Disjunctive optokinetic nystagmus in a naturally esotropic macaque monkey: interaction between nasotemporal asymmetries of versional eye movement and convergence

OBJECTIVE: To assess the interaction between versional and vergence eye movements in normal and strabismic monkeys. METHODS: Horizontal optokinetic nystagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had naturally occurring early-onset esotropia. Mean eye velocity and vergence angles were calculated during the slow phases of OKN. RESULTS: The strabismic monkey had a nasotemporal asymmetry of OKN favoring nasally directed motion in each eye. During monocular optokinetic stimulation, mean eye velocities were substantially greater for the adducting as compared to the abducting eye. The velocity of the abducting eye was between 55 and 80% of the velocity of the adducting eye (p < 0.01). As a consequence of the disjunctive movements, the eyes converged an average of 4 +/- 2.8 degrees during OKN. Saccadic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey. CONCLUSION: Disjunctive OKN in the esotropic monkey suggests that the cerebral maldevelopment responsible for nasally biased OKN also contributes to nasal biases in vergence pathways.     

Latency of saccades, vergence and combined saccade vergence movements in a subject with manifest latent nystagmus

PURPOSE: To study eye movements in 3D space - saccades, vergence and combined eye movements - in a subject with Manifest Latent Nystagmus (MLN). METHODS: A 13-year-old girl diagnosed with MLN participated in this study. Saccades, pure vergence along the median plane and combined saccade-vergence movements were recorded under both binocular and monocular viewing. Horizontal eye movements from both eyes were recorded simultaneously with a photoelectric device (Bouis Oculometer). RESULTS: The recordings of saccades, vergence or both components of combined movements show that such movements have a staircase trajectory. The consequence of this staircase behavior is that the time for approaching the target is prolonged. The latency of all types of eye movements is extended when the subject is viewing binocularly, while latency values are normal when viewing monocularly; the difference between the viewing conditions is significant for vergence. CONCLUSION: The normal latency values under monocular viewing are attributed to facilitation of eye movement initiation by the increased nystagmus.     

The effects of short-term experimental strabismus on the visual system in Macaca mulatta.

Experimental esotropia was produced surgically in infant rhesus monkeys (Macaca mulatta) for brief periods of time. Electrophysiological studies of the visual cortex showed that esotropia of only 2 weeks duration in an infant monkey is sufficient to cause a marked shift of dominance in favor of the fixating eye and to virtually extinguish cortical neuronal responses from the esotropic eye. In the lateral geniculate nucleus cell (LGN), shrinkage of 6% to 8% occurred in the parvocellular layers connected with the esotropic eye, the magnocellular layers showing no changes. After the fixating eye had been sutured for 3 weeks, a complete reversal of the cortical physiology in favor of the esotropic eye occurred, whereas no recovery in cell size was observed in the LGN. Surgical realignment of an esotropic eye caused recovery of cortical neuronal responses from the formerly esotropic eye, but the number of binocularly responsive cells remained reduced.     

Speed and accuracy of saccades, vergence and combined eye movements in subjects with strabismus before and after eye surgery

The purpose of the study was to examine spatio-temporal characteristics of horizontal eye movements in the natural space (saccade, vergence and combined movements) in young subjects with early onset convergent or divergent strabismus. Nine young subjects (8-20 years old) were tested: three with divergent strabismus, six with convergent strabismus. A standard paradigm was used to elicit pure horizontal saccades at far and at close viewing distance, pure vergence along the median plane (convergence and divergence) and saccades combined with vergence movements. Horizontal eye movements from both eyes were recorded by a photoelectric device. Eye movements were recorded before surgery, and, for the majority of the subjects, two times after surgery. Before surgery the accuracy of convergence and divergence movements in their pure or combined form was poor with respect to normal values. The mean velocity of convergence was also abnormally slow. Strabismus surgery improved significantly the accuracy of these types of eye movements. The speed of pure convergence and of divergence combined movements increased significantly after surgery. We concluded that poor vergence eye movement’s performance, particularly those found for convergence in strabismic subjects could be due to impairment in the central structures related to sensory disparity inputs. Adaptive mechanisms promoted by the realignment of the eyes could be at the origin of the improvement in the vergence performances observed in our subjects after strabismus eye surgery.     

