Orbit, eye, and vision Flashcards
Cornea
- the transparent portion of the eye that covers the anterior portion of the eye
- this is part of the fibrous layer
- this is avascular
- is continuous with the sclera
- covered by a delicate stratified squamous epithelium
- has many free nerve endings –> sensitive to pain
what is the fibrous layer and what are the functions
- this is made up of the cornea and the sclera
- this is the outer most layer of the eye
functions:
- provides mechanical support and physical protection
- attachment site for the extraocular muscles
- contains structures involved in focusing process
sclera
this is the white portion of the eye
- this is part of the fibrous layer of the eye
what is the vascular layer
- this includes blood vessels, lymphatics, and the intrinsic eye muscles
- has the iris, pupil, and choroid
functions of the vascular layer of the eye
functions:
- provides routes for blood and lymph vessels supplying the eye tissues
- regulates the amount of light entering the eye
- secreting and reabsorbing the aqueous humor circulating within the eye
- controls the shape of the lens (essential part of focusing)
iris
- this is a contractile muscle made up of smooth muscle that forms the colored portion of the eye
- this is deep to the cornea
- contains blood vessels, pigment cells, and two layers of smooth muscle
sphincter pupillae
this is one of the layers of smooth muscle within the iris
- this is contracted to decrease the diameter of the pupil in response to brighter and more light that is entering the eye (this Limits the light entering the eye and allows for protection of the photoreceptors and structures from UV)
- innervated by parasympathetic innervation from the autonomic nervous system
describe the sympathetic input to the dilator pupillae
- this causes contraction of the dilator pupillae in response to dim light or darkness
- this allows for more light to enter the eye to figure out what is going on in the environment
- the fibers come from the superior cervical ganglion and jump on to the CN 3 to get to the dilator pupillae (they are acquired fibers since they do not originate in CN 3)
dilator pupillae
- this is one of the layers of smooth muscle within the iris
- this contracts to increase the diameter of the pupil to allow for more light to enter the eye
- this is innervated by the sympathetic portion of the autonomic nervous system
describe the parasympathetic input to the sphincter pupillae
- causes the contraction go the muscle to decrease the diameter of the pupil in response to brighter and more light that is entering the eye
- this is from CN 3 and ciliary ganglion
- this is good for protecting the eye and limiting the amount of light entering the eye
- CN 3 will travel through the superior orbital fissure and the fibers will then synapse at the ciliary ganglion
- the postsynaptic fibers will then travel to the pupillae
pupil
this is the opening in the center of the iris in which light enters the eye
ciliary body
this is a thickened portion of the choroid that encircles the lens of the eye
ciliary muscles
- this is a muscular ring projecting into the interior of the eye
- this can apply or take away tension on the ciliary processes and this changed the amount that the ligaments pull on the lens, which allows for a change in the shape of the lens
ciliary processes
these are folds in the epithelium of the ciliary body where the suspensory ligaments attach
suspensory ligaments
- also called ciliary zonule
- these run from the ciliary process to the lens and they create a circle around the lens
- the lens is essentially suspended by these ligaments
lens
- this is responsible for accomodation
- this is a transparent, deformable, biconcave disc
- bends light rays that enter the eye and focus the light on the retina with the highest acuity
accommodation:
changing the shape of the lens to focus on objects near and far
the choroid
the middle vascular layer in the wall of the eye
- delivers oxygen and nutrients to 1/3 of the retina
retina
this is the inner layer of the eye
- this has two layers, the pigmented layer and the neural layer
- this is the first place we process visual information
- one of the few places in the body with bipolar cells
pigmented layer
this is the thin outer layer of the retina
- this is where the rods and cones process the information
- this absorbs light after it passes through the retina
- this has important biochemical interactions with retinal photoreceptors
neural layer
- this is a thicker inner layer of the retina that contains visual receptors and associated neurons
- contains photoreceptors
- supporting cells and neurons for the processing and integration of visual information
- blood vessels that supply tissues lining the posterior cavity
photoreceptors
- these are receptors that are sensitive to light
- monitor a specific location on the retinal surface and process info to form visual images
- two types:
rods
cones
rods
photoreceptors responsible for vision in dim lighting
- do not detect different colors of light
- these are highly sensitive to light
- these are concentrated in the periphery
- 125 million rods
cones
photoreceptors responsible for sharp vision and color vision
- these require more intense light than rods
- these are concentrated at the macula
- 6 million cones
bipolar cells
- these are the cells that the rods and cones synapse with
- the retina is one of the few places in the body with bipolar cells
- these go on to synapse with the ganglion cells
ganglion cells
- these are what the bipolar cells synapse at
- these are the only cells in the retina wither an action potential is generated and then travels to the brain
- these are the first order neurons in the optic pathway
optic disc
this is where the axons of the ganglion cells converge
- this is a circular region just medial to the fovea centralis on the posterior aspect of the eye
- this is the origin of the optic nerve
- no photoreceptors are on the optic disc
- this creates the blind spot because light striking the area goes unnoticed since there are no photoreceptors
- involuntary eye movements fill in the missing information
fovea centralis
this is the center of the macula and this is the site with the highest concentration of cones
- this is the area that produces the sharpest vision
macula
this is where the visual image arrives after it passes through the cornea and lens
- this contains no rods
what muscle(s) do(es) CN VI innervate?
