Disorders of eyes and vision

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The neuro-ophthalmological examination combines aspects of the neurological examination and ophthalmic assessment in order to identify ophthalmic disorders arising from diseases affecting the nervous system. This chapters covers neuro-ophthalmological assessment, neuro-ophthalmic syndromes.

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10.1 Evaluation of the eyes should be performed even when neuro-ophthalmological abnormalities are not suspected. The anterior uveitis and retinal vasculitis evident in this cat with episodes of opisthotonus are suggestive of infection, most probably with feline coronavirus (the causative agent of feline infectious peritonitis, FIP). FIP was confirmed at post-mortem examination. (Courtesy of J Mould, Eye Veterinary Practice)
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10.2 Structure of the retina. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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10.3 The visual pathways demonstrating how each side of the visual field is represented within the opposite occipital (visual) cortex. As the degree of binocular vision in different species decreases, so a greater proportion of optic nerve fibres decussate at the optic chiasm. (© Jacques Penderis)
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10.4 The menace response is assessed by making a threatening movement towards each eye in turn. Usually the visual stimulus is only directed at the nasal retina and not the temporal (lateral) retina and therefore only assesses the contralateral visual cortex. (© Jacques Penderis)
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10.5 The menace response pathway – a lesion interrupting any part of the pathway may result in a menace deficit. (© Jacques Penderis)
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10.6 Severe cerebellar lesions, as seen in this example of a cerebrovascular incident within the right cerebellum, may result in ipsilateral loss of the menace response without causing visual or facial nerve deficits. (© Jacques Penderis)
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10.7 The pathway of the pupillary light reflex (divergence of the conscious visual pathway is detailed in light grey). (© Jacques Penderis)
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10.8 The postulated pathway of the dazzle reflex – a subcortical reflex blink associated with a bright light stimulus. (© Jacques Penderis)
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10.9 Innervation of the extraocular muscles (besides the retractor bulbi and levator palpebrae muscles). (© Jacques Penderis)
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10.10 Sensory innervation fields of the three branches of the trigeminal nerve. Motor innervation of the mandibular branch of the trigeminal nerve to the muscles of mastication. (© Jacques Penderis)
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10.11 The pathway of the sympathetic innervation to the eye and adjacent structures of the head. (© Jacques Penderis)
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10.12 Electroretinography. Normal waveform. With diseases that result in the loss of rod and cone photoreceptors, the normal waveform is abolished. (© Jacques Penderis)
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10.13 Corneal clouding in a Domestic Shorthaired cat with mucopolysaccharidosis type VI. (© Jacques Penderis)
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10.14 Domestic Shorthaired kitten with a congenital portosystemic shunt presented with copper-coloured irises. (© Jacques Penderis)
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10.15 The iris thickening and corneal precipitates evident in this cat with central vestibular disease suggest that infectious agents or lymphoma may be the cause of the neurological deficits. CSF analysis confirmed the presence of lymphoma. (© Comparative Ophthalmology Unit, Animal Health Trust)
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10.16 Papilloedema in a Boxer with a large forebrain tumour. Note the irregular and swollen optic disc margin. The identification of papilloedema should alert the clinician to the probability of raised intracranial pressure. (© Jacques Penderis)
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10.17 Parasagittal post-contrast T1-weighted fat saturation MR images of the optic nerves from a Golden Retriever with left blindness and a prominent optic nerve on fundic examination. There is enlargement and increased contrast medium uptake in the left optic nerve (arrowed). The lesion is consistent with neoplasia or focal inflammation. Compare the normal right optic nerve (arrowed) with the left optic nerve in (a). The lesion is consistent with neoplasia or focal inflammation. (© Jacques Penderis)
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10.18 MR image of a contrast-enhanced mass (arrowed) at the level of the optic chiasm in a dog. The appearance and clinical findings were consistent with a pituitary macroadenoma. (© Jacques Penderis)
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10.19 Central blindness may be seen in association with hydrocephalus. Affected dogs have an enlarged, dome-shaped skull. Blindness results from the vulnerability of the optic radiations adjacent to the enlarged lateral ventricles as evident in this MR image. (© Jacques Penderis)
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10.20 This dog presented with acute onset blindness and loss of the PLR, suggestive of a retinal, optic nerve or optic chiasm lesion. The evidence of scleral haemorrhage indicates the possibility of an underlying bleeding disorder and this was later confirmed as the cause of the blindness. (© Jacques Penderis)
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10.21 Cerebrovascular accidents are occasional findings in dogs and may result in blindness if the visual pathways are affected. One site of predilection is the thalamus (arrowed) and contralateral visual deficits, conscious proprioceptive deficits and vestibular dysfunction may be evident. (© Jacques Penderis)
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10.22 Right Horner’s syndrome in a dog showing miosis, ptosis and protrusion of the third eyelid. Enophthalmos is the fourth feature associated with Horner’s syndrome but cannot be appreciated on this image. (© Jacques Penderis)
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10.23 Left Horner’s syndrome in a cat showing miosis, ptosis and protrusion of the third eyelid. Enophthalmos is the fourth feature associated with Horner’s syndrome. (© Jacques Penderis)
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10.24 Bilateral Horner’s syndrome in a Golden Retriever. Third eyelid protrusion may interfere with vision in cases of bilateral Horner’s syndrome, whereas in unilateral cases it can be considered mainly cosmetic. (© Jacques Penderis)
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10.25 Following topical administration of phenylephrine into the right eye of the bilateral Horner’s syndrome case from Figure 10.24 , the miosis resolved rapidly (<20 minutes) indicating a third order neuron lesion. (© Jacques Penderis)
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10.26 Pourfour du Petit syndrome in the left eye of a cat. The cat has left peripheral vestibular syndrome with irritation to the sympathetic supply at the same level. The excessive sympathetic tone results in pupil dilatation and (not apparent on this image) an enlarged palpebral fissure and subtle exophthalmos on the affected side. (© Jacques Penderis)
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10.27 Idiopathic internal ophthalmoplegia in the right eye of a Flat-coated Retriever. Pharmacological testing confirmed a CN III parasympathetic lesion. No other clinical signs were evident on examination, MRI and other investigations were normal and the lesion resolved spontaneously over the course of a month. (© Jacques Penderis)