Comparison of latent nystagmus and nasotemporal asymmetries of optokinetic nystagmus in adult humans and macaque monkeys who have infantile strabismus

To determine whether macaque monkeys with infantile strabismus have latent nystagmus and directional asymmetries of horizontal optokinetic nystagmus (OKN) similar to those of humans with infantile strabismus, the authors recorded eye movements under conditions of monocular viewing. The presence of latent fixation nystagmus was tested by requiring the subjects to steadily fixate a stationary target subtending less than I deg of visual arc. OKN was tested using high-contrast, vertically-oriented moving stripes that filled 80 deg of the visual field. A macaque monkey who had infantile strabismus induced by alternating occlusion from birth showed latent nystagmus highly similar to that recorded in an adult human subject with infantile strabismus. The strabismic monkey also had asymmetric OKN similar to that of the strabismic human, favoring nasally-directed stimulus motion when viewing with either eye. Neither nystagmus nor an OKN asymmetry was observed in a normal macaque or in humans who had normal binocular vision. The findings of latent nystagmus and OKN asymmetries in the strabismic monkey support the notion that monkeys who have infantile-onset strabismus are an appropriate ocular motor model of human infantile strabismus.     

Effect of infantile strabismus on visuomotor development in the squirrel monkey (Saimiri sciureus): Optokinetic nystagmus,motion VEP and spatial sweep VEP

PURPOSE. To determine whether squirrel monkeys made artificially strabismic in infancy had ocular fixation abnormalities, directional asymmetries of horizontal optokinetic nystagmus (OKN) and asymmetries of motion visually evoked potentials (MVEPs) similar to those of humans with infantile strabismus. METHODS. Esotropia was produced in a newborn squirrel monkey by surgical tenotomy of both lateral rectus muscles. The alignment and eye rotations of the monkey were examined longitudinally and VEP testing was performed at the age of one year. Visual acuity was measured using spatial frequency sweep VEPs (SSVEP) in response to grating stimulation. OKN was tested under conditions of monocular viewing using full-visual-field, vertically oriented, moving stripes. MVEPs in response to horizontal motion were recorded with the animal sedated to reduce the possibility of eye movement artifact. RESULTS. The artificially strabismic squirrel monkey displayed a constant, comitant esotropic strabismus accompanied by latent nystagmus. Monocular SSVEP acuity was subnormal in one eye, consistent with mild monocular strabismic amblyopia. The monkey demonstrated asymmetric OKN favoring nasally-directed stimulus motion when viewing with either eye. Monocular MVEPs were also characterized by a horizontal asymmetry with a directional bias inverted 180 degrees between the right and the left eyes. The eye movements and MVEP asymmetries were similar to those observed in strabismic macaque monkeys and humans with early-onset strabismus. Neither the OKN asymmetry nor the MVEP asymmetry was evident in a normal squirrel or normal macaque monkey. CONCLUSION. The artificially strabismic squirrel monkey is an appropriate eye movement and VEP model for the study of neural mechanisms in human infantile strabismus.     

Neuronal basis of optokinetic reflex pathology in naturally strabismic monkeys

The optokinetic reflex and neuronal response properties in the central visual pathway were studied in three macaque monkeys (Macaca nemestrina) with early childhood strabismus of various origin. Binocularity in the primary visual cortex (VI) measured electrophysiologically was reduced both in a monkey with resolved strabismus and in a monkey with accommodative strabismus when compared to normal controls. By contrast, binocularity in the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) was only reduced in the monkey with resolved strabismus ('resolved'), but appeared normal in animals with accommodative strabismus ('accom. 1 'and 'accom. 2'). Sub-threshold binocular interactions were normal in all animals. The velocity tuning curves of retinal slip neurons in the NOT-DTN of all strabismic monkeys were not different from normal controls. Horizontal optokinetic nystagmus was asymmetric in monkey 'accom. 2', and for the non-fixating eye in monkey 'resolved'. In monkey 'accom. 1' OKN was normal. Open loop eye velocity was lower in the monkey with resolved strabismus than in monkeys with accommodative strabismus. These data suggest that different causes of strabismus may affect neuronal response properties and behavior to different degrees. The effects on the optokinetic reflex of resolved, but early onset strabismus were more severe than those of accommodative strabismus. This corresponds to the wide variability of defects in the optokinetic system of strabismic humans.     

