19th annual Frank Costenbader Lecture--the origins of congenital esotropia

The distribution characteristics of strabismus surgery types in a tertiary hospital in the Central Plains region during the COVID-19 epidemic

OBJECTIVE

This study aimed to analyze the distribution of different types of strabismus surgery in a tertiary hospital in Central China during the three-year period of the COVID-19 pandemic.

METHODS

A retrospective analysis was conducted on the clinical data of strabismus patients who underwent surgery and were admitted to the Department of Strabismus and Pediatric Ophthalmology at the First Affiliated Hospital of Zhengzhou University between January 2020 and December 2022.

RESULTS

A total of 3939 strabismus surgery patients were collected, including 1357 in 2020, 1451 in 2021, and 1131 in 2022. The number of surgeries decreased significantly in February 2020, August 2021, and November and December 2022. Patients aged 0-6 years accounted for 37% of the total number of strabismus surgery patientsr. The majority (60%) of all strabismus surgery patients were diagnosed with exotropia, with intermittent exotropia accounting for the highest proportion (53%). There was no statistically significant difference in the proportion of intermittent exotropia and constant exotropia during the three-year period (χ2 = 2.642, P = 0.267 and χ2 = 3.012, P = 0.221, respectively). Among patients with intermittent exotropia, insufficient convergence type was the most common form of strabismus (accounting for over 70%). Non-accommodative esotropia accounted for more than 50% of all internal strabismus cases.

CONCLUSION

During the period from 2020 to 2022, the total number of strabismus surgeries in our hospital did not show significant fluctuations, but there was a noticeable decrease in the number of surgeries during months affected by the pandemic. Exotropia accounted for the highest proportion among strabismus surgery patients. Intermittent exotropia was the most common type among patients undergoing surgery for exotropia, and the most prevalent subtype was the insufficient convergence type. The age distribution of patients varied in different months, with a concentration of surgeries for strabismus patients in the 7-12 years old age group during the months of July and August each year.

Multiple Short Daily Periods of Normal Binocular Vision Preserve Stereopsis in Strabismus

Purpose

Infantile strabismus impedes the development of stereopsis. In optically strabismic monkeys, 2 continuous hours of normal binocular vision per day has been shown to preserve near-normal stereopsis. In this study, we investigated whether, as in learning, multiple shorter periods of intervention would further boost performance.

Methods

To simulate infantile esotropia, infant monkeys were reared with 30 prism diopters base-in starting at 4 weeks of age. Daily periods of normal binocular vision were provided by replacing prisms with plano lenses. Altogether, 14 monkeys were prism reared: 2 with continuous prism, 2 with 2 continuous hours of normal binocular vision per day, 6 with 2 noncontinuous hours, and 4 with 1 noncontinuous hour of binocular vision each day. Seven normally reared monkeys provided control data. Behavioral methods were employed to measure spatial contrast sensitivity, eye alignment, and stereopsis.

Results

One monkey reared with continuous prism had poor stereopsis, and the other had no stereopsis. Ten of the 12 monkeys reared with periods of normal binocular vision had stereopsis, and those with longer and more continuous periods of binocular vision had stereopsis approaching that of normally reared monkeys.

Conclusions

During early development, multiple short periods of binocular vision were effective in preserving clinically significant stereopsis in monkeys. These results suggest that by providing relatively short multiple daily intervention periods, stereopsis may be preserved in strabismic human children.

Late Surgical Correction of Longstanding Constant Strabismus in Adults: Is Fusion Possible in All Successfully Aligned Patients?

PURPOSE

To determine whether late surgical correction provides fusion in adults who have constant strabismus beginning in early childhood.

MATERIALS AND METHODS

This was a prospective study that included 34 consecutive adults with a history of early onset strabismus who had not previously undergone surgery. They were tested with the Bagolini striated glasses (BSG), Worth four-dot (W4D) test, cover test, and four-prism diopter (4-PD) test, preoperatively, and 6 weeks after surgery.

