Vertical Vergence Research Articles

Regulation of static and dynamic ocular alignment in patients with trochlear nerve pareses

Ocular alignment and saccades were studied in seven patients with trochlear nerve pareses, before and after strabismus surgery. Prior to surgery, a position-dependent vertical ocular misalignment was present, and downward saccades were hypometric in the paretic eye. Strabismus surgery reduced the magnitude and position-dependence of the static misalignment. Saccade conjugacy improved in the patients with congenital pareses, and in the patient with a gradual-onset acquired paresis, but less improvement occurred in subjects with traumatic pareses. The post-operative change in saccade conjugacy relative to the change in static alignment correlated with pre-operative vertical vergence, suggesting that changes in saccade yoking depend on an interaction between saccades and vertical vergence.

Rotation of Listing's plane by horizontal, vertical and oblique prism-induced vergence

We examined the changes in Listing's plane resulting from prismatically induced vergence. The three-dimensional angular positions of the two eyes were compared in normal subjects wearing search coils and gazing at targets 1.9 m away with and without prisms. For horizontal base-out prisms each degree of convergence in one eye yielded 0.72 deg of temporal rotation of Listing's plane in that eye. The results from vertical prisms were not what was expected from the horizontal results. A base-up prism on the right eye induced a downward and temporal rotation of Listing's plane. A base-down prism on the right eye induced an upward and nasal rotation of Listing's plane. The effects of oblique prisms were those expected from combining the effects of horizontal and vertical prisms. Thus in addition to producing a horizontal or vertical misalignment of the gaze line, prisms induce an unexpected position-dependent torsional disparity.

Excess cyclovergence in patients with intermittent exotropia

Recently, we developed a model of binocular fixation. This model predicts the amount of cyclovergence as a function of target elevation and horizontal target vergence. The prediction derives from the assumption that version and vergence add linearly and that the eye positions are constrained in three respects: (1) the foveae of the two eyes are directed towards the target, (2) the version component follows Listing's law, i.e. cycloversion, and horizontal and vertical version are not independent, (3) the vergence component is restricted to a plane approximately perpendicular to Listing's plane, i.e. horizontal, vertical and torsional vergence are not independent. The version and the vergence components are characterized by a common primary direction for the two eyes. We applied this model to data of patients with intermittent exotropia. In two patients with an amblyopic eye we found that the common primary direction rotates towards the amblyopic eye. In the third patient, not suffering from amblyopia, the common primary direction was practically straight ahead. In all three patients, cyclovergence angles were larger than those found in normal subjects. We found that the increased cyclovergence was compatible with our model for normal subjects if an offset on the horizontal vergence was given. This offset represents the additional convergence effort required in these patients to overcome the exodeviation of the eyes. According to our model the increased horizontal vergence effort results in excess cyclovergence. The relation between horizontal vergence and cyclovergence offers a new method for measuring the angle of exotropia.

“Starkfest” Vision and Clinic Science Special Issue

Vertical vergence can be trained to respond to vertical and/or horizontal conjugate eye position, horizontal vergence, and vertical head tilt. This cross-coupling is manifest as a vertical phoria aftereffect (monocular vertical vergence response) that varies with direction and distance of gaze. The function of the spatially dependent adaptation is to maintain the calibration between vertical eye alignment and intended placement of the two retinal images. Oculomotor adaptation stabilizes our sense of spatial localization and calibrates a body-referenced coordinate representation of visual space that is necessary for visually guided motor responses. We have tested the possible association of vertical phoria adaptation with perceptual cues to distance in the absence of any other associated motor activity. During adaptive training, vertical disparity vergence was associated with variations of perceptual distance cues (including loom, overlap, relative size, and relative motion), oculomotor distance cues (horizontal vergence), or a combination of both classes of cues. We observed that in a 2-h period the open-loop (monocular) vertical vergence response could not be trained to occur as an aftereffect in association with the perceptual cues to distance, whereas it could be trained in association with oculomotor cues. We conclude that the spatial specificity of vertical vergence aftereffects caused by short-term adaptation results from an associated cross-coupling with supranuclear sources of oculomotor activity.