Horizontal saccade disconjugacy in strabismic monkeys

PURPOSE: Previous studies have shown that binocular coordination during saccadic eye movement is affected in humans with large strabismus. The purpose of this study was to examine the conjugacy of saccadic eye movements in monkeys with sensory strabismus. METHODS: The authors recorded binocular eye movements in four strabismic monkeys and one unaffected monkey. Strabismus was induced by first occluding one eye for 24 hours, switching the occluder to the fellow eye for the next 24 hours, and repeating this pattern of daily alternating monocular occlusion for the first 4 to 6 months of life. Horizontal saccades were measured during monocular viewing when the animals were 2 to 3 years of age. RESULTS: Horizontal saccade testing during monocular viewing showed that the amplitude of saccades in the nonviewing eye was usually different from that in the viewing eye (saccade disconjugacy). The amount of saccade disconjugacy varied among animals as a function of the degree of ocular misalignment as measured in primary gaze. Saccade disconjugacy also increased with eccentric orbital positions of the nonviewing eye. If the saccade disconjugacy was large, there was an immediate postsaccadic drift for less than 200 ms. The control animal showed none of these effects. CONCLUSIONS: As do humans with large strabismus, strabismic monkey display disconjugate saccadic eye movements. Saccade disconjugacy varies with orbital position and increases as a function of ocular misalignment as measured in primary gaze. This type of sensory-induced strabismus serves as a useful animal model to investigate the neural or mechanical factors responsible for saccade disconjugacy observed in humans with strabismus.     

The effect of distractors on saccades and adaptation of saccades in strabismus

This paper reports two experiments to determine the contribution of the suppressing eye to the generation of saccadic eye movements in constant strabismus. Eye movements were recorded using a Skalar infra-red recorder. Experiment 1 tested six participants with constant strabismus, pathological suppression and no clinically demonstrable binocular single vision (BSV). We explored the effect of visual distractors presented monocularly (to either the fixing eye or the strabismic eye) and binocularly, on saccade latency and accuracy. Saccade latency significantly increased when distractors were presented to the strabismic eye compared to the no distractor condition. In all participants the effect on latency, with distractors presented to the strabismic eye, was maximum when distractors were presented towards the location of the anatomical fovea. Saccade accuracy was reduced with ipsilateral distractors to the target when presented binocularly or monocularly to the fixing eye but not affected by distractors presented to the strabismic eye. Experiment 2 investigated fast disconjugate saccade adaptations in six participants with constant strabismus, pathological suppression and no clinically demonstrable BSV and for comparison 8 with normal bifoveal BSV. Saccade disconjugacy was induced using an electronic feedback system in which the calibrated eye movement position signal could be scaled by a factor (the feedback gain) to move the target visible to one eye during binocular viewing. In all BSV participants and 3 of 6 participants with constant strabismus, saccadic adaptation occurred rapidly such that under conditions of visual feedback saccades became increasingly disconjugate. These disconjugacies persisted when normal viewing conditions were restored. The presence of an adaptive mechanism to adjust the binocular co-ordination of saccades in the presence of constant strabismus with suppression and no clinically demonstrable BSV has been demonstrated. Mechanisms that might explain such results are discussed.     

The effect of distractors on saccades and adaptation of saccades in strabismus

This paper reports two experiments to determine the contribution of the suppressing eye to the generation of saccadic eye movements in constant strabismus. Eye movements were recorded using a Skalar infra-red recorder. Experiment 1 tested six participants with constant strabismus, pathological suppression and no clinically demonstrable binocular single vision (BSV). We explored the effect of visual distractors presented monocularly (to either the fixing eye or the strabismic eye) and binocularly, on saccade latency and accuracy. Saccade latency significantly increased when distractors were presented to the strabismic eye compared to the no distractor condition. In all participants the effect on latency, with distractors presented to the strabismic eye, was maximum when distractors were presented towards the location of the anatomical fovea. Saccade accuracy was reduced with ipsilateral distractors to the target when presented binocularly or monocularly to the fixing eye but not affected by distractors presented to the strabismic eye. Experiment 2 investigated fast disconjugate saccade adaptations in six participants with constant strabismus, pathological suppression and no clinically demonstrable BSV and for comparison 8 with normal bifoveal BSV. Saccade disconjugacy was induced using an electronic feedback system in which the calibrated eye movement position signal could be scaled by a factor (the feedback gain) to move the target visible to one eye during binocular viewing. In all BSV participants and 3 of 6 participants with constant strabismus, saccadic adaptation occurred rapidly such that under conditions of visual feedback saccades became increasingly disconjugate. These disconjugacies persisted when normal viewing conditions were restored. The presence of an adaptive mechanism to adjust the binocular co-ordination of saccades in the presence of constant strabismus with suppression and no clinically demonstrable BSV has been demonstrated. Mechanisms that might explain such results are discussed.     