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10.28 This dog presented with pupillary dilatation (which did not constrict on light stimulation), lateral strabismus and ptosis of the right eye. Vision was intact. These clinical signs are suggestive of a lesion affecting CN III. (© Jacques Penderis)
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10.29 Transverse, post-gadolinium T1-weighted MR image at the level of the thalamus of the dog in Figure 10.28 demonstrating contrast enhancement and enlargement of the oculomotor nerve, which is suggestive of neoplasia. (© Jacques Penderis)
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10.30 Reverse D-shaped pupil in a cat indicating damage to the nasal ciliary nerve of the left eye. Cats presenting with ciliary nerve damage should be investigated for FeLV as well as for other viral agents and lymphoma. (© Comparative Ophthalmology Unit, Animal Health Trust)
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10.31 Dysautonomia in a dog and a cat with protrusion of the third eyelids, pupillary dilatation and bilateral xeromycteria (dry nose) (a = © Jacques Penderis; b = Courtesy of the Royal (Dick) Veterinary School)
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10.32 Divergent strabismus in a Cavalier King Charles Spaniel suggestive of a pathological cause. However, subsequent examination revealed normal eyeball movement and function. The strabismus was ascribed to an extreme form of divergent strabismus (exotropia) due to brachycephalia. (© Jacques Penderis)
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10.33 Trochlear nerve lesions in isolation are extremely rare. Lesions manifest as rotation of the contralateral eyeball with the dorsal portion (12 o’clock position) being temporally (laterally) deviated. This is apparent in cats as rotation of the vertical pupil (left) but in dogs is only apparent on fundic evaluation of the dorsal retinal arteriole and vein (right). (© Jacques Penderis)
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10.34 Lesions of the abducent nerve cause medial strabismus, but can be easily differentiated from the congenital medial strabismus in this cross-breed dog by assessing the corneal reflex. With abducent nerve lesions, eyeball retraction is absent when the reflex is performed. (© Jacques Penderis)
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10.35 Congenital divergent strabismus (exotropia) in a Golden Retriever puppy. (© Jacques Penderis)
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10.36 Visual pathway abnormalities in Siamese and related cat breeds. In normal animals the temporal retinal afferents (blue) do not cross at the optic chiasm. In Siamese and related cat breeds information from the temporal retina is abnormally crossed at the optic chiasm. This misrouted information is then mapped to the wrong lateral geniculate nucleus and visual cortex. Affected cats compensate by blocking the cortical projections of the incorrect afferent at the level of the lateral geniculate nucleus, but the result is that the perceived visual field and consequently binocularity are dramatically reduced. However, this inappropriately crossed visual information is still used for eyeball position and visual tracking and this may explain the medial strabismus and abnormal nystagmus. (© Jacques Penderis)
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10.37 Convergent strabismus (esotropia) in a Siamese cat with congenital abnormalities of the visual pathways. (© Jacques Penderis)
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10.38 Divergent strabismus (exotropia) is recognized in brachycephalic dogs, but the underlying cause has yet to be fully elucidated. (© Jacques Penderis)
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10.39 Spontaneous nystagmus associated with vestibular disease may indicate the site of the lesion. Horizontal and rotary nystagmus are seen with both peripheral and central vestibular disease, but vertical nystagmus is only associated with central vestibular disease. (© Jacques Penderis)
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10.40 Ipsilateral ventrolateral strabismus in the right eye of a Pug induced by raising the head. This is a frequent feature of vestibular disease. (© Jacques Penderis)
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10.41 Bilateral ventrolateral strabismus in a Boxer, which occurred upon raising the head. This is an indication of bilateral vestibular disease. (© Jacques Penderis)
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10.42 Congenital hydrocephalus in a Jack Russell Terrier puppy associated with bilateral ventrolateral strabismus (‘setting-sun sign’). (© Jacques Penderis)
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10.43 Lateral strabismus in a dog with acute extraocular myositis. The subsequent fibrosis of the extraocular muscles (following resolution of the acute inflammation) may also result in strabismus. (© Jacques Penderis)
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10.44 MR images showing the acute stage of extraocular myositis. Note the enlargement of the extraocular muscles (solid arrows) and more widespread inflammation in the masticatory muscles (open arrows). The masticatory muscles are more accessible, allowing a confirmatory muscle biopsy sample to be obtained. (© Jacques Penderis)
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10.45 Fibrosing esotropia in a Shar Pei. The severe convergent strabismus in this case means that the pupils are occluded behind the medial canthus. The sclera is mainly visible. (© Jacques Penderis)
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10.46 MR image of a retrobulbar mass (arrowed) causing exophthalmos and interfering with normal eyeball movement. (© Jacques Penderis)
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10.47 Left retrobulbar mass. Exophthalmos, protrusion of the third eyelid and mild lateral strabismus are evident in this case. (© Jacques Penderis)
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10.48 Typical appearance of tetanus with the ears held close together and the forehead wrinkled. Dogs with tetanus may demonstrate lateral strabismus (as in this case), intermittent protrusion of the third eyelids and photophobia. (© Jacques Penderis)
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10.49 Right forebrain mass lesion resulting in a right lateral strabismus when the head is held facing forward. The underlying basis for the lateral strabismus ipsilateral to the side of the lesion is unclear, but may be related to a similar mechanism that causes ipsilateral circling and head turn with some asymmetrical forebrain lesions. (© Jacques Penderis)
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10.50 Neurogenic corneal ulcer (neuroparalytic keratitis) in the left eye of a Dachshund secondary to loss of corneal sensation due to a lesion affecting the ophthalmic branch of the trigeminal nerve. Before and after fluorescein staining. Neurogenic ulcers tend to be central, situated over the exposed region of the cornea. (© Jacques Penderis)
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10.51 Enophthalmos of the right eye secondary to masticatory muscle atrophy as a result of a lesion affecting the mandibular branch of the trigeminal nerve. (© Jacques Penderis)
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10.52 MR images showing a tumour of the trigeminal nerve root (open arrow) and consequent atrophy of the masticatory muscles on the affected side (closed arrows). (© Jacques Penderis)
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10.53 Right-sided hemifacial spasm in a Golden Retriever. Note the increased tone on the affected side of the face with the lip and ear pulled up in contrast with the normal left side. Although not apparent in this case, hemifacial spasm often causes a narrowed palpebral fissure on the affected side. (© Jacques Penderis)
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10.54 Right facial nerve paralysis with involvement of the parasympathetic innervation to the lacrimal gland and lateral nasal gland, resulting in neurogenic keratoconjunctivitis sicca and ipsilateral xeromycteria (dry nose). (© Jacques Penderis)


