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At least 793 records · Page 44Linked to original sources
PubMed1989

Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes.

Strabismic amblyopia is associated with a distorted perception of visual space. The aim of our study was to investigate the monocular space perception of strabismic observers at several locations in the central and peripheral visual field. We tested nine observers with strabismic and/or anisometropic amblyopia, two strabismic subjects with alternating fixation and two normal control subjects. The task was to align a light stimulus with two vertically arranged reference marks. Testing conditions included three separations of the references along the vertical meridian (10 degrees, 20 degrees and 40 degrees) as well as several presentation sites of the vertical references in the nasal and temporal peripheral visual field (5 degrees, 10 degrees and 20 degrees from fixation). Performance with the amblyopic eye was clearly impaired as compared to the nonamblyopic eye. For alignment along the vertical meridian, all amblyopic eyes showed increased uncertainty in their position judgements. Most of the squinting eyes of amblyopes also displayed a systematic lateral displacement of the test stimulus in relation to the reference marks, in the most extreme case up to almost 7 degrees. Usually, larger errors were found with wider separations of the reference marks. In the peripheral field, the differences between the amblyopic and the nonamblyopic eye diminished or disappeared. Thus, monocular geometry appears to be selectively impaired in the central visual field of the deviated eye of strabismic amblyopes. These spatial distortions might be related to the different states of binocular correspondence in the central vs. peripheral visual field, shown by some strabismic amblyopes.

Amblyopia↗
PubMed2003

Facilitation and disruption of lateralized syllable processing by unattended stimuli in the opposite visual field.

The influence of lateralized unattended stimuli on the processing of attended stimuli in the opposite visual field can shed light on the nature of information that is transferred between hemispheres. On a cued bilateral task, participants tried to identify a syllable in the attended visual field, which elicits a left hemisphere (LH) advantage and different processing strategies by the two hemispheres. The same or a different syllable or a neutral stimulus appeared in the unattended field. Transmission of unattended syllable codes between hemispheres is symmetric, as revealed by equal interference for the two visual fields. The LH is more accurate than the RH in encoding unattended syllables, as indicated by facilitation in the left but not right visual field and a greater frequency of identifiable intrusions into the left than right field. However, asymmetric encoding strategies are different for attended and unattended syllables.

Attention↗
PubMed2001

Localised changes in glaucomatous visual fields after trabeculectomy.

BACKGROUND AND OBJECTIVE: Modern techniques of automated perimetry have shown that surgical reduction of intraocular pressure (IOP) may have a beneficial effect on the glaucomatous visual field. The purpose of the present study was to analyse and quantify the changes in the visual fields of glaucoma patients after trabeculectomy. MATERIALS AND METHODS: Octopus visual fields of twenty-seven glaucoma patients were analysed. Change in visual field mean sensitivity (MS) was calculated to detect total field changes. A clinical and a statistical analysis of small clusters of test points were used to define whether local changes had occurred. RESULTS: MS in the operated eyes improved significantly from 16.4+/-5.6 to 18.2+/-5.5 dB. The patients had on average 3.9+/-6.2 clusters where the retinal sensitivity had improved at least 5 dB and only 0.4+/-0.9 clusters where sensitivity had deteriorated at least 5 dB after trabeculectomy. 17 patients had more improved than deteriorated clusters postoperatively. CONCLUSION: Statistically significant improvement was seen in the MS, but improvement was also found in small local areas of the visual fields after trabeculectomy.

Glaucoma↗
PubMed2002

Visual field and electrophysiological abnormalities due to vigabatrin.

The purpose of this study was to determine the electrophysiological changes in patients using the anti epileptic drug vigabatrin and to correlate these findings with the previously reported risk for visual field loss in these patients. In 1998 the neurologists of both involved hospitals referred all patients on vigabatrin medication for ophthalmological examination to the outpatients clinics. Of the 33 patients whom were referred to our outpatient clinics, four had to be dropped from the study because of disability to perform the examinations the remaining 29 patients were included in the study. Standard ophthalmological investigations were carried out, and contrast sensitivity, visual field (Humphrey 30-2 and Esterman or Octopus 32), colour vision (panel D15), ERG and EOG according to ISCEV standards were tested. 18 patients continued the medication and 11 stopped taking the drug during the study. Nine of the patients who stopped the drug were followed during at least half a year afterwards, this group will be described in the combined article 'Electro ophthalmic recovery after withdrawal from vigabatrin' (Graniewski and Van der Torren, this issue). The electro-ophthalmological findings in the group of 29 patients were correlated with the visual fields and the daily and cumulative dosages of vigabatrin. Of the patients, 32% showed no visual field constriction at all; from these patients 64% had EOG and/or ERG changes. Of the patients with slight to marked visual field constriction, 90% presented EOG and/or ERG changes. Significant correlation between daily dosages of vigabatrin and visual field defects was shown as well as between visual field defects and rod and cone b wave amplitude reductions. Cumulative vigabatrin dosages presented a significant correlation with EOG ratio and ERG rod b-wave amplitude. Conclusively EOG and ERG testing were found to be even an more accurate way to monitor the direct vigabatrin effect on the outer retina and is possible different from the visual field testing.

