Central Visual Pathways and the Perceived Visual Field Flashcards
why is visual assessment limited in veterinary speices and what are the methods of assessing
because of interence of behaviour
- observation, unfamiliar environment
- ability to track (silent movement, ex. cotton balls)
- visual placing (if small animal)
- menace response (other reasons for failure)
what is the visual pathway
- retina
- optic nerve
- optic chiasm
- optic tract
- lateral geniculate nucleus
- optic radiation
- occipital cortex
what is the visual field
total area in whcih objects can be seen in the peripheral vision as you focus your eyes on a central point
ex. predator –> more forward vision
prey –> more vision towards behind
what is the pathway in the pupillary light relfex (PLR)
- retina
- optic nerve (CNII) –> afferent
- optic chiasm
- optic tract
- pretectal nucleus
- parasympathetic nucleus of CNIII –> efferent
- bilateral pupil constriction
what is the menace response pathway
- retina
- optic nerve (CNII) –> afferent
- optic chiasm
- optic tract
- lateral geniculate nucleus
- optic cortex
- motor cortex
- pontine nucleus
- cerebellum
- facial nerve nuclei (CNVII) –> efferent
what is central (cortical) blindness
amaurosis
blindness without apparent lesion of the eyes
involves processing system
where is the lesions in central (cortical) blindness
- lateral geniculate nucleus
- optic radiation
- occipital cortex
what are the clinical signs of central (cortical) blindness
normal PLR
absent menace response
blind
what is peripheral (subcortical) blindness
involves collection/distribution system
what are the lesions of peripheral (subcortical) blindness
- eye
- optic nerves
- optic chiasm
- optic tract
what are the clinical signs of peripheral (subcortical) blindness
- absent PLR
- absent menace
- blind
what is the pathway of the dazzle reflex
- retina
- optic nerve (CNII) –> afferent
- optic chiasm
- optic tract
- pretectal nucleus
- facial nerve nuclei (CNVII) –> efferent
- bilateral blinking
what is the innervation of the extraocular muscles
- dorsal rectus –> CN III
- dorsal oblique –> CN IV - trochlear
- medial rectus –> CN III
- ventral oblique –> CN III
- ventral rectus –> CN III
- lateral rectus –> CN VI - abducens
what are the functional classifications of cranial nerve III (occulomotor)
GSE: dorsal rectus, medual rectus, ventral rectus, ventral oblique, levator plapebrae
GVE: parasympathetic for pupil
what are the functional classifications of cranial nerve IV (trochlear)
GSE: dorsal oblique
what are the functional classifications of cranial nerve VI (abducent)
GSE: lateral rectus
retractor bulbi muscle in the eye
what is strabismus
cross eyed
lateral or medial
what causes lateral strabismus
cranial nerve II affected
what causes medial strabismus
cranial nerve VI
what causes strabismus in both eyes
cranial nerve IV
what causes lateral strabismus and dilated pupil
CN III occulomotor nerve
dilated pupil because CN III innervates pupil
what is eye position controlled by
the vestibular system