this is the abducens nerve
- innervates the lalteral rectus
what muscle(s) do(es) CN III innervate?
this is the oculomotor nerve - innervates: medial rectus inferior rectus superior rectus inferior oblique
what muscle(s) do(es) CN IV innervate?
- this is the trochlear nerve
- innervates the superior oblique
eyebrows
- these are along the superior orbital ridge of the frontal bone
- these prevent sweat from dripping into the eye and shade the eyes from sunlight
eyelashes
- these are the hairs on the margins of the eyelids
- these prevent large foreign objects from contacting the eyes
- these are highly innervated and can trigger the blink reflex to stop things from getting into the eye that are not supposed to
palpebrae
anatomical term for eyelids
Medial and lateral Canthi
these are the medial and lateral angles that the eyelids meet at
palpebral fissure
this is the opening between the eyelids
tarsal plates
- this is stiff plates of connective tissue that give the eyelids shape each time they move so they do not fold up in random ways
- they also serve as attachment sites for the muscles that help us close the eyes
tarsal glands
- these are modified sebaceous glands
- they secrete an oily substance
functions:
- lubricate the surface of the eye
- help keep tears in our eyes; prevent overflow
- prevent eyelids from sticking together
**these are important and the first function is very important because we do not want friction between the eyes and the eyelids each time we close our eyes and we do not want our eyelids to dry out
conjunctiva
transparent mucous membrane made of stratified squamous epithelium on the inner side of the eyelid and the inner layer attaches to the sclera
- there are two layers (the palpebral and bulbar) (these are continuous and there is a fold where it transitions)
- contains goblet cells
palpebral conjunctiva
- this lines the inner aspect of eyelid
bulbar conjunctiva
- this lines the sclera
- not the cornea, only the sclera
what is the importance of goblet cells in the conjunctiva
these secrete mucin and when it mixes with water it becomes mucous
what are the three places that act to lubricate and moisten the surface of the eye?
- the tarsal glands of the eyelid
- the goblet cells of the conjunctiva
- the lacrimal fluid (tears) from the eyes
lacrimal fluid
- tears
this is the 3rd secretion that acts to lubricate and moisten the eye
lacrimal puncta
- in the medial angle of the eye
- this is what drains the lacrimal fluid from the eyes and puts it into the lacrimal canaliculi
lacrimal canaliculus
- this receives lacrimal fluid from the lacrimal puncta and allows the fluid to collect in the lacrimal sac
lacrimal sac
this is where tears collect
nasolacrimal duct
- this is what lacrimal fluid drains through after being in the lacrimal sac
- this allows the fluid to enter the nasal cavity
- this is why when we are extremely emotional, teh nose seems to get stuff because there is excess fluid entering the nasal cavity
lacrimal apparatus
this is what produces, collects and drains lacrimal fluid from the eye
- this helps prevent bacterial infections through the antibiotic like enzyme lysosome
how does lacrimal fluid get dispersed across the eye
- we actually brink lateral to medial so that moves the fluid lateral to medial
why do eyes water when someone is sick
- this is because the nasolacrimal duct can become blocked with mucus and inflamed and then the lacrimal fluid is not able to drain and the eyes begin to water due to the excess tears
lacrimal gland and ducts
- the gland is in the superior lateral aspect of the orbit a
- the ducts carry fluid to the superior lateral surface of the eye
lateral rectus
action: this abducts the eye
innervation: innervated by CN VI (abducens nerve)
location: this is on the lateral side of each eye and has straight fibers that when constricted cause the eye to abduct
medial rectus
action: adducts eye
innervation: CN III (oculomotor nerve)
location: this is on the medial side of each eye and has straight fibers that when constricted cause the eye to adduct
inferior rectus
action: depresses eye
innervation: CN III (oculomotor nerve)
location :this is on the inferior side of each eye and has straight fibers that when constricted cause the eye to look downward
superior rectus
action: elevates eye
innervation: CN III (oculomotor nerve)
location :this is on the superior side of each eye and has straight fibers that when constricted cause the eye to look upward
inferior oblique
action: elevates and abducts eye
innervation: CN III (oculomotor nerve)
location : this is inserting inferiolateral side of each eye and has curving fibers that when constricted cause the eye to look upward and outward
this is the only extrinsic muscle that doesn’t originate at the common tendinous ring (originates at the inferior medial corner of the eye
superior oblique
action: depresses and abducts eye
innervation: CN IV (trochlear nerve)
