Intercalary staphyloma after strabismus surgery in a patient with Marfan syndrome: A case report

RATIONALE

A few cases of intercalary staphyloma have been reported in patients with Marfan syndrome, but we believe that this is the first case of intercalary staphyloma in Marfan syndrome developing after strabismus surgery.

PATIENT CONCERNS

A 9-year-old girl diagnosed with Marfan syndrome visited a strabismus clinic for treatment of esotropia. Both eyes were aphakic and had 60 prism diopter esotropia at distance and 55 prism diopter esotropia at near. There were no corneal, conjunctival, or scleral abnormalities. Six millimeters of recession was performed on both medial rectus muscles via an inferonasal fornix approach under general anesthesia. 5 days after surgery, a dark gray protruding lesion was observed on the upper nasal side of the left eye.

DIAGNOSES

Intraocular ultrasonography showed no bleeding, retinal detachment, or other abnormal findings. Computed tomography showed a conical protrusion of the scleral wall which was diagnosed as intercalary staphyloma.

INTERVENTIONS

To reduce risk of progression of the staphyloma in the left eye and to reduce risk of development of a new staphyloma, intraocular pressure lowering eye drops were administered.

OUTCOMES

We just observed it without any intervention except the intraocular pressures lowering eye drops. It remained stable for 12 months.

LESSONS

Clinicians need to be alert to the possibility of this serious complication in Marfan syndrome patients after minor surgical trauma, which can occur during uneventful strabismus surgery.

The reliability of the angle of deviation measurement from the Photo-Hirschberg tests and Krimsky tests

OBJECTIVE

To compare the angle of deviation measured from Photo-Hirschberg testing and Krimsky testing, with that from an alternate prism cover test (APCT) in strabismus patients.

METHODS

A cross-sectional study was conducted in Songklanagarind Hospital, Thailand. Thirty-three strabismus patients were photographed for analysis by Photo-Hirschberg testing using computer software. The corneal light reflex displacement, converted into prism diopter (PD), was compared to the angle of deviation measured with APCT. Twenty-eight strabismus patients were tested with the Krimsky test. Data were analyzed using Pearson correlation and paired t-tests. The study excluded 4 intermittent exotropia cases, 1 intermittent esotropia case and 2 which cases missing data for krimsky test.

RESULTS

The mean±SD of the deviation angle, measured by APCT with a fixation target at 30 cm and 6 m; were 48.09±16.34PD and 47.82±15.73 PD, respectively. At 1 m, the difference in the angle of deviation measured from APCT and the Photo-Hirschberg test within 10 PD were 58.8% and 63.6%, for ET and XT, respectively. The difference in the angle of deviation measured from APCT and Krimsky tests within 10 PD in ET and XT were 86.7% and 80.0%, respectively. At 4 m, the difference in angle of deviation measured from APCT and Photo-Hirschberg tests within 10 PD in ET and XT were 58.8% and 54.5%, respectively; whereas, the difference in the angle of deviation measured from APCT and Krimsky tests within 10 PD in ET and XT were 80.0% and 70.0%, respectively.

CONCLUSION

The reliability of Krimsky test was better than Photo-Hirschberg test for measuring an angle of deviation.

"Pulsating proptosis and heavy eye syndrome precipitated by neurofibromatosis type 1: A case report"

RATIONALE

Neurofibromatosis type 1 (NF1) is a hereditary disease characterized by café-au-lait spots, peripheral neurofibromas, Lisch nodules, optic nerve glioma, and sphenoid wing dysplasia. Pulsating proptosis is associated with a sphenoid bony defect. Heavy eye syndrome is characterized by acquired esohypotropia in patients with high myopia. This study aimed to describe the presentation of pulsating proptosis and heavy eye syndrome precipitated by NF1 and its management.

PATIENT CONCERNS

A 41-year-old woman presented with progressive pulsating proptosis and hypodeviation of the right eye over the past 2 years. The axial length of the right eye was 36.81 mm. The right eye presented with esohypotropia and hypoglobus. The ocular motility examination showed limitations in all directions, especially in supraduction. Brain computed tomography revealed sphenoid wing dysplasia of the right orbit. The meningocele protruded through the orbital defect, lifting the globe. Brain magnetic resonance imaging demonstrated superior rectus muscle (SR) medial displacement and lateral rectus muscle inferior displacement. Physical examination revealed café-au-lait macules and neurofibromas on the trunk.

DIAGNOSIS

NF1 with pulsating proptosis and heavy eye syndrome.

INTERVENTIONS

The patient declined neurosurgery due to risk and economic reasons. To manage her main concern regarding cosmetics, we performed orbital floor decompression, SR resection with advancement, maximal hang-back recession of the inferior rectus muscle, and a partial Jensen's procedure.

OUTCOMES

Proptosis was reduced. The eye position became more symmetrical. The range of eye movements was also increased.

LESSONS

This case describes a rare synchronous presentation of pulsating proptosis and heavy eye syndrome precipitated by NF1. Adult-onset presentation implied a progressive process in NF1. The case also showed a different etiology from that of typical heavy eye syndrome. It reminds ophthalmologists that orbital imaging should be performed in high myopia patients with strabismus to evaluate the extraocular muscle pathway. Furthermore, the case demonstrated a management that avoided the risk and expensive cost of neurosurgery, which has not been reported.

GWAS Hits for Bilateral Convergent Strabismus with Exophthalmos in Holstein Cattle Using Imputed Sequence Level Genotypes

Bilateral convergent strabismus with exophthalmos (BCSE) is a malformation of the eyes and is recognized as a mild but progressive disorder that affects cattle in the first two years of life. This most likely inherited disorder is rarely described in cattle resembling autosomal dominantly inherited forms of human progressive external ophthalmoplegia (PEO). In German Braunvieh cattle, two linked genome regions were found that could be responsible for the development and/or progression of BCSE. The goal of this study was to phenotypically characterize BCSE in Holstein cattle from Germany and Switzerland as well as to identify associated genome regions by GWAS. The clinicopathological phenotype of 52 BCSE-affected Holstein cattle was in accordance with the phenotype described in German Braunvieh cattle, but in addition, signs of degeneration and cellular infiltration in the eye muscles were found. By using imputed sequence level genotype data, three genome-wide significant GWAS hits were revealed on different chromosomes that were not detected by initial GWAS based on high density SNP array data highlighting the usefulness of this approach for mapping studies. The associated genome regions include the ABCC4 gene as well as markers adjacent to the NCOR2 and DNAJC3 genes all illustrating possible functional candidate genes. Our results challenge a monogenic mode of inheritance and indicate a more complex inheritance of BCSE in Holstein cattle. Furthermore, in comparison to previous results from German Braunvieh cattle, it illustrates an obvious genetic heterogeneity causing BSCE in cattle. Subsequent whole genome sequencing (WGS)-based analyses might elucidate pathogenic variants in the future.

