L26 Visual System Flashcards
what is the fundus?
back portion of the interior of the eyeball as it is seen through an ophthalamoscope (fundoscopy)
what is mitosis?
constricted pupil
what is mydriasis
dilated pupil
what is neovascular associated with
abnormal new blood vessel formation
describe the sclera
continuation of the dura mater from the optic n. that wraps around and becomes the cornea anteriorly!
where is aqueous humor found?
anterior and posterior chambers
where is the vitreous humor found?
the rest of the eye (aka everything but A/P chambers)
which is more viscous - aqueous humor or vitreous humor
vitreous humor
through what structure does light enter the eye?
pupil and iris
what makes up the optic apperatus of the eye?
cornea and lens
what structures play a role in accomodation
ciliary muscles and suspensory ligaments (zonule fibers)
what 3 structures constitute the occular funds?
optic disc
fovea
macula
what is the optic disc and what are its characteristics
location of the optic n. ending/head
NO photoreceptors
Blindspot!
can see in ophthalamoscope - all vessels emerge form here
define photoreceptor
specialized type of neuron found in the retina that is capable of phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cellās membrane potential.
what is papilledema?
increase ICP = remember that optic n. has meninges and CSF so they can swell too!
decrease in venous drainage leading to dilation of retinal veins
the disc will appear white not pink (ophthalamascope)
where is the fovea located and what are its characteristics?
in the center of the retina
- superficial layers of the retina are pushed laterally so there is easier exposure of the cones to light
- highest density of CONES (no rods) = creates the highest point of visual acuity
when do rods function optimally
low light - dark
when do cone function optimally
light and color
what is the macula and where is it located
region of high visual acuity
surrounds the fovea
define refractive power
inverse of the focal distance in meters = measured in Diopters āDā
what is the refractive power of the cornea?
42 D - cornea is responsible for the main refractive power of the eye
what is the refractive power of the lens
13D to 26D - responsible for the modulation of refractive power (plasticity) during accommodation
Far vision - what is the state of ciliary muscle, lens, suspensory ligaments, refractive power
ciliary muscle - relaxed
lens - flattened
suspensory ligaments - tight
refractive power - reduced (image falls deeper into the eye)
Near vision - what is the state of ciliary muscle, lens, suspensory ligaments, refractive power
ciliary muscle - constricted
lens - round
suspensory ligaments - loose
refractive power - increased (image is pulled back so the image is more forward in the eye so it can land properly on retina)
define refractive plasticity
refractive power variability of the lens from 13-26D
declines with age -
define presbyopia
lens looses its elasticity during aging, thereby reducing the ability to focus on near objects
the lens will stay more flattened thus better able to maintain far sight but near sight diminishes thus the use of +D reading glasses
define visual acuity
ability to distinguish between 2 nearby points
high when 2 point discrimination threshold is low (high spatial resolution)
what are the factors that visual acuity depend on?
- density of photoreceptors
2. lens accomodation
what is the general distribution of photoreceptors?
best at fovea - highest visual acuity
better at macula
absent in optic disc
what happens when lens accommodation is not working properly?
inability to focus image on the retina results in blurry image which decreases acuity
define emmetropia
normal sightedness - the length of the eyeball matches correctly with the refractive power of the optical apparatus
define myopia
nearsightedness
the lens is TOO powerful for the length of the eyeball so the image is focused before reaching the retina
why do they call it nearsighted and farsighted?
nearsighted - vision is best during near vision
farsighted - vision is best during far vision
what type of glasses will correctly place the image more posterior to match the retina in nearsightedness?
concave (-) D glasses
)( = concave
define hyperopia
farsightedness
the lens is too weak for the length of the eye so the image is focused beyond the retina
what type of glasses will correctly place the image more anterior to match the retina in farsightedness?
convex (+) D glasses
() = convex
what does a score of 20/200 mean?
you can read the same number at a distance of 20 feet which a person with normal vision could read at a distance of 200 feet!
what happens with a detached retina?
retina separates from the retinal pigment epithelium and those detached areas lose their function
lazer surgery can stop the detachment process but will not correct the damage that already occurred
explain macula degeneration
most common cause of vision loss
often due to neovascular causes
most ppl can see enough to dress, eat, walk etc.
lazer tx is the only choice but has low effectiveness and recurrence is very common
explain diabetic retinopathy
begins with development of SCOTOMAS
usually unnoticed by pt until the macula is involved - then vision REALLY decreases
retinal defects are caused by blood supply dysfunction including decreased permeability and aneurisms
what is a scotoma?
pathological blind spot - ring of lost vision surrounded by ring of decreased light
