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PubMedDate not supplied

Depth perception and evoked brain activity: the influence of horizontal disparity and visual field location.

The perception of dynamic random-dot stereograms (RDS) depends on the physiological fusion of horizontally disparate binocular visual input. Thus, the use of RDS offers the possibility to study selectively cortical processing of visual information in man. We investigated the influence of horizontal disparity on the scalp topography of RDS evoked brain activity in 33 healthy subjects. Stereoscopic checkerboard patterns were presented in the center or lateralized in the left or right visual field with horizontal disparities changing at temporal frequencies of six or eight depth reversals/s using different disparity values ranging from 3.5 to 28 min of arc. In 11 subjects evoked potential fields were recorded from 16 electrodes, and 21 subjects participated in 30-channel recordings with electrodes located over the parietal and occipital brain areas. Stimulation frequency-related brain activity was obtained with all disparity values; however, with large or small disparities the potential field strength decreased significantly while largest responses were obtained with intermediate disparities. Significant differences were observed in RDS evoked brain activity when central and lateralized stimulus locations were compared. With lateral stimuli (extending from the fovea to 17.1-deg eccentricity) maximal amplitudes were obtained at larger disparities than with central stimuli. In addition there were pronounced differences between brain activity evoked with stimuli presented in the left or right visual field; however, there were very similar evoked potential signals recorded from electrodes located over the left and right hemispheres. Our findings indicate that the processing of disparity information with lateralized stimuli is different from the processing in the center of the visual field. In addition, lateralized stimulation yields a significant disparity tuning mainly with stereoscopic targets occurring to the right from the fixation point (but not with stimuli to the left) suggesting a functional difference between the visual half-fields.

Adult↗
PubMed2005

Causes of incident visual field loss in a general elderly population: the Rotterdam study.

OBJECTIVE: To determine the incidence and causes of visual field loss (VFL) in a general elderly population. METHODS: Central visual fields of both eyes were examined with suprathreshold perimetry in 3761 persons aged 55 years or older and free of VFL at baseline from the population-based Rotterdam Study. Goldmann perimetry was performed to confirm suprathreshold VFL. Causes of incident VFL (iVFL) were assessed based on all available ophthalmologic and neurological examination data and medical records. RESULTS: After a mean follow-up time of 6.3 years, 175 persons developed VFL. The overall incidence rate of iVFL was 7.4 per 1000 person-years, increasing to 21.1 per 1000 person-years in those aged 80 years and older. Glaucoma was the leading cause of iVFL in all age categories. The overall incidence of glaucomatous VFL was 2.0 per 1000 person-years. CONCLUSIONS: The incidence of all VFL increased 5-fold between 55 years and 80 years of age or older. After glaucoma, stroke was the second most common cause of iVFL in persons younger than 75 years, followed by age-related macular degeneration and retinal vascular occlusive disease.

Aged↗
PubMed2003

Does frequency doubling technology perimetry reliably detect neurological visual field defects?

AIM: To determine the ability of frequency doubling technology (FDT) perimetry to detect visual field defects of neurological origin. METHODS: A total of 15 eyes of nine patients who all had complete hemianopias or quadrantanopias underwent the FDT 20-5 screening mode test and Humphrey 24-2 SITA Fast visual field test (HFA). The FDT results were scored according to the number of abnormal test locations (out of a maximum of 4) in each affected quadrant. FDT locations showing a defect of P< 2% were considered abnormal. RESULTS: Of the 15 eyes, six showed complete superior quadrantanopic and nine complete hemianopic field defects on HFA. Of 96 FDT test locations in these quadrants or hemifields only 38 were abnormal on FDT testing (40%). For the quadrantanopic field defects, five out of 24 locations were abnormal (21%). For the hemianopic field defects, 33 out of 72 locations were abnormal (49%). In three eyes (two with quadrantanopias and one with complete hemianopia), FDT perimetry failed to demonstrate any corresponding abnormality. CONCLUSIONS: The FDT screening test can fail to demonstrate complete hemianopic and quadrantanopic field defects. Users should be aware of this deficiency when using FDT to screen for field defects.