RESULTS

The mean age was 23.8 years, 17 patients had esotropia and 17 patients had exotropia. Preoperatively, all patients demonstrated a manifest horizontal deviation ranging from 30^∆ to 60^∆ and had suppression. At 6 weeks postoperatively, 33 patients had a horizontal manifest deviation of <15^∆ (range, 2^∆-14^∆; median, 6^∆), and none were orthotropic as determined by the cover test together with the 4-PD test. All of these 33 patients achieved anomalous retinal correspondence (ARC) with the BSG at near, and 25 (75%) had ARC with the W4D test at near.

CONCLUSIONS

Although our study has limited number of patients its findings suggest it is possible to develop ARC after surgery in almost all adult patients with childhood-onset strabismus associated with suppression, and who have not previously been operated upon, if satisfactory alignment is achieved in adulthood.

Horizontal gaze palsy with progressive scoliosis: a case report with magnetic resonance tractography and electrophysiological study

Background

Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare autosomal recessive congenital anomaly characterized by horizontal gaze limitation and progressive scoliosis. We investigated the underlying pathogenesis by incorporating diffusion tensor imaging and an electrophysiological study.

Case presentation

A 55-year-old female patient presented to our clinic due to a chronic history of eye movement limitation since childhood. Her eye problem was followed by a progressive scoliotic change in her torso during junior high school. Neurological examinations revealed remarkable conjugate horizontal but not vertical gaze palsy. Her pupils were isocoric, with a prompt response to light reflex and convergence. Her vision, including visual acuity and field, were normal. No pathological signs of muscle tone, muscle power, deep tendon reflex or coordination were revealed. There was no associated family history, and no diseases involving other systems were noted. On reviewing her past medical history, X-rays revealed scoliotic changes of her thoracic and lumbar spine. Brain magnetic resonance imaging showed a midline cleavage at the tegmentum (split pons sign) and butterfly configuration of the medulla, consistent with HGPPS. Color-coded diffusion tensor imaging in our patient revealed absence of decussation of the superior cerebellar peduncle. In tractography, the pontocerebellar tracts and fibers within the inferior cerebellar peduncle, deemed to be primarily dorsal spinocerebellar and vestibulocerebellar tracts, appeared to be agenetic. The tegmentum was compromised secondary to dorsal displacement of the corticospinal tracts. Of note, the bilateral corticospinal tracts remained uncrossed at the level presumed to be the pyramidal decussation. A somatosensory evoked potential study also revealed predominantly ipsilateral cortical sensory responses.

Conclusions

Our study confirmed that a compromised tegmentum secondary to dorsal displacement of the corticospinal tracts and poorly-developed afferent fibers within the pontocerebellar tracts and inferior cerebellar peduncle to be the main neuroanatomical anomalies responsible for the clinical presentations of HGPPS. In addition, the uncrossed nature of the majority of pyramidal and proprioceptive sensory systems was confirmed.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1081-9) contains supplementary material, which is available to authorized users.

Outcome of early surgery in infantile esotropia: Our experience in tertiary care hospital

BACKGROUND

Infantile esotropia is a convergent strabismus presenting before 6 months of age and is the most common strabismus disorder presenting in the ophthalmology OPD. The dilemma of whether to go for early surgery and how early has been a matter of research for the last 50 years. We describe our results of surgery in infantile esotropia at variable age groups, as well as with different reoperation rates and compare with the results in western literature.

METHODS

A prospective study was carried out through a review of 113 cases operated for infantile esotropia between February 2013 and August 2014. The variables studied were: age at surgery, type of fixation, refractive error, associated nystagmus, inferior oblique overaction or dissociated vertical deviation (DVD), type of surgery performed and pre- and postoperative deviation angles.

RESULTS

There were 67 male and 46 female cases of infantile esotropia. The age group of patients varied from 6 months to 12 years. Latent nystagmus was seen in 22 cases, inferior oblique overaction in 49 cases and DVD (mild) in 14 cases. Bimedial rectus recession was done in 78 cases and recession-resection in non-dominant eye in remaining 35 cases. The postoperative residual deviation was <10 PD in 102 cases, between 10 and 16 PD in 5 cases and more than 16 PD in 6 cases. Only 6 cases (5.3%) required reoperation for correction of residual deviation.

