Medial strabismus (esotropia) at rest associated with contralateral paramedian thalamic ischemic infarction in 2 dogs

Pseudoabducens paralysis resulting in resting medial strabismus (esotropia) is a rare consequence of a contralateral paramedian thalamic ischemic infarction in people. To date, esotropia has been reported in dogs in association with ipsilateral abducens neuropathy or extraocular myopathy, but not secondary to thalamic lesions. A 7-year-old male neutered Border Collie and a 12-year-old female neutered cross-breed dog were presented with peracute nonprogressive vestibular ataxia. Neurological examination identified right esotropia, nonambulatory tetraparesis, right head tilt, vestibular ataxia and nystagmus. Lesions in both dogs were localized to the vestibular system with thalamic involvement. Magnetic resonance imaging of the brain identified a left paramedian thalamic lacunar ischemic infarct in both dogs. Interruption of descending inhibitory pathways that decussate in the subthalamic region and innervate the contralateral motor nucleus of the oculomotor nerve leads to hypertonicity of the medial rectus. These cases indicate that esotropia is a rare but highly localizing sign in dogs with contralateral thalamic infarcts.

Suspected hypothyroid-associated neuropathy in a female rottweiler dog

A 7-year-old, 46-kg spayed female rottweiler dog was presented with sudden onset of disorientation, bilateral convergent strabismus, and enophthalmos. Diagnostic workup revealed hypothyroid-associated cranial neuropathy. Symptoms abated considerably upon treatment with levothyroxine-sodium (T4) at an initial dose of 800 μg/kg body weight (BW), PO, q12h, which was reduced 3 days later to 600 μg/kg BW, q12h due to severe agitation and panting. Two weeks later the dosage of the levothyroxine-sodium (T4) was reduced to 400 μg/kg BW in the morning and 600 μg/kg BW in the evening. Eight weeks after the initial presentation, the dog had recovered with only mild convergent strabismus in the right eye. This is the first case report of suspected hypothyroid-associated neuropathy resulting in these symptoms.

Effects of extraocular muscle tenotomy on congenital nystagmus in macaque monkeys

INTRODUCTION

Extraocular muscle tenotomy has been reported to damp congenital nystagmus in an achiasmatic sheepdog. We performed extraocular muscle tenotomy to evaluate its effects on congenital nystagmus in primates.

METHODS

Magnetic search coil eye movement recordings were used to document the presence of horizontal congenital nystagmus in 2 adult macaque monkeys that also had naturally occurring infantile strabismus. Extraocular muscle tenotomy was performed by operating on all 4 horizontal recti, surgically detaching the muscles from the globe and suturing them back to their original insertions without resection or recession. Eye movement recordings were repeated 4 months after the procedure, comparing the waveform, amplitude, retinal slip velocity, and intensity (frequency x amplitude) of the nystagmus before and after tenotomy. Visual acuity was also measured before and after surgery in 1 animal.

RESULTS

Preoperatively, a disconjugate, pendular nystagmus was evident in 1 monkey, and the other had a conjugate pendular-jerk nystagmus damped by convergence. After tenotomy, nystagmus mean amplitude decreased 18% to 52% in 1 monkey but increased 14% in the other (t test, P <.002). Retinal slip velocity and nystagmus intensity increased in both monkeys. After tenotomy, mean velocity increased 22% to 218%, while mean intensity increased 40% to 208% (t test, P <.002). Visual acuity measured after tenotomy decreased an average of 20% ( approximately 2.0 cycles per degree) in each eye. Tenotomy had no noteworthy effects on eye alignment or other aspects of visual behavior other than the congenital nystagmus.

CONCLUSION

Nystagmus velocity and intensity increased after extraocular muscle tenotomy in 2 monkeys. Further studies are required to establish the clinical value of this procedure as a treatment for various subtypes of congenital nystagmus in humans.

