Properties of receptive field on binocular fusion stimulation in the central visual field

BACKGROUND: Visual information projected onto corresponding points on the right and left retinas converges on the binocular cells in the visual cortex. The aim of this study is to investigative the characteristics of the receptive field for binocular stimulation in the central visual field of normal-sighted human subjects. METHODS: We investigated the receptive field for binocular stimulation under fusion conditions by combining the Octopus 201 with the space synoptophore. We measured binocular and monocular sensitivities while the fusion patterns were projected onto the Octopus 201 cupola, using the space synoptophore. We designed a new program to test 37 points in the central 6 degrees visual field. Six target sizes were tested: the white-spot targets of 0.054 degrees, 0.108 degrees, 0.216 degrees, 0.431 degrees, 0.862 degrees and 1.724 degrees projected diameters. RESULTS: The threshold energy necessary for binocular stimulation was lower than that for the monocular stimulation in all subjects. This difference was more obvious on the test points that were more distant from the fovea when target sizes of 0.054 degrees and 0.108 degrees were used. The amount of binocular summation ratio was highest for target size 0.054 degrees in each stimulus area in the central 6 degrees of the visual field. When we measured binocular summation using target sizes larger than 0.108 degrees, the result was the constant summation. CONCLUSIONS: The size of the receptive field for binocular stimulation is smaller than monocular stimulation under the same fusion condition. The amount of binocular summation varies as a function of target size.     

The normal visual field on the Humphrey field analyzer

To provide a bank of normal perimetric data, we tested the central and peripheral visual fields of 102 novice normal subjects using the Humphrey automated perimeter. All eyes used for visual field testing were first carefully examined to be sure that they were, indeed, normal. We calculated population means and standard deviations of each test location and for each decade for age. Average differential light sensitivity decreased with advancing age: -0.5 dB/decade at fixation, -0.6 dB/decade in the central (30-2) field, and -06. dB/decade in the peripheral (30/60-2) field. However, neither the slope nor the shape of the hill of vision changed with aging. Short-term fluctuation was not constant throughout the visual field, but instead was greater in the periphery than the center.     

A static perimetric technique believed to test receptive field properties: Responses near visual field lesions with sharp borders

The organization of the ‘Westheimer function’ in the retina has been further analysed. Patients with sharp visual field cuts caused by chiasmal and cortical lesions have been studied. Data were generally obtained from points approximately 10°–15° from the fovea (where areas of spatial interaction and the magnitude of the inhibitory component were large). The center of the three field display was placed just within the boundary of the sighted area of the visual field. Hence, a substantial part of the background field fell on nonsighted areas, which presumably retained retinal function. If the inhibitory part of the function originates proximal to the retinal ganglion cell layer (or the underlying retina was nonfunctional), then the basic ‘Westheimer function’ probably would be altered when these data are compared with findings obtained at a normal point in the visual field of the affected eye. All cases measured to date exhibited essentially unaltered functions. This finding, plus previous studies of patients with inner retinal diseases, places the locus of the measured inhibitory component of the Westheimer function most probably in the inner retina. This research has been supported in part by Research Grants No. EY 00204 and EY 00233 and Career Development Award No. K3 EY 15138 (to J.E.) of the National Eye Institute, National Institutes of Health, Bethesda, Maryland.     

Macular drusen and the sensitivity of the central visual field

Macular drusen are one of the earliest signs of age-related macular degeneration but little information is available on the functional aspects of macular area in patients with drusen. To determine if drusen are associated with changes in central visual field sensitivity, one eye of each of 35 subjects (mean age 64.9 years) with bilateral drusen and visual acuity of 1.0 (20/20) underwent automated static threshold perimetry of the central 10°. 16 normal subjects (mean age 65.8 years) were used as controls. 30° fundus photographs were graded in a masked fashion for the clinical characteristics of drusen: type, size and number. The mean sensitivity (MS) of the central 10° was significantly lower in eyes with drusen compared to normal eyes (p=.0001). After grading drusen eyes for size ( 63µ) and type (presence of soft drusen), MS significantly deteriorated when large and soft drusen were present. These results suggest that central visual field sensitivity is precociously affected in eyes with drusen and that testing central visual field sensitivity may be useful as functional parameter in long term studies on the evolution of age-related macular degeneration.This paper was partly presented at the XVIII Meeting of the Club Jules Gonin, Vienna, 1992.     