Adolescent↗
PubMed1985

Allocation of attention in the visual field.

This research investigated whether attentional resources can be simultaneously allocated to several locations in a visual display, whether the mode of processing (serial or parallel) can be switched within a trial, and the nature of the costs when attentional resources are concentrated on an invalid location. Subjects were required to determine which of two target letters was present in eight-letter circular displays. In precue conditions, a primary and a secondary target location were designated 150 ms before target onset by an indicator that varied in validity. In the control conditions no cue was provided. A second experiment verified several assumptions that had been made in interpreting the data of Experiment 1. Modifications in Jonides' (1983) two-process model were suggested in terms of a zoom lens model of attentional resources. Instead of two alternative processing modes, attentional resources are conceived as capable of distribution over the visual field, but with low resolving power, or as continuously constricting to small portions of the visual field with a concomitant increase in processing power.

Adolescent↗
PubMed1993

[A comparative study of visual field damage in low-tension and primary open-angle glaucoma].

We compared the results of visual field examination obtained with a Humphrey 30-2 program between 57 eyes of 57 low-tension glaucoma (LTG) and 57 eyes of 57 primary open-angle glaucoma (POAG; max IOP > or = 25 mmHg) cases, whose mean deviation (MD) given by STATPAC was > -10 dB. MD, age, and refraction showed no differences between the two groups. Corrected pattern standard deviation (CPSD) was significantly higher in the LTG group (p < 0.01). The total deviation (TD), deviation from the age-corrected normal reference, was found to be significantly lower by about 5 dB in the LTG group at two test points nasal-superior to the fixation point (Wilcoxon rank sum test, p < 0.01). Logistic discriminant analysis carried out to exclude a subtle difference in the distribution of the stage of disease between the two groups confirmed a significant between-group difference at the above-mentioned points. Furthermore, to compare the unevenness of visual field in the two groups, [TD-mean TD] was calculated, where mean TD was the average of 70 points of TD excluding the uppermost four points, and the same two points obtained above were found to decrease significantly in LTG, while all points were diffusely damaged in POAG. These results may imply a difference in the mechanism of visual field damage between LTG and POAG.

Adult↗
PubMed2005

[Intracranial hypertension with severe and irreversible reduced acuity and impaired visual fields after oral tetracycline].

A young, non-obese woman aged 24 years with normal blood pressure developed intracranial hypertension after the oral use of tetracycline. Neuro-ophthalmologic examination revealed severely reduced acuity, papilledema, and concentric impaired visual fields. She was treated with acetazolamide and recurrent lumbar punctures and recovered, but without improvement in either acuity or visual fields. Intracranial hypertension is a fairly rare disease characterised by increased intracranial pressure without structural abnormalities in the brain or hydrocephalus, and is termed idiopathic in the absence of an underlying cause. Tetracycline should be considered as a cause of intracranial hypertension if a patient complains of previously unknown headache a few days after its ingestion. Headache and the presence of bilateral papilledema, decreased visual acuity and visual-field defects are indications for urgent referral to a neurologist. Therapy consists of a combination of repetitive lumbar punctures and medication. Surgical interventions include lumboperitoneal shunting and optic nerve fenestration. Intracranial hypertension may lead to irreversible decreased visual acuity and visual-field defects resulting in disability.

Acetazolamide↗
PubMed1985

Manipulation of sensitivity in visual field investigation.

Sophistication of computer software and flexibility of stimulus and background luminance parameters in static perimeter design offer the opportunity for increased information in the assessment of the visual field. Relationships between dynamic ranges and resulting sensitivity gradients in a group of 10 normal 21 year old subjects using the Octopus automated perimeter, the Dicon Autoperimeter 2000 and the Friedmann VFA II are assessed. Inadequacies in the use of normative data to assess the visual field are noted. Implications for the use of dynamic range/sensitivity gradient relationships in visual field assessment without reliance on normative data are discussed.

