Vertical vergence movements

In a preliminary report (Houtman et al., 1977) some of the characteristics of vertical vergence movements were mentioned. One of the most striking features appeared to be their slowness, compared to the horizontal disjunctive eye movements. This is a report of further studies on the dynamic characteristics of the vertical disjunctive eye movements. Their velocity appears to be independent of the magnitude of the disparity. Also in contrast to horizontal disjunctive eye movements, the gain of the system is not linear to the amplitude of the stimulus.     

Vertical accommodative vergence]

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.     

Vertical vergence adaptation does improve with practice.

PURPOSE: To investigate the effect of repeated testing on adaptation to a 2 Delta vertical prism in subjects with normal binocular single vision. METHODS: Subjects were required to have good visual acuity and normal binocular single vision. The residual deviation was measured after a 1-min period of adaptation to a 2 Delta vertical prism using a modified Maddox Rod technique. This measurement was repeated 10 times, with a 5-min rest period between each trial. RESULTS: For eight young adult subjects, the mean residual deviation at 1 min reduced with consecutive trials, and this effect was statistically significant (p < 0.0001). No significant correlation was present between the amplitude of vertical vergence and the increase in adaptation with repeated demand. CONCLUSIONS: A practice effect for vertical vergence adaptation appears to be present in young adult subjects with normal binocular single vision.     

Vertical vergence adaptation in cases of superior oblique palsy

PURPOSE: To investigate the characteristics of vertical adaptation (VA) in superior oblique muscle palsy (SOP). SUBJECTS AND METHODS: VA was examined in 15 patients with unilateral congenital SOP, 7 patients with unilateral acquired SOP, and 35 normal volunteers. An adaptive change in the fusion-free ocular alignment, VA, was measured with a computer-aided mirror haploscope. The fusion-free ocular alignment was measured before inserting a 3 prismdiopter vertical prism, immediately after inserting the prism, and at 10 minutes and 30 minutes after insertion. We investigated VA gain, age, vertical fusional range, response of prism adaptation test (PAT), and superior oblique muscle atrophy in magnetic resonance imaging (MRI). RESULTS: The VA gain (mean +/- standard deviation, %) at 30 minutes in congenital, acquired, and normal groups was 86 +/- 53, 34 +/- 23 and 58 +/- 16, respectively. The mean of the VA gains at 30 minutes in the congenital group was greatest, and that in the acquired group was least(p < 0.01). In the congenital group there was a correlation between VA gain and response of PAT (p = 0.02, r = 0.60). The VA gain did not significantly correlate with age, vertical fusional range, or muscle atrophy. CONCLUSION: The VA gain observed in congenital SOP was greater than that of acquired SOP, and affected the response of PAT.     

Distance vergence adaptation is abnormal in subjects with convergence insufficiency

It is well known that in convergence insufficiency (CI) prism adaptation is reduced in response to base-out (BO) prisms at near. There have also been some suggestions in the literature that adaptation is reduced at other distances as well. The present data show that in CI adaptation is not only reduced in response to BO at near, but also in response to base-in (BI) at near and for both BI and BO at distance. This raises the interesting question whether distance adaptation becomes reduced because of reduced near adaptation or whether these subjects have a generally reduced horizontal adaptation mechanism.     

Vertical vergence in nonhuman primates depends on horizontal gaze position

ABSTRACT

The goal of this study was to compare vertical fusion capability at different orbital eye positions in normal nonhuman primates and attempt to use this information to isolate the extraocular muscles (EOMs) that mediate vertical vergence. Scleral search coils were used to record movements of both eyes as two normal nonhuman primates (M1, M2) performed a vertical vergence task at different horizontal eye positions. In a control experiment, M1 was also tested at different angles of horizontal vergence. To elicit vertical vergence, a 50° x 50° stimulus comprising a central fixation cross and random dots elsewhere was presented separately to each eye under dichoptic viewing conditions. Vertical disparity was introduced by slowly displacing the stimulus for one eye vertically. Vertical fusion amplitude (maximum disparity that the monkey was able to fuse) and vertical vergence (maximum difference in vertical position of the two eyes) were measured. Vertical fusion capability differed at different orbital eye positions. Monkey M1 had significantly smaller vertical fusion capabilities when the right eye (RE) was abducted than left eye (LE) while M2 had significantly smaller vertical fusion capabilities when the RE was adducted and LE abducted. M1 also showed greater vertical fusion capability for near gaze. M1 data suggested that the vertical recti mediated vertical vergence in the RE and the oblique muscles in the LE while M2 data suggested that the oblique muscles mediated vertical vergence in the RE and the vertical recti in the LE. The variable results within the same animal and across animals suggest that EOM involvement during vertical fusional vergence is idiosyncratic and likely a weighted combination of multiple cyclovertical muscles.     

