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At least 235 records · Page 13Linked to original sources

PubMed2006

On-line attentional selection from competing stimuli in opposite visual fields: effects on human visual cortex and control processes.

We used fMRI to investigate competition and on-line attentional selection between targets and distractors in opposite visual hemifields. Displays comprised a high-contrast square-wave grating, defined as target by its orientation, presented alone (unilateral) or with a similar distractor of orthogonal orientation in the opposite hemifield (bilateral displays). The target appeared unpredictably on the left or right, precluding anticipatory attention to one side. We found greater activation in target-contralateral superior occipital gyrus for unilateral than for bilateral displays, indicating suppression of the target's visual representation by distractor presence despite the competing distractor projecting to a different occipital hemisphere. Several frontal and parietal regions showed greater activation for bilateral than unilateral trials, suggesting involvement in on-line attentional selection. This was particularly pronounced for regions in bilateral intraparietal sulcus (IPS), which also showed greater functional coupling with occipital cortex specifically on bilateral trials that required selection plus some repetition-suppression effects when target side was repeated, but again only on bilateral trials requiring selection. Our results indicate that competition between visual stimuli in opposite hemifields can influence occipital cortex, and implicate IPS in resolution of this competition by selection.

Adult↗

PubMedDate not supplied

Multifocal magnetoencephalogram applied to objective visual field analysis.

PURPOSE: To establish an objective visual field analysis by visual evoked magnetic fields. METHODS: Forty-eight focal areas of the visual field were stimulated by the visual evoked response imaging system (VERIS). The multifocal visual evoked magnetic fields (mfVEFs) of 11 healthy subjects were recorded. The output signals were recorded with VERIS, and the second-order kernel was calculated. The equivalent current dipoles (ECDs) were estimated, and the relative positioning of ECDs was determined by a magnetoencephalography (MEG) system. RESULTS: The mfVEFs consisted of either two- or three-peak waves. Large amplitude mfVEFs were elicited when the stimulus was confined to 6 degrees of the central visual field, but a strong response could not always be obtained between 6 degrees and 12 degrees. All ECDs were estimated to originate in the occipital striate cortex. The ECDs for the upper (lower) field stimulations were estimated to be on the lower (upper) cortex, while those for right (left) field stimulations were on the left (right) cortex. CONCLUSIONS: The locations of mfVEF peak ECDs were correlated with the stimulated visual field and generally matched the cruciform model. In combination with the multifocal technique, MEG can be used for objective visual field analysis.

Adult↗

PubMed1997

Apparent glaucomatous visual field defects caused by dermatochalasis.

We have studied the effects of dermatochalasis on Humphrey automated perimetry of the central 24 degrees visual field. Fifteen visual fields of 9 ocular hypertensive patients (18 eyes) were found to be incongruous with their apparently healthy optic discs. Examination revealed dermatochalasis, which was felt to be responsible for the field defects. This was confirmed by reversal of the defects on repeating the field test (programme 24-2) with the redundant upper lid skin taped up, or in 2 cases following blepharoplasty. The defects always involved the superior visual field. The deepest and largest defects were sited in the supero-temporal quadrant in 13 of the 15 affected fields and the supero-nasal quadrant in 2 fields. The most common pattern was a temporally skewed defect which reflected the tendency of the loose upper lid skin to be greater in extent temporally than nasally. In 7 fields the supero-temporal defect extended to fuse with the blind spot, mimicking a superior arcuate scotoma. Temporal extension of the field defects below the horizontal meridian occurred in 5 fields. In cases where visual field testing was repeated without taping up the lid inter-test fluctuation in scotoma size and depth was observed, although the position of scotomas when present within the visual field remained constant. We conclude that dermatochalasis has the potential to confound diagnostic automated visual field testing for glaucoma.

Aged↗

PubMed1980

The distribution of interhemispheric projections in area 18 of the cat: coincidence with discontinuities of the representation of the visual field in the second visual area (V2).