location: this is on the superior portion of the eye and when the muscle constricts it causes the eye to look downward and outward
common tendinous ring
this is at the posterior orbit and it is where the the four rectus muscles and the superior oblique muscle originates
what are the three principal layers that form the wall of the eye
- the fibrous tunic
- the vascular tunic
- the retina
functions of the eye
- protect and support the photoreceptors
- gather, focus, and process light into precise images
how do the lateral and medial muscles work to move the eyes together
- the lateral muscle of the right eye will work with the medial muscle of the left eye to get the eyes to look toward the right direction
- the lateral and medial muscles on the same eye oppose each other
what shape of lens allows for seeing far away
a flat lens
what shape of lens allows for seeing close up
a round lens
describe what happens to see far away
- this is sympathetic innervation
- the sympathetic input will relax the ciliary muscle
- this causes the space to open up
- this causes more tension to be on the suspensory ligaments
- this extra tension causes the lens to flatten
describe what happens to see close up
- this is parasympathetic innervation
- the parasympathetic input will contract the ciliary muscle
- this causes the space to become smaller
- this causes a decrease in tension to be on the suspensory ligaments
- less tension causes the lens return to its natural shape of being rounded
cateracts
- these are small opacities within the lens that can completely obscure the lens with time
- this is most common with aging, diabetes, ocular infections and UV light
- this is why it’s super important to have glasses that block UV light
why are cheap sunglasses worse than not wearing sunglasses
- cheap sunglasses do not block the UV protection but they do have dark lens which cause the pupil to dilate
- this dilation causes more light to enter the eye (more UV to enter as well) and this can cause more damage
anterior cavity
- this is anterior to the lens
- contains the anterior chamber and the posterior chamber
- both chambers contain aqueous humor
anterior chamber
- this is between the cornea and the pupil
posterior chamber
- this is between the iris and the lens
aqueous humor
- this is a clear fluid that is similar to blood plasma and is being constantly produced
glaucoma
this occurs when aqueous humor is produced in larger quantities than can be drained from the anterior cavity
- this increases the pressure on the eye and can put pressure on the optic nerve and could even lead to blindness
posterior chamber
- this is a large space forming the majority of the eye and is between the lens and the retina
- it contains the vitreous chamber filled with the vitreous body
- this chamber contains vitreous fluid
vitreous fluid
this is a jelly like substance that helps to support the eye and allows light to go through the eye and hit the retina in the right place
describe what happens to light as it enters the eye
- when light enters the eye, it has to go through the neural layer, past the rods and cones, into the pigmented layer and then it is processed back in the opposite direction
- the light is not processed until it reaches the retina
true end artery
this means that the artery does not have an anastomosis
- there is no collateral circulation
ophthalmic artery and vein
- this is the blood supply to the inner 2/3 of the retina
- this runs through the middle of the optic nerve –> cranial nerve II (which gives some protection to the vessels since it travels through it)
- this is a true end artery
- this means that the only way blood can get here is through this artery and that is very important to realize because if something happens to the artery the eye will get damaged and can lead to blindness
(the choroid is what supplies the other 1/3 but it alone can not sustain the retina)
nasal retina
this is the retina on the medial aspect of each eye (near the nose)
- due to the rounded shape of the retina, the nasal retina takes in info from the lateral aspect of the visual field
- the information form the nasal retina is the info that crosses at the optic chiasm
temporal retina
- this is the retina on the lateral aspect of each eye (near the temporal bone)
- this takes in information from the medial portion of the opposite visual field
- this information does not cross at the optic chiasm
optic chiasm
- this is where the optic nerves meet
- this is where the nasal retina fibers cross and enter the optic tract to travel with the opposite temporal retina fibers
lateral geniculate nucleus
this is where 90% of the optic nerve fibers travel to and synapse at
- this is in the thalamus
optic nerve
- cranial nerve II
- these carry information from one eye, one retina but both sides of the visual field
optic tract
- these carry information from both eyes, both retinas, but one visual field
