Comfortable Binocular Vision Research Articles

Balanced, Orientation-Dependent Dichoptic Masking in Cortex of Visually Normal Humans Measured Using Electroencephalography (EEG).

In the human visual system, cerebral cortex combines left- and right-eye retinal inputs, enabling single, comfortable binocular vision. In visual cortex, the signals from each eye inhibit one another (interocular suppression). While this mechanism may be disrupted by e.g. traumatic brain injury, clinical assessments of interocular suppression are subjective, qualitative, and lack reliability. EEG is a potentially useful clinical tool for objective, quantitative assessment of binocular vision. In a cohort of normal participants, we measured occipital, visual evoked potentials (VEPs) in response to dichoptically-presented vertical and/or horizontal sine-wave gratings. Response amplitudes to orthogonal gratings were greater than that of parallel gratings, which were in turn greater than that of monocular gratings. Our results indicate that interocular suppression is (normally) balanced, orientation-tuned, and that suppression per se is reduced for orthogonal gratings. This objective measure of suppression may have application in clinical settings.

A differential role for the posterior cerebellum in the adaptive control of convergence eye movements

IntroductionThe vergence oculomotor system possesses two robust adaptive mechanisms; a fast “dynamic” and a slow “tonic” system that are both vital for single, clear and comfortable binocular vision. The neural substrates underlying these vergence adaptive mechanisms in humans is unclear. MethodsWe investigated the role of the posterior cerebellum in convergence adaptation using inhibitory continuous theta-burst repetitive transcranial magnetic stimulation (cTBS) within a double-blind, sham controlled design while eye movements were recorded at 250hz via infrared oculography. ResultsIn a preliminary experiment we validated our stimulation protocols by reproducing results from previous work on saccadic adaptation during the classic double-step adaptive shortening paradigm. Following this, across a series of three separate experiments we observed a clear dissociation in the effect of cTBS on convergence adaptation. Dynamic adaptation was substantially reduced while tonic adaptation was unaffected. Baseline dynamic fusional vergence response were also unaffected by stimulation. ConclusionsThese results indicate a differential role for the posterior cerebellum in the adaptive control of convergence eye movements and provide initial evidence that repetitive transcranial magnetic stimulation is a viable tool to investigate the neurophysiology of vergence control. The results are discussed in the context of the current models of implicit motor adaptation of vergence and their application to clinical populations and technology design in virtual and augmented head mounted display architectures. Significance statementThe cerebellum plays a critical role in the adaptive control of motor systems. Vergence eye movements shift our gaze in depth allowing us to see in 3D and exhibit two distinct adaptive mechanisms that are engaged under a range of conditions including reading, wearing head-mounted displays and using a new spectacle prescription. It is unclear what role the cerebellum plays in these adaptive mechanisms. To answer this, we temporarily disrupted the function of the posterior cerebellum using non-invasive brain stimulation and report impairment of only one adaptive mechanism, providing evidence for neural compartmentalization. The results have implications for vergence control models and applications to comfort and experience studies in head-mounted displays and the rehabilitation of clinical populations exhibiting vergence dysfunctions.

Convergence Insufficiency: When and how to Treat

Introduction and PurposeThe purpose of this paper is to identify conditions prompting consideration of therapy for convergence insufficiency, to recognize the symptoms of convergence insufficiency and the presenting complaints of adults with asthenopia. The evaluation of the patient with convergence insufficiency and the Convergence Insufficiency Symptom Score (CISS) questionnaire are reviewed. A “Trio for Treatment” is identified. The goals for the classic treatment for convergence insufficiency are highlighted.MethodThe ophthalmologic and optometric literature on convergence insufficiency were reviewed including treatment modalities employed from 1850 to the present. A summary of this literature, along with historical data and current multi-centered nationwide randomized studies, provide data that concludes that under certain clinical conditions therapy for convergence insufficiency is both necessary and productive. Results of recent studies show the majority of patients reporting abatement of symptoms and a CISS score less than 16.ConclusionTreatment of convergence insufficiency is suggested when the patient has symptoms, presents with clinical signs and has a CISS score greater than 16. Goals of treatment are to eliminate and relieve symptoms for comfortable binocular vision at near, improve the near point of convergence, increase fusional amplitudes, increase diplopia awareness, and lower the CISS score to less than 16. Success is achieved when the patient has fewer and less severe symptoms related to reading and near work.