An alternative three-dimensional interpretation of Hering's equal-innervation law for version and vergence eye movements

In the context of Hering's equal-innervation law, this paper discusses the problem of how the three-dimensional positions of the two eyes, each expressed by a rotation vector, can be separated into contributions of the version and vergence system. As proposed by Van Rijn and Van den Berg [(1993) Vision Research, 33, 691–708], this can be done by taking the sum and difference of the position rotation vectors of each eye. In our alternative procedure the vergence signal is defined as the rotation which transforms the left eye position into the right eye position and the version signal is the common factor in both eye positions that remains after removing the vergence signal. The version and vergence contributions, defined in this way, can be interpreted straightforwardly as rotations. When Van Rijn and Van den Berg applied their definitions to their own data, they obtained the interesting result that the reconstructed version and vergence contributions were effectively limited to two dimensions (2D). The version signal was confined to Listing's plane (no torsion) whereas the vergence signal remained within a horizontal-torsional plane (no vertical vergence). They showed theoretically that a model based on 2D version/2D vergence control will indeed produce the torsional eye positions in near fixations found in their experiments. This model cannot account for a second set of data in the literature [Mok, Ro, Cadera, Crawford & Vilis (1992) Vision Research, 32, 2055–2064]. With our definitions, we found that the simple 2D version/2D vergence control strategy cannot account for the Van Rijn and Van den Berg (1993) data but is nicely compatible with the considerably smaller amount of cyclotorsion in the data collected by Mok et al. (1992). We also show that, in such a system, having 2D vergence control is compatible with minimization of torsional disparity and provides the cyclovergence signals suitable for stabilizing the eyes in the non-Listing positions caused by a vertical saccade in near vision.

Eye torsion associated with disparity-induced vertical vergence in humans

Recently, Enright described an unexpected association between disparity-induced vertical vergence and cycloversion (conjugate eye torsion) [ Enright (1992) Vision Research, 415, 279]. The present experiments were performed to verify these findings and investigate the nature of this association. We presented subjects with a dichoptic image of concentric circles in which a step in vertical disparity of 1 deg was introduced. After 4 sec the disparity was eliminated. Eye movements were measured with scierai coils. We confirmed Enright's findings in that a left-over right vertical vergence was associated with levo-cycloversion (upper poles towards left shoulder) and vice versa. The size of the cycloversion and the vertical vergence were in the same range. In addition we found that part of the cycloversion response was in the form of a torsional nystagmus and that the relative contribution of the left and right eyes was independent of the horizontal gaze angle. These additional findings are in conflict with the hypothesis, offered by Enright, that the association is caused by a bilateral activity of the superior oblique muscles.

Isovergence surfaces: the conjugacy of vertical eye movements in tertiary positions of gaze

Conjugate gaze is often defined as the equal angle rotation of the two eyes. For fixation at far distances, the optical axes are parallel and conjugacy is defined irrespective of the coordinate system. For nearby or finite fixation distances, the evaluation of conjugacy for many gaze postures depends on the coordinate system used to measure it. For example, if the eye is elevated or depressed and the eye is rotated about a vertical axis, the intersections of lines of sight with a tangent screen will describe either straight lines or arcs depending on whether the vertical axis is fixed with respect to the head or to the eye. Because of the horizontal separation of the two eyes, the binocular fixation of near targets at tertiary positions of gaze will require a vertical vergence component for head-referenced but not eye-referenced measurements. The vertical gaze alignment of three human subjects was measured as they viewed targets placed at secondary and tertiary eye positions at two different distances. Vertical vergence was either held open or closed-loop. The lines of sight were found to intersect (i.e. vertical gaze was aligned) regardless of target position or viewing condition.

Facilitation of vertical vergence by horizontal saccades, found in a patient with dissociated vertical deviation

The authors examined vertical vergence in a 15-year-old girl with dissociated vertical deviation, a 6d` convergent strabismus, no binocular vision, latent nystagmus, and a minimal left amblyopia. Eye movements were recorded during 4s-periods of (1) both eyes open, alternated with 4s-periods of (2a) right eye covered, (2b) left eye covered or (2c) both eyes closed. The patient preferred fixation with the right eye; when this eye was covered, the left eye took over fixation with an almost completely monocular, downward saccade (a horizontal saccade occurred at the same time). The right eye only made a very small saccade, and then started to drift upward with an exponentially decreasing velocity. Enright has shown that fast convergence or divergence may occur when a horizontal saccade is performed at the same time. Similarly, the authors suspected that, in their patient, vertical vergence was facilitated by the horizontal saccade that resulted, in this case of horizontal strabismus, from alternation of fixation. To examine whether this was the case, they compensated for the horizontal strabismus by placing a 30 prism-dioptre base-out prism in front of the left eye (the patient had no binocular vision). With the prism in place, the horizontal saccade that occurred when the right eye was covered was smaller, and only little vertical vergence occurred together with the horizontal saccade. It seems possible that vertical vergence is also facilitated by horizontal saccades.