Serum outperforms plasma in small extracellular vesicle microRNA biomarker studies of adenocarcinoma of the esophagus

BACKGROUND

Circulating microRNAs (miRNAs) are potential biomarkers for many diseases. However, they can originate from non-disease specific sources, such as blood cells, and compromise the investigations for miRNA biomarkers. While small extracellular vesicles (sEVs) have been suggested to provide a purer source of circulating miRNAs for biomarkers discovery, the most suitable blood sample for sEV miRNA biomarker studies has not been defined.

AIM

To compare the miRNA profiles between matched serum and plasma sEV preparations to determine their suitability for biomarker studies.

METHODS

Matched serum and plasma samples were obtained from 10 healthy controls and 10 patients with esophageal adenocarcinoma. sEV isolates were prepared from serum and plasma using ExoQuick^TM and quantified using NanoSight. RNA was extracted from sEV preparations with the miRNeasy Serum/Plasma kit and profiled using the Taqman Openarray qPCR. The overall miRNA content and the expression of specific miRNAs of reported vesicular and non-vesicular origins were compared between serum and plasma sEV preparations. The diagnostic performance of a previously identified multi-miRNA biomarker panel for esophageal adenocarcinoma was also compared.

RESULTS

The overall miRNA content was higher in plasma sEV preparations (480 miRNAs) and contained 97.5% of the miRNAs found in the serum sEV preparations (412 miRNAs).The expression of commonly expressed miRNAs was highly correlated (Spearman’s R = 0.87, P < 0.0001) between the plasma and serum sEV preparations, but was consistently higher in the plasma sEV preparations. Specific blood-cell miRNAs (hsa-miR-223-3p, hsa-miR-451a, miR-19b-3p, hsa-miR-17-5p, hsa-miR-30b-5p, hsa-miR-106a-5p, hsa-miR-150-5p and hsa-miR-92a-3p) were expressed at 2.7 to 9.6 fold higher levels in the plasma sEV preparations compared to serum sEV preparations (P < 0.05). In plasma sEV preparations, the percentage of protein-associated miRNAs expressed at relatively higher levels (Ct 20-25) was greater than serum sEV preparations (50% vs 31%). While the percentage of vesicle-associated miRNAs expressed at relatively higher levels was greater in the serum sEV preparations than plasma sEV preparations (70% vs 44%). A 5-miRNA biomarker panel produced a higher cross validated accuracy for discriminating patients with esophageal adenocarcinoma from healthy controls using serum sEV preparations compared with plasma sEV preparations (AUROC 0.80 vs 0.54, P < 0.05).

CONCLUSION

Although plasma sEV preparations contained more miRNAs than serum sEV preparations, they also contained more miRNAs from non-vesicle origins. Serum appears to be more suitable than plasma for sEV miRNAs biomarkers studies.

Botulinum toxin in the treatment of partially accommodative esotropia with high AC/A ratio

Purpose

To study the outcome of botulinum toxin (BTX) treatment (group 1) in partially accommodative esotropia with high accommodative convergence/accommodation (AC/A) ratio, in comparison with bilateral medial rectus muscles recessions and posterior fixation (group 2).

Methods

In a retrospective comparative study, children aged 3–8 years old treated between 2011 and 2016, with partially accommodative esotropia with high AC/A ratio, deviation at distance of 10 prism diopters or more, and at least 1 year of follow-up, were included. Visual acuity, alternate prism and cover test, stereoacuity, biomicroscopy, and cycloplegic retinoscopy were carried out at initial, baseline visit, 6 months and 1 year after BTX injection or surgery. Main outcome variables were deviation at distance and near, improvement in stereoacuity, and percentage of success. We used multiple regression or proportional odds analysis to control for potential confounding variables.

Results

Of 95 patients, 84 were eligible, 48 children in group 1 and 36 in group 2. Deviation and stereoacuity were similar in the two groups at 6 months, but significantly better in the BTX group at 1 year (median distance deviation 0 prism diopters vs 5 prism diopters, p<0.01), although differences were not clinically relevant. Percentage of success was also significantly better only at 1 year (93% vs 72%, p = 0.01). Change in distance-near disparity was not significantly different in the two groups in the period of study.

Conclusions

Botulinum toxin could be superior to, or as effective as surgery, at middle term, in the treatment of partially accommodative esotropia with high AC/A ratio.

Esotropia and Pseudoexotropia in Acute Rop Sequelae: Clinical Features and Suggestions for Treatment

We report five cases with a mixture of esotropia and pseudoexotropia due to macular ectopia related cicatricial retinopathy of prematurity (ROP). On inspection, the patients, aged from 9 to 28 years, presented a divergence of the eyes and a nasally decentralised corneal light reflex. The cover test showed esodeviation. All the cases presented some clinical features common to congenital strabismus. Fundus examination showed temporal traction of vascular and retinal tissues and macular ectopia, referrable to cicatricial sequelae of spontaneously regressed severe ROP. Treatment is limited to follow-up, with attention being paid to the control of retinal damage rather than to resolving the esthetic defects. Despite cryotherapy, these conditions are increasing with the increase in severe ROP and are now relatively frequent. We suggest that they be carefully identified in order to avoid incorrect orthoptic or surgical treatment.

Clinical features of acute acquired comitant esotropia in the Chinese populations

Acute acquired comitant esotropia (AACE) is an unusual presentation of esotropia that occurs after infancy. This study was aimed to study the clinical features and the differences between children and adult patients with AACE in the Chinese populations.This was a retrospective analysis of patients diagnosed with AACE over 4 years; 69 patients (25 females and 44 males) were identified. The patients were divided into 3 groups: < 10 year-old (n = 6, 8.7%), 10-18 year-old (n = 23, 33.3%), and ≥18 year-old (n = 40, 58.0%). Patients underwent medical history, brain and orbital computed tomography, and ophthalmological and orthoptic examinations.The refractions of AACE patients varied among age groups: patients < 10 year-old had mild hypermetropia, while older children and adults showed moderate-to-high myopia (P < .001). The mean angles of esotropia were significantly larger in young children compared with older children and adults (P = .005). There was no significant difference in binocularity detected by either synoptophore or TNO stereoscopic testing among different disease durations. Stereopsis detected by synoptophore and TNO testing showed no significant difference at duration within half a year, but the stereopsis measured by TNO was significantly worse than that detected by synoptophore with extending disease duration (P < .05).AACE seems to occur mostly in older children and adults in the Chinese population. Younger children with AACE seem to demonstrate a common trait of mild hypermetropic refractive errors, while myopia can be seen in older children and adult patients. The duration from onset to treatment of esotropia does not affect the preoperative binocularity.

