Gross anatomy of the eyeball Flashcards
where is the eyeball embedded
in orbital fat
the eyeball is separated from the orbital fat by what
fascial sheath of the eyeball
what are the 3 layers (tunics) of the eye
-outer fibrous coat
-middle vascular pigmented coat i.e. the uvea
-inner nervous coat i.e. the retina
what is the outer fibrous coat like
its an inelastic coat
what makes up the outer fibrous coat
-cornea (anteriorly)
-opaque sclera (posteriorly)
what makes up the uvea
-choroid
-ciliary body
-iris
where does the retina extends to
forwards to within 6mm of the limbus
the opaque sclera is composed of what
dense fibrous tissue
what colour is the sclera
white
what pierces the sclera posteriorly
optic nerve
the sclera is fused with what
dural sheath of the optic nerve
what do you call the area of the sclera that is pierced by the nerve fibers of the optic nerve
lamina cribrosa
what other things pierce the sclera
ciliary arteries and nerves and their associated veins
the sclera is directly continuous with what in front
with the cornea at the corneoscleral junction/ limbus
whats at the junction of the sclera and cornea
an opening i.e. the scleral venous sinus
what colour is the cornea
transparent
what does the cornea do
it refracts the light entering the eye
what is the cornea in contact with posteriorly
the aqueous humor
whats the blood supply of the cornea
it is avascular and devoid of lymphatic drainage.
how is the cornea nourished
by diffusion from the aqueous humor and from the capillaries at its edge
whats the nerve supply of the cornea
long ciliary nerves from the ophthalmic division of the trigeminal nerve
why are cornea transplants common and successful
because the cornea has no blood vessels therefore there are no antibodies to cause rejection
whats the limbus
the junction between the cornea and the sclera
what does the limbus nourish
peripheral cornea
how is a cornea nourished in a cornea transplant
by tears and aqueous humor
what does the limbus assist in
corneal wound healing
the limbus has the pathway for what
aqueous outflow
whats the conjunctiva
the translucent mucous membrane that joins the eyeball to the lids ( it lines the posterior surface of the eyelids and anterior aspect of the eyeball)
whats the normal conjunctiva like
-pink
-smooth
-thin
-transparent
what runs within conjunctiva
large deep blood vessels that run vertically
what does the conjunctiva form at the upper and lower reflections between the eyeball and eyelid
2 sacs i.e. the superior and inferior fornices
whats the function of the conjunctiva
it helps lubricate the eye by producing mucus and tears (but a small volume of tears compared to the lacrimal gland)
it contributes to the immune surveillance and helps to prevent the entrance of microbes into the eye
what are the 3 parts of the conjunctiva
-bulbar conjunctiva
-palpebral conjunctiva
-forniceal conjunctiva
what does the conjunctiva contain
-stroma ( has no adenoid tissues until 3 months after birth)
-follicles and papillae
what are some conditions of the conjunctiva
-conjunctival injection
-chemosis
describe the palpebral conjunctiva
its richly vascular, extremely thin and strongly bound to the tarsal plate
the palpebral conjunctiva is subdivided into what
-marginal
-tarsal
-orbital
whats the extension of the marginal conjunctiva
it extends from the lid margin to about 2mm back of the lid upto the sulcus subtarsalis
whats the marginal conjunctiva
its actually a transitional zone between skin and the conjunctiva proper
what opens in the marginal zone
lacrimal puncta
whats the bulbar conjunctiva
its transparent and lies loose over the underlying structures ( so can be moved easily)
what separates the bulbar conjunctiva from the anterior sclera
episcleral tissue and tenons capsule
whats the blood supply of the conjunctiva
-marginal arcade of the eyelid
-peripheral arterial arcade of the eyelid
-anterior ciliary artery
what supplies the palpebral conjunctiva and the fornices
branches from the marginal and peripheral arcades of the artery
where do veins of the conjunctiva drain into
venous plexus of the eyelids which then drain into the superior and inferior ophthalmic veins
where does the cicumcorneal zone of the limbus drain into
the anterior ciliary veins
the lateral side of the conjunctiva drains into what lymph nodes
the periauricular lymph nodes
the medial side of the conjunctiva drains into what lymph nodes
the submandibular lymph nodes
whats the nerve supply of the bulbar conjunctiva
long ciliary nerve branches of nasociliary nerve from the ophthalmic division of the trigeminal nerve
whats the nerve supply of the superior palpebral and forniceal conjunctiva
frontal and lacrimal branches of V1
what are clinical correlates of the conjunctiva
-conjunctivitis
-malignant lymphoma
-conjunctival papilloma
what does the middle layer of the eye contain
blood vessels
what is the small opening in front of the middle layer
pupil
what is the choroid
its the vascular layer of the eye containing connective tissues
where does the choroid lie
between the retina and sclera
what is the choroid composed of
an outer pigmented layer and an inner highly vascular layer
what does the choroid do
provides oxygen and nourishment to the outer layers of the retina as well as the ciliary body and iris
whats the blood supply of the choroid
branches of the ophthalmic artery (which enter the eyeball without passing with the optic nerve)
what is the ciliary body continuous with
posteriorly with the choroid and anteriorly it lies behind the peripheral margin of the iris
what is the ciliary body composed of
-ciliary ring
-ciliary processes
-ciliary muscles
whats the ciliary ring
its the posterior part of the body and its surface has shallow grooves i.e. the ciliary striae
what are the ciliary processes
are radially arranged folds which are connected to the suspensory ligaments of the lens
whats the ciliary muscle composed of
meridional and circular fibers of smooth muscle
how do meridional fibers run
backward from the limbus to the ciliary processes
where do the circular fibers of the ciliary body lie
internal to the meridional fibers
whats the nerve supply of the ciliary body
-the ciliary muscle is supplied by parasympathetic fibers from the oculomotor nerve
whats the action of the ciliary body
contraction of the ciliary muscle especially the meridional fibers pulls the ciliary body forward, which relieves tension in the suspensory ligament causing the elastic lens to become more convex, increasing the refractive power of the lens
the tension on suspensory ligaments does what
changes the shape of the lens depending on the distance of the object being viewed, this process is called accommodation
whats the iris
its the coloured part of the eye and is the most anterior portion of the vascular tunic
what makes up the iris
radial and circular muscles
what does the iris do
controls the amount of light entering the eye
whats the opening in the middle of the iris
pupil
what happens to the iris in bright light
the parasympathetic nervous system causes the circular muscles to contract and the radial muscles to relax, causing the pupil to constrict and less light enters the eye.
