Suppression Scotoma Research Articles

Suppression and the pattern visual evoked potential.

We assessed the effect of amblyopic suppression on the pattern visual evoked potential (P-VEP). Since anisometropic amblyopia is associated with the monofixation syndrome and a central suppression scotoma in the amblyopic eye, patients with this functional defect were used for the study. Five anisometropic amblyopes and four normal subjects were studied using the P-VEP test. A modified haploscope was used to present a pattern stimulus to the area of suppression. By comparing responses generated under monocular conditions (non-suppression) with monocular responses under binocular viewing conditions (suppression), we measured the effect of suppression on the P-VEP. Our results show that amblyopic suppression completely abolishes P-1 amplitudes in patients with large suppression scotomas; in patients with small suppression scotomas the P-1 amplitudes were greatly reduced. Rivalry in normals also caused a reduction in P-1 amplitudes, but to a much lesser degree than that associated with anisometropic suppression. Patients with significant amblyopia did not show a rivalry effect on the P-VEP. Because the P-1 wave of the transient P-VEP is thought to represent activity at the level of the striate cortex, our results indicate that suppression probably occurs at the striate cortex or lateral geniculate nucleus.

Suppression and retinal correspondence in intermittent exotropia.

Suppression scotomas and retinal projection (retinal correspondence) were measured in six intermittent exotropes during deviation. Measurements used red-green anaglyph stimuli presented on a black background which could be varied from 3.4 minutes of arc to 3 degrees 24'. Results showed non-suppression of all points between the fovea and the diplopia point. Harmonious anomalous retinal correspondence was usually observed. Two subjects had spontaneous changes from anomalous retinal correspondence to normal retinal correspondence without a concurrent change in ocular position. Conventional testing resulted in more variable results in regard to retinal correspondence and suppression, suggesting that non-suppression and anomalous retinal correspondence occur when black backgrounds are used for testing.

Binocular Polaroid test.

A test is presented for the detection of small suppression scotomas in strabismic and in anisometropic patients. Three small light-spots (the central is polarized) are viewed through Polaroid filters placed in front of the eyes. This arrangement produces the perception of the central spot only from one eye, but normal fusion provides the perception of three light-spots. Complete suppression of the central light indicates the presence of a scotoma in the binocular visual field. An inhibition scotoma in the non-dominant eye was found in all cases of small angle esotropia and of anisometropic amblyopia.

Suppression in strabismus--an update.

Previous reports have described suppression scotomas, suppression varying with the type of strabismus and suppression confined to one half of the retina (hemiretinal suppression). Our findings show that suppression in all varieties of strabismus, with the exception of the monofixation syndrome, involves the whole of the visual field of the deviating eye except for its monocular temporal crescent. In the monofixation syndrome our findings show a small central suppression scotoma involving the fovea but leaving the rest of the visual field of the deviating eye unsuppressed. We could find no evidence to support the concept of hemiretinal suppression but found evidence to support the presence of a trigger mechanism for suppression which operates on a hemiretinal basis.

Binocularity in comitant strabismus: binocular visual fields studies.

A critical review is made of the literature on binocular perimetry in strabismus. A broad range of results was obtained by various authors, because different testing techniques were used. The concept of sensory testing of strabismic patients in casual seeing condition should be introduced also into binocular perimetry. Therefore a series of experiments is presented in which patients with small-angle comitant strabismus were tested. It was shown that: a) in small-angle esotropia the areas of single vision previously thought to be due to suppression are, instead, areas of binocular vision sustained by anomalous retinal correspondence (ARC); b) this can be seen only when using fusable stimuli as test targets; c) no suppression scotomas were found in patients with small-angle strabismus in the whole visual field; d) appropriate control-marks for binocularity are necessary, i.e. monocularly presented items. They influence the results, as well e) the area of binocular single vision in strabismus (called pseudo-Panum's area) is wider than the Panum's area of normals. Moreover it is easier to disrupt binocular cooperation sustained by ARC causing diplopia than binocular cooperation in normals; f) ARC seems to be more deeply rooted in the center than in the periphery of the visual field; g) superimposable findings were obtained in small-angle constant exotropia; h) in large-angle exotropia wide suppression scotomas were found, which often override the midline. Hemianopic suppression scotomas in exotropia can be found only when 'dissociating' testing techniques are used; i) the same group of patients with small-angle esotropia was examined with the author's technique and with the classical method proposed by Harms. The results were strongly dependent on the method used and the same patient responded differently to the two tests. It is concluded that in small-angle strabismus there is an anomalous type of binocular single vision, which can be tested with binocular visual field techniques. This binocularity can only be found when non-artificial testing conditions are used. The usefulness of this anomalous binocular vision in the every day seeing condition of the patient is discussed.