Check-size specific changes of pattern electroretinogram in patients with early open-angle glaucoma

The pattern electroretinogram was recorded in patients with initial stages of visual field defects due to open-angle glaucoma and in age-matched normal subjects. Both normal subjects and glaucoma patients had a visual acuity above 0.8. Counterphasing checkerboard patterns were used as visual stimuli with a range of check sizes from 0.8° to 15° at 7.8 reversals/s. Whereas the amplitude in glaucoma patients was nearly normal for large check sizes, it was significantly reduced for small check sizes (p = 0.003). Possibly two separate mechanisms that generate the pattern electroretinogram for small and large checks are differentially affected; they may be related to the magnocellular and parvocellular systems. The difference between normals and glaucoma patients was even more significant when the ratios of the amplitudes at small and large check sizes were compared (p < 0.0002). When this ratio is used, the amplitude variability can be partly overcome and the pattern electroretinogram can be a sensitive indicator of ganglion cell function.     

Is visual field evaluation using multiple correlations and linear regressions useful? An evaluation of Delphi perimetry

· Background: Delphi perimetry is a method of visual field examination which produces a statistical estimation of the visual field by testing only four critical points of the central visual field. This study was performed to evaluate this technique for the detection of glaucomatous field loss. · Method: Patients with glaucoma and ocular hypertension underwent Delphi perimetry and Humphrey visual field analysis (HVFA) program 24-2. The visual field results of both examination were compared. · Results: Of 262 eyes from 199 patients, 120 eyes showed glaucomatous defects by HVFA and 142 were normal. Delphi perimetry showed abnormal visual fields in 107 eyes, 13 of which were false-positive results as Humphrey visual fields were normal. Delphi classified 155 fields as normal, of which 26 were false negatives as Humphrey visual fields showed glaucomatous defects. Therefore, the sensitivity of Delphi perimetry for the detection of glaucomatous visual field defect was 78% and the specificity was 91%. In the 26 false-negative eyes, the most common defect missed was an isolated paracentral scotoma or an early nasal step. Furthermore, 27 of the 94 glaucomatous eyes classified as abnormal by Delphi had defects estimated by Delphi perimetry that corresponded poorly to the field loss demonstrated by Humphrey visual field analysis. Therefore, qualitative sensitivity and specificity of Delphi perimetry for producing an accurate representation of the location, extent and defect depth of glaucomatous visual field loss would be 48.8% and 72% respectively. · Conclusion: In this study Delphi perimetry failed to give an accurate statistical estimation of the visual field in an unacceptably high number of cases; therefore, it cannot be recommended for clinical use. Received: 12 June 1997 Revised version received: 11 November 1997 Accepted: 13 November 1997     

Effect of stimulus field size and localization on the binocular pattern reversal visual evoked response

The role of the central and peripheral stimulus fields on monocular and binocular amplitude and binocular summation of the pattern reversal visual evoked response were investigated. When the central stimulus field size was smaller than 2.4 °, there was no significant difference between the amplitude of the monocular and the binocular responses, but when it was equal to or larger than 3.2 ° × 3.2 °, the binocular amplitude was significantly larger than the monocular. The value of binocular summation was highest at the central stimulus field of 4.0 ° × 4.0 °; at larger sizes, there were no significant changes in the value. Use of a central stimulus field size larger than 3.2 ° × 3.2 ° was therefore considered a prerequisite for the effective assessment of visual function, especially binocular function, by means of the pattern reversal visual evoked response.With regard to the role of peripheral stimulus field on pattern reversal response, both the monocular and binocular responses, but particularly the latter, were found to be sensitive to a scotoma produced by covering the center of a full-field stimulus. The value of the binocular summation showed a significant reduction with a small central scotoma. We concluded that the pattern reversal visual evoked response is very sensitive to a central scotoma and that binocular function is mediated mainly through the central stimulus field.     

Bilateral field advantage in visual crowding

Thirty randomly oriented T’s were presented in a circle around fixation at an eccentricity of 11° such that each T was crowded by its neighbors. Two locations within the same hemifield (unilateral condition) or one location in each hemifield (bilateral condition) were precued for subsequent probing. Observers were then asked to report the orientation of a target T at one of these locations. A bilateral field advantage was found: target identification was better when the two precued targets were in different hemifields than when they were within the same hemifield. This bilateral advantage was absent when only targets were presented, without any distracters. Further controls showed that this advantage could not be attributed to differences between horizontal and vertical target alignments or to visual field anisotropies. A similar bilateral advantage has been reported for multiple object tracking (Alvarez, G. A., & Cavanagh, P. (2005). Independent resources for attentional tracking in the left and right visual fields. Psychological Science 16(8), 637-643) and other attentional tasks. Our results suggest that crowding also demonstrates separate attentional resources in the left and right hemifields. There was a cost to attending to two targets presented unilaterally over attending to a single target. However, this cost was reduced when the two crowded targets were in separate hemifields.     