CONCLUSION

The authors recommend surgery before 12 months in all cases of infantile esotropia. The reoperation rates in the current study were considerably low.

Variables associated with the incidence of infantile esotropia

PURPOSE

Infantile esotropia (manifesting from birth to 6 months) is a common type of strabismus, accounting for 28% to 54% of all esotropias and with an incidence of 1% of the general population. The purpose of this cohort study was to evaluate risk factors for infantile esotropia. Such information may aid in early intervention to prevent manifestation of infantile esotropia.

METHODS

A retrospective chart review of 5,347 records (October 1, 1993, to September 30, 2003) of birth mothers and infants at the W.W. Hastings Indian Health Science Hospital in Tahlequah, Oklahoma, was performed to identify children with varying degrees of Native American blood who had infantile esotropia. A nonstrabismic birth cohort control group was also identified. Twenty-three medical records indicating a diagnosis of infantile esotropia that were complete enough to be used in analysis were identified. Normal infants were compared with infants with esotropia.

RESULTS

Infantile esotropia in this preliminary study was associated with 24 factors including prematurity, family ocular history, cardiovascular disease, systemic disease, pregnancy-associated hypertension and low birth weight (<2,500 g) among others.

CONCLUSIONS

Prematurity, family history or secondary ocular history, perinatal or gestational complications, systemic disorders, use of supplemental oxygen as a neonate, use of systemic medications, and male sex were found to be significant risk factors for infantile esotropia. Our results provide additional evidence that might help facilitate early detection and intervention in cases in which these risk factors are identified.

Are Duane syndrome and infantile esotropia allelic?

PURPOSE

To evaluate the clinical overlap of families with Duane syndrome and infantile esotropia to determine whether the identification of genes for Duane syndrome may explain some cases of infantile esotropia.

METHODS

Three separate groups of patients were evaluated. 1) Families with features of infantile esotropia were identified through the Strabismus Inheritance Study Tasmania (SIST). Clinical details of participants and their families were reviewed for any cases of Duane syndrome. 2) Cases of Duane syndrome were identified through the clinical diagnostic database at the Royal Children's Hospital, Melbourne, and private ophthalmology clinics in Melbourne and Tasmania. Previous medical notes were reviewed and family history of strabismus noted. All affected individuals were invited for re-examination in cases where a positive family history of strabismus was reported; siblings, parents, and other family members, where appropriate, were invited to be examined for signs of Duane syndrome or infantile esotropia. 3) Cases of mosaic trisomy 8, which has been associated with Duane syndrome and infantile esotropia, were reviewed for signs of strabismus.

RESULTS

A total of 133 families from the SIST were reviewed, but no 'pure' families of Duane syndrome were identified. Two families with infantile esotropia had several members affected with Duane syndrome. Of the 40 index cases with Duane syndrome whose families agreed to be involved in the study, 21 had a family history of ocular motility disorders, but only two of these families had multiple cases of Duane syndrome. From 24 cases with mosaic trisomy 8, one individual case had Duane syndrome and another had mild congenital cataracts and infantile esotropia.

CONCLUSIONS

There is clinical overlap in families with Duane syndrome and infantile esotropia. We confirmed the previous association of mosaic trisomy 8 with both Duane syndrome and infantile esotropia. These data suggest that the two conditions may be allelic and may be due to a gene on chromosome 8.

Surgery and botulinum toxin in congenital esotropia

BACKGROUND

In a previous study we investigated the advantages and drawbacks of early and delayed injection of botulinum toxin as primary treatment of infantile esotropia with nystagmus in abduction (IENA). We carried out a further study to investigate the role and efficacy of surgery in this condition and to determine the possible effect of previous injection of both medial recti with botulinum toxin in patients requiring a final horizontal surgical correction.

