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Describe the localization of afferent lesions causing anisocoria. (4)
retina, optic nerve, optic chiasm, optic tracts
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Describe the localization of efferent lesions causing anisocoria. (3)
- parasympathetic
- sympathetic
- mechanical
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With a unilateral afferent lesion causing anisocoria, there is ___________ because...
- mild anisocoria; of unequal distribution of decussated fibers.
- In the dark, pupils will dilate to equal sizes b/c sympathetic innervation is not affected
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When there is a unilateral pre-chiasm lesion, describe the resultant anisocoria.
- ipsilateral pupil more dilated
- [this is b/c of decussation of optic nerve fibers; each optic tract contains most fibers from the opposite eye]
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When there is a unilateral post-chiasm lesion, describe the resultant anisocoria.
- contralateral pupil more dilated
- [this is b/c of decussation of optic nerve fibers; each optic tract contains most fibers from the opposite eye]
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If there is a unilateral afferent lesion, the __________ pupil is more dilated
ipsilateral
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Describe the ipsilateral (affected) pupil with a unilateral afferent lesion. (4)
- absent direct PLR
- positive consensual PLR (unaffected eye)
- positive marcus gunn response
- complete loss of vision on affected side
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Describe the results of an optic chiasm lesion.
- complete destruction- vision and PLR are absent
- partial destruction- loss of lateral/ peripheral vision, maintained central visual field
- may be causes by pituitary tumors, very rare
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Describe the results of an optic tract lesion.
- mild static anisocoria w/ contralateral pupil MORE dilated b/c of decussation [most of the fibers come from the opposite eye]
- more mydriatic pupil in contralateral eye persists despite which eye is stimulated
- lateral visual field loss on contralateral eye d/t loss of medial side retina's optic tract fibers
- medial visual field loss on ipsilateral side d/t loss of lateral side of retina's optic tract fibers
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When might there be blindness without anisocoria?
- lesions of the lateral geniculate nucleus, optic radiations, visual cortex
- [b/c pupillary fibers split off before LGN]
- clinically, patient may seem completely blind on contralateral side b/c 75-90% of fibers from that side are lost
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Anisocoria with _________ lesions are more marked than with _________.
efferent; afferent
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Efferent lesions typically result in ___________.
complete loss of pupil function
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Anisocoria resulting from an efferent lesions to the sympathetic innervation-->
- static anisocoria with ipsilateral miosis
- affected pupil does not dilate in the dark
- anisocoria more dramatic in the dark, when normal pupil dilates
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Anisocoria resulting from an efferent lesions to the parasympathetic innervation-->
- all lesions affect the ipsilateral pupil--> mydriasis and static anisocoria
- pupils dilate in the dark to equal sizes b/c sympathetic innervation of contralateral eye is intact
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Describe a PS or CN III lesion in dogs and in cats.
- Dogs: complete pupil dilation, ptosis, ventrolateral strabismus- internal and external ophthalmoplegia
- Cats: as above OR they may have a selective lesion of the nasal or temporal short ciliary nerve, leading to a D-shaped pupil
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What is cavernous sinus syndrome?
- CN 3, 4, 5, and 6 and autonomic nerves pass through the cavernous sinus
- neoplastic or inflammatory masses result in progressive neurologic signs
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What are clinical signs of cavernous sinus syndrome? (6)
- internal ophthalmoplegia (CN 3 PSN fibers)
- external ophthalmoplegia (loss of ocular movement and ventrolateral strabismus)
- ptosis (CN 3)
- extorsion (lateral globe deviation- CN 3)
- loss of corneal and ocular sensation (CN 5)
- loss of globe retraction// corneal reflex (CN 6)
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4 ways in which bilateral changes can affect vision.
- opacification of the clear ocular media (cornea, aqueous, lens, vitreous)
- failure of retina to process images
- failure in transmission of image by optic nerve
- failure in final processing of image by visual cortex in brain
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What can cause opacities of the cornea, leading to decreased vision? (5)
pigment, scar, vessels (vascularization d/t chronic irritation), edema, cells
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What can cause increase opacity of the aqueous humor, leading to decreased vision? (3)
severe aqueous flare (lipid, etc), hyphema (hypertension, etc), fibrin (d/t uveitis)
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What causes opacity of the lens, leading to decreased vision?
cataracts
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What can cause increased opacity to the vitreous, leading to decreased vision? (3)
flare, cells (infectious), blood (trauma, hypertension, retinal detachment)
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Most patients blinded by retinal degeneration will have ___________ and __________
visible changes on fundic exam; abnormal PLRs
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What are signs of retinal lesions that lead to decreased vision? (4)
- vessel attenuation
- tapetal hyperreflectivity
- optic nerve atrophy/ pallor
- pigmentary disturbances and accumulations
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What are nutritional retinal diseases? (4)
- taurine deficiency in cats--> feline central retinal degeneration
- equine motor neuron disease
- Vit E deficiency--> hunting dogs
- Vit A deficiency--> cattle
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Lesions causing blindness with loss of the PLR. (2)
- optic nerve atrophy
- optic nerve elevation (papilledema- usually vision still present, papillitis)
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What are examples of some optic nerve/ conducting system lesions? (7)
- optic nerve hypoplasia
- granulomatous encephalomyelitis
- CDV- related encephalitis
- FIP meningoencephalitis
- systemic mycoses
- optic chiasm tumors
- traumatic optic nerve avulsion (proptosis)
- [vision loss, normal PLR, normal electroretinogram--> dx of exclusion, but you know it's in the conducting system b/c of big 3 things i just said]
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Describe cortical blindness.
- blindness with normal PLR [b/c PLR pathway branches off before LGN]
- lesions in LGN, optic radiations, or visual cortex
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What are causes of cortical blindness? (7)
- hydrocephalus
- cerebral malformations
- distemper encephalomyelitis
- systemic mycosis
- GME
- hepatoencephalopathy
- head trauma
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