Dissociated vertical deviation (DVD): The saccadic and slow eye movements

Dissociated vertical deviation (DVD), a vertical strabismus, is often associated with infantile esotropia, latent nystagmus and excyclo-torsion. DVD usually becomes apparent at about three years of age. The authors wished to determine whether DVD is a manifestation of an abnormal motor vergence system or is part of a visual system disorder. Vertical eye movements of six subjects with DVD, on cover-uncover and alternate cover tests, were studied using the magnetic search eye coil system. Asymmetry between the eyes' saccades were quantified during the DVD upward movement and during a trial of pure vertical saccades. In three subjects the vertical deviation increased to its full amount through a smooth vertical divergence movement, and in the other three patients through a combination of smooth and asymmetrical saccade-like movements. The latencies of the DVD, the peak velocity of the deviation movements, its time constant and the asymmetries in the saccades suggest that DVD represents an abnormal vertical vergence system.

Facial asymmetry in superior oblique muscle palsy.

Facial asymmetry is an underrecognized association or sequela of torticollis in congenital or very early onset superior oblique muscle palsy, which when present in an adult, helps to confirm chronicity and prevent unnecessary neurologic evaluation. Nineteen cases of superior oblique muscle palsy were studied prospectively. Of 12 unilateral palsies presenting in adulthood, 9 were considered congenital by history and 7 (77%) of these had facial asymmetry. Large vertical fusional vergence amplitudes and torticollis, on review of childhood photographs, confirmed the early onset of the palsy in each facial asymmetry patient. In addition, two children presenting at age 18 months and 3 years of age with constant head tilting had facial asymmetry. If torticollis is corrected before maturation of the facial structure, resolution of the asymmetry may occur.

Binocular eye orientation during fixations: Listing's law extended to include eye vergence

Any eye position can be reached from a position called the primary position by rotation about a single axis. Listing's law states that for targets at optical infinity all rotation axes form a plane; the so-called Listing plane. Listing's law is not valid for fixation of nearby targets. To document these deviations of Listing's law we studied binocular eye positions during fixations of point targets in the dark. We tested both symmetric (targets in a sagittal plane) and asymmetric vergence conditions. For upward fixation both eyes showed intorsion relative to the position that would have been taken if each eye followed Listing's law. For downward fixation we found extorsion. The in- or extorsion increased approximately linearly with the vergence angle. The direction of the Listing axis and the turn angle about this axis can be described by rotation vectors. Our observations indicate that for fixation of nearby targets the rotation vectors of the two eyes become different and are no longer located in a single plane. However, we find that it is possible to decompose the rotation vector of each eye into the sum of a symmetric and an anti-symmetric part, each with its own properties. (1) The symmetric part is associated with eye version. This component of the rotation vector is identical for both eyes and lies in Listing's plane. In contrast to the classical form of Listing's law, this part of the rotation vector lies in Listing's plane irrespective of the fixation distance. (2) The anti-symmetric part of the rotation vector is related to eye vergence. This component is of equal magnitude but oppositely directed in each eye. The anti-symmetric part lies in the mid-sagittal plane, also irrespective of fixation distance. For fixation of targets at optical infinity the anti-symmetric part equals zero and the eye positions obey the classical form of Listing's law. Thus, the symmetric and anti-symmetric parts of the rotation vectors are restricted to two perpendicular planes. Combining these restrictions in a model, with the additional restriction that the vertical vergence equals zero during fixation of point targets, we arrive at the prediction that the cyclovergence is proportional to the product of elevation and horizontal vergence angles. This was well born out by the data. The model allows to describe the binocular eye position for fixation of any target position in terms of the bipolar coordinates of the target only (i.e. using only three degrees of freedom instead of the six needed for two eyes).

Vertical vergence adaptation for normal and hyperphoric patients.

This paper discusses the use of vertical fixation disparity (VFD) measurements to determine a patient's ability to adapt to vertical prism. Vertical vergence adaptation for orthophoric patients, hyperphoric patients, and patients with vertical deviations associated with superior oblique paresis is reported. The effect of orthoptic training on the ability to adapt to vertical prism is also reported.

Vertikale akkommodative Vergenz

Five patients showed vertical accommodative vergence during which the strabismic eye deviated either up- or downwards. Additional components of strabismus included intermittent or constant exotropia, dissociated vertical divergence, and various incomitancies. There were no signs of misdirected regeneration after oculomotor palsy. We interpret vertical accommodative vergence as a supranuclear abnormality, most likely congenital.

Alternating hyperphoria

Alternating hyperphoria (synonyms: dissociated vertical deviation (DVD) or occlusion hyperphoria) and variants like 'unilateral patching hyperphoria' ('periodic vertical squint') and monocular vertical nystagmus, which may arise after strabismus operations or loss of the function of one of the eyes, have dynamic properties which differ from those of the vertical vergences or fusional movements in normal binocular vision. Alternating hyperphoria is the result of an early intense disturbance of binocular vision, leading to the absence of vertical fusional vergence or the detection of disparity necessary for this. Vertical disparity vergence is essentially a stabilizing and adaptive system.