METHODS

Review of the records of 44 patients (24 girls and 20 boys) with IENA seen between 1979 and 1998 who had undergone at least one horizontal surgical procedure. The outcomes in the 16 patients who had previously received botulinum toxin were compared with those in the 28 patients for whom surgery was the primary treatment.

RESULTS

There was a negative correlation between the pretreatment esotropic angle and age (Pearson's r = -0.45, p < 0.05). The first visit to a surgical specialist took place very late (mean age 43 months [standard deviation (SD) 39 months]). Of the 35 children seen during the period in which botulinum toxin was available, 20 (57%) had additional factors inducing unsteadiness of binocular vision (e.g., moderate to severe initial relative amblyopia, initial ametropia). Administration of 5 units of botulinum toxin before 18 months of age destabilized dissociated vertical deviation. Overall, 39 patients (89%) had a final residual deviation of less than 10 prism dioptres. The first surgical correction was horizontal and vertical-torsional in 30 patients (68%). A total of 23 patients (52%) required some retreatment (botulinum toxin or surgery or both). Children treated initially with botulinum toxin had less surgery than those with initial surgery (mean recession or resection 8.9 mm [SD 4.5 mm] vs. 14.2 mm [SD 4.0 mm]) as well as fewer horizontal muscles operated (mean 1.6 [SD 0.6] vs. 2.3 [SD 0.6]).

INTERPRETATION

Surgery with or without further interventions is a reasonable approach for IENA with delayed diagnosis and in cases associated with unsteadiness of binocular vision or with nonhorizontal deviations. Initial treatment with botulinum toxin, injected into both medial recti, is effective, reducing the amount of further horizontal surgery and favouring postoperative stability, except in children under 18 months, in whom injection of 5 units induces unbalanced dissociated vertical deviation.

Botulinum treatment of infantile esotropia with abduction nystagmus

PURPOSE

To examine the effect of botulinum toxin type A (BTA) on the final correction of esotropia, A and V patterns, overaction of the oblique muscles, and dissociated vertical deviation (DVD) in infantile esotropia with nystagmus in abduction.

METHODS

This retrospective study examined 54 patients treated with simultaneous bilateral medial injection of BTA. Subjects were divided into two groups: group 1 (first injection <18 months of age) and group 2 (first injection >18 months of age).

RESULTS

Pre-BTA, group 1 patients had an angle of esotropia noticeably higher and fewer A patterns than group 2 patients. Post-BTA, group 2 received significantly fewer injections of BTA than group 1. The magnitude of the A patterns improved. Prior frequency of DVD increased significantly in group 1 (100%): 79% of DVD was decompensated compared with 47% in group 2. Overall success was obtained in 14% and 58% of groups 1 and 2, respectively.

CONCLUSION

We do not support BTA treatment in infantile esotropia with nystagmus in abduction prior to age 18 months. After 18 months, the horizontal results are excellent and neither the incidence nor the degree of previous DVD are decompensated, resulting in high success rates for overall deviation and improving anisotropy in A.

Duane's syndrome

Duane's syndrome is an unusual congenital form of strabismus where there is paradoxical anomalous lateral rectus innervation of the affected eye due to misdirection of axons destined for the medial rectus. Three types of Duane's syndrome are recognized. Most cases of Duane's syndrome are sporadic but up to 10% are familial, usually with autosomal dominant inheritance. Several autosomal dominant syndromes with dysmorphic features are associated with Duane's syndrome. Chromosomal loci for genes contributing to Duane's syndrome have been suggested at 4q, 8q and 22q. Duane's syndrome is heterogeneous at multiple levels with variations in its ocular manifestations, accompanying systemic manifestations and in the chromosomal loci with which it may be associated. The definition clinically and genetically of the various subgroups of Duane's syndrome will provide a valuable insight into brainstem axonal guidance to the extraocular muscles during human development.

Long-term results of bimedial rectus recessions in infantile esotropia

BACKGROUND

Congenital esotropia has a deviation of 50 or more prism diopters (delta). Generally, surgical alignment of the eyes is the accepted treatment but surgical techniques differ.