Adolescent↗
PubMed2003

Comparison of different methods for detecting glaucomatous visual field progression.

PURPOSE: To compare the performance characteristics of seven methods for analyzing glaucomatous visual field progression, using a combination of real patient data and computer simulation techniques. METHODS: The initial and final visual field results, separated by 7 years and measured with the full-threshold 30-2 program of the Humphrey Field Analyzer (Carl Zeiss Meditec, Dublin, CA) of 76 patients with open-angle glaucoma were used. A computer simulation program generated 14 interim semiannual visual fields under conditions of high, moderate, and no variability. Progression was analyzed using the methods of the Advanced Glaucoma Intervention Study (AGIS), the Collaborative Initial Glaucoma Treatment Study (CIGTS), three criteria based on the Glaucoma Change Probability (GCP) analysis, and two criteria based on point-wise linear regression analysis (PLRA). Specificities were calculated by using the same visual field of each patient as both the initial and final field (no progression) under conditions of moderate and high variability. RESULTS: Under the no-variability condition, progression rates were 18% for the AGIS, 36% for CIGTS, 47% to 62% for the three GCP methods, and 72% and 84% for the two PLRA methods. Progression rates increased with greater variability with the three GCP methods and decreased with all other methods. The time to detect confirmed progression was longest for the PLRA methods and shortest for the CIGTS and GCP methods. Under the moderate-variability condition, all methods yielded high specificity. The AGIS, CIGTS, and one of the GCP and PLRA methods were relatively resistant to high variability and maintained high specificities. CONCLUSIONS: The AGIS and CIGTS methods had high specificity, but classified fewer cases of progression than the other methods. The GCP methods determined progression earliest; however, they were generally not as specific. Methods based on PLRA were specific but times to confirmed progression were the longest.

Computer Simulation↗
PubMed1982

The development of the kitten's visual field.

We tested the monocular visual field of 16 kittens aged 13-56 days, by observing their unreinforced visual orienting. At 13-14 days the kittens oriented toward stimuli out of 45 degrees in the nasal field. Until 7-8 weeks, performance was significantly poorer in the nasal field than in the temporal field. This delayed development of the nasal field may be related to the relatively slow development of the uncrossed retino-geniculate projection and of the pathway through the visual cortex to the superior colliculus.

Aging↗
PubMed2000

Visual field constriction on vigabatrin.

(1) Vigabatrin carries a high risk of concentric visual field constriction, sometimes associated with a drop in visual acuity. The changes in the visual field appear to be irreversible. (2) Consequently, vigabatrin can be considered only as a last resort for infantile spasms refractory to steroid therapy and for partial epilepsy refractory to other anticonvulsants. (3) Patients treated with vigabatrin must have their visual fields monitored regularly.

Adult↗
PubMed1999

Improvement of the osteo-odonto-keratoprosthesis according to Strampelli: influence of diameter of PMMA cylinder on visual field.

BACKGROUND: In surgical management of severe corneal scarring, the osteo-odonto-keratoprosthesis (OOKP) according to Strampelli is recognised as the best choice. Nevertheless, the patients are handicapped by a restricted visual field. Enlarging the optical cylinder diameter should allow better rehabilitation of the patients. PATIENTS AND METHODS: A mathematical model to calculate the theoretical maximum visual field according to the length and the diameter of the cylinder of a keratoprosthesis was developed. The theoretical values were compared with our findings in three OOKP patients operated on in our hospital. RESULTS: The theoretical extent of the visual field with a cylinder of 8 mm length is 55 deg if the diameter is 3 mm and 62 deg if the diameter is 3.5 mm. The visual fields of our OOKP patients in both types of keratoprosthesis are, however, below the theoretically calculated values. Implantation of a prosthesis with a diameter of 3 mm produced horizontal visual fields of 30 and 36 deg in two patients. In one patient with a prosthesis diameter of 3.5 mm the field was 53 deg. CONCLUSIONS: The diameter of the visual field increases with the diameter and decreases with increasing length of the optical cylinder. In OOKP the implantation of a PMMA cylinder with a diameter of 3.5 mm is possible. The enlargement of the diameter of the optical cylinder leads to significant enlargement of the visual field. The size of the cylinder is limited by the diameter of the available root of the tooth.

