vision A Flashcards
how is vision on the back of the eye (retina)
reduced, upside down
where is visual information transmitted to
the visual cortex
what does the vestibular apparatus cotnrol
balance
VOR purpose
keeps vision steady as head moves
orbit
bony cavity protecting the eye
nasolacrimal duct
drains tears into nasal cavity
lacrimal gland
secretes tears
retinal photoreceptor layers
ganglion cells
amacrine cells
bipolar cells
horizontal cells
cones and rods
rays must pass through
cornea
anterior chamber
pupil
lens
vitreous
inner retinal layers (ganglion, amacrine, bipolar, horizontal) to reach photocereptors
rays do not have to pass through
iris, retinal pigment epithelium, choriocapillaris, sclera
visual based neural signals pass thorugh
photoreceptors, intermediate retinal neurons, retinal ganglion cells (optic nerve) to LGN to visual cortex
where are blood vessels located in the eye
choroid layer
what absorbs excess light in the retina
pigment epithelium
what cell axons become the optic nerve
retinal ganglion
where must light rays focus
fovea
what initiates resolution of the finest detail
on the fovea, maximally focused image. bc light strikes the photoreceptors directly in the fovea bc the overlying neurons are pushed aside. photoreceptors at the fovea are less obscured by inner retinal layers
is the lens convex or concave when it becomes more powerful
convex. converges divergent rays coming from close objects onto fovea
focal length
distance from the centre of the lens to the focal point
what needs no lens accomidation
far objects farther than 20 ft lead to parallel rays
what controls lens shape
muscles in ciliary body
far focus
ciliary body muscles relax. zonule ligaments tighten, lens is stretched.
decrease power
rays focus on fovea
far focus PANS OR SANS
sympathetically controlled
near focus
ciliary body muscles contract moving it inwards. zonule ligaments loosen, lens is fatter and convex. converge rays from behind fovea
increase power
near focus PANS OR SANS
Parasympathetically controlled
ciliary body shape
donut of muscle around base of iris
normal eye
emmetropic
far focused as default
near needs accomidation
lens gets fatter to converge and move light rays forward onto fovea as objects get closer
neural pathways mediating accomodation
optic nerves to oculomotor nuclei to oculomotor nerves to ciliary body muscles
oculomotor nuclei
edinger westphal nuclei
optic nerve afferents
are driven from each eye and lead to binocular efferents controlling both eyes which leads to accomodation reflex
low light conditions
iris dilator pupilae muscles contract
radial fibres shorten
pupil diameter increases
high light conditions
iris constrictor pupilae muscles contract
concentric fibres shorten
pupil diameter decreases
neural pathways mediating pupillary reflex
optic nerve to oculomotor nuclei to oculomotor nerves to iris muscles contrictor pupilae and dialator pupilae
binocular efferents from optic nerve afferents
visual acuity
spatial resolving capacity of visual system ability to see fine detail
what is visual acuity limited by
diffraction, abherrations and photoreceptor density in the eye
what does visual acuity target
recognition tasks, used in clinical visual acuity measurements that require the recognition or naming of a target such as snellen letters
factors affecting visual acuity
refractive error
size of pupil
illumination
time of exposure of the target
area of the retina stimulated
state of adaptation of the eye
eye movement
normal visual acuity
20/20 or 6/6 is the ability to resolve a spatial pattern separated by a visula angle of one minute of arc at 20 feet or 6 meters
first number in snellen
test distance
second number snellen
distance that the normal eye can see the same letters on the eye chart
visual acuity
distance away from object that a normal subject can be to clearly see the detail
how many min of arc are in the letter e
5 since there are 5 vertically contrasting parts to the e
why are snellen letters sometimes sideways
to test ability to resolve a spatial pattern separted by a visual angle of one minute of arc
legal blindness
20/200
what does light not have to pass through that you keep forgetting
retinal pigment epitheliium and choriocapillaris