METHODS

A total of 54 patients were evaluated. Surgery was done at a mean age of 28 months. Bimedial rectus recessions up to 8 mm were performed.

RESULTS

The mean preoperative deviation was 70 delta of esotropia. Our success rate with a uniform approach was 66.6%.

CONCLUSIONS

Contrary to the selective approach for large angle congenital esotropia, we do not consider initial surgery on three or more muscles. Our method is quicker, simpler, less traumatic, and leaves the lateral rectus muscles unoperated for patients requiring a second surgery.

The timing of surgical alignment for congenital (infantile) esotropia

At this time, the beneficial effect of accurate alignment by age 2 in congenital esotropia has been well established by clinical and laboratory studies. There is, however, only scanty clinical evidence that alignment before age 1, much less before 6 months of age, may yield a better quality of binocularity (i.e., refined stereoacuity) than alignment by age 2. Pitfalls of very early alignment are present. In addition, the ophthalmologist must be vigilant in following the initially aligned patient and be ready to treat vertical motor defects, amblyopia, and acquired refractive errors. The need for additional horizontal surgery after initial alignment is also common. The optimum result in the surgical treatment of congenital esotropia generally shows binocularity that is within the confines of a monofixation syndrome, and refined stereoacuity remains an elusive target and a rare outcome, no matter at what age the alignment is achieved.

Untreated essential infantile esotropia: factors affecting the development of amblyopia

PURPOSE

A concomitant esotropia, presenting within the first 6 months of life, associated with a high incidence of dissociated vertical deviation, manifest latent nystagmus and asymmetric optokinetic nystagmus is termed essential infantile esotropia. Most studies concern patients diagnosed in infancy and treated throughout childhood. This paper addresses the factors that may influence the development of amblyopia in patients who remain untreated until visual adulthood.

METHODS

During a 3 year period 113 patients aged 8 years or more with a history of esotropia occurring within the first 6 months of life were examined for the study. All patients underwent full ocular motility assessment and cycloplegic refraction, and only those with one or more signs of essential infantile esotropia were included.

RESULTS

Of the 113 patients, 16 (14.3%) had a difference of 2 or more lines in the visual acuity of the two eyes and were diagnosed as having amblyopia. Anisometropia was present in 10 of the 16 (62.5%). The correlation between anisometropia and amblyopia was statistically significant (p = 0.0001).

CONCLUSIONS

Amblyopia following early surgical intervention in essential infantile exotropia is well documented, but the risk is outweighed by the chance of obtaining some form of binocular vision. However, where access to ongoing therapy is not available, patients with essential infantile esotropia, free alternation and no anisometropia have a significant chance of retaining good visual acuity in both eyes if surgery is delayed until visual adulthood.

Stereopsis and disparity vergence in monkeys with subnormal binocular vision

The surgical treatment for strabismus in infants generally results in microtropia or subnormal binocular vision. Although the clinical characteristics of these conditions are well established, there are important questions about the mechanisms of binocular vision in these patients that can best be investigated in an appropriate animal model. In the present psychophysical investigations, spatial frequency response functions for disparity-induced fusional vergence and for local stereopsis were studied in macaque monkeys, who demonstrated many of the major visual characteristics of patients whose eyes were surgically aligned during infancy. In six rhesus monkeys, unilateral esotropia was surgically induced at various ages (30-184 days of age). However, over the next 12 months, all of the monkeys recovered normal eye alignment. Behavioral measurements at 4-6 years of age showed that the monkeys' prism-induced fusional vergence responses were indistinguishable from those of control monkeys or humans with normal binocular vision. Investigations of stereo-depth discrimination demonstrated that each of the experimental monkeys also had stereoscopic vision, but their stereoacuities varied from being essentially normal to severely stereo-deficient. The degree of stereo-deficiency was not related to the age at which surgical esotropia was induced, or to the presence or absence of amblyopia, and was not dependent on the spatial frequency of the test stimulus. Altogether, these experiments demonstrate that a temporary, early esotropia can affect the binocular disparity responses of motor and sensory components of binocular vision differently, probably because of different sensitive periods of development for the two components.