Pattern electroretinogram and visual evoked potential amplitudes are influenced by different stimulus field sizes and scotomata

The pattern electroretinogram and the visual evoked potential were recorded simultaneously with various stimulus fields and artificial scotomata of increasing sizes. In contrast to an earlier study, a smaller check size (20) and two stimulus field sizes (20° × 20° and 10° × 10°) for the scotomata were used. With a concentric decreasing stimulus field, a reduction of both the pattern electroretinogram and visual evoked potential was found. Both showed a simultaneous reduction of amplitudes, but, compared with the amplitude in the full field, the reduction was more extensive for the pattern electroretinogram at each test field size. This implies a greater contribution to the pattern electroretinogram from more eccentric retinal parts. An artificial central scotoma of increasing size in the 20° × 20° field had less influence on the pattern electroretinogram than on the visual evoked potential. The percentage amplitude loss of the visual evoked potential was more pronounced. The visual evoked potential was eventually abolished by a scotoma size from 10° × 10° upward, while the pattern electroretinogram was still registrable. When scotomata of similar size were introduced in a smaller (10° × 10°) field, percentage pattern electroretinogram and visual evoked potential amplitude losses were less separated than in a larger (20° × 20°) test field.     

Effect of test field size on the results of automated perimetry in normal subjects and patients with optic neuritis

The mean sensitivities of the same 8 central test points were compared in two different programs of an automated Octopus perimeter in normal subjects and in patients recovered from optic neuritis (visual acuity 0.8 or better). The programs differed in terms of the size of the stimulated visual field. One program tested the central 30 degrees and the other, central 8.4-degree visual field. It was found that the mean sensitivity tended to become higher when stimulating small field size in both normal persons and patients with optic nauritis.     

A comparison of central visual field measurement by automated perimetry in optic neuritis due to multiple sclerosis and of unknown etiology

We compared the visual field in 46 eyes of 34 cases with optic neuritis, which included 17 cases with multiple sclerosis (MS) and 17 cases with unknown causes. The visual field examination was measured by program 31 of the Octopus automated perimeter, which tests the central 30 degree field in a 6-degree grid. All eyes had visual acuity of 0.2 or better. The mean visual acuity was 0.97 in MS and 0.83 in the unknown etiology cases. There were no differences in the rate of abnormalities in the 30 degree-field between MS and unknown cases. The mean sensitivity loss of the abnormal visual field with MS was significantly greater than that of the unknown cases. The 30 degree field was divided into 3 sections. MS had almost the same mean sensitivity loss in each section. The cases of unknown etiology had a greater mean loss in 0-10 degrees than that in the other sections. We could conclude therefore that diffuse visual field loss was caused by MS and central depression of 0-10 degrees in the 30 degree field was secondary to an unknown cause. In comparison to the affected eyes seventeen eyes with normal visual acuity and no history of optic neuritis were tested by program 31. Results showed that 3 eyes had abnormal points in 10-30 degree sections.     

早期糖尿病患者中心视野改变分析

目的通过检测早期糖尿病患者和正常人群中心视野(30°)改变,分析探讨糖尿病视网膜病变早期的损伤机制。方法应用国产TEC3全自动视野检查仪对早期糖尿病眼底血管无异常改变的患者38例76眼和正常对照组32例64眼,行常规中心视野检查:检测平均光敏感度、平均缺损和短期波动。检测结果行统计学处理。结果早期糖尿病患者组76眼中有40眼出现中心视野异常,占52.63%;与正常对照组相比,平均光敏感度、平均缺损、短期波动3项指标均相差非常显著(P<0.01)。结论糖尿病患者的糖代谢紊乱首先影响了视网膜的感觉神经功能,中心视野检查对糖尿病视网膜病变前期有一定的临床诊断价值。     

Visual field constriction and electrophysiological changes associated with vigabatrin