Adult↗
PubMed1989

Visual field testing with reduced sets of test points. A computerized analysis.

A computerized analysis of visual fields is described. In a second step these results are condensed into a 'reduced' set of test points so constructed that if testing is limited to 6-8 points nearly all defective visual fields would have been spotted with at least one defective point. The 'reduced' set involves the testing of few points several times in a session rather than spending very few trials on a great number of points. This is a new approach which merits further investigation.

Algorithms↗
PubMed2005

Distortions in length perception: visual field anisotropy and geometrical illusions.

Psychometric experiments were performed to study the effects of visual field anisotropy and geometrical illusions on the accuracy of comparison of objects in terms of length. Stimuli consisting of V-shaped symbols were used, made up of three light spots or one spot plus components of illusory figures, which were pairs of Müller-Layer wings or an interval of the Oppel-Kundt figure filled with spots of light. Relationships between the length comparison errors and the orientations of the reference and test parts of the stimulus were obtained. The experimental data showed that the simultaneous appearance of illusions and visual field anisotropy can be summed algebraically.

Anisotropy↗
PubMed2006

What determines sustained visual attention? The impact of distracter positions, task difficulty and visual fields compared.

We quantified the interference of distracter stimuli on sustained visuo-spatial attention as a function of the distribution of attended positions in the visual fields (bilateral/unilateral, left/right, upper/lower), distracter positions (peripheral, between attended positions, between fixation and attended positions) and task difficulty. Compared to distinct distracter positions, bilateral field and lower field presentation had much stronger influence on the performance. Additionally, interactive effects between task difficulty and distracter position were found. This result was at variance with the previous models of visuo-spatial attention, which attached much more importance to the role of distracter positions compared to visual field effects. In directly comparing the impact of the abovementioned factors, the converse finding is evident-visual field effects, in particular bilateral presentations have a much stronger importance. Moreover, metaphoric concepts of attention like the "zoom lens" are not compatible with these results. The findings are discussed in the light of alternative models of sustained visuo-spatial attention. The visual system architecture and top-down mechanisms are considered.

Adult↗
PubMed2006

The effect of artificial tear administration on visual field testing in patients with glaucoma and dry eye.

AIM: To examine the effects of artificial tear administration on perimetry of primary open-angle glaucoma patients with dry eye. METHODS: A total of 40 patients with primary open-angle glaucoma experienced in automated perimetry with symptoms of dry eye were enrolled in this study. After their pretest visit, they were instructed to use artificial tear four times a day in both eyes for 1 week. After 1 week, patients had visual field testing. Test taking time, reliability parameters (false-positive and false-negative errors) visual field indices and number of depressed points at different probability levels (P<5%, P<2%, P<1%, P<0.5%) in both total and pattern deviation plots were compared using paired Ttest. RESULTS: We found significant improvement in reliability parameters (false-positive errors from 2.4+/-2.1 to 2.1+/-1.9, P=0.02; and false-negative errors from 7.3+/-6.4 to 4.8+/-3.6, P=0.01) and visual field indices (MD increased from 5.97+/-5.61 to 4.57+/-4.53, P=0.001; PSD from 4.67+/-2.95 to 4.13+/-2.77, P=0.04 and SF decreased from 2.24+/-1.23 to 1.83+/-0.77, P=0.04) in the second testing after artificial tear administration. Test time significantly increased from 11.66+/-2.55 min to 14.26+/-1.36, P=0.001. The number of depressed points at probability levels P<1% (P=0.03) and P<0.5% (P=0.04) at total deviation plot and P<2% (P=0.02) and P<0.5% (P=0.009) in pattern deviation plot decreased significantly. CONCLUSION: Artificial tear administration in glaucomatous patients with dry eye seems to improve significantly reliability parameters and visual field indices.

Administration, Topical↗
PubMed1996

[Central visual field in patients with multiple sclerosis without symptoms of optic neuritis].