Biocompatible Materials↗
PubMed1995

Altered visual field asymmetries for letter naming and letter matching as a result of concurrent presentation of threatening and nonthreatening words.

Thirty-two right-handed subjects (16 male and 16 female students) were administered a unilateral letter-naming task and two unilateral letter-matching tasks: physical-identity letter matching (shape task) and nominal-identity letter matching (name task). Each task contained three conditions. In control conditions, no concurrent task was given. In threat and nonthreat conditions, each unilateral stimulus was preceded by a centrally presented threatening or nonthreatening word. Subjects were instructed to recall this word after their response to the lateral stimulus. With letter naming, each trial consisted of three consonants presented horizontally to the left or right visual field. Across conditions, subjects identified more letters correctly in the right visual field than in the left visual field. The concurrent presentation of threatening words resulted in a selective enhancement of left visual-field performance. In the control condition of the shape task, same letter pairs were identified faster than different pairs when they were presented to the right visual field. The concurrent presentation of threatening words resulted in a selective shortening of left visual-field latencies to same pairs. In the name task, the concurrent presentation of threatening words resulted in improved accuracy on left visual field trials. No sex differences in perceptual asymmetries and in emotional priming effects were found. The results demonstrate that threatening stimuli can activate the right hemisphere and alter the laterality patterns for several tasks.

Affect↗
PubMed2004

Interocular asymmetry of visual field defects in primary open angle glaucoma and primary angle-closure glaucoma.

AIM: To compare the interocular asymmetry in visual field loss of patients with primary open-angle (POAG) and primary angle-closure glaucoma (PACG). METHODS: Subjects entering a prospective, randomised, controlled trial of intraoperative 5-fluorouracil in glaucoma surgery in Singapore were included. Preoperative visual field testing was performed using automated white-on-white perimetry (24-2 test pattern, threshold program, Mk II, Model 750, Zeiss-Humphrey, San Leandro, CA, USA). A minimum of two tests were required with mean deviation within 2 dB on two tests, fixation losses <20%, false positives <33%, and false negatives <33%. The second field was scored using AGIS II criteria and the 'mean asymmetry score' defined as the mean difference between eyes for both AGIS scores and global indices. RESULTS: In 230 subjects assessed (128 POAG, 102 PACG), mean interocular asymmetry of visual field loss was greater for the PACG group. The mean AGIS asymmetry scores for total (PACG=9.21+/-6.87 vs POAG=6.48+/-5.58, P=0.001), superior (PACG=4.31+/-3.39 vs POAG=3.35+/-3.13, P=0.035), and inferior (PACG=4.43+/-3.31 vs POAG=2.64+/-2.77, P<0.0001) areas and mean deviation (MD) asymmetry scores (PACG=6.89+/-13.22 vs POAG=1.66+/-16.97, P=0.012) were all significantly different. Interocular correlation of visual field loss for POAG was significant; total AGIS, r=0.27 (P=0.003), superior field AGIS, r=0.24 (P=0.008), inferior field AGIS, r=0.34 (P=0.0001), and MD, r=0.27 (P=0.003). In PACG, there was no significant correlation between eyes; total AGIS, r=-0.02 (P=0.85), superior field AGIS, r=-0.02 (P=0.82), inferior field AGIS, r=-0.17 (P=0.87), and MD, r=0.015 (P=0.89). CONCLUSION: There was a greater asymmetry of visual field loss between eyes, as measured by AGIS scores and MD, in PACG than that in POAG.

Aged↗
PubMed1981

Computer processing of visual data. II. Automated pattern analysis of glaucomatous visual fields.

Machine algorithms have been developed for automated detection and characterization of glaucomatous defects in visual field records stored in a computer. Using elementary techniques of pattern analysis, the contours defining each visual field are described by a set of primitive graphic and type-descriptive features. A hierarchical structure of logical tests is then used to arrive at intermediate and higher-level conclusions. Decision procedures are tailored for the detection of features commonly found in glaucomatous visual fields. Application of these analysis procedures to a large group of visual field records having a broad range of glaucomatous defects shows a very high sensitivity for detection. Specificity is limited by the extent to which defects are "typical" or obey expected patterns of field loss.