Purpose: We investigated functional, morphological and electrophysiological changes in patients under anti-epileptic therapy with vigabatrin (VGB), a GABA aminotransferase inhibitor. Methods: 20 epileptic patients treated with vigabatrin (age range 25–66 years) were enrolled in this study. The referrals were made by the treating neurologist, based on suspected or known visual field changes in these patients. Two patients had vigabatrin monotherapy, 18 patients were treated with vigabatrin in combination with other antiepileptic drugs. None of the patients reported visual complaints. Patients were examined with psychophysical tests including colour vision (Farnsworth D15), dark adaptation threshold, Goldmann visual fields and Tuebingen Automated Perimetry (90°). A Ganzfeld ERG and an EOG following the ISCEV standard protocol were also obtained. Additionally, all patients were examined with the VERIS multifocal ERG including recordings of multifocal oscillatory potentials. Results: Visual acuity, anterior and posterior segments, colour vision and dark adaptation thresholds were normal in all patients. Of 20 patients, 18 presented visual field constriction. All patients with visual field defects revealed altered oscillatory potentials waveforms in the ERG, especially in those patients with marked visual field defects. Multifocal oscillatory potentials were also delayed in those patients. In some patients a delayed cone single flash response (6/20), a reduced mERG amplitude (12/20) and a reduced Arden ratio (9/20) were found. Conclusions: The present data indicate an effect of vigabatrin on the inner retinal layers. Since abnormalities of the oscillatory potentials were seen in all patients with visual field defects a dysfunction of GABA-ergic retinal cell transmission might be assumed.     

Collision avoidance in persons with homonymous visual field defects under virtual reality conditions

The aim of the present study was to examine the effect of homonymous visual field defects (HVFDs) on collision avoidance of dynamic obstacles at an intersection under virtual reality (VR) conditions. Overall performance was quantitatively assessed as the number of collisions at a virtual intersection at two difficulty levels. HVFDs were assessed by binocular semi-automated kinetic perimetry within the 90° visual field, stimulus III4e and the area of sparing within the affected hemifield (A-SPAR in deg²) was calculated. The effect of A-SPAR, age, gender, side of brain lesion, time since brain lesion and presence of macular sparing on the number of collisions, as well as performance over time were investigated. Thirty patients (10 female, 20 male, age range: 19-71 years) with HVFDs due to unilateral vascular brain lesions and 30 group-age-matched subjects with normal visual fields were examined. The mean number of collisions was higher for patients and in the more difficult level they experienced more collisions with vehicles approaching from the blind side than the seeing side. Lower A-SPAR and increasing age were associated with decreasing performance. However, in agreement with previous studies, wide variability in performance among patients with identical visual field defects was observed and performance of some patients was similar to that of normal subjects. Both patients and healthy subjects displayed equal improvement of performance over time in the more difficult level. In conclusion, our results suggest that visual-field related parameters per se are inadequate in predicting successful collision avoidance. Individualized approaches which also consider compensatory strategies by means of eye and head movements should be introduced.     

Progressive color visual field loss in glaucoma.

Twenty one eyes with primary open angle glaucoma were tested with standard (white stimulus-on-white background) and color (blue stimulus-on-yellow background) visual fields over a range of 6-26 mo. There was no significant increase in threshold between the initial and final standard fields overall or by quadrant (P less than 0.188, overall field). A significant increase in mean log thresholds for all areas of the color visual field (P less than 0.019, overall field) was found. Of the 21 patients, nine worsened by greater than 0.2 log units, two improved by greater than 0.2 log units, seven worsened by less than 0.2 log units, and three improved by less than 0.2 log units. When these same patients were matched to 21 normal eyes by age, lens density, and acuity they showed significantly reduced thresholds throughout their color visual fields (P less than 0.023). Whereas normal age-related increases in threshold for the short-wavelength system are only 0.10 log units per decade (n = 88), 10 glaucomatous eyes with increases of 0.14-0.75 log units were found within only 26 mo. The authors conclude that color visual fields may indicate significant change in visual function before it is apparent on standard visual fields.     