Vergence adaptation: a phenomenon of normal binocular vision

Aim: To describe vergence adaptation and how it may affect clinical practice. Method: A literature-based essay is presented, which includes a review of published work over the last 7 years and older literature as appropriate. Results: Vergence adaptation is a normal phenom­enon which occurs in the presence of binocular single vision to induced concomitant and incomitant devia­tions. It may be affected by age and practice. It may mask larger deviations than those initially seen during clinical testing and may be of significance in the aetiology of some forms of strabismus. Conclusion: Vergence adaptation has previously been acknowledged as being important in the maintenance of comfortable binocular vision. Consideration of the phenomenon is useful in explaining many observa­tions seen during orthoptic practice.

Vergence adaptation maintains heterophoria in normal binocular vision.

This investigation sought to determine whether vergence adaptation serves to maintain orthophoria or heterophoria in normal binocular vision. While wearing prisms which neutralized their nearpoint (40 cm) heterophorias, 27 of 30 nonstrabismic subjects adapted from their prismatically created orthophoria toward their habitual heterophoria. Three subjects showed no adaptive response. A symptom questionnaire distributed to these subjects determined that the maintenance of heterophoria by vergence adaptation is: characteristic of normal and comfortable binocular vision, and neither an entirely necessary nor sufficient condition for normal and comfortable binocular vision.

Spectacle correction for aphakia. The prismatic effect

Because spectacle lenses are fixed in position relative to the eyes, the visual axes during convergence pass nasal to the optical centers, and create a prismatic effect. The eye rotates less than 15° before the head is turned; therefore for central vision, only an area of the lens about 13 mm wide is used. A reading addition of +6.00 D is probably the maximal power bifocal addition that can be prescribed for comfortable binocular vision in a high plus correction. The distance correction produces a base-out effect of at least 4 Δ for each eye at the reading distance, even though the bifocal segments are adequately decentered.

Illustration of the incomitance pattern in congenital unilateral obliquus superior paresis with the synoptometer (author's transl)

The step-by-step measurement of VD (vertical deviation) by means of the synoptometer demonstrates the incomitance pattern clearly. This procedure was applied in 28 cases of congenital trochlear palsy. Three incomitance patterns of VD produced by the horizontal change of gaze were found: Adduction type: Absence of VD in abduction and primary position, marked increase in adduction. A zone of relative concomitance with comfortable binocular vision may be found. Linear type: Linear increase of VD with the movement toward adduction. Marked VD in primary position. Compensation more difficult. Mixed type: Linear type with marked VD in abduction. In all cases, the horizontal angle was very small, often together with a moderate V-incomitance. The incomitance caused by vertical change of gaze was only moderate. It occurred mainly between the horizontal and elevated positions. The above-mentioned classification and the classification based on incomitance with vertical change of gaze are compared.

Rearview periscope comprised of two concave cylindrical mirrors

Using novel ray-tracing techniques and methods of evaluation, optical devices comprised of two cylindrically concave mirrors have been designed and constructed which function satisfactorily as periscopic rearview systems. By following the design principles as described, mirror positions and curves are determinable which result in systems which are free of objectionable amounts of distortion and astigmatism over large fields of view. Comfortable binocular vision is obtainable along with latitude for movements of the observer's head. Examples of successful designs are given.

The Estimated Prismatic Corrections for Some Close‐Range Visual Problems*

Many subjects present for optometrical advice with problems associated with prolonged use of the eyes on tasks at close range. In many of these cases, comfortable binocular vision is achieved by attention to the accommodative state and/or a series of orthoptic procedures. However, in others further attention in the form of prismatic correction is required. In general this paper looks at the question of the prescribing of prisms and the suggestion is made that more attention should be paid to the estimation of the prism power. The necessity for the placement of a prismatic component in an optical device is examined in the conditions of exophoria and esophoria with respect to age group.

Surgical torsion of the globe as treatment for retinal detachment.

A patient with a retinal detachment resulting from a giant retinal tear was treated wih scleral buckling and intorsion of the globe 90° to place the tear in a dependent position. The retina was successfully reattached, but intolerable diplopia resulted. Comfortable binocular vision was reestablished only after the performance of appropriate oblique muscle surgery.

