Central Visual Pathways & Perceived Visual Field Flashcards
what is vision
the conscious perception of information from the eye –> processed in the occopital cortex (mammals)
visual system is part of the CNS which gives organisms the ability to process info that is contained in visible light
why is vision assessment limited in vet med and how can it be assessed
because of interference of behaviour
- observation, unfamiliar environment
- ability to track (silent movement, cotton balls)
- visual placing (small animal)
- menace response (other reasons for failure)
what is the visual field
total area in which objects can be seen in the peripheral vision as you focus your eyes on a central point
what is the cross over at the optic chiasm between different species
humans 50%
cats 65%
dogs 75%
horses 80%
birds and fish 100%
what is the cross over at the optic chiasm related to
inversely related to binocular vision
what is the pupillary light relfex pathway
- retina
- optic nerve (CN II) = afferent
- optic chiasm
- optic tract
- pretectal nucleus
- parasympathetic nucleus of CN III = efferent
- bilateral pupil constriction
what is central (cortical) blindness
also known as amaurosis
blindness without apparent lesion of eyes
involves processing system
where are 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
where are the possible sites for lesions in peripheral (subcortical) blindness
- eye
- optic nerves
- optic chiasm
- optic tract
what are the clinical signs of peripheral (subcortical) blindness
- absent PLR
- absent menace response
- blind
what is the pathway of the dazzle reflex
reflex –> no cortical involvement
- retina
- optic nerve (CN II) = afferent
- optic chiasm
- optic tract
- pretecta nucleus
- facial nerve nuclei CN VII = efferent
- bilateral blinking
what is the menace response pathway (10)
response cortical involvement
- retina
- optic nerve (CN II) = afferent
- optic chiasm
- optic tract
- lateral geniculate nucleus
- optic cortex
- motor cortex
- pontine nucleus
- cerebellum
- facial nerve nuclei CN VII = efferent
what is the innervation of the extraocular muscles