Suppression scotomata in concomitant strabismus with harmonious anomalous correspondence.

With binocular scotometry it was shown how the peripheral suppression scotoma of the squinting eye in cases of concomitant strabismus with harmonious anomalous correspondence can be split into 2 parts by a vertical prism. The parts are called the rivalry scotoma and the residual scotoma. This observation has not been described earlier.

Ocular motility in alternating squints: an electro-oculographic study.

Ocular movements were studied electro-oculographically in 10 normal subjects and 10 patients with alternating strabismus. Fixation and pursuit movements and to a less extent the saccadic movements were observed to be abnormal in patients with alternating strabismus. The defect in pursuit movements was shown to be statistically significant. There was no correlation between the extent of ocular motor abnormalities and the angle of deviation or the size of facultative suppression scotoma. The possible common pathological mechanism leading to the ocular motor abnormalities qualitatively similar to those reported earlier in strabismus and anisometropic amblyopes are discussed.

The conservative treatment of a squint.

The ideal purpose of squint treatment is threefold: to obtain a normal and equal vision in both eyes, orthophoria in all directions of gaze and a good binocular cooperation between both eyes; this means bifoveal fusion and a good fusional range. It is often not possible to obtain this ideal. Therefore the practical aims we look for in all-day practice are to obtain a normal vision in both eyes, a cosmetically acceptable strabismus (with an angle of deviation as near to 0° as possible) and a binocular cooperation as good as possible, often limited to peripheral fusion with a little foveal suppression scotoma in the slightly deviating eye.

Colored filters and screens for studying monocular perception in binocular vision.

Mutually exclusive red and green glasses can be used with white, black, or colored (red or green) screens to study monocular perception in binocular vision. An unmarked white screen viewed through the glasses is a simple test for anomalous retinal correspondence in strabismus. These patients observe a characteristic division of colors in accordance with alignment of their visual axes because the macular region of the deviating eye predominates over the functionally corresponding peripheral area of the fixating eye. This ‘divided color field’ phenomenon in anomalous correspondence also can be demonstrated by having the patient note changes in the color of a white test object against a black screen or dark colorless background; however, a red or green screen adds additional refinement. The field of perception of one eye then can be plotted while the other eye maintains fixation and a full field of vision. Also, suppression scotomas and the position of the blind spot of the deviating eye can be plotted. Either white cards with red and green spots, or colored cards (red or green) with black and white spots are useful with mutually exclusive red and green glasses to test binocular perception in near vision. Three vertically aligned spots are used. Two are perceived through one filter and one through the other filter. In contrast to the conventional Worth four-light test, transparencies and retroillumination are not required, and the spots easily can be varied in size and separation. Dots are used to test bifoveal versus bimacular perception.

Etiology and Pathogenesis of Fixation Anomalies in Strabismus. IV: Roles of Suppression Scotoma and of Motor Factors

Etiology and Pathogenesis of Fixation Anomalies in Strabismus. IV: Roles of Suppression Scotoma and of Motor Factors

THE BLINDSPOT SYNDROME

IN 1947 a squint syndrome was described in which the physiologic blindspot, created by the optic papilla, seems to play an especial role. 1 Recognition of this syndrome resulted from a study of the field of binocular vision in 296 cases of concomitant esotropia in older children and adults. For distant fixation the physiologic blindspot of the deviating eye was found to overlie the point of fixation in 80 cases; i.e., the deviation was 12 to 18 degrees. In most of these cases the physiologic blindspot was only part of a suppression scotoma and its position was inconstant; however, there were 7 cases in which it seemed probable that the physiologic scotoma provided the essential mechanism for the alleviation of diplopia and played an important role in maintaining the esotropic state. These 7 cases had in common certain symptoms and signs, and the responses to treatment and clinical courses were

A SQUINT SYNDROME

IN 1934 Braun 1 called attention to the fact that the normal blindspot, resulting from the absence of perceptive elements in the optic papilla, may form the nucleus of a suppression scotoma in the squinting eye. Seven cases of esotropia are now reported as representative of a clinical entity in which the physiologic seems to play an exceptional role as a central scotoma in the squinting eye. Recognition of the blindspot syndrome is important because it seems common and remediable. Restoration of comfortable single binocular vision results if treatment is properly directed, whereas partial or improper measures are of little benefit and may add to the patient's distress. Recognition of this syndrome resulted from determination of the field of binocular vision in 296 cases of concomitant esotropia in older children and adults. The field of binocular vision was plotted by the use of colored filters and twin projection systems