Inflection in inactive lateral rectus muscle: evidence suggesting focal mechanical effects of connective tissues

PURPOSE

Paths of inactive lateral rectus (LR) muscles were studied to investigate putative roles of orbital fat and intrinsic muscle stiffness suggested to be alternatives to connective tissue pulleys as determinants of pulling direction.

METHODS

Surface coil orbital magnetic resonance imaging was performed in axial planes in adult humans: seven with chronic unilateral LR paralysis, three with nonparalytic concomitant esotropia of similar angle, and 15 healthy controls. Fixation was controlled using targets placed at a broad range of horizontal positions.

RESULTS

Paralyzed LRs exhibited marked atrophy compared with functional contralateral LRs and LRs of orthotropic and esotropic subjects without LR paralysis. The normal LR exhibited a gradual 18.8 degrees +/- 4.5 degrees (mean +/- SD) lateral inflection 14.4 +/- 2.6 mm posterior to the globe center, bowing the LR away from the orbital center. The paralyzed LR exhibited a significantly (P < 0.002) larger and typically more discrete 29.2 degrees +/- 8.8 degrees lateral inflection, similar to that observed in concomitant esotropia in maximal adduction. Average position of this inflection was 11 to 14 mm posterior to the globe center in all three subject groups, but in LR palsy only the inflection of the paralyzed LR-0.17 mm further posterior per degree of abduction (linear fit, R = 0.85)-depended on horizontal gaze. The behavior of the paralyzed LR inflection was consistent with LR pulley anatomy.

CONCLUSIONS

Sharper lateral inflection in the flaccid rather than the tense LR seems inconsistent with intrinsic muscle stiffness or diffuse orbital fat pressure but suggests the influence of discrete connective tissue.

Horizontal rectus muscle anatomy in naturally and artificially strabismic monkeys

PURPOSE

Structural abnormalities of extraocular muscles (EOMs) or their pulleys are associated with some forms of human strabismus. This experiment was conducted to investigate whether such abnormalities are associated with artificial or naturally occurring strabismus in monkeys.

METHODS

Binocular alignment and grating visual acuities were determined in 10 monkeys representing various species using search coil recording and direct observations. Four animals were orthotropic, two had naturally occurring "A"-pattern esotropia, two had concomitant and one had "V"-pattern esotropia artificially induced by alternating or unilateral occlusion in infancy, and one had "A"-pattern exotropia artificially induced by prism wear. After euthanasia, 16 orbits were examined by high-resolution magnetic resonance imaging (MRI) in the quasi-coronal plane. Paths and sizes of horizontal rectus EOMs were analyzed quantitatively in a standardized coordinate system. Whole orbits were then serially sectioned en bloc in the quasi-coronal plane, stained for connective tissue, and compared with MRI. Nerve and EOM features were analyzed quantitatively.

RESULTS

Quantitative analysis of MRI revealed no significant differences in horizontal rectus EOM sizes or paths among orthotropic or naturally or artificially strabismic monkeys. Histologic examination demonstrated no differences in EOM size, structure, or innervation among the three groups, and no differences in connective tissues in the pulley system. The accessory lateral rectus (ALR) EOM was present in all specimens, but was small, inconsistently located, and sparsely innervated. Characteristics of the ALR did not correlate with strabismus.

CONCLUSIONS

Major structural abnormalities of horizontal rectus EOMs and associated pulleys are unrelated to natural or artificial horizontal strabismus in the monkeys studied. The ALR is unlikely to contribute to horizontal strabismus in primates. However, these findings do not exclude a possible role of pulley abnormalities in disorders such as cyclovertical strabismus.

Pseudopterygium arising in a patient with multiple keloids

We describe an unusual case of mechanical restriction of the globe caused by pseudopterygium formation at the site of a minor ocular injury, which led to a possible link between Ebstein's anomaly and keloids.

Ocular dominance column width and contrast sensitivity in monkeys reared with strabismus or anisometropia

PURPOSE

To study the relationship between the width of ocular dominance columns in primary visual cortex and spatial contrast sensitivity functions in monkeys with strabismus or anisometropia during infancy.

METHODS

Adult monkeys having had monocular visual abnormalities induced in infancy were tested behaviorally for spatial contrast sensitivity and then subjected to functional enucleation of one eye to reveal the ocular dominance columns (ODCs) of the primary visual cortex by cytochrome oxidase (CO) staining. The relative widths of the left and right eyes' ODCs were measured and related to the contrast sensitivity functions.

RESULTS

The relative widths of the ODCs having input from eyes with strabismic or anisometropic amblyopia were reduced in proportion to the age of onset and the duration of the early visual abnormality. The relative losses in contrast sensitivity were in ordinal agreement with the losses in relative width of the ODCs.

CONCLUSIONS

Amblyopia induced by the early monocular abnormalities of strabismus or anisometropia is proportional to the loss in cortical afference as reflected in the reduction in width of the respective ODCs in the primary visual cortex.

Surgical results of patients with A-pattern horizontal strabismus

PURPOSE

To investigate the surgical results of patients having horizontal strabismus with A-pattern associated with superior oblique overaction (SOOA).

METHODS

Twenty patients with horizontal strabismus (12 exotropia [XT] and 8 esotropia [ET] with no previous strabismus surgery) with SOOA-associated A-pattern were analyzed retrospectively. Motor success was defined as a horizontal deviation of 8 prism diopters (PD) or less, 6 PD or less of vertical deviation in all gazes, and no greater than 8 PD of A-pattern. Stereoacuity was measured using the Titmus test (Stereo Optical, Chicago, IL).

RESULTS

Sixty percent of patients had successful results at the final examination. No significant difference was found between the XT and ET patients in preoperative and postoperative horizontal deviations in the primary position, A-pattern collapse, or success rate (P >.05). Four patients had an induced postoperative vertical deviation. Among eight patients without stereoacuity preoperatively, four showed an average of 910 seconds of arc (40 to 3000 seconds of arc) after surgery.