Binocular eye movements during accommodative vergence

Binocular eye position was monitored by the photoelectric technique during accommodative vergence. Contrary to previous reports indicating that accommodative vergence was a uniocular phenomenon, without exception, binocular accommodative vergence movements were recorded. The total vergence amplitude in the viewing eye was reduced, on the average, by approximately 88% with respect to the vergence movement measured in the covered eye. Some saccadic eye movements that occurred during vergence movements were likewise reduced in amplitude in the viewing eye by up to 20%. Smooth eye movements were utilized to counteract the vergence movement in the viewing eye. This smooth movement alone, or in conjunction with a late saccade, returned the eye to the target and helped to maintain the retinal image of the target coincident with the foveal center for the duration of the accommodative vergence movement. Thus, there appears to be a fixation-holding mechanism which produced a general attenuation of both vergence and some saccadic movements in the viewing eye. Although this control strategy produced violations of Hering's law with respect to the magnitude of the movements in the eyes but not with respect to the direction of the movement, it was implemented in the interest of retaining the target within the sensitive foveal region.     

The latency of saccades,vergence, and combined eye movements in children and in adults

PURPOSE: To examine the latency of eye movements in three-dimensional space (saccade, vergence, and combined saccade-vergence) in children and adults. METHODS: Fifteen normal children (4.5-12 years of age) and 15 normal adults (22-44 years of age) were tested. A standard paradigm was used to elicit pure lateral saccades at far and close viewing distance, pure vergence (convergence and divergence), and saccade combined with vergence movements. Horizontal eye movements from both eyes were recorded simultaneously by the oculometer, a photoelectric device. RESULTS: The mean latency in saccades, vergence, and combined eye movements was longer in children than in adults; the variability of such latency values was also larger in children. There was a progressive decrease with age in mean latency. All latencies approached or reached adult levels at approximately 10 to 12 years of age. Latency of saccades at close viewing distance was shorter than that at far in both adults and children. Convergence latency was longer than divergence latency in adults and most of the children. Latency of components of combined movements was longer than that of corresponding pure movements. Children initiated combined movements by triggering the vergence component first, whereas adults did not show a dominant pattern. The percentage of synchronous start of the two components was significantly higher in adults. CONCLUSIONS: Saccade- and vergence-triggering mechanisms are distinct and mature progressively and in parallel with age. The capacity for synchronization of the two components of combined eye movements develops more slowly and remains below adult level, even at the age of 12 years.     

Early versus delayed repair of infantile strabismus in macaque monkeys: I. ocular motor effects.

INTRODUCTION: The appropriate age for surgical correction of esotropic strabismus in human infants is controversial; some clinicians advocate surgery before age 6 months, and others recommend observation and surgery at older ages. Infantile (congenital) esotropia in humans and monkeys is known to be accompanied by a constellation of eye movement abnormalities caused by maldevelopment of cerebral visual motor pathways. The purpose of this study was to determine how early versus delayed correction of strabismus influences development and/or maldevelopment of these eye movement pathways. METHODS: Optical strabismus was created in infant macaques by fitting them with prism goggles on day 1 of life. The early correction group (2 experimental and 1 control) wore the goggles for a period of 3 weeks (the equivalent of 3 months before surgical repair in humans). The delayed correction group (3 experimental and 1 control) wore the goggles for a period of 3 or 6 months (the equivalent of 12 or 24 months before surgical repair in humans). Several months after the goggles were removed, the monkeys were trained to perform visual fixation, smooth pursuit, and optokinetic nystagmus (OKN) tasks for a juice reward. Eye movements were recorded using binocular search coils. The performance of the early versus delayed infant monkey groups was also compared with that of a group of adult monkeys who had unrepaired, naturally occurring infantile esotropia. RESULTS: Early correction monkeys developed normal eye movements and exhibited ocular motor behaviors that were indistinguishable from normal control animals. They regained normal binocular eye alignment and showed stable fixation (no latent nystagmus). Monocular horizontal smooth pursuit and large field OKN were symmetric. In contrast, delayed correction monkeys showed persistent esotropia, latent fixation nystagmus, dissociated vertical deviation, and pursuit/OKN asymmetry. Animals who had the longest delay in correction of the optical strabismus exhibited eye movement abnormalities as severe as those of adult animals with uncorrected, natural esotropia. CONCLUSIONS: Early correction of strabismus in primates prevents maldevelopment of eye movements driven by cerebral motor pathways. Our results provide additional evidence that early strabismus correction may be beneficial for brain development in human infants.     