A Contrast in National Techniques for the Clinical Investigation of Visual Dysfunction

Summary 1 The success claimed from the use of the Infinity Balance test would, upon close analysis of the principles underlying its design and application, suppose and/or depend upon the existence predominantly of refractive anomalies, imperfections arising out of the usual monocular methods for estimating the ametropic correction, and errors of binocular balance, in the scheme of functional visual disorder.2 By simultaneous binocular parallax and alternate monocular macular fixation of separate test objects, the Infinity Balance test facilitates the visual balancing and adjustment of the ametropic correction necessary to permit both comfortable binocular vision and the efficient performance of the prescription. It helps to detect the presence of lateral and vertical imbalances opposing binocular equilibrium.3 Infinity Balance viewing under the conditions imposed by the intervention of a septum dividing the central field of binocular vision affords the detection of abnormal suspension or suppression. In this connection its extension to orthoptics for the reeducation of simultaneous vision must be approached with caution. Simultaneous perception under this test involves the macular image of the test object engaging the fixation of one eye and the extra‐macular image of the other test object for the other eye. Each eye alternates between macular and extra‐macular image representation as fixation is divided between the two eyes for viewing and assessing the visual quality of the laterally separated test objects. In cases of abnormal retinal correspondence the continued application of Infinity Balance viewing under these conditions serves only to consolidate anomalous correspondence at a stage where simultaneous (contemporaneously) foveal stimulation and macular perception are necessary for the rehabilitation of normal correspondence and fusion censolidation upon this alliance. As a precursor only, to the re‐education of simultaneous macular perception, Infinity Balance viewing may well prove an invaluable techníque both as a method for the breaking down of abnormal suspension or suppression and establishing simultaneous vision. Its later application to stereoscopic viewing is another usefui adaption of its clinical use.4 Aniseikonia and its measurement has been discussed in the light of perceptual ocular image difference. It is a condition affecting binocular vision and is measured under carefully‐controlled binocular conditions which reveal relative ocular image differences. Anomalous incongruity of the ocular images is known to effect disturbance of binocular spatial perception and orientation, and hinder the normal processes of binocular vision. The correction of anisometropia may introduce image differences which render binocular vision uncomfortable. There is no essential, concomitant, or linear relationship between anisometropia and aniseikonia. Aniseikonia can exist where there is no anisometropia, or in emmetropia. Because it is not known whether the ametropia is axial or refractive in a case of anisometropia, the amount of aniseikonia cannot he predicted, hut has to he determined by measurement.5 The evidence available reveals that aniseikonia may well he the potent and initial source of conflict encouraging and contributing to the development of conditions, a number of which we may see manifested under Infinity Balance viewing, e.g., abnormal suspension or suppression, binocular imbalance, imperfections of the unilaterally estimated ametropic correction, etc. In this connection eikonometric procedure is more introspective than Infinity Balance procedure as a diagnostic probe, and further for its special ability to screen anomalous image incongruities which affect hinocular vision. The Infinity Balance test is not a reliable screening test for the various forms of anomalous ocular image difference.A comparison can be made, but the sensitivity would he poor and, moreover, fail to detect the meridional differences. Large differences can, of course, be detected by rapid monocular comparison, e.g., corrected unilateral athakia. An estimation of aniseikcnia with any precision, using the Infinity Balance Test, would be difficult and the method of evaluation uncertain.

DIAGNOSTIC VALUE OF MONOCULAR OCCLUSION

The ophthalmologist frequently fails to give his patient comfortable binocular vision in spite of the fact that he has adequately corrected errors of refraction and motility and has eliminated the possibility of ocular disease and inflammation. The reason for this may be that some disorder of binocular vision is at fault. Of interest, therefore, is a report of the results obtained in a series of cases studied at the Dartmouth Eye Institute in which monocular occlusion was used for the purpose of determining whether binocular anomalous vision was at fault. The chief disorders affecting the comfortable and efficient cooperation of the two eyes in binocular vision are heterophoria, accommodation-convergence imbalance and aniseikonia. Binocular single vision is not present in cases of strabismus, and symptoms in such cases cannot be due to disorders of the binocular processes. On the contrary, correction of the deviation and restoration of binocular vision may result

BINOCULAR REFRACTION WITH CROSS CYLINDER TECHNIC

To Editor: —major H. Saul Sugar, in his article Binocular Refraction with Cross Cylinder Technic, published in January issue (Arch. Ophth. 31: 34, 1944), states that many persons who wear corrective lenses prescription for which has been determined by accurate monocular refraction and who do not have abnormal lateral or vertical phorias are uncomfortable during binocular vision. He then asserts that the trouble is due to changes in axes of cylinders when both eyes are used together for distant vision and during convergence accommodation. On page 37 he further states that principle of is important in obtaining of comfortable binocular vision in cases of anisometropia. This statement is followed by a brief resume of principle of spherical equivalents and rule for reduction of cylinder. Refractionists have long known that in cases both of high and of moderately