CONCLUSION

Simultaneous surgery on the horizontal and SO muscles in patients with horizontal strabismus with SOOA-associated A-pattern can achieve a relatively high surgical success rate and restore binocular function.

Negative social bias against children with strabismus

PURPOSE

To determine whether the presence of noticeable strabismus creates a negative social bias against children.

METHODS

Photographs of two boys and two girls were digitally altered to create photographs of the same child in orthotropic, esotropic and exotropic states. Elementary school teachers rated their perceptions of the children's personal characteristics (using a 10-item list of personal characteristics) based on their responses to these whole-face photographs. The participants were also asked to answer five questions related to the first impressions created by the photographs.

RESULTS

Children with esotropia and exotropia were rated more negatively than orthotropic children on all 10 characteristics. Children with esotropia were rated more negatively than those with exotropia on most of these characteristics.

CONCLUSIONS

Children with noticeable strabismus are viewed negatively. Hence, correction of strabismus may provide psychosocial benefits even when there is no hope of improving visual function.

Monocular estimate method retinoscopy: central tendency measures and relationship to refractive status and heterophoria

BACKGROUND

Monocular estimate (estimation) method (MEM) is a widely used clinical test of accommodative response. Normative data for MEM are available based on the central tendency measures from a population of schoolchildren but not a clinical population. Also, the relationship of accommodative response to refractive status and heterophoria has been researched, but not with MEM as the determinant of the manifestation of accommodative response.

METHODS

A group of 211 pre-presbyopic clinical subjects were tested with MEM for purposes of comparing the central tendency measures of a clinical population to established normative data and determining whether MEM varied with refractive status or near phoria.

RESULTS

A lag of about one-third diopter was the mean MEM result for this clinical population. The median was +0.25 D. Myopia and near esophoria have a statistically significant relationship to MEM.

CONCLUSIONS

The central tendency measures derived from MEM administered to this population replicate the central tendency measures found in a previous normative study. This study provides preliminary evidence that the difference between accommodative response and accommodative stimulus, as measured by MEM, may be influenced by myopia and esophoria.

[Morphological findings in progressive esotropia with high myopia]

PURPOSE

Esotropia with high myopia is due to elongation of the eyeball, which becomes too large to fit within the muscle cone. To demonstrate the elongation, we measured the size of the eyeballs.

SUBJECTS AND METHODS

Five patients with esotropia with high myopia(myopic esotropia group), 8 patients with high myopia without esotropia(high myopia group), and 10 controls(control group) were examined. Using magnetic resonance imaging, we measured the outer axial length and the maximum transverse size of the eyeballs.

RESULTS

The outer axial length(mean +/- standard deviation) was greater in the order of the myopic esotropia group(31.6 +/- 1.59 mm), the high myopia group(27.9 +/- 2.22 mm), and the control group(23.7 +/- 1.59 mm) (p < 0.01). The maximum transverse size was also greater in the order of the myopic esotropia group(25.0 +/- 0.99 mm), the high myopia group (24.9 +/- 1.27 mm), and the control group(23.1 +/- 1.38 mm). The outer axial length of the eyeballs in the myopic esotropia group was significantly longer than in the high myopia group and the control group, and the maximum transverse size was significantly longer than in the control group.

CONCLUSIONS

The elongation of the eyeballs of the myopic esotropia group was demonstrated. A high incidence of esotropia may occur when the outer axial length of high myopia is longer than 30 mm.

Altered expression of alternatively spliced isoforms of the mRNA NMDAR1 receptor in the visual cortex of strabismic cats

PURPOSE

Although much has been written about the role of the NMDA receptor's role in experience dependent visual plasticity, the function of the NMDAR1 receptor subunit in the post-plasticity stage of development is still not well understood. However, in the well studied model of strabismic amblyopia where binocularity is reduced, but where most primary visual cortex neurons can be driven by one or other eye, the density of expression of NMDAR1 receptor protein is significantly reduced, compared to normals. This study aims to identify which of eight isoforms of the spliced heterogeneous variants of the NMDAR1 mRNA receptor gene are associated with this decrease in expression as a means of elucidating possible function.

METHODS

A series of digoxygenin-labelled oligonucleotide probes based on the human gene sequence have been used for in situ hybridization (ISH) of sections from the striate cortex of four adult cats. The probes were used to uniquely detect the expression of alternatively spliced mRNA variants in 66,487 cells from sections from the area centralis projection of two normal cats and two cats made esotropic as kittens by tenotomy at two weeks of age.

RESULTS

As expected, total NMDAR1 mRNA isoform expression was significantly lower in the striate cortex of strabismic compared to normal cats. The proportion of cortical cells expressing the R1-a, R1-b, and R1-1 isoforms in strabismic animals was decreased while the proportion expressing R1-3 was increased, especially in layers V and VI. No significant difference in expression of the R1-2 and R1-4 isoforms was seen comparing strabismic and normal cats.

CONCLUSIONS

These results confirm our previous findings and suggest that transcriptional inhibition of specific isoforms of NMDAR1 mRNA may underlie the change in receptor expression. This preferential reduction in the proportion of neurons bearing particular NMDAR1 isoforms, i.e. isoforms R1-a and b, and R1-1 with partial compensation through the expression of the R1-3 isoform, is more likely related to lowered proportion of binocularly activated neurons in the strabismic cat than to changes in eye dominance or the presence of amblyopia in one eye.

Comparison of clinical characteristics of familial and sporadic acquired accommodative esotropia

PURPOSE

To compare the clinical characteristics of patients with familial and nonfamilial acquired accommodative esotropia.

METHODS

We recruited 48 patients from 33 families with acquired accommodative esotropia (an inward deviation of the eyes of 10 PD or more, a hypermetropia greater than or equal to +1.50 D, and an onset of esotropia at, or later than, 1 year of age). Our control group consisted of 20 patients with no known family history. Spherical error of refraction, stereoacuity, and need for strabismus surgery were determined and the 2 groups were compared.

RESULTS

No statistically significant difference was found between the spherical equivalent error of refraction in familial cases (mean = +4.50 OD, +4.63 OS; range = +1.50 to +10.30 OD, +2.00 to +9.38 OS) versus those with nonfamilial disease (mean = +4.93 OD, +5.02 OS; range = +2.50 to +11.00 OD, +2.50 to +10.90 OS) (P =.47 OD; P =.47 OS). There also was no difference between the percentage of patients with familial disease who had some degree of stereoacuity (58%) and those without a family history (59%) (P > .99). Patients with familial acquired accommodative esotropia did not require more surgical interventions (26%) than those with nonfamilial acquired accommodative esotropia (30%) (P = .79).

