differences between languages induce differences in perception and/or cognition in their speakers. Much of the experimental work pursuing this idea has focused on the domain of color and has centered on the issue of whether linguistically coded color categories influence color discrimination. A new perspective has been cast on the debate by recent results that suggest that language influences color discrimination strongly in the right visual field but not in the left visual field (LVF). This asymmetry is likely related to the contralateral projection of visual fields to cerebral hemispheres and the specialization of the left hemisphere for language. The current study presents three independent experiments that replicate and extend these earlier results by using different tasks and testing across different color category boundaries. Our results differ in one respect: although we find that Whorfian effects on color are stronger for stimuli in the right visual field than in the LVF, we find that there are significant category effects in the LVF as well. The origin of the significant category effect in the LVF is considered, and two factors that might account for the pattern of results are proposed.

Adult↗

PubMed1990

Representation of the ipsilateral visual field in the transition zone between areas 17 and 18 of the cat's cerebral cortex.

The representation of the visual field in the architectonically defined transition zone between areas 17 and 18 of cat cerebral cortex was assessed by recording the activities and plotting the receptive fields of neurons at 2327 sites along 148 electrode penetrations made in 19 cats. The results show that the transition zone contains a significant representation of the ipsilateral visual hemifield although not all elevations in the visual field are represented to the same extent. The shape of the field region represented resembles an hour glass, for the region represented is narrowest on the 0-deg horizontal meridian and increasingly wider at progressively more positive and negative elevations. When receptive-field centers are considered, the extent of the representation reaches to -2.5 deg on the 0-deg horizontal meridian and to 10 or more degrees towards the field periphery. When receptive-field areas are considered, the representation at the 0-deg horizontal meridian extends to -3.6 deg and to beyond 20 deg at other elevations. In contrast, the visual-field representations in flanking areas 17 and 18 are essentially limited to the contralateral hemifield. The presence of a distinct representation of part of the ipsilateral hemifield in the transition zone suggests that the zone may have connections distinctly different from those of the adjacent areas. The observations bear on the problems of understanding the visual pathways in hypopigmented cats and binocular disparity mechanisms about the midline.

Animals↗

PubMedDate not supplied

Stimulus configuration and location in the visual field affect appetitive responses by the praying mantis, Sphodromantis lineola (Burr.).

Adult female praying mantises, Sphodromantis lineola (Burr.), were presented with computer-generated black rectangular stimuli that moved horizontally or vertically at 82 deg/s against a homogeneous white background. Both stimulus configuration (orientation in relation to direction) and the retinal location of the stimulus image affected the rate at which mantises responded appetitively (approached or struck at the stimulus). Mantises responded most to square stimuli (12.5 deg x 12.5 deg) when they moved horizontally or vertically through, or horizontally at 24.5 deg below the center of their visual field. Mantises also responded most to vertically (vs. horizontally) oriented rectangular stimuli (12.5 deg x 47 deg) that moved through their visual-field center, irrespective of whether the stimuli moved downward or horizontally. Upward moving stimuli elicited intermediate amounts of behavior with no configuration preference. Mantises did not demonstrate a configuration preference when rectangular stimuli moved > or = 24.5 deg outside of the visual-field center. Furthermore, mantises responded very little and demonstrated no configuration preferences to stimuli that moved less than approximately 83 deg through their visual field even if the stimuli moved through the visual-field center.

Animals↗

PubMed1994

[The relationship between stereoacuity and contracted visual field].

The stereoacuity (SA) was measured by means of the Titmus test, Random Dot E stereotest and Yan's stereoscopic test charts in 90 cases of glaucoma or retinitis pigmentosa with visual field contraction and 28 normal subjects. Significant reduction in SA was observed in all patients with contracted visual field, and markedly so (> 130") in cases with bilateral or unilateral tubular vision. The SA was reduced with visual field loss of over 30% and there was a positive correlation between the SA reduction and the area of visual field loss.

Adolescent↗

PubMed1995

Effects of instruction on a divided visual-field task of face processing.

The purpose of the present study was to document that instruction effects can occur on tasks typically yielding left visual-field advantages. In a lateralized face-recognition task, 40 right-handers (20 men, 20 women) had to memorize pairs of faces and to respond to a probe face displaying positive or negative emotion and presented for 100 msec. 3.8 degrees on the left or right of a fixation cross. Half of the subjects had been instructed to learn the faces through a verbal strategy and the other half through an imagery strategy. Analysis of reaction times yielded significant complex interactions involving gender, coding instruction, visual field, and emotion for both Yes and No responses. A global left visual-field advantage was obtained in the analyses of accuracy and sensitivity data, but no significant effects were recorded in the analysis of decision rule. Thus, the instruction effects on left visual-field advantages were obtained through complex interactions on reaction times only. Further replication of these data would provide a more secure basis for causal interpretations.

Attention↗

PubMed1991

Visual-field map in the callosal recipient zone at the border between areas 17 and 18 in the cat.