Sino-orbital aspergillosis in a dog

Fungal rhinitis-sinusitis with orbital involvement was diagnosed in a dog with profuse unilateral ocular and bilateral nasal discharge, enophthalmos, and a corneal descemetocele. The descemetocele was treated with a conjunctival pedicle graft. Frontal sinusotomy was performed, and clotrimazole was infused through catheters placed in the frontal sinuses and nasal cavities to saturate the tissues for 1 hour. Successful resolution of orbital infection may have been aided by a fistula between the frontal sinus and orbit that allowed delivery of clotrimazole to the orbit. The dog retained sight in the affected eye, and clinical signs of infection were not detected 14 months later, although enophthalmos and medial strabismus may have been caused by persistent postinflammatory fibrosis.

Use of computed tomography in the diagnosis of a cerebral abscess in a goat

A 7-month-old La Mancha doe was presented with a right head tilt and ventral strabismus while circling to the left. History and physical examination led to a tentative diagnosis of a cerebral abscess. Computed tomography revealed a large, complex mass with ring enhancement in the left cerebral hemisphere, supporting the diagnosis. Postmortem examination confirmed the cerebral abscess. Bacterial cultures yielded heavy growth of Actinomyces pyogenes.

Nasotemporal asymmetries in V1: ocular dominance columns of infant, adult, and strabismic macaque monkeys

To quantify asymmetries of input from the two eyes into each cerebral hemisphere, we measured ocular dominance column (ODC) widths and areas in the striate visual cortex (area V1) of macaque monkeys. Ocular dominance stripes in layer 4C were labeled by using transneuronal transport of intraocularly injected wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cytochrome oxidase (CO) histochemistry, after deafferentation of one eye or even by leaving afferent input intact. In infant monkey aged 4 and 8 weeks, ocular dominance stripes labeled by WGA-HRP appeared adultlike with smooth, sharply defined borders. In normal infant and normal adult macaque, ocular dominance stripes driven by the nasal retina (i.e., contralateral eye) were consistently wider than stripes driven by the temporal retina (i.e., ipsilateral eye). Asymmetries in the percentage of area V1 driven by nasal vs. temporal ODCs showed a similar "nasal bias": in infant macaque, approximately 58% of ODCs in V1 were driven by nasal retina, and in adult macaque approximately 57%. The asymmetries tended to be slightly smaller in opercular V1 and greater in calcarine V1. "Spontaneous" ocular dominance stripes were revealed by CO staining of V1 in a naturally strabismic monkey and in a monkey made strabismic by early postnatal alternating monocular occlusion. In these animals, ocular dominance stripes and CO blobs corresponding to the nasal retina stained more intensely for CO in both the right and left V1. ODC spacing and the nasotemporal asymmetry in ODC width and area were similar in strabismic and normal monkeys. Our results in normal monkeys extend the observations of previous investigators and verify that nasotemporal inputs to opercular and calcarine V1 are unequal, with a consistent bias favoring inputs from the nasal retina. The CO results in strabismic macaque suggest that the nasal ODC bias promotes interocular suppression when activity in neighboring ODCs is decorrelated by abnormal binocular experience in infancy.

Optokinetic nystagmus in cats with congenital strabismus

1. Eye movements were recorded in seven innately esotropic cats during monocular and binocular horizontal optokinetic stimulation, using the search coil technique in five cats and electrooculography in two cats. 2. During closed loop measurements in these strabismic cats, slow phases of optokinetic nystagmus (OKN) were characterized by an overall reduced gain when compared with normal controls. In addition, response gain to monocular nasotemporal stimulation was even more reduced than that to temporonasal stimulation, resulting in an increased asymmetry of closed loop gain. 3. During open loop measurements, eye velocity in strabismic cats was very low at all velocities tested. 4. Differential analysis of the symmetry of OKN revealed that all our strabismic cats had a "good" or more symmetric and a "poor" or more asymmetric eye. In addition, when analyzed separately at individual velocities, the symmetry index of the good eye was fairly constant over the velocity range tested. By contrast, the symmetry index of the poor eye dropped dramatically at higher stimulus velocities. 5. To analyze the relationship of OKN symmetry and cortical physiology, we calculated the ratio between the percentage of neurons driven by one eye in the ipsilateral and the contralateral cortical hemisphere. We found a weak correlation between OKN symmetry and this cortical symmetry index (P < 0.05, analysis of variance). 6. In conclusion, slow eye movements in cats with congenital esotropia are characterized by extremely low gain, especially at higher stimulus velocities. In addition, OKN symmetry during monocular stimulation is decreased. Our data suggest that OKN symmetry is weakly correlated with the proportion of binocular neurons in the visual cortex ipsilateral to the stimulated eye. However, OKN characteristics seem to reflect to a higher degree the response properties of neurons in the pretectal nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system than properties of neurons in the visual cortex.