CONCLUSIONS

The general clinical characteristics of familial and nonfamilial acquired accommodative esotropia are very similar.

Measurements for horizontal extraocular muscle surgery from the suture site: outcome and influencing factors

BACKGROUND

Measurement of recession in strabismus surgery is performed either from the limbus or from the muscle insertion. These measurement methods may result in inaccuracies that may influence the outcome of the procedure. We prospectively evaluated the outcome of recessions measured from the extraocular muscle suture site to its insertion in an incidence cohort.

METHODS

Thirty-six consecutive surgical procedures for infantile esotropia and 23 for constant exotropia were performed in which measurements were performed from the suture site. A successful surgery for esotropia was defined as an orthophoria of up to +10 prism dioptres of deviation for non-accommodative targets at a distance of 20 feet, measured by cover and prism test. A successful surgery for exotropia was defined as a residual deviation between -10 and +10 prism dioptres. The statistical significance of the outcome influencing factors was assessed by chi-square test.

RESULTS

Six weeks following surgery, 28 procedures (78%) for infantile and non-accommodative esotropia and 19 procedures (83%) for exotropia were successful. At the end of the follow-up period (mean 13.7 months +/- 9.4 for esotropia and 11.6 months +/- 12.8 for exotropia), the success rate was 77% for esotropia and 75% for exotropia. Prematurity and mental retardation in esotropia, exotropia with pre-operative deviations larger than -45 prism dioptres and amblyopia in exotropia were related to unfavourable outcome (p < 0.05).

CONCLUSIONS

Measurement for muscle recession can be performed from the suture site. The outcome is comparable to the outcome when measurements are performed from the limbus or the insertion, probably due to the incidence cohort. Refinement of the technique and defining other factors influencing the outcome of strabismus surgery may improve the outcome.

Periodic alternating nystagmus in two children with a similar, unusual phenotype

The report describes two unrelated male children, aged 6 and 8 years, respectively, with congenital periodic alternating nystagmus, congenital strabismus, microcephaly with cortical and cerebellar hypoplasia, mental retardation, low stature, and bat ears. Karyotypes were normal. Neuropediatric and ophthalmologic examinations, radiologic imaging of the brain, and laboratory analyses were performed to exclude other causes of periodic alternating nystagmus, such as ataxia-telangiectasia, acquired disease of the caudal brainstem or the cerebellum, albinism, or loss of vision resulting from cataract or vitreous hemorrhage. The similar morphologic and clinical features of both patients raise the possibility that they have an identical syndrome.

A biomechanical model of congenital/infantile esotropia and its treatment

PURPOSE

To evaluate the ability of a computer assisted model of ocular motility, to reproduce this syndrome using known ocular anatomic biomechanical muscular parameters, and to hypothesize pathogenetic mechanisms deduced from clinical and laboratory experiences.

METHODS

The manipulation of anatomic, elastic, contractile and innervational parameters available in the computer software program Orbit 1.6, were used to model: a) anatomic ocular and orbital parameters found in the 12 months old infant; b) static (biomechanical) changes measured intraoperatively in the extraocular muscles (medial and lateral rectus muscles) of infantile esotropes; and c) dynamic components of the horizontal deviation, including crossed fixation and bilateral limitation of abduction. Bilateral medial rectus recession surgery was also simulated on the completed model by moving backwards the insertions of both medial rectus muscles.

RESULTS

Small, fairly comitant, esotropic deviation were simulated using real data of the mechanical status of medial and lateral rectus muscles collected intraoperatively (length-tension measurements). The more typical large esotropic deviations with bilateral limitation of abduction of the congenital/infantile esotropia syndrome were only obtained when subtle modifications of the medial and lateral rectus muscles' thresholds to innervation were added to the anatomical-mechanical model. An orthotropic primary position binocular alignment with full rotations was obtained in this model following standard bilateral medial rectus recessions, showing surgical dose/response figures close to those usually found in the treatment of real cases of congenital/infantile esotropia.

CONCLUSIONS

This biomechanical computer-assisted model may provide a very useful tool not only to test new or different surgical procedures and dosages but also to explore different pathogenetic mechanisms.

Modifications of and special operating tricks in the classical technique of surgery against strabismus

Even nowadays the idea of most of the operations against strabismus is based on myectomy and reposition of the rectus muscles. At the Department of Ophthalmology of the University Medical School of Debrecen we use mainly these two methods of operation. At our Department we performed 1605 operations against strabismus during the last 10 years. 1269 of our patients had convergent, 336 had divergent strabismus. The majority of the operations were performed on patients less than 6 years of age, under general anesthesia. The outcome of the operation is successful if it results in a situation, in which torque affecting the eyeball stabilizes it in the normal position. The advantage of the combined surgical procedure is that the former muscular balance remains intact, and by relatively small intervention good results can be achieved. In the rectus muscles of squint patients anatomical and histopathological changes could be found, especially if they did not receive pleoptic treatment preoperatively. Depending on the direction of the strabismus one of the muscles is thicker, while the other is thinner, due to hyper- and hypofunction. Our surgical experience of many years showed that by modifying the classical technique of the operations with some fine technical tricks it was possible to increase the success rate. In our film we presented the right way of incising and handling the subconjunctival connective tissue (Tenon capsule) thus making it possible to lay it back to its original place at the end of the operation. This way the chance of postoperative scarring is reduced. We demonstrated how to test the contractility of the muscles by using muscle-hooks, that replaces the forceps test. In case of myectomy we demonstrated the tricks of how to handle the easiest and the finest way. In case of retroposition we can achieve perfect reconstruction and wound healing by using the shown simple technique. We also take much care of suturing the conjunctiva during operations performed on infants that is important because of their undisciplined behavior.

Photorefractive keratectomy in refractive accommodative esotropia

Photorefractive keratectomy (PRK) was performed on a 19-year-old man with hyperopic astigmatism and refractive accommodative esotropia. The patient was orthophoric while wearing spectacles, but had an esotropia of 30 prism dioptres at near and distance vision without spectacles. The best corrected visual acuity of the right eye was 20/50 and of the left eye was 20/20. The excessive accommodative convergence of the patient was eliminated by correcting the hyperopic refractive error by performing PRK, and the patient became orthophoric after the treatment.