Strabismus in children with cerebral palsy

In 48 children with cerebral palsy the characteristics of the squint and amblyopia were analyzed, also with respect to the features of cerebral palsy and to birth weight. Strabismus of congenital esotropia type was found to be common, as was also exotropia of early onset. Spontaneous alternation or an accommodative component of the squint was present only in a few cases. There was no evidence of an accumulation of any strabismus type in the different subgroups of cerebral palsy, whereas amblyopia or an obvious risk for amblyopia was found in the great majority of the cases. Some kind of amblyopia treatment was given to 34. Most of them showed improvement of the visual capacity which encourages treatment of amblyopia, even in children with cerebral palsy.

Binocular cortical interactions in the monofixation syndrome

This study examines the relationship between clinically assessed binocular sensory status and binocular visual evoked potentials (BVEPs) in 11 patients with monofixation syndrome (MFS) and in 12 patients with absent binocular fusion (ABF). BVEPs were elicited using a two-sinusoid "beat" technique. The luminances of red/green anaglyphic circular fields were modulated independently at temporal rates of 6 and 8 Hz. This stimulus elicits a BVEP at 14 Hz in children with normal stereoscopic vision. In this study, we found that this BVEP also is present in patients with MFS, whereas it is near background noise levels in patients with ABF. These results demonstrate the presence of functional binocular cortical mechanisms in patients with MFS. The findings are consistent with the hypothesis that elicitation of this class of BVEPs requires gross sensory fusion, but not fine stereoscopic vision.

The relationship between dissociated vertical divergence (DVD) and head tilts

INTRODUCTION

Dissociated vertical divergence (DVD) has been associated with manifest head tilts. Also, DVD has been described as demonstrating a characteristic response to forced head tilt by increasing the size of the DVD on contralateral tilt.

METHODS

A series of 116 consecutive patients with DVD associated with infantile esotropia were examined according to a predetermined protocol between 1989 and 1994. Each patient was examined for a manifest head tilt. Also, the response of the DVD to forced ipsilateral and contralateral head tilt was analyzed. In addition, 100 consecutive patients with manifest head tilts were examined and the etiology of the tilt determined.

RESULTS

A manifest head tilt was present in 35% (26/74) of patients with an ocular fixation preference and no prior vertical muscle surgery. None of the patients with alternating fixation and a history of no vertical muscle surgery manifested a head tilt. Most patients responded in the classically described manner by increasing the size of the DVD on forced contralateral tilt and decreasing the size of the DVD on ipsilateral tilt. Atypical responses were not related to the presence of oblique overaction. DVD was the etiology in 9 of 100 consecutive patients with a manifest head tilt.

CONCLUSIONS

Patients with DVD often manifest a head tilt. Most respond by increasing the size of the DVD on forced contralateral head tilt and decreasing on ipsilateral tilt. Atypical responses did not appear to be influenced by oblique overaction. DVD is a relatively frequent cause of manifest head tilts.

Preschool vision screening: rationale, methodology and outcome

Although population outcome studies support the utility of preschool screening for reducing the prevalence of amblyopia, fundamental questions remain about how best to do such screening. Infant photoscreening to detect refractive risk factors prior to onset of esotropia and amblyopia seems promising, but our current understanding of the natural history of these conditions is limited, thus limiting the prophylactic potential of early screening. Screening for strabismic, refractive and ocular disease conditions directly associated with amblyopia is more clearly proven, but the diversity of equipment, methods and subject populations studied make it difficult to draw precise summary conclusions at this point about the efficacy of photoscreening. Sensory-based testing of preschool-age children exhibits a similar combination of promise and limitations. The visual acuity tests most widely used for this purpose are prone to problems of testability and false negatives. Moreover, the utility of random-dot stereograms has been confused by misapplication, and new small-target binocularity tests, while attractive, are as yet inadequately field-proven. The evaluation standard for any screening modality is treatment outcome. However, variables in amblyopia classification and quantitative definition differences, timing of presentation, nonequivalent treatment comparisons, and compliance variability have been uncontrolled in virtually all extant studies of amblyopia treatment outcome, making it difficult or impossible to evaluate either the relative efficacy of different treatment regimens for amblyopia or the effects of age on treatment outcome within the preschool age range. The latter issue is a central one, since existence of such an age effect is the primary rationale for screening at younger rather than older preschool ages. The relatively low prevalence of amblyopia makes it difficult to achieve a high screening yield in terms of predictive value, but functionally increasing prevalence by selective screening of high risk populations causes further problems. Unless a "supertest" can be devised, with very high sensitivity and specificity, health policy decisions will be required to determine which of these two characteristics should be emphasized in screening programs. Performance of screening tests can be optimized, however, with adequate training, perhaps via instructional videotapes.