Diagnostic Occlusion and Clinical Management of Latent Hyperphoria

Occasionally in patients who have symptoms suggestive of a vertical heterophoria no deviation is found, even on careful examination. Six days of occlusion have been recommended for uncovering such "latent" vertical deviations. We investigated prolonged monocular occlusion (Part I) and found that vertical deviations of varying amounts manifested on symptomatic and asymptomatic subjects. Thus, results of prolonged occlusion can be difficult to interpret. Nonadaptive vertical vergence systems have been implicated in development of symptoms. Therefore, it may be that diagnostic monocular occlusion is not appropriate unless patients have symptoms of vertical imbalance. We used (24 h) occlusion and associated phoria measurements (Part II) to determine vertical prism prescriptions which eliminated symptoms of seven symptomatic patients who did not show significant vertical heterophoria on routine clinical testing. We present data and case reports which elucidate the efficacy of this procedure.

Preferred vertical gaze direction and observation distance

Hill and Kroemer (1986) and Kroemer and Hill (1986) found that the preferred vertical direction of gaze is lower with a nearer binocular stimulus than with a more distant one. A model is proposed that relates this phenomenon to characteristics of the resting state of the oculomotor system. Three predictions of the model were tested, based on measurements of the preferred vertical gaze direction and dark vergence in the same subject sample. On average the effect of observation distance on the preferred vertical gaze direction served to reduce the discrepancy between the resting state of vergence, operationally defined as dark vergence, and actual convergence during inspection of the binocular stimulus. Second, dark vergence data from individual subjects could be successfully used to predict whether they raised or lowered their eyes on inspection of a binocular stimulus as compared with the preferred vertical gaze direction while viewing a monocular stimulus. Finally, predictions of the size of the change of the preferred vertical gaze direction on introduction of a binocular stimulus produced only small and non-significant correlations.

Vertical Fusional Vergences in Patients with Superior Oblique Muscle Palsies

Patients with diplopia of acute onset are referred for neurological or other evaluation because of the suspicion of underlying systemic diseases such as diabetes mellitus, hypertension, cerebral va...

Horizontal and vertical vergence training and its effect on vergences, fixation disparity curves, and prism adaptation: II. Vertical data.

The purpose of this study was to assess the effects of horizontal and vertical vergence training on vertical fusional amplitudes, the vertical fixation disparity (VFD) curve, and prism adaptation. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. We hypothesized that subjects in the vertical group would manifest increased vertical vergence amplitude and coefficients of adaptation in concert with flatter VFD slopes. Before and after the 4-week training period, vertical vergences, fixation disparity (FD) curves, and coefficients of vertical prism adaptation were measured by a single individual who was intentionally uninformed of each subject's group. Analysis of the data suggests that changes in the vertical fusional amplitudes increased slightly. Although changes in the VFD slope and coefficient of prism adaptation were not statistically significant, the changes were much greater in the vertical group and in the hypothesized direction. We suggest that the results offer preliminary support for our hypothesis.

Horizontal and vertical vergence training and its effect on vergences and fixation disparity curves: I. Horizontal data.

The purpose of this study was to assess the effects of horizontal and vertical vergence training on fusional vergences and the fixation disparity (FD) curve. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. Before and after the 4 week training period, vergences and FD curves were measured by a single individual who was intentionally uninformed of each subject's group. We hypothesized that the subjects in the horizontal training group would have increased vergence amplitudes and flatter FD slopes. Our analysis revealed that the positive vergences increased significantly for those in the horizontal group. No evidence was found to suggest changes in any variables related to the FD curve. Because type II errors were likely to be unacceptably large, further work is necessary to determine the relation between fusional vergence training and variables derived from the FD curve.

Effect of vertical prism imbalance on fixation performance.

It is well known that induced vertical imbalance will bring about deviation from central fixation in the vertical meridian. This study seeks to determine if vertical imbalance will affect the fixation performance in the horizontal meridian as well. For this purpose, a technique previously developed for monitoring fixation eccentricity was used. The technique, which is based on the effect of fixation eccentricity on border enhancement, is unaffected by adaptive changes in perceived visual direction. The results show a rapid increase in horizontal fixation misalignment with the first increments of vertical prism difference, followed by a slower increase for additional prism differences. When horizontal forced vergence was applied in addition, fixation misalignment increased throughout the range of vertical vergences. Similarly, vertical fusion misalignment was increased by horizontal fusion stress. It was concluded that forced vergence presented in one meridian will amplify any fusion misalignment that might exist in other meridians. This calls for a reevaluation of existing methods of assessing binocular fixation performance.