Cell size in the lateral geniculate nucleus of cats reared with esotropia and sagittal transection of the optic chiasm

We have attempted to investigate the role of extraretinal influences in controlling visual system development by rearing cats with esotropia in combination with sagittal transection of the optic chiasm. This combination leave two intact A1 laminae, one innervated by the deviated eye and one innervated by the unoperated eye and thus minimizes the contributions of retinally mediated influences. Cell size measurements in the dorsal lateral geniculate nucleus revealed that the neurons in the A1 lamina innervated by the deviated eye were, on average, 10-15% smaller than their counterparts in the contralateral A1 lamina.

Pattern of ocular dominance columns in human striate cortex in strabismic amblyopia

Previous experiments in animals have shown that early unilateral eyelid suture, a model of amblyopia induced by cataract, causes shrinkage of ocular dominance columns serving the deprived eye in the striate cortex. It is unknown whether the ocular dominance columns are affected in amblyopia produced by strabismus. We examined specimens of striate cortex obtained postmortem from a 79-year-old woman with a history of amblyopia in her left eye (20/800) since age 2 from accommodative esotropia. Four years prior to her death, she suffered an ischemic infarct of the left optic disc. This injury to the left optic disc made it possible to label the ocular dominance columns using cytochrome oxidase histochemistry. The pattern of ocular dominance columns was reconstructed throughout most of the right striate cortex. No shrinkage of columns was found. In the left cortex only half the column mosaic was labelled, because the patient had some residual vision in the temporal retina of her left eye. The columns within the labelled portion of the overall mosaic appeared normal. These findings indicate that shrinkage of ocular dominance columns does not occur in humans with amblyopia caused by accommodative esotropia. The ocular dominance columns are probably no longer susceptible to shrinkage at the age when most children with this condition begin to develop amblyopia.

Surgical implications of the rectus extraocular muscle pulleys

PURPOSE

Magnetic resonance imaging (MRI) shows that the paths of rectus extraocular muscle bellies remain fixed in the orbit during large ocular rotations, and across large surgical transpositions of their insertions. This stability of muscle paths is due to their passage through pulleys which are coupled to the orbit and located in a coronal plane anterior to the muscle bellies near the equator of the globe. Autopsy studies have shown the pulleys to be fibroelastic sleeves consisting of dense bands of collagen and elastin, suspended from the orbit and adjacent extraocular muscle sleeves by bands of similar composition. Immunohistochemical studies have revealed substantial smooth muscle in the pulley suspensions and in posterior Tenon's fascia. The pulleys function as mechanical origins of the rectus extraocular muscles in the sense of determining extraocular muscle pulling directusons. This study was conducted to determine the theoretical effects of the pulleys on the outcome of rectus transposition surgery.

METHODS

The functional and anatomical evidence for the existence of the rectus extraocular muscle pulleys was reviewed. In two patients, binocular alignment data were collected using the Hess screen test before and after vertical rectus transposition surgeries for lateral rectus paralysis. Paths of the rectus extraocular muscles were determined using high resolution MRI. The OrbitTM 1.5 extraocular biosimulation program was employed to compute theoretical binocular alignment and muscle paths, under alternative conditions including or omitting the pulleys.

RESULTS

Pulleys are required to account for observed paths of rectus extraocular muscles following transposition surgery. In the absence of pulleys, transposition of the superior and inferior rectus muscles to the lateral rectus insertion for abducens paralysis would result in bizarre ocular misalignments not observed clinically.

CONCLUSIONS

The human orbit contains specialized musculofibroelastic tissues in and just posterior to Tenon's fascia, which serve as pulleys, determining actions of rectus extraocular muscles. These pulleys are located in a roughly coronal plane just posterior to the equator of the globe. Unimpaired pulley function is essential to effective muscle transposition surgery.

Factors influencing the successful outcome and response in strabismus surgery

In this retrospective study based on 140 esotropic and 51 exotropic patients, the factors influencing successful outcome and response to strabismus surgery were investigated. Thirteen independent variables were chosen. The pre-operative deviation was found to be the only discriminant factor for early and late successful surgical outcomes in esotropic patients. For exotropic patients the visual acuity of the left eye was the discriminant factor for early successful surgical outcome. In esotropic patients the response to surgery increased with increasing amounts of pre-operative deviation. It was lower for patients with older age of onset and larger amounts of medial rectus recession. For exotropic patients the response to surgery was higher for larger pre-operative deviations. Eliminating possible sources of error when determining the pre-operative deviation will improve the predictability of the response to surgery and surgical outcome.

Distribution of visual callosal neurons in normal and strabismic cats

It has been suggested that synchronous activation of cortical loci in the two cerebral hemispheres during development leads to the stabilization of juvenile callosal connections in some areas of the visual cortex. One way in which loci in opposite hemispheres can be synchronously activated is if they receive signals generated by the same stimulus viewed through different eyes. These ideas lead to the prediction that shifts in the cortical representation of the visual field caused by misalignment of the visual axes (strabismus) should change the width of the callosal zone in the striate cortex. We tested this prediction by using quantitative techniques to compare the tangential distribution of callosal neurons in the striate cortex of strabismic cats to that in normally reared cats. Animals were rendered strabismic surgically at 8-10 days of age and were allowed to survive a minimum of 18 weeks, at which time multiple intracortical injections of the tracer horseradish peroxidase (HRP) were used to reveal the distribution of callosally projecting cells in the contralateral striate cortex. HRP-labeled cells were counted in coronal sections, and data from four animals with divergent strabismus (exotropia) and four with convergent strabismus (esotropia) were compared to those from four normally reared animals. Although our data from strabismic cats do not differ markedly from those reported previously, we find that the distribution of callosal cells in the striate cortex of these cats does not differ significantly from that in our normally reared control cats. These results do not bear out the prediction that surgically shifting the visual axes leads to stabilization of juvenile callosal axons in anomalous places within the striate cortex.

Inferior oblique overaction in infantile esotropia: fundus extorsion as a predictive sign

BACKGROUND

Inferior oblique overaction develops in 72% of patients with infantile esotropia but generally is not recognized until the patient is between 2 and 4 years of age.

METHODS

While undergoing bilateral medial rectus recessions, photographs were taken of the posterior pole of 27 eyes in 14 patients with infantile esotropia and graded for the presence or absence of torsion by a masked observer. Follow up ranged from 10 months to 6 years.

RESULTS

Oblique muscle overaction developed in 15 of the 27 eyes. Of these 15, six demonstrated fundus torsion in infancy, before the oblique dysfunction was recognized clinically.