In normal adult cats three regions with callosal projections from the contralateral visual areas 17, 18, and 19 have been identified at the lateral border of area 18 by degeneration techniques (Sanides, 1978). The visuotopic distribution of these callosal patches has now been investigated by combining anatomical with physiological techniques. The centers of the receptive fields recorded in the callosal patches are located on or close to the vertical meridian in the contralateral hemifield reaching eccentricities of about 15 deg. Some of these fields are of extraordinary size crossing the vertical meridian and covering large areas of the ipsilateral hemifield. On the other hand, receptive fields recorded from the acallosal parts of lateral area 18 may reach eccentricities of more than 50 deg. Thus, the callosal patches of lateral area 18 are wedged in between parts of lateral area 18 which represent the periphery of the contralateral hemifield. It is concluded that the retinotopic arrangement at lateral area 18 (the second visual area) distinguishes this area fundamentally from area 17, the primary visual area.

Animals↗

PubMed2002

Sensitivity differences between real-patient and computer-stimulated visual fields.

PURPOSE: The authors sought to verify computer simulation of visual fields by comparing thresholds of real and corresponding simulated visual fields. METHODS: Four patients with stable glaucomatous visual fields and three patients with progressing glaucomatous visual fields were chosen for the study. Visual fields had been recorded at 6-month intervals for 5 to 7.5 years. A previously described computer simulation program was used to generate a corresponding simulated visual field for each of the real fields. Twenty different levels of response variability and long-term variability were used in the simulations. Pointwise sensitivity differences between real and simulated fields were calculated. The average difference and 95% interval of the differences were analyzed for the different simulation conditions, for the pointwise sensitivities in the real patient fields, and to determine whether the field was stable or progressing. RESULTS: In almost all simulation conditions, the average pointwise sensitivity differences ranged from -1 to 1 dB and were not significantly different among different simulation conditions. The 95% interval of the average difference increased significantly with response variability, whereas long-term variability failed to show any apparent effect. Average pointwise differences and the 95% intervals were greatest in locations where the real-patient field had reduced sensitivity of 14 dB or worse. CONCLUSION: The simulation program provided good estimates of visual field sensitivities. Increasing amounts of response, but not long-term variability, produced a linear increase in the variability of threshold sensitivities. This finding implies that short-term rather than long-term fluctuation is the most important factor determining the variability of thresholds.

Aged↗

PubMed2002

[The study on binocular visual field summation and its possible mechanism].

PURPOSE: To observe the summation effect of binocular visual field in persons with normal or abnormal visual field and study the validity of four kinds of theory (best eye, average eye, best location, binocular summation) on binocular visual field formation. METHODS: The monocular and binocular visual field were tested in 15 cases with normal visual field and 58 cases of different kinds of ocular diseases with abnormal visual field. RESULTS: The mean rates of summation in normal visual field group and abnormal group were 93.00% and 93.10% respectively with no significant difference (P > 0.05). The mean degree of binocular visual field summation of normal visual field group was 7.05. The abnormal group had a greater variation of summation degree than that of normal group. The comparison of four theoretic simulating mathematical methods with the tested mean retinal sensitivity (MS) of binocular visual field in both groups showed minimum difference between the MS calculated by the model of best location and the actual MS value. CONCLUSIONS: Binocular summation is a common vision phenomena. In the four kinds of theory on binocular visual field formation, the model of best location can best reveal the phenomena of binocular visual field summation.

Adolescent↗

PubMed1990

[Gradation of visual field loss in glaucoma].

In order to unify assessment of visual field damage, the visual field charts of 77 glaucoma patients were given "educated estimation" by 3 ophthalmologists in 5 grades of early, mild, moderate, severe and late stages. Then the Esterman Grid Scoring was adopted to evaluate each chart. With regard to defects of the early and late stages, there were no difference between these two methods which, however, disagreed for the mild, moderate and severe stages. For the sake of accuracy, criteria for each stage were postulated in writing and 10 selected charts of glaucomatous visual field defects were given evaluation accordingly by 6 ophthalmologists, followed by assessment with the Esterman Grid; the results were similar. The authors, therefore, recommend that the Esterman Grid be adopted for unification and dependability, the standards being visual field loss of 10 units as the early stage, 20 units as the mild stage, 30-50 units as the moderate stage, 50-80 units as the severe stage, and over 80 units as the late stage. Gradation of visual field loss by numerals also facilitates computer storage of the records.

Glaucoma↗

PubMed1977

The effect of cortical and tectal lesions on the visual fields of binocularly deprived cats.