What happens to binocularity in primate strabismus?

Normal humans for whom the positions and movements of the two eyes are constrained to be yoked together are able to extract rich binocular sensory information from the environment. Humans with strabismus are deficient in extracting some of this information. Studies of strabismus in non-human primates can augment what has been learned from humans about relationships between strabismus and sensory binocular function. For example, speculation about the role of binocular vision in primate evolution can help us understand why it is that the advantages of sensory binocular function outweigh the disadvantages of having the positions of the two eyes yoked together. Physiological optics assessments of fixation patterns and accommodative responses in monkeys provide information about how the brain accomplishes and coordinates motor and sensory binocular functions, and sets the stage for determining underlying neural mechanisms responsible for this coordination. Finally, a developmental perspective, concerned with events that occur during an early sensitive period in the life span of an infant primate, can help us understand how nature and nurture interact to set up this complex neural system in normal individuals, and how this process is disrupted in conditions such as strabismus.

Neonatal ophthalmology

This discussion of normal and abnormal findings on routine ophthalmic examination of the foal should prove useful to the equine practitioner who must provide counsel to the concerned owner and/or breeder. Early diagnosis and treatment of ocular abnormalities improve the prognosis for continued function and aid determination of the significance of lesions observed in later life.

Frequency of naturally occurring strabismus in monkeys

A colony of Macaca nemestrina monkeys was screened for naturally occurring strabismus. Thirteen cases of naturally occurring strabismus were documented, 12 esotropes and one exotrope. The characteristics of the strabismus in these monkeys were similar to those of human clinical cases. Four of the affected monkeys showed interocular differences in grating acuity. We estimated the incidence of strabismus in the monkey colony to be 4%.

Naturally occurring strabismus in monkeys (Macaca nemestrina)

Seven naturally strabismic monkeys (Macaca nemestrina) was identified. Five of these monkeys were examined by ophthalmologists. No ophthalmoscopically obvious cause for the squint was found in any case. Of those five animals, two were tested behaviorally on visual responsiveness and visual acuity. The acuity of both eyes of both monkeys was somewhat poorer than normal. In addition, an amblyopia of 0.8 octaves was found for one monkey and 0.6 octaves for the others. The existence of naturally strabismic monkeys supports the utility of the macaque as an animal model for studying strabismus and amblyopia.

Nervous signs in bovine coccidiosis

In 2 outbreaks of coccidiosis due to E bovis and/or E zurnii infection in Canadian cattle, nervous signs included opisthotonos, medial strabismus, hypersensitivity, tetanic spasms, and convulsions. All of the affected animals died in convulsions after an illness of one to several days during which time they showed periodic nervous signs. Necropsy revealed a very severe enteritis with the most severe lesions in the spiral colon. Much of the intestinal mucosa in this area had been destroyed by the parasite. None of several suggested causes of such nervous signs was indicated by laboratory findings, but the possibility of toxins produced by the coccidia could not be ruled out.

Anomalous retinal pathways in the Siamese cat: an inadequate substrate for normal bioncular vision

All major retinal pathways in the Siamese cat are abnormal, with almost total crossing of the projections to the pretectum and superior colliculus. These projections represent a marked disruption in the customary neural substrate for binocular vision, which implies a consequent impairment in stereoscopic depth perception. Crossed eyes, commonly seen in the Siamese cat, may therefore arise from a neuroanatomical defect in the primary visual pathways.