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.     

Nonlinear alteration of transient vergence dynamics after sustained convergence.

BACKGROUND: Adaptation models of the horizontal disparity vergence system assume a nonadaptable transient component. They also predict identical postadaptation dynamics during convergence and divergence movements. METHOD: To test the adaptation property of the transient component, a set of experiments were performed in which closed-loop vergence dynamics measured before and after sustained convergence were compared, primarily by comparing the peak vergence velocity, occurrence time of peak vergence velocity, and steady-state vergence posture. Vergence dynamics after durations of 30, 60, and 90 s of sustained convergence were compared with those after a control duration of 5 s. RESULTS: The peak divergence velocity was reduced by about 25% within 30 s of sustained vergence. However, the peak convergence velocity was unchanged for all the exposure durations. Additionally, for all durations, the peak divergence velocity was significantly higher than peak convergence velocity. In contrast to peak velocities, the occurrence time of peak convergence and divergence velocity did not differ significantly and remained unchanged for all durations. CONCLUSIONS: The transient component is adaptable. Furthermore, the adaptation is direction dependent and affects divergence and convergence dynamics differently, thereby suggesting involvement of separate pathways for convergence and divergence in the vergence sensorimotor control.     

The role of accommodative convergence at the limits of fusional vergence.

Two possible explanations are presented for the mechanism which limits the maximum fusional vergence response. An experimental paradigm is developed to differentiate between these alternatives. Experimental results indicate that the blur generally associated with strong fusional effort is due to convergence accommodation "overdrive." Th important theoretical and clinical implications of this finding are presented.     

Independence of convergence and divergence: norms, age trends, and potentiation in mechanized prism vergence tests

Motor-driven prism stereoscope vergence tests, base in break, base in recovery, base out break, and base out recovery, repeated three times (BIB, BIR, BOB, BOR X 3) were given to three separate groups. Two instruments with different speeds were used. Repeated testing shows a slight trend to convergence in slower machines. The results from both machines are still comparable. Means are similar to previously published norms from hand-turned instruments, but the variance of scores is about twice as large and there is an eso trend at near. The motor drive aids discrimination, since Ss who are capable can now follow with smooth vergences over a wider range. In general, there is no substantial trend with age between 3 and 25 years other than those which may be due to decreasing response times. Vergence scores can be adequately reduced to two independent factors, loading on convergence and divergence, respectively, which suggests that there are two processes varying independently in maturation and therapy as well as assessment.     

Vertical fixation disparity curve and the effects of vergence training in a normal young adult population.

BACKGROUND: The vertical forced vergence fixation disparity (VFD) curve represents the amount of vertical fixation disparity, the steady-state vertical bifixation error of the eyes, at various levels of vertical vergence demand. The main aim of the present study was to examine the effects of vertical vergence training on the slope of the VFD curve in a normal, young adult population. METHODS: Forty-five subjects with normal vision and binocular function underwent vertical vergence training for 1 week. The training was done using a vertical prism bar, and the vertical fixation disparity was measured using the Disparometer. RESULTS: The mean slope of the VFD curve in a normal, young adult population was 1.103 min arc/delta. The slope of the VFD curve decreased significantly after the training and remained flattened for at least 3 months. There was no evidence to support the idea that the decrease in the VFD slope was related to the increase of vertical fusional amplitude. CONCLUSIONS: Vertical prism bar training provided a long-term effect, both increasing the vertical fusional amplitude and flattening the slope of the VFD curve. The decrease in the slope of the VFD curve was thought to be independent of the increase of vertical fusional amplitude.     

Dynamic vergence eye movements in strabismus and amblyopia: asymmetric vergence.

This report investigates line-of-sight asymmetric disparity vergence in patients having either intermittent strabismus, constant strabismus with amblyopia, or amblyopia without strabismus. We find an absence of disparity vergence in all patients with strabismus and in some with amblyopia only. Accommodative vergence and saccades place the dominant eye on the targets moving in depth. These accommodative vergence responses have normal dynamic characteristics, thus indicating a properly functioning vergence motor system. We purpose there is a higher-level central defect in which incoming information of one eye is suppressed, so that the disparity vergence system is rendered inoperable.