Central vestibular disease

(a) Head and body tilt. Adult miniature Dachshund demonstrating a left head tilt, and left truncal deviation on being held. The dog also prefers to lie with the left side down and becomes distressed when held with the left side uppermost. Testing of the righting reflex (when a dog is held horizontally the normal response is to reach upwards or right itself). The righting reflex is lost when the dog is held with the left side down. These combination of clinical signs indicate left vestibular syndrome.

Central vestibular disease

(b) Proprioceptive placing. Testing of proprioceptive placing using tactile placing response testing. There is loss of tactile placing in the left thoracic and pelvic limbs. When combined with the left vestibular syndrome in the previous video clip this is indicative of central left vestibular syndrome.

Central vestibular disease

(c) Strabismus. Ventrolateral strabismus of the left eye indicative of left vestibular syndrome. The strabismus becomes more obvious if the head is moved from the left head tilt position to horizontal. There is also an intermittent pathological vertical nystagmus, but this is less obvious on the basis of the video clip.

Central vestibular disease

(d) Sensory testing. Loss of sensation of the inner nasal mucosa suggestive of a lesion affecting the ophthalmic branch of the trigeminal nerve (the ophthalmic branch innervates the nasal mucosa, while the nasal planum is innervated by the maxillary branch of the trigeminal nerve). The dog also demonstrates a fluorescein-positive corneal ulcer within the central region of the cornea with no evidence of a painful eye, which is also consistent with damage to the ophthalmic branch of the trigeminal nerve. The presence of a left trigeminal nerve lesion in addition to the left vestibular syndrome is further evidence of a central left vestibular lesion. (See page 188 in the Manual)


Electroretinography can be performed under general anaesthesia, or under sedation in a cooperative patient. A corneal contact lens electrode is used to record retinal voltage changes that occur in response to a defined flash of light or repeated flashes of light. The response is expressed as a waveform. (See page 174 in the Manual)

Pendular nystagmus

Albino and imperfect albino animals (including Siamese, Birman and Himalayan cats) demonstrate congenital disorganization of the retina and visual pathways. The consequent clinical anomalies seen in Siamese and related breeds include convergent strabismus (esotropia) and occasionally spontaneous pendular nystagmus. Pendular nystagmus is characterized as a spontaneous horizontal nystagmus with an equal velocity of eye movements in both directions (i.e. not a jerk nystagmus). (See page 187 in the Manual)

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