Decision Making↗
PubMed1988

The role of perceptual reference frames in visual field asymmetries.

The direct access model of hemispheric asymmetry was tested in a letter reflection (normal of reflected) judgement task. In the baseline condition letters were presented in their upright orientation, and reaction times were faster to letters presented in the right visual field than to those presented in the left visual field. In two other conditions the slides, and thus the letters, were rotated +90 degrees clockwise (Rotated +90) from upright or -90 degrees counterclockwise (Rotated -90). This resulted in the letters in both rotated conditions being shown in the upper or lower visual field through the sagittal plane but rotated 90 degrees. Despite this fact a "right field" advantage was again found when the right field was defined relative to the orientation of the tops of the rotated letters (lower visual field in the Rotated +90 condition and upper visual field in the Rotated -90 condition). These results demonstrate that the internal representation of locations in space is more important in predicting visual field asymmetries, at least in the present task, than the field of stimulus presentation relative to the fovea.

Adult↗
PubMed1985

Effects of visual-field and matching instruction on event-related potentials and reaction time.

Vertical letter pairs were presented randomly in the left and right visual hemifields in a physical identity match and name identity match condition. The reaction times showed a right visual field superiority for name matches, and a left visual field superiority for physical matches. Event-related potentials to letter pairs showed a sequence of three waves: a negative wave (N2, around 270 msec), a positive wave (P3, around 500 msec), and a broad positive slow wave (SW, around 600-700 msec), respectively. P3 and SW amplitudes were consistently larger at the left hemisphere than at the right hemisphere, regardless of the field of stimulation. At both hemispheres, N2 waves were always larger to stimuli presented in the visual field contralateral to a hemisphere than stimuli presented in the visual field ipsilateral to a hemisphere. The positive waves (P3, SW) showed the opposite pattern: smaller amplitudes to stimuli that were presented contralaterally than stimuli that were presented ipsilaterally to a given hemisphere. These results were attributed to a shift in sustained negativity on the directly stimulated hemisphere, relative to the indirectly stimulated hemisphere, reflecting either sensory at attentional processes in the posterior cerebral hemispheres.

Adult↗
PubMed1980

Visual fields and hysteria.

Hysteria has long been recognized as a cause of subjective visual field defects. This paper will review the visual field associated with hysteria and examine patient characteristic of those who have shown this type of visual field loss.

Age Factors↗
PubMed1988

Visual field in dark-reared cats after an extended period of recovery.

The visual field of dark-reared cats was behaviourally measured after several years of recovery in a normal environment. A reduction of the visual field was observed and affected the contralateral field as well as the ipsilateral field when tested in monocular viewing. The longer the deprivation period, the more reduced was the visual field. Our results suggest that binocular deprivation might have stabilized the visual system in an immature state.

Animals↗
PubMed2005

Visual-field asymmetry in dual-stream RSVP.

The attentional blink (AB) refers to a decrement in detecting the occurrence of a probe item if it closely follows a previous target item in rapid serial visual presentation (RSVP). In the present study we presented target and probe stimuli in two parallel RSVP streams, one in each visual field, in order to address the question of whether the AB might differ between the cerebral hemispheres. The characteristic AB, with reduced detection of the probe at post-target Lags 2-5, but no such deficit at Lag 1 (Lag 1 sparing), was observed when target and probe were both in the right visual field. When they were both presented in the left visual field the AB was attenuated. When the target and probe were in opposite visual fields, probe detection was again reduced when it was in the left visual field, and there was no Lag 1 sparing. The left-visual-field advantage in performing the AB task may reflect a general right-hemispheric specialization for attentional processing.

Adult↗
PubMed2002

Practice effects on reaction time for peripheral and central visual fields.

The present study examined whether EMG-RT (RT) for a key press to stimulus in peripheral and central visual fields decreases with practice. 16 male students were divided into two groups, one practicing using peripheral vision, the other practicing using central vision. Before and after practice, RT was measured for peripheral and central visual fields. Each group practiced three blocks of 25 trials five days a week for three weeks. RT for peripheral and central visual fields decreased with practice. Practice effects on RT for the peripheral visual field extended to RT for the central visual field, and vice versa. It is suggested that the transfer may reflect the decrease in the central nervous system's processing time in common between two RT tasks.

Adult↗