10 - NS Eye & Vision Flashcards
What are the types of tunics of the eye
- fibrous tunic
- vascular tunic
- retina
which are fibrous tunics
sclera and cornea
which are vascular tunics
choroid, ciliary body and iris
what type of layers is the retina
pigmented and nervous
how does the retina work
- incident light passes through the neural layers of the retina to reach the photoreceptors
- the pigmented retina absorbs excess light
- interneurons preprocess sensory info
What are retinal ganglion cells
they form CN II (optic nerve)
receive signals from photoreceptors and retinal interneurons
RGC projections transmit signals via the optic nerve to the areas in the brain used for visual processing
What are the interneurons
amacrine cells
bipolar cells
horizantal cells
parts of the retina
macula
fovea
Macula
3-5 mm oval region w/in the central region of the retina
surrounds the fovea
our central vision, most of our colour vision and the fine detail of what we see
Fovea
central fixation point for each eye
highest visual acuity (eye focusing)
- avascular (so u don’t see vessels)
What is the tool used to view the retina and how does it work
ophthalmoscope
dilates the pupil
What is the optic disc
beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together.
blind spot
What happens aar of high CSF presure in the retina
buldge
what happens aar of loss of RGC axons
cupping
what is hyperopia + what lens is used
farsightedness - hard to read books(60% of population)
- eyeball is flattened
- focal point is behind the eye
positive diopter lense
What is presbyopia + what lens is used
can’t focus on objects that are near, far is fine
in old people
positive diopter lens
what is Myopia + what lens is used
nearsightedness - 20-30% of the population
eyeball is elongated
- focal point is before
negative diopter lens
what is lens cataracts
vision loss
begins at the age of 40
may also affect the cornea
can be corrected with surgery
- looks like many focal point
which SENSORY cranial nerves are involved in vision
CN II (optic): light detection
CN V (trigeminal): cornea sensation
Which MOTOR cranial nerves are involved in vision
CN III (oculomotor)
CN IV (trochlear)
CN VI (abducens)
CN VII (facial): lacrimal secretions
What are the structures of the primary visual pathway
optic nerve (CN II)
optic chiasm
optic tract
lateral geniculate nucleus (LGN)
optic radiations
primary visual cortex
What happens at the optic chiasm
optic nerves come together in order to allow for the crossing of fibers
enables vision from one side of both the eyes to be appreciated by the occipital cortex of the opposite side
Lateral geniculate nucleus
passes through the thalamus
What are the visual field defects
- monocular blindness (loss of vision in one eye)
- bitemporal hemianopia (temparol visual fields are gone - peripheral gone)
- homonymous hemianopia (half visual field gone - can’t see one side)
What causes glaucoma
increased intraocular pressure (excess production or insufficient drainage of aqueous humor)
How is vision affected by glaucoma
vision loss b/c damage to reinal ganglion cells -> cupping in optic disc
progresses from the periphery to the center of the visual field
what is aqueous humor
produced by the ciliary body and drained by the trabecular meshwork
What are the motor nerves
3 -> occulomotor
4 -> trochlear
6 -> abducens
7 -> facial (lacrimal secretions)
what does CN III do
occulomotor
levator palpebrae (opens eyelid)
what does CN VII do
facial
orbicularis oculi (closing eyelid)
innervates lacrimal glands which secrete tears
What is saccadic eye movements
expose the fovea of the retina to the entire visual scene
- involves engaging the extraocular muscles of the eye
Where do extraocular eye muscles origniate
from the bones of the orbit and insert on the sclera of the eye
- medial (nasal) aspect of the orbit
What are the rectus muscles
lateral, inferior, superior, medial
straight
pulls up and towards nose
What are the oblique muscles
superior, inferior
angled
pulls down and out
What nerve controls the lateral rectus
CN VI
What nerve controls the superior rectus
CN III
What nerve controls the medial rectus
CN III
What nerve controls the superior oblique
CN IV
Which muscles allow u to look up
CN III superior rectus and CN III inferior oblique
Which muscles allows you to look down
CN III inferior rectus and CN IV superior oblique
What is diplopia
double vision caused by problems with conjugate eye movements
What are the types of diplopia
occulomotor palsy/paralysis (CN III) - cant open eyelid
trochelar palsy (CN IV) - can’t rotate eyes within orbit
Abducens palsy (CN VI) - cant not adbuct eye
What is ptosis
dropping of the eyelid
- weakness of the levator palpebrae
What is exotropia
‘down and out’ deviation of the eye
- decreased tone of all muscles except the lateral rectus (‘out’) and the superior oblique (‘downward’)
lesion with CN III occulomotor nerve
What is esotropia
medial deviation of one or both eyes
- lack of muscle tone of the lateral rectus muscle
lesion with abducens (CN VI) nerve
How does lateral gaze work
brainstem circuits help
- tying together r/l abducens nucleus with the opposite occulomotor nucleus to contract the l/f lateral rectus muscle and the l/r medial rectus muscle
What is convergence and accommodation
external eye muscles and pupils work together to position the eyes and the lens to focus
What happens when you change from far to near vision
- contraction of both medial rectus m. (CN III)
- contraction of ciliary body to focus lens
- constriction of pupil to increase depth of field
what happens to the parts of the eyes when viewing a distant object
ciliary muscles relax, zonular fibers raunt and lens flattens = distant object
nearly parallel light rays
What happens to parts of the eyes when viewing a close object
via accommodation
ciliary muscles contract, zonular fibers lloose, lens becomes more spherical
divergent light rays
how are pupillary constrictions accomplished
What is it used for
through parasympathetic stimulation of the pupillary sphincter
(limits light coming in)
reduce light intensity and increase the depth of field for near vision
how are pupillary dilations accomplished
What is it used for
through sympathetic stimulation of the radial muscles of the pupil
increases light intensity and increases light exposure to the parafoveal regions of the retina
useful to increase peripheral vision during a flight or fight response
What is ptosis
which system causes this
dropping of eyelid
sympathetic nerve