The visual fields of seven cats raised with binocular lid suture were measured before and after various neural lesions. Each of the cats preoperatively responded with each eye to stimuli from 90 degrees ipsilateral through to the midline. A transection of the optic chiasm rendered one cat blind on the visual field tests. Large bilateral occipito-temporal cortical ablations (4 cats) did not measurably affect orienting responses or the extent of visual field. Unilateral occipito-temporal cortical ablations (2 cats) also had no affect on the visual fields, but subsequent ablations of the contralateral superior colliculus produced permanent blindness in the hemifield contralateral to the ablated tectum. These two cats also were apparently blind with the eye contralateral to the ablated tectum; but with the other eye, the cats retained their preoperative orienting responses. These data are consistent with the hypothesis that, with early binocular deprivation, cats develop dependence upon retinotectal and not thalamocortical pathways for visually guided orienting behavior.

Animals↗

PubMed1986

Frequency distribution of early glaucomatous visual field defects.

The optimization of visual field screening programs for glaucoma requires precise knowledge of where glaucoma defects occur and whether any relation exists between the size of defects and the associated retinal disease. The visual field results from 109 eyes of patients with early glaucomatous damage were investigated with a Friedmann Mark II Visual Field Analyser. The frequency distribution of scotomas as a function of location demonstrated that the tested field could be divided into four zones, one where scotomas occur frequently, one where scotomas occur a reasonable number of times, one where scotomas occur rarely, and one which corresponds to the blind spot (BS) region. The distribution of scotoma size in the first three zones was found to be about the same. Differences among the distributions of defects measured in this study and those of previous studies are attributed to different examination techniques.

Glaucoma↗

PubMed1997

Rate of visual field loss in retinitis pigmentosa.

PURPOSE: The authors quantitate the rate of visual field loss in patients with retinitis pigmentosa as it relates to different clinical field phenotypes. PATIENTS AND METHODS: Goldmann visual fields were obtained with target V4e in 77 patients and with target II4e in 71 patients who had either isolated or various genetic types of retinitis pigmentosa and who met certain entrance criteria. The visual fields were categorized into five distinct clinical field phenotypes on the basis of their pattern of field loss. Mixed-model methods for the analysis of longitudinal data were used to model the natural logarithm of the visual field area as a function of patient age and clinical field phenotype. The average half-life (time over which half of the remaining field area would be lost) of the visual field area for each phenotype was computed from the results of this analysis. Visual field data were not analyzed for patients with a normal clinical field phenotype (type 1). RESULTS: Independent of the field phenotype, average half-life values were 7.3 years for target V4e and 6.8 years for target II4e, which were not statistically different (P = 0.16). Visual fields with partial or complete midperipheral ring scotomas (type 2) and those with only a residual central field (type 4) had a half-life of 9.5 and 9.4 years, respectively, for target V4e, and 8.9 and 8.0 years, respectively, for target II4e. Patients with partial peripheral restriction (type 5) lost visual fields with a half-life of 9.5 years for target V4e and 7.3 years for target II4e. None of these differences in the half-lives between the different phenotypes were statistically significant for either targets V4e or II4e. Fields with a residual central area and remaining temporal and/or nasal islands (type 3) had a half-life of 4.8 years for target V4e and 6.0 years for target II4e. The differences in half-lives between type 3 and each of the other field phenotypes were statistically significant for the V4e target, but not for the II4e target. CONCLUSIONS: The results of this study can be useful for counseling patients with retinitis pigmentosa and various visual field phenotypes as to their potential rate of visual field loss.

Half-Life↗

PubMed2005

Dynamic visual fields of one-eyed observers.

BACKGROUND: The horizontal binocular visual field can extend to more than 200 degrees, while a monocular field is limited to 160 degrees. Additionally, the nose and other facial structures may block the monocular field further during certain eye movements. The purpose of this study was to compare the monocular against the binocular visual field and determine if head and eye movements can functionally overcome any measured deficit. METHODS: In Experiment 1, visual fields were measured monocularly with a bowl perimeter using 5 fixation positions. Binocular visual fields were calculated by combining the monocular visual field with its mirror image. In Experiment 2, subjects were allowed to make head, eye, and body movements to search for flashing lights 360 degrees around them, spaced every 45 degrees. The numbers of lights identified were compared for the subjects performing monocularly versus binocularly. RESULTS: The size of the overall monocular visual field was found to vary between 48% and 76% of the binocular visual field, depending on eye position. For the flashing light experiment, head and eye movements could not overcome the entire visual-field deficit with monocular viewing. Monocular performance remained 11.4% less than binocular performance. CONCLUSIONS: The visual-field deficit seen with monocular viewing is greatest with nasal fixation, and head and eye movements cannot totally compensate for this deficit when viewing time is limited. Vision standards that require full visual fields in each eye are more appropriate for occupations in which peripheral visual targets must be identified and visual search time is limited.