PURPOSE: To estimate central visual field (30 degrees) of patients suffering from multiple sclerosis (SM). SM was confirmed by magnetic resonance imaging. MATERIAL AND METHODS: There was no posterior optic neuritis in the history of the disease. The visual acuity of examined the 28 eyes was 1,0. The results of static perimetry were analysed by regression analysis. RESULTS: There were significant relationships between mean sensitivity (MS) and duration of the disease, stage of the disease (in Kurtzke gradation scale) and age. Mean defect (MD) was significantly higher in the upper half of central visual field and between 15-30 degrees (p < 0.05). We observed positive relationships between MD, short time fluctuation (STF) and corrected loss variance (CLV). We found negative correlations between MS, MD, CLV and STF. Mean reliability factor RF was < 10%. CONCLUSION: Static perimetry seems to be a useful test in early diagnosis and monitoring of optic nerve neuropathy in SM.

Adult↗
PubMed1995

Effects of exposure to simulated altitudes on visual fields, contrast sensitivity, and dazzle recovery.

Previous studies have shown that visual performance may be impaired at altitudes above 12,000 ft when supplementary oxygen is not used. What is not known is whether there may be subtle changes in visual function at altitudes to which airline cabins are usually pressurized. In this study, we measured spatial and temporal contrast sensitivity, central visual field thresholds, and macular photostress recovery time in 12 male subjects at sea level and at simulated altitudes of 7000 ft and 12,000 ft. Our results showed insignificant changes in spatial and temporal contrast sensitivity, central visual field thresholds and dazzle recovery time with respect to simulated altitudes.

Adult↗
PubMed1994

Visual fields and eye movements in herons (Ardeidae).

The visual fields and eye movements of three heron species (Ardeidae; Ciconiiformes): the cattle egret (Bubulcus ibis), the squacco heron (Ardeola ralloides), the western reef heron (Egretta gularis schistacea) were determined in alert, restrained birds using an ophthalmoscopic technique. All three species can gain panoramic visual coverage of the frontal field around the bill, and a bird standing with its bill horizontal can view its own feet binocularly. The region in which binocular overlap is possible is long (approximately 170 degrees) and narrow (maximum width approximately 20 degrees). Monocular field width in a horizontal plane is approximately 170 degrees. Retinal binocular overlap can be abolished by eye movements at all elevations in the frontal field. At the frontal margins of the monocular fields the retinal and optical field margins do not coincide; the retinal field margin lies between 9 degrees and 12.5 degrees inside the optical field margin. This results in a blind sector at the margin of each eye's optical field. Consequently the visually functional retinal binocular field widths are significantly narrower than the optical binocular fields. When retinal binocularity is abolished by eye movements, optical binocular fields are still retained. Thus, estimates of binocular overlap based only upon the appearance of the pupils will be erroneous. The comprehensive nature of vision beneath the bill is probably closely associated with the herons' visually guided, stealthy, foraging techniques, which result in the single-strike capture of mobile, highly evasive prey.

Animals↗
PubMed2003

Neural correlates of the left-visual-field superiority in face perception appear at multiple stages of face processing.

Studies in healthy individuals and split-brain patients have shown that the representation of facial information from the left visual field (LVF) is better than the representation of facial information from the right visual field (RVF). To investigate the neurophysiological basis of this LVF superiority in face perception, we recorded event-related potentials (ERPs) to centrally presented face stimuli in which relevant facial information is present bilaterally (B faces) or only in the left (L faces) or the right (R faces) visual field. Behavioral findings showed best performance for B faces and, in line with the LVF superiority, better performance for L than R faces. Evoked potentials to B, L, and R faces at 100- to 150-msec poststimulus showed no evidence of asymmetric transfer of information between the hemispheres at early stages of visual processing, suggesting that this factor is not responsible for the LVF superiority. Neural correlates of the LVF superiority, however, were manifested in a shorter latency of the face-specific N170 component to L than R faces and in a larger amplitude to L than R faces at 220-280 and 400-600 msec over both hemispheres. These ERP amplitude differences between L and R faces covaried across subjects with the extent to which the face-specific N170 component was larger over the right than the left hemisphere. We conclude that the two hemispheres exchange information symmetrically at early stages of face processing and together generate a shared facial representation, which is better when facial information is directly presented to the right hemisphere (RH; L faces) than to the left hemisphere (LH; R faces) and best when both hemispheres receive facial information (B faces).