The representation of the visual field in the callosal fiber recipient zone of area 17 and the adjacent area 17/18 transition zone was determined in the cat. The callosal fiber recipient zone was identified by anterograde transport of tritiated amino acids that had been injected into transcallosal sending zone of the opposite hemisphere. Application of autoradiographic procedures revealed that transcallosal projections are densest in the area 17/18 transition zone, and that their density in area 17 diminishes within 1-2 mm of the transition zone. Of 980 sites sampled in the visual-field mapping part of the study, 507 proved to be in the zone demarcated by transcallosally transported label. In this zone, both ipsilateral- and contralateral-field positions are represented, and the representation of the visual field at the different elevations is not equal. When ipsilateral-field positions are considered, the representation extends to about 4 deg close to the visual axis, and to 15-20 deg at elevations greater than +/- 30 deg, the representation is approximately mirror-symmetric about the horizontal meridian, and the representation is concordant with that of the representation in the area 17 transcallosal sending zone of the opposite hemisphere.

Animals↗

PubMed1976

Iconic recognition of musical symbols in the lateral visual fields.

Subjects with formal musical training were tested tachistoscopically in order to obtain thresholds for recognizing single notes a staff, presented successively to the lateral visual fields. They were also tested on backward visual making of the same stimuli to determine the interstimllus interval needed to escape the masking effect (critical ISI). Response requirements in threshold and ISI conditions were nonverbal (depressing an organ key), or verbal (indicating the stimulus by name). Recognition threshold for notes were lower in the right visual field than in the left, and verbal responses were easier than manual responses in the threshold condition. However, critical ISIs were lower in the left field than in the right, and ISIs from the left visual field were lower with manual responses than with verbal responses. These findings support the idea that (a) threshold and ISI represent separate levels of perceptual processing, and (b) in trained subjects, the ability to recognize musical symbols may be governed by the left hemisphere, while the information-processing stage of iconic storage may occur in the right hemisphere.

Adolescent↗

PubMed1997

Variation of topographic visually evoked potentials across the visual field.

We examined the variation of monocular pattern reversal topographic visually evoked potentials across a 13.6 degrees visual field and measured the parameters of the VEP waveforms in 37 locations across the field. Eighteen right and 20 left normal eyes were tested from 23 subjects. The mean response densities of the VEP decreased with increasing eccentricity; response densities are higher in the lower hemifield than in the corresponding mirror symmetric locations in the upper hemifield. The incidence of polarity reversal is higher in the upper hemifield, especially in more superior locations. The latency in the temporal field is shorter than that in the other locations. The coefficients of variations (CVs) of latencies are less than those of amplitudes in corresponding locations and the CVs of latencies of P1 and N2 components are less than those of the N1 component in corresponding locations. The CVs of amplitudes of the waveforms in mid-peripheral locations are larger than those of the other central areas. The parameters of the human topographic visually evoked potential are distributed regularly across the visual field and appear to reflect the underlying anatomy of the retina and visual cortex, and the placement of the recording electrode.

Adolescent↗

PubMed1998

Functional hemianopias on Humphrey visual field analysis.

We report two cases of uniocular hemianopia that we first detected on Humphrey visual field analysis, with one patient having additional constriction of his peripheral visual fields bilaterally. These field defects were confirmed to be functional in nature after characteristic changes on Goldmann perimetry and spontaneous improvement towards normal. This type of functional field loss is rare and the unusual pattern on computerised perimetry should be recognised for managing the patient appropriately.

Adult↗

PubMed1999

Representation of the visual field in the human occipital cortex: a magnetic resonance imaging and perimetric correlation.

OBJECTIVES: To evaluate the retinotopic map of the human occipital cortex by correlating magnetic resonance imaging (MRI) findings with visual field defects in patients with occipital lobe infarcts and to assess the compatibility between our cliniconeuroimaging findings and the location of lesions predicted by the classic Holmes map and a revised map. METHODS: Magnetic resonance images were obtained in 14 patients with occipital lobe infarcts. Visual field analysis was performed with tangent screen, the Goldmann perimeter, and the Humphrey Field Analyzer. Based on the pattern of visual field deficit, the location of the lesion in the mesial occipital lobe in each patient was predicted using the Holmes map and other retinotopic maps of the occipital cortex. The predicted location of the lesion was then compared with its actual location shown on MRI to assess the compatibility between our data and the other maps. These maps determine retinotopic correlates of the medial occipital lobe, but they cannot establish correlates of the striate cortex (V1). The medial occipital representation of central vision was evaluated by regression analysis. RESULTS: The MRI correlations in this study confirmed gross estimates of the retinotopic organization of the occipital cortex. However, our findings did not correlate exactly with the Holmes map. We determined that the central 15 degrees of vision occupies 37% of the total surface area of the human medial occipital lobe. Based on our data, a refined retinotopic map is presented. CONCLUSIONS: The resolution of conventional MRI testifies to its considerable value in localizing occipital lobe lesions. Our findings support, and refine, the Holmes map of the human occipital cortex.

Adolescent↗