Adult↗

PubMed2001

Fundus changes corresponding to visual field defects after vitrectomy for macular hole.

OBJECTIVE: Visual field defects are one of the complications of macular hole surgery, and mechanical retinal damage induced by infusion air is a proposed causative factor of this complication. In this study, we examined the fundus to see whether the changes observed corresponded to postoperative visual field defects. DESIGN: Observational case series. PARTICIPANTS: Seventeen eyes of 17 patients who had postoperative visual field defects after vitrectomy for idiopathic macular hole were examined. METHODS: The fundus was examined by ophthalmoscopy and by fluorescein and indocyanine green angiography. MAIN OUTCOME MEASURES: Fundus changes corresponding to postoperative visual field defects. RESULTS: In eight eyes, detectable fundus changes were observed, including regional mottling and degeneration of the retinal pigment epithelium, filling delay of the choroidal circulation, subretinal fibrosis, and epiretinal membrane formation. These findings corresponded exactly to the visual field defects observed. Although the visual field defects had been detected shortly after surgery, fundus changes were detected, on average, more than 8 months after surgery. CONCLUSIONS: Fundus changes become apparent after surgery, and they are progressive. Therefore, it is important to examine eyes with visual field defects for a follow-up period of several years.

Aged↗

PubMed1998

A method of scoring automated visual fields to determine field constriction causing blindness.

Blindness is usually defined by visual acuity criteria. Patients with markedly constricted visual fields are visually impaired even if they have good visual acuity. To our knowledge, no standardised criteria exist to determine the extent of constriction for fields done with the currently used automated static perimetry. The purpose of this study was to suggest a simple method to do so which would help in determining blindness due to field constriction. We reviewed a number of constricted visual fields obtained with Humphrey automated static perimetry. The central 30 degrees field was divided into six concentric zones. By trial and error, we devised criteria for defining visual field constriction based on absolute loss of sensitivity (< or = 0 dB) and relative loss of sensitivity (< or = 5 dB). We suggest that if a zone has at least 75% test points < or = 0 dB and no point > 10 dB, it be considered to have absolute loss of sensitivity for the purpose of defining visual field blindness. Two exceptions to this are also suggested to prevent this criterion from becoming too rigid. Examples are shown to demonstrate application of these criteria in defining blindness due to visual field constriction to < 10 degrees as suggested by the World Health Organization. Standardised determination of visual field constriction with automated perimetry could be useful in more accurate estimation of blindness in surveys, as well as in assessing eligibility for being classified as blind for legal benefits.

Blindness↗

PubMed1991

The accuracy of confrontation visual field test in comparison with automated perimetry.

The accuracy of confrontation visual field testing was determined for 512 visual fields using automated static perimetry as the reference standard. The sensitivity of confrontation testing excluding patchy defects was 40% for detecting anterior visual field defects, 68.3% for posterior defects, and 50% for both anterior and posterior visual field defects combined. The sensitivity within each group varied depending on the type of visual field defect encountered. Confrontation testing had a high sensitivity (75% to 100%) for detecting altitudinal visual loss, central/centrocecal scotoma, and homonymous hemianopsia. Confrontation testing was fairly insensitive (20% to 50% sensitivity) for detecting arcuate scotoma and bitemporal hemianopsia. The specificity of confrontation testing was high at 93.4%. The high positive predictive value (72.6%) and negative predictive value (75.7%) would indicate that visual field defects identified during confrontation testing are often true visual field defects. However, the many limitations of confrontation testing should be remembered, particularly its low sensitivity for detecting visual field loss associated with parasellar tumors, glaucoma, and compressive optic neuropathies.

Adolescent↗

PubMed1978

Central and peripheral object distances as determinants of the effective visual field in early infancy.