The relationship between infantile strabismus and latent nystagmus

The so-called infantile strabismus syndrome consists, among other signs, of (1) strabismus, (2) a defect of pursuit and optokinetic tracking with particular involvement of temporally directed responses on monocular viewing, (3) latent nystagmus and (4) adduction preference of the fixating eye. The following causal relationship between these three phenomena is suggested. (1) Binocularity in the visual cortex is impaired, either as a primary defect or as a consequence of misalignment of the eyes. (2) The reduced binocularity prevents maturation of signal transmission from the visual cortex to the brainstem such that slip control is evident in poor pursuit and optokinetic responses, particularly to monocular, temporally directed stimuli. (3) The asymmetry of the pursuit and optokinetic systems is also evident in latent nystagmus which reflects a tonic preponderance, directed nasally with reference to the fixating eye. The directional preponderance drives the slow phases of latent nystagmus if the visual input is unbalanced in favour of one eye. Because of the maldeveloped slip control latent nystagmus is not inhibited by visual contours. When both eyes are open the better-functioning nasally directed pursuit and optokinetic control systems of the two eyes complement each other and largely prevent drifting of the eyes. The defect responsible for the abnormal motor control cannot be located between the retina and the visual cortex because perception of motion is only slightly impaired and a nasal-temporal asymmetry of the motion VEP, typically encountered in infantile strabismus, does not correlate quantitatively with the asymmetry of the motor control. Rather, the defect is located between the cortex and the brainstem. (4) Adduction preference of the fixating eye with a compensatory headturn is due to a gaze-evoked component added to the latent component of the nystagmus. The gaze-evoked component is a purposeful reaction that allows dampening of the nystagmus in adduction at the expense of an increase in abduction.

Handedness in strabismics. Etiological implications

The incidence of non right handedness was found to be significantly higher in a group of 228 strabismics when compared with a control group of neurologically normal non strabismic subjects. The difference was still present after elimination of strabismics with known neurological or general health problems, or who were born prematurely. The strabismics showed no inter group differences in handedness in relation to the type of retinal correspondence present or the ability to achieve normal or abnormal binocular single vision. Evidence is reviewed for the presence of a developmental defect leading to strabismus, and results of this survey support a previously proposed idea that a developmental defect leads to strabismus, the type of which reflects the severity of the defect (although external factors may also be an influence).

Early versus late alignment of infantile esotropia

Fifty-two children with infantile esotropia had surgery for their esotropia between two and seven years of age. Another 49 had similar surgery before the age of two years. Of these 101 operated children, the esotropia in 70 patients was aligned to within 10 prism diopters. The patients with successful alignment were reviewed to study the effect of early versus late surgical intervention of their deviation, i.e. before and after two years of age. The motor and sensory states of the selected patients were analysed before and after surgical correction. The choice and number of surgical procedures employed are discussed. It appears that patients two years and older when strabismus was surgically corrected have a good chance of alignment, but less chance of attaining binocularity. In many cases there was a V-pat-tern esotropia, requiring surgery on the overacting inferior oblique muscles. In comparison, the younger group with earlier surgery appeared to show a better chance of attaining binocularity and fewer patients had significant V-pattern requiring surgery on the inferior oblique muscles.