Eye-movement responses to disparity vergence stimuli with artificial monocular scotomas

The effects of artificial monocular scotomas on eye-movement responses to horizontal disparity vergence stimuli were studied in six subjects with normal binocular vision. Subjects viewed stereoscopic 1.5 degrees horizontal step disparity vergence stimuli through liquid crystal shutter glasses. The central portion of the stimulus presented to the right eye was removed to simulate monocular artificial scotomas of variable diameters (2 degrees to 10 degrees ). Eye movements were recorded with a binocular head-mounted eye tracker. Responses included pure vergence, vergence followed by saccades, and pure saccadic eye movements. The rate of responses with saccadic eye movements increased with the diameter of the artificial scotoma (p < 0.0001); there was an increase in the rate of responses starting with saccades (p < 0.0001), as well as an increase in the rate of saccades after initial vergence responses (p < 0.01). The probability of saccades after initial vergence responses was affected by the open-loop gain of the vergence response (p < 0.001). The open-loop gain decreased with increased diameters of the artificial scotomas (p < 0.0001). As the diameter of the artificial scotomas increased, the amplitude of the initial vergence eye-movement responses decreased, and the prevalence of saccadic eye movements and asymmetric vergence increased. The effects of the diameter of artificial monocular scotomas on eye-movement responses in subjects with normal binocular vision are consistent with the effects of diameter of suppression scotomas on eye-movement responses to disparity vergence stimuli in patients with infantile esotropia.     

Incomitance in monkeys with strabismus

PURPOSE: Rhesus monkeys reared with restricted visual environment during their first few months of life develop large ocular misalignment (strabismus). The purpose of this study was to describe 'A and V' patterns and DVD in these animals during fixation and eye movements and suggest that this form of rearing produces animals that are suitable model to study the mechanisms that might cause 'A/V' pattern incomitant strabismus and dissociated vertical deviation (DVD) in humans. METHODS: Eye movements were recorded during fixation, smooth-pursuit and saccades using binocular search coils in one monkey with esotropia, three monkeys with exotropia and one normal monkey. RESULTS: 1) Monkeys reared with Alternating Monocular Occlusion or Binocular deprivation (tarsal plates intact) showed both horizontal and vertical misalignment during monocular and binocular viewing. 2) Large 'A' patterns were evident in 2 out of 3 exotropes while a 'V' pattern was observed in the esotrope. 3) Similar 'A/V' patterns were observed with either eye viewing and during fixation or eye movements. 4) The vertical misalignment, which consisted of the non-viewing eye being higher than the fixating eye, appeared to constitute a DVD. CONCLUSION: Visual sensory deprivation methods that induce large strabismus also induce 'A/V' patterns and DVD similar to certain types of human strabismus. The source of pattern strabismus could be central, i.e., altered innervation to extraocular muscles from motor nuclei, or peripheral, i.e., altered location of extraocular muscle pulleys.     

Changing fixation in the transverse plane at eye level and Hering's law of equal innervation

Binocular eye movements were recorded photoelectrically while observers looked from one target to a second, located in a different direction and at a different distance. When the two targets were “real” with no accommodation convergence mismatch, there was (a) eye movement which included symmetrical vergence and conjugate saccades or (b) accommodative vergence which is known to occur in J. Müller's stimulus situation. Hering's law concerning equal innervation for vergence and saccadic eye movements holds best in two special situations, one in which accommodation and convergence are dissociated and the stimulus configuration is far from the observer, and another which entails the limiting case for real targets where the near target occludes the far target for one eye.     

Natural strabismus in monkeys. Convergence errors assessed by cover test and photographic methods.

A standard set of clinical prism and cover tests and a recently developed photographic method were used to assess binocular alignment in ten monkeys that previously were determined to have a naturally occurring infantile strabismus. Extensive measurements of the alignment state were made for fixation attempts throughout the field of gaze. Patterns of alignment errors were examined in an attempt to compared the strabismus found in individual monkeys with common syndromes of human infantile strabismus. Two monkeys showed patterns consistent with the syndrome of essential infantile esotropia. Five monkeys had patterns consistent with accommodative esotropia. One monkey that had bilateral anterior chamber hemorrhage at birth had a constant-angle esotropia. One monkey that previously had been shown to have a large-angle esotropia during development exhibited only exophoria, and in a final monkey in which large-angle esotropia was found during development, the strabismus had resolved. These results demonstrate that naturally occurring strabismus in monkeys might be related to syndromes seen in children. In addition, they provide extensive information about other characteristics of strabismus that have not been examined previously. These include a characterization of the magnitude of the misalignment in terms of error surface plots of bias and a detailed analysis of scatter in the measurements that show coupling relationships between the two eyes.     

