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