Asymmetries in visual acuity around the visual field

Human vision is heterogeneous around the visual field. At a fixed eccentricity, performance is better along the horizontal than the vertical meridian and along the lower than the upper vertical meridian. These asymmetric patterns, termed performance fields, have been found in numerous visual tasks, including those mediated by contrast sensitivity and spatial resolution. However, it is unknown whether spatial resolution asymmetries are confined to the cardinal meridians or whether and how far they extend into the upper and lower hemifields. Here, we measured visual acuity at isoeccentric peripheral locations (10 deg eccentricity), every 15° of polar angle. On each trial, observers judged the orientation (± 45°) of one of four equidistant, suprathreshold grating stimuli varying in spatial frequency (SF). On each block, we measured performance as a function of stimulus SF at 4 of 24 isoeccentric locations. We estimated the 75%-correct SF threshold, SF cutoff point (i.e., chance-level), and slope of the psychometric function for each location. We found higher SF estimates (i.e., better acuity) for the horizontal than the vertical meridian and for the lower than the upper vertical meridian. These asymmetries were most pronounced at the cardinal meridians and decreased gradually as the angular distance from the vertical meridian increased. This gradual change in acuity with polar angle reflected a shift of the psychometric function without changes in slope. The same pattern was found under binocular and monocular viewing conditions. These findings advance our understanding of visual processing around the visual field and help constrain models of visual perception.     

Visual field representations and locations of visual areas V1/2/3 in human visual cortex

The position, surface area and visual field representation of human visual areas V1, V2 and V3 were measured using fMRI in 7 subjects (14 hemispheres). Cortical visual field maps of the central 12 deg were measured using rotating wedge and expanding ring stimuli. The boundaries between areas were identified using an automated procedure to fit an atlas of the expected visual field map to the data. All position and surface area measurements were made along the boundary between white matter and gray matter. The representation of the central 2 deg of visual field in areas V1, V2, V3 and hV4 spans about 2100 mm2 and is centered on the lateral-ventral aspect of the occipital lobes at Talairach coordinates -29, -78, -11 and 25, -80, -9. The mean area between the 2-deg and 12-deg eccentricities for the primary visual areas was: V1: 1470 mm2; V2: 1115 mm2; and V3: 819 mm2. The sizes of areas V1, V2 and V3 varied by about a factor of 2.5 across individuals; the sizes of V1 and V2 are significantly correlated within individuals, but there is a very low correlation between V1 and V3. These in vivo measurements of normal human retinotopic visual areas can be used as a reference for comparison to unusual cases involving developmental plasticity, recovery from injury, identifying homology with animal models, or analyzing the computational resources available within the visual pathways.     

Testing of concentric visual field constriction by means of scotopic visually evoked potentials

Using scotopic visually evoked potentials (VEP), an objective test of concentric absolute field defects is presented. At 0.8 log units above the mean VEP threshold, the full field, the central area of 50° diameter, and the complementary peripheral field were flash stimulated. In 13 normal subjects the peripheral VEP response was larger in amplitude and shorter in latency compared to the central response. In four cases of concentric field restriction due to hysteria and malingering, the same results were found. In three cases of retinitis pigmentosa and advanced glaucoma, the peripheral VEP sensitivity was worse than the central one or no response could be found. The amount of stray light was estimated as the difference of the thresholds for central and peripheral stimulation (1.6 to 1.8 log units) in a patient with a residual central field of 20°.     

Resolution of static and dynamic stimuli in the peripheral visual field

In a clinical setting, emphasis is given to foveal visual function, and tests generally only utilize static stimuli. In this study, we measured static (SVA) and dynamic visual acuity (DVA) in the central and peripheral visual field on healthy, young emmetropic subjects using stationary and drifting Gabor patches. There were no differences between SVA and DVA in the peripheral visual field; however, SVA was superior to DVA in the fovea for both velocities tested. In addition, there was a clear naso-temporal asymmetry for both SVA and DVA for isoeccentric locations in the visual field beyond 10° eccentricity. The lack of difference in visual acuity between static and dynamic stimuli found in this study may reflect the use of drift-motion as opposed to displacement motion used in previous studies.     

Electrophysiology and perimetry in acute retrobulbar neuritis

Eighteen patients with acute retrobulbar neuritis were examined by visual field analysis and electroophthalmological recordings. The visual fields were measured to 30° with the automatic perimeter Octopus 201. The pattern-evoked cortical potential showed an increased P-100 latency followed by a decrease in 12 patients during the first two weeks of the disease. This latency change cannot be explained by remyelinization. The positive component of the pattern ERG (P-50) was reduced in all acutely affected eyes in comparison with the fellow eye. During recovery, the amplitude of the positive PERG component increased to normal, but remained slightly reduced in comparison with the response from the fellow eyes. Thirteen patients out of 18 were clinically and electrophysiologically diagnosed as having unilateral retrobulbar neuritis. However, static perimetry showed paracentral scotomas in the fellow eye in 5 cases. Recovery of the severely affected eye was accompanied by complete normalization of the visual field in the fellow eye. Thus static perimetry seems to be a more sensitive test than even the visual evoked potentials for detecting lesions in the visual pathway.