Recording of disparity vergence in comitant esotropia

Vergence movements induced by base-out prisms were recorded, with an infrared eye movement recording system, in 5 patients with comitant esotropia and anomalous retinal correspondence and in 5 normal volunteers. The findings support the hypothesis that vergence movements in strabismus are induced by disparity, since accomodative as well as proximal vergence had been ruled out. Vergence movements are much slower and with different characteristics in strabismic patients with respect to normals. It may be argued that vergence movements represent the motor fusion component left over in strabismus. They may be considered the objective representation of the well-known phenomenon of prism compensation or adaptation, found in many strabismic patients.     

Inhibition of saccade and vergence eye movements in 3D space

Inhibitory capacity was investigated by measuring the eye movements of normal subjects asked to fixate a central point, and to suppress eye movements toward visual distracters appearing in the periphery or in depth. Eight right-handed young adults performed such a suppression or distracter task. In different conditions, the distracter could appear at 10 degrees left or right at a distance of 20, 40, or 150 cm (calling for horizontal saccades), or in a central position far or close (calling for convergence or divergence), or 7.5 degrees up or down at 40 or 150 cm (calling for vertical saccades). Eye movements were recorded binocularly with an infrared light eye-movement device. Results showed that (1) suppression performance was not perfect, as the subjects still produced eye movements; (2) errors were distributed unequally in three-dimensional space, with more frequent errors toward distracters calling for convergence, or leftward and downward saccades at a close distance; (3) distracters calling for saccade suppression yielded saccades in the direction of the distracter (that we called prosaccades), and saccades directed away from it (that we called spontaneous antisaccades); (4) for vergence, only distracters calling for convergence yielded errors, which were always promovements; (5) in addition, a small convergent drift was found for convergence distracters. Differences in the errors between saccade and vergence suggest that different inhibitory mechanisms may be involved in the two systems. Spatial left/right, up/down, and close/far asymmetries are interpreted in terms of attentional biases.     

Suppression of metabolic activity caused by infantile strabismus and strabismic amblyopia in striate visual cortex of macaque monkeys.

INTRODUCTION: Suppression is a major sensorial abnormality in humans and monkeys with infantile strabismus. We previously reported evidence of metabolic suppression in the visual cortex of strabismic macaques, using the mitochondrial enzyme cytochrome oxidase as an anatomic label. The purpose of this study was to further elucidate alterations in cortical metabolic activity, with or without amblyopia. MATERIALS AND METHODS: Six macaque monkeys were used in the experiments (four strabismic and two control). Three of the strabismic monkeys had naturally occurring, infantile strabismus (two esotropic, one exotropic). The fourth strabismic monkey had infantile microesotropia induced by alternating monocular occlusion in the first months of life. Ocular motor behaviors and visual acuity were tested after infancy in each animal, and development of stereopsis was recorded during infancy in one strabismic and one control monkey. Ocular dominance columns (ODCs) of the striate visual cortex (area V1) were labeled using cytochrome oxidase (CO) histochemistry alone, or CO in conjunction with an anterograde tracer ([H 3 ]proline or WGA-HRP) injected into one eye. RESULTS: Each of the strabismic monkeys showed inequalities of metabolic activity in ODCs of opposite ocularity, visible as rows of lighter CO staining, corresponding to ODCs of lower metabolic activity, alternating with rows of darker CO staining, corresponding to ODCs of higher metabolic activity. In monkeys who had infantile strabismus and unilateral amblyopia, lower metabolic activity was found in (suppressed) ODCs driven by the nondominant eye in each hemisphere. In monkeys who had infantile esotropia and alternating fixation (no amblyopia), metabolic activity was lower in ODCs driven by the ipsilateral eye in each hemisphere. The suppression included a monocular core zone at the center of ODCs and binocular border zones at the boundaries of ODCs. This suppression was not evident in the monocular lamina of the LGN, indicating an intracortical rather than subcortical mechanism. CONCLUSION: Suppression of metabolic activity in ODCs of V1 differs depending upon whether infantile strabismus is alternating or occurs in conjunction with unilateral amblyopia. Our findings reinforce the principle that unrepaired strabismus promotes abnormal competition in V1, observable as interocular suppression of ODCs.