- this carries the information from the optic chiasm to the lateral geniculate nucleus
primary visual cortex
this receives and processes incoming visual information
- this is at the calcarine fissure
- this is the first cortical area where we process visual information
posterior calcarine cortex
this is the high resolution area
- most of the information from the cones
anterior calcarine cortex
this is the peripheral vision
how does the rounded aspect of the retina affect the information that is processed in the calcarine cortex
- what is on the lower aspect of the visual field in processed by the superior retina
- the visual field is upside down on the retina
- by the time the info reaches the calcarine cortex it flips right side up again
- the inferior calcarine sulcus processes info from the inferior visual field and the superior calcarine does the superior visual felid
what is important to remember about after the optic chiasm
- important to remember that everything after the optic chiasm is processing the information of the opposite side
right visual cortex
this is the right half of each retina and it processes the left visual field
left visual cortex
this is the left half of each retina and it processes the right visual field
where can the other 10% of fibers go other than the lateral geniculate nucleus
- edinger- westphal nucleus
- superior colliculus
- suprachiasmatic nucleus
edinger- westphal nucleus
- this is in the midbrain
- parasympathetic info leads to the pupillary reflex and lens control
- this causes the ciliary muscle to constrict in response to visual info when looking at something nearby and causes the pupil to constrict with brighter light
superior colliculus
- this is in the midbrain
- Visual reflexes: orienting movements of the head and eyes and reflexively directing the eyes to areas of interest
- if we see something move in our periphery that info is sent to the superior colliculus and this initiates a reflex that causes us to turn our heads and focus our eyes
suprachiasmatic nucleus
- this is in the hypothalamus
- info about light and dark for the circadian rhythm sleep/wake cycle)
- if it is light out, this sends a signal to the pineal gland to suppress the release of melatonin
- when it is dark, this signals the pineal gland in the epithalamus to secrete melatonin
visual association areas
- think of these as layers in the process of processing visual information and that at each layer different elements are added
- these are retinotopic maps and each layer processes the entire visual field in its own way
V1
- this is the primary visual cortex
V2 and V3
- these can see the whole visual field but it is in black and white
V4
this allows for us to see color vision
dorsal stream
- this is the where pathway
- this is telling us where something is
- this is in the parietal lobe
ventral stream
- this is the what pathway
- this is telling us what something is
- this is in the temporal lobe
V5
this is motion sensitivity
- this allows us to string together different images to recognize that something is moving, allows us to watch a car move down the street
cerebral achromatopsia
- this is damage to the V4
- this leads to no color sight
- this is not color blindness, this means everything is black and white
cerebral akinesia
- this is damage to the V5
- this means there is impaired motion detection
- the world is viewed like a strobe light and you can not sting images together to recognise that something is moving
- you see things in one spot and then the next and there is no stringing them together
fusiform face area
this is where we recognise faces
- this is very posterior temporal lobe adjacent to the occipital lobe
prosopagnosia
this is damage to the fusiform face area and ou cannot recognise faces
- you could see someone you have known your whole life and not recognise them
- you would be able to recognise them by their voice
inferotemporal complex
- this is where we tie emotion to what we see
- damage here would cause the inability to attach emotion to visual stimuli
- if you saw something incredibly heartwarming or something very sad, you would just think “whatever”
- if you heard a scream tho you would be able to trigger emotion based on the auditory stimuli
visuospatial neglect
- this is damage to the parietal regions
- a person will neglect an entire portion of a visual field
- might only eat the food on half the plate unless someone turns the plate so that the other food can be seen
- if coping down a drawing, may only draw half of it
- this is more common to have the left visual field neglected because there is typically more visual and spatial information being processed in the right hemisphere
what is a common cause of visuospatial neglect
- this would be a stroke in the right middle cerebral artery because that feeds the right hemisphere
- 2/3 of right sided stroke patients experience this