While visually fixating on a central, coloured object, thirty-six infants aged between two and five months were presented with a peripheral target to the right or to the left of midline. Both objects were presented at two distances: either 30 or 90 cm from the infant. The extent of the effective visual field was measured by the presence and the latency of saccadic shifts of gaze from the fixation object toward the target object placed at varying degrees of eccentricity. The effective visual field expanded between two and four months. Near peripheral targets were detected at greater angles of eccentricity than those more distant, but this effect was modified both by age and by the distance of central fixation. For two- and three-month infants the effective visual field was most reduced when the central fixation object was placed at 30 cm and the target object at 90 cm. The ability to respond to peripheral objects more distant than the fixation object develops after three months.

Age Factors↗

PubMed1998

Visual acuity and visual field impairment in Usher syndrome.

OBJECTIVE: To determine the extent of visual acuity and visual field impairment in patients with types 1 and 2 Usher syndrome. METHODS: The records of 53 patients with type 1 and 120 patients with type 2 Usher syndrome were reviewed for visual acuity and visual field area at their most recent visit. Visual field areas were determined by planimetry of the II4e and V4e isopters obtained with a Goldmann perimeter. Both ordinary and logistic regression models were used to evaluate differences in visual acuity and visual field impairment between patients with type 1 and type 2 Usher syndrome. RESULTS: The difference in visual acuity of the better eye between patients with type 1 and type 2 varied by patient age (P=.01, based on a multiple regression model). The maximum difference in visual acuity between the 2 groups occurred during the third and fourth decades of life (with the type 1 patients being more impaired), while more similar acuities were seen in both younger and older patients. Fifty-one percent (n=27) of the type 1 patients had a visual acuity of 20/40 or better in at least 1 eye compared with 72% (n=87) of the type 2 patients (age-adjusted odds ratio, 3.9). Visual field area to both the II4e (P=.001) and V4e (P<.001) targets was more impaired in the better eye of type 1 patients than type 2 patients. A concentric central visual field greater than 20 degrees in at least 1 eye was present in 20 (59%) of the available 34 visual fields of type 1 patients compared with 70 (67%) of the available 104 visual fields of type 2 patients (age-adjusted odds ratio, 2.9) with the V4e target and in 6 (21%) of the available 29 visual fields of type 1 patients compared with 36 (38%) of the available 94 visual fields of type 2 patients (age-adjusted odds ratio, 4.9) with the II4e target. The fraction of patients who had a visual acuity of 20/40 or better and a concentric central visual field greater than 20 degrees to the II4e target in at least 1 eye was 17% (n=5) in the type 1 patients and 35% (n=33) in the type 2 patients (age-adjusted odds ratio, 3.9). CONCLUSIONS: Visual acuity and visual field area were more impaired in patients with type 1 than type 2 Usher syndrome. Of note, 27 of 53 type 1 (51%) and 87 of 120 type 2 (72%) patients had a visual acuity of 20/40 or better in at least 1 eye. These data are useful for overall counseling of patients with Usher syndrome.

Adult↗

PubMed1984

A longitudinal study of the development of visual field advantage for letter matching.

The visual field advantage for letter matching was investigated longitudinally from 5 to 7 yr. A right visual advantage was found with very little indication of any increase with age. Cross-sectional controls exhibited somewhat less of a right visual field advantage. In a group of 4-yr-olds who could not name letters a left visual field advantage was observed for boys. It is suggested that the right visual field advantage for visual-verbal material occurs from a mapping on to an already existing left hemisphere language system.

Child↗

PubMed1985

Should visual field examination be a routine part of ophthalmic practice?

Visual field screening conducted on indication was compared with routine visual field screening to determine the effectiveness of these strategies in identifying patients with normal and abnormal visual fields. The sample consisted of 1,500 consecutively presenting patients. Each patient was screened with the Friedmann Visual Field Analyser Mark II. Visual field defects were detected in 3.0% of eyes. Routine visual field screening detected a very high proportion of these defects. The two indications approaches which were tested achieved only slightly lower sensitivities and specificities, while necessitating that only approximately 20% of patients required screening. The most effective strategy for screening on indication was based on overall clinical assessment of each case, although the optimal criteria relied on low levels of suspicion.

Diagnostic Tests, Routine↗