Adult↗
PubMed2006

Microcirculation at optic disc rim is correlated with visual field defects in cases of anterior ischaemic optic neuropathy.

We report two cases of anterior ischaemic optic neuropathy in whom tissue blood flow at the disc rim was correlated with the visual field defect. Tissue blood flow of each eye was evaluated with Heidelberg retina flowmeter. Both cases experienced acute visual loss and an altitudinal hemianopsia associated with optic disc oedema in the affected eye. In each case, the tissue blood flow at the affected (upper or lower half) disc rim corresponding to visual field deficit was reduced compared with that at the opposite-sided half disc rim in the affected eye and with the corresponding area in the fellow eye. The reduction of blood flow in the affected half disc rim associated with the visual field defect demonstrated that retina flowmetry can detect differences in tissue blood flow between superior and inferior sectional disc rim areas as well as between eyes non-invasively.

Blood Flow Velocity↗
PubMed2006

Assessment of cortical visual field representations with multifocal VEPs in control subjects, patients with albinism, and female carriers of ocular albinism.

PURPOSE: In human albinism, part of the temporal retina projects abnormally to the contralateral hemisphere. This study was undertaken to test whether this abnormality can be identified with multifocal visual evoked potentials (mfVEPs) and whether it is evident in carriers of ocular albinism (OA1). METHODS: In 12 control subjects, 11 patients with albinism, and 5 female carriers of OA1 monocular pattern-reversal mfVEPs were recorded for 60 locations comprising a visual field of 44 degrees diameter (VERIS ver. 4.8; EDI, San Mateo, CA). For each eye and each stimulus location interhemispheric difference potentials were calculated and correlated with each other to assess the lateralization of the responses: positive and negative correlations indicate lateralization on same or opposite hemispheres, respectively. Misrouted optic nerves are expected to yield negative interocular correlations. Visual field locations without recordable responses were excluded from the analysis using a signal-to-noise threshold. The analysis also allowed assessment of the sensitivity and specificity of the detection of projection abnormalities. RESULTS: Sizable mfVEPs were obtained in all control subjects, carriers, and the three patients with albinism who had negligible nystagmus and visual acuity>0.25. Ninety-seven percent and 99% of the visual field locations were identified as normal in control subjects and carriers, respectively. While this indicates a specificity of the procedure of 97%, the sensitivity was estimated as 75%. Finally, in albinism, 55% percent of the responses were abnormally represented. CONCLUSIONS: In the absence of nystagmus mfVEPs are a powerful tool to identify, in a spatially resolved manner, abnormal visual field representations. No local representation abnormalities were evident in the female carriers of OA1.

Adult↗
PubMed1993

Nursing implications of visual fields in successfully treated retinoblastoma patients.

Very little data has been published on the long term peripheral vision of patients diagnosed and successfully treated for retinoblastoma. Nursing should address the patient's response to vision-conserving treatment and their adaptation to decreased peripheral vision. Computerized Humphrey's Central 30/Peripheral 30-60 visual fields were performed on ten patients (all with greater than ten year follow-up) who were successfully treated for retinoblastoma. All ten visual fields revealed an absolute and relative scotoma in the affected eye. Visual field loss was always worse than one would have predicted based upon the fundus examination of the tumor(s). Decisions for treatment must be based upon an interdisciplinary approach of nursing and medicine to evaluate patient survival and visual outcome. Nursing interventions include utilizing the visual field as a teaching aid, preparing the patient and the family for potential future visual loss and adaptation of lifestyle, and providing emotional support and realistic reassurance.

Child, Preschool↗