CONCLUSION

The presence of abnormal fundus torsion can serve as a marker for patients with infantile esotropia who ultimately will develop overt oblique muscle dysfunction.

A clinical study of the craniofacial features in Apert syndrome

A clinical study of the craniofacial features in Apert syndrome is based on our experience with 136 cases. Characteristics included hyperacrobrachycephaly, steep wide forehead, flat occiput, common craniofacial asymmetry, ocular hypertelorism and proptosis, downslanting palpebral fissures, divergent upgaze and esotropic downgaze, a tendency towards large ears, and marked depression of the nasal bridge. The nose is short and wide with a bulbous tip, and the anterior facial height is reduced. Common features during infancy included horizontal grooves above the supraorbital ridges that disappear with age, a break in the continuity of the eyebrows, and a trapezoidal-shaped mouth at rest. Radiographic aspects of Apert syndrome were also assessed. Tables are provided which compare the craniofacial features of Apert and Crouzon syndromes.

[Functional and structural abnormalities in the visual cortex in early childhood strabismus]

BACKGROUND

To investigate the structural basis for functional deficits in infantile strabismus we used a neuroanatomic tracer and a histochemical label to examine the primary visual cortex (area V1) of adult esotropic macaque monkeys.

ANIMALS AND METHODS

The animals had developed natural esotropia in the first months of life, alternated fixation, and exhibited the ocular motor signs that typify strabismus with onset in infancy. After behavioral and VEP testing, ocular dominance columns (ODCs) in V1 were injected with a neuronal traser and labeled for cytochrome oxidase activity.

RESULTS

The strabismic monkeys showed striking deficits in binocular luminance visually-evoked potentials (VEPs) and characteristic directional asymmetries in motion VEPs. Binocular horizontal connections between ODCs were reduced an average of 50-60% in strabismic as compared to normal monkeys. ODCs also showed unequal metabolic activity with contralaterally (i.e. nasal retina) driven ODCs showing greater activity in each V1.

DISCUSSION AND CONCLUSION

The maldevelopment of connections in upper V1 layers correlates with the abnormalities in binocular and motion VEPs. The unequal metabolic activity suggests interocular suppression. These results provide the first neuroanatomic evidence for cerebral cortex maldevelopments in natural infantile esotropia.

Neuroanatomic abnormalities of primary visual cortex in macaque monkeys with infantile esotropia: preliminary results

To explore the structural basis for visuomotor deficits in infantile esotropia, we examined binocular connections and metabolic activity in the primary visual cortex of two strabismic macaque monkeys. The animals were documented to have onset of natural esotropia in early infancy. Behavioral testing showed that the animals had normal visual acuity in both eyes and the ocular motor deficits that characterize strabismus with onset in infancy. The neuronal tracer substance biotinylated-dextran-amine was injected into ocular dominance columns (ODC) in area V-1 (striate cortex), revealing a paucity of binocular connections between right-eye and left-eye ODCs. The metabolic label cytochrome-oxidase was used to stain neighboring right-eye and left-eye ODCs, revealing inequalities in metabolic activity compatible with interocular suppression. These results show that infantile esotropes have abnormalities of visual cortex structure that correlate with abnormalities in binocular behaviors.

[Excentric lentiglobus posterior]

BACKGROUND

The posterior lentiglobe is a rare anomaly of the lens shape. Two cases of excentric protuberance of the posterior capsule are presented. To our knowledge, only one description of a similar case exists so far.

PATIENTS

An eight-year-old girl (diagnosis by routine examination, V.A. 20/20) and a six-year-old boy (V. A. 20/200, esotropia) are presented. Apart from a persistent hyperplastic primary vitreous and a posterior pole cataract a vitreous cyst adherent to the posterior surface of the lens has to be considered as differential diagnosis. The etiology remains unclear.

CONCLUSION

In excentric posterior lengtiglobe a good vision is possible. However, if visual acuity is impaired by posterior pole opacity or distortion of the spherical surface, removal of the lens followed by optical correction (contact lens, intraocular lens) of aphakia should be performed.

Tenon's capsule: ultrastructure of collagen fibrils in normals and infantile esotropia

No detailed information about the ultrastructure of Tenon's capsule has been published. The purpose of the present study was to compare the ultrastructural features of collagen fibrils from Tenon's capsule in a nonstrabismic control group (seven children) to those in an infantile esotropic group (10 children). Small biopsy specimens from Tenon's capsule were taken during various operations to be examined by electron microscopy. On electron microscopy, the capsule was found to be composed of groups of collagen fibrils arranged irregularly in different orientations, forming a three-dimensional network that provides tissue resistance to stress. The cross-sectioned collagen fibrils were studied by an image analyzer. In both study groups, all fibrils had a round, regular contour. In the esotropic group, the Tenon's collagen fibrils were thicker, as reflected by their significantly greater mean diameter: 101 +/- 5 nm (mean +/- standard deviation) compared to 86 +/- 5 nm in the control group. Also, significantly greater heterogeneity was found in the collagen fibril thickness of each individual in the esotropic group compared to the control group. Moreover, the mean number of collagen fibrils per unit area was significantly higher in the esotropic group: 98 +/- 13 fibrils per 10(6) nm2 compared to 73 +/- 5 fibrils per 10(6) nm2 in the control group. These ultrastructural changes may be stress-induced secondary alterations of the Tenon's collagen fibrils resulting from prolonged deviation of the eye in infantile esotropia. The significantly denser collagen fibrils may cause a decrease in the elasticity of Tenon's capsule in infantile esotropia.

End-stage fibrosis of the lateral rectus muscle in myopia with esotropia. An ultrastructural study

The fibrotic lateral rectus muscle and the medial rectus muscle of 4 patients with esotropia and myopia who underwent surgical correction were studied ultrastructurally. All patients revealed underactivity of the lateral rectus muscle. In 3 patients the underactive lateral rectus was completely fibrotic; in 1 patient there was 80% fibrosis, and the rest of the muscle showed different stages of degeneration. The fibrotic lateral recti were composed of collagen fibrils and remnants of degenerated organelles. The collagen fibrils of the lateral recti were of different sizes, and the mean diameter varied from 65 to 92 nm. On the other hand, the interstitial collagen fibrils of nonfibrotic medial rectus muscles of these patients and also of control muscles showed less variation in size, and the mean diameter was smaller as compared with the fibrotic lateral rectus. It is suggested that the collagen fibrils that compose the fibrotic lateral rectus muscle probably develop under conditions which differ from the normal development of collagen fibrils.

The influence of axial length on the response to strabismus surgery

We performed axial length determinations preoperatively on a series of patients undergoing strabismus surgery. A statistically significant inverse correlation was found between axial length and the response (prism diopters per millimeter of medial rectus recession) for esotropic patients. The data suggest that a surgical formula designed to take axial length into account would decrease the variability in response to strabismus surgery in esotropic patients. Poor correlation was found between axial length and response to surgery in exotropic patients. We feel this poor correlation was due, in part, to the postoperative drift rate in exotropic patients as well as inaccuracies with the standard techniques used to determine the basic deviation on which surgery in exotropic patients is based.

Acute thalamic esotropia

Three men developed acute esotropia, stupor, and impaired upward gaze. Vestibulo-ocular stimulation showed that the adducted eye remained immobile while the fellow eye responded normally. The alteration of consciousness, the long-tract neurologic signs, and the esotropia quickly resolved. Upgaze paresis and brief bursts of convergence-retraction nystagmus were the major residual signs. Imaging techniques demonstrated lesions of the contralateral posterior thalamus in each patient. Several mechanisms are proposed to explain the acute esotropia. Impairment of monocular projections in the contralateral posterior thalamus could disinhibit neurons in the oculomotor complex, or ischemia of inputs to neurons involved with vergence control in the midbrain could result in tonic activation of the medial rectus. The clinical and radiographic findings are consistent with infarction in the territory of penetrating branches of the basilar-communicating (mesencephalic) artery. Embolism to the top of the basilar artery is presumed to be the precipitating event.

Management of large-angle esotropia

If large-angle esotropia is defined as 80 D or more, and if the surgery induces no limitation of movement or incomitance, there is an excellent likelihood that four-muscle surgery in one operation will result in a residual deviation between 15 D of convergent strabismus and 15 D of divergent strabismus.

Convergent strabismic amblyopia in cats

Experiments were carried out to determine the effects of different types of experimental strabismus on the acuities of retinal ganglion cells. Six kittens were raised from twenty-one days of age with an esotropia surgically induced by myectomy of the lateral rectus muscle and a large portion of the superior oblique muscle. The results are compared with those, previously reported, from five other cats also made esotropic, but by tenotomy of the lateral rectus. All animals tested behaviourally were amblyopic in the strabismic eye. For square wave gratings, the visual acuities were 1.0 to 2.5 cyc/deg through the strabismic eye compared with 6.0 to 7.5 cyc/deg through the non-deviating eye. The cut-off spatial frequencies were determined for 132 brisk sustained cells from five of the myectomized strabismic cats. There was a loss of approximately 20% in cut-off spatial frequency when compared with both normal and tenotomized cats. A correlate of the physiologically observed difference between the tenotomized cats and the myectomized cats was also found in the morphology of cells in the lateral geniculate nucleus. The tenotomized cats showed no evidence of cell shrinkage in laminae receiving a projection from the amblyopic eye whereas in the myectomized cats large differences were observed in cell cross-sectional areas between laminae receiving input from the amblyopic eye and those receiving input from the non-deviating eye. Together, these findings indicate that the presence of a neural deficit in the retina of strabismic cats is associated with the actual removal of extra-ocular muscle and probably has little to do with the optical quality of images arriving at the retina.

A randomized comparison of surgical procedures for infantile esotropia

In a prospective, randomized, masked study we compared the treatment of infantile esotropia using bilateral medial rectus muscle recessions of a graded amount from the insertion to standard 10.5-mm recession from the corneoscleral limbus. Of the patients undergoing recession of the medial recti muscles 10.5 mm from the corneoscleral limbus, 33 of 39 (84%) achieved a final ocular alignment within 10 prism diopters of straight with one operation, compared to 26 of 41 (63%) of the patients undergoing a graded recession from the insertion. The difference was significant (.01 less than P less than .05 by the chi-square test).

Shortage of binocular cells in area 17 of visual cortex in cats with congenital strabismus

Twenty-nine pigmented offspring of an innately esotropic female cat exhibited varying deficits in the number of binocular cells recorded in area 17 of the visual cortex as compared to 12 normal cats. Misalignment of the two eyes in these cats was found in the awake as well as in the paralysed state. Pupillography combined with measurements of visual disparity yielded abnormal esotropia of up to 8.4 degrees under paralysis, which corresponds to an abnormal convergence of the freely moving eyes of up to 14 degrees (average 7.4 degrees). In the majority of animals cortical binocularity was found reduced by the two eyes controlling independent sets of separate units (U-shaped ocular dominance distribution) whereas in 7 cats the reduction was due to a partial loss of one eye's influence. The proportion of monocular units correlated with the degree of crossover of the visual axes (r = 0.73). Anatomical investigation of the retinofugal projections revealed normal appearance in three previously recorded cats in which more than 50% of cortical units had been monocularly driven. The small angles of esotropia and the "normal" appearance of eye position judged by the pupillary positions in the orbit of these cats, might suggest that we found an animal model for microstrabismus.

Primary and secondary overacting inferior oblique muscles: an ultrastructural study

Biopsy material from primary and secondary overacting inferior oblique muscles were examined by light and electron microscopy. Most muscle fibres were in different stages of atrophy. A high variation of alterations was encountered in all muscles. The most striking abnormalities were huge accumulations of mitochondria and muscle vacuolisation related mainly to the enlargement of the tubules of sarcoplasmic reticulum. The mitochondrial aggregates and vacuolisation occupied more muscle surface in the inferior muscles of primary overaction than those of secondary overaction.

Alterations in connections of the corpus callosum following convergent and divergent strabismus

The connectivity of the corpus callosum in visual cortical areas 17 and 18 was studied in normal cats, in cats reared with unilateral convergent or divergent surgically-induced strabismus, and in a Siamese cat. The extents of the callosal cell and terminal zones were determined following multiple injections of horseradish peroxidase and tritiated amino-acids into one hemisphere. Following surgically-induced strabismus, abnormally wide callosal cell zones were seen in both the left and the right hemisphere irrespective of the direction of eye misalignment. Abnormally wide callosal terminal zones were seen in the hemisphere ipsilateral to the deviating eye in cats reared with unilateral convergent and divergent strabismus. Abnormally wide callosal zones were seen in cats which had strabismus induced as late as postnatal day 36. In a Siamese cat with a naturally-occurring convergent strabismus, callosal cells had a different distribution and were fewer in number compared to normal cats or cats with surgically induced strabismus. This implies that the abnormal callosal connectivity of Siamese cats is not a simple result of strabismus.