what happens to the iris in dim light
the sympathetic nervous system causes the circular muscles to relax and radial muscles to contract, which causes the pupil to dilate and more light enters eye
what causes constriction of the pupils
contraction of the circular fibers because of parasympathetic control through the short ciliary nerves
what causes dilation of the pupils
contraction of the radial fibers because of sympathetic control through the long ciliary nerves
what does the drug atropine do
it inhibits the parasympathetic nervous system causing the pupil to dilate
what are the 3 chambers of the eye
-the anterior chamber
-the posterior chamber
-the vitreous cavity
where is the anterior and posterior chamber located
how do these 2 chambers communicate
what fills these 2 chambers
infront of iris and behind iris respectively
communicate through pupil
are filled with clear aqueous humour
what fills the vitreous cavity
a gel like structure i.e. the vitreous fluid
what makes aqueous humor
ciliary body
aqueous humor is continually drained by what
scleral venous sinus/ canal of schlemm
how often is aqueous humor replaced
90 mins
what is a glaucoma
its increased intraocular pressure that can cause blindness due to compression of the retina and its blood supply. It is caused by problems with drainage of aqueous humor
whats aqueous humor
its a clear liquid produced by the ciliary body and secreted onto the posterior chamber
how does the aqueous humor get into the anterior chamber
through the pupil
where is the scleral venous sinus located
junction between the cornea and the iris
what maintains the pressure within the eye
by continuous formation and drainage of aqueous
whats the normal intraocular pressure (IOP)
10-21mmHg
what causes high IOP
obstruction of aqueous outflow
whats the function of the aqueous humor
-supplies nutrients to avascular cornea and lens
-maintains intraocular pressure
what part of the eyeball is continuously growing throughout life
crystalline lens
what do lens do
-separates the anterior 1/5 of the eyeball and posterior 4/5
-its a changeable refractive media i.e. focuses image on retina
what controls the lenswhat is the lens composed of
-capsule
-epithelium
-lens fibers
what disease affects the lens
cataracts (opacity of the lens)
what controls the lens to focus images on the retina
suspensory ligaments and ciliary muscles
whats accommodation
it refers to the ability of the eye to alter its focus so that clear images of both close and distant objects can e formed on the retina
what are the light rays like for distant objects
they are almost parallel so dont need much refraction to focus on the retina
what should the lens for a distant object be like
thin and weak (have long focal length)
what are the light rays for a close object like
they are diverging so need more refraction to focus them onto the retina
what should the lens for close objects be like
thick and strong ( have a sort focal length)
what is the posterior cavity filled with
vitreous humor (its jelly like)
what does the posterior cavity do
holds retina in place
how often is vitreous humor formed
once during embryonic life
what are floaters
debris in vitreous of older individuals
the retina makes up what of the eye
posterior 3/4 of eyeball
anterior margin of retina contains what
ora serrata retina (rods only)
whats the optic disc
its where theres attachment of the optic nerve/ its the blind spot
optic disc has no what
photoreceptors
where is the fovea centralis
near the middle of the retina
whats does the fovea centralis contain
has high conc of cones
the fovea centralis is a region of high what
visual acuity
whats the blood supply of the retina
-central retinal artery
-choroid
how do the retinal vessels enter and leave the eye
through the optic nerve and run in the nerve fibre layer
what supplies each of the retinal quadrants
major arterial and venous branch that form an arcade
the retina has a superficial layer of what
pigment epithelium (melanin)
what is the superficial layer of pigment epithelium
-its a non visual portion
-it absorbs stray light and helps keep image clear
what are the layers of the retina
-photoreceptor layer
-bipolar neuron layer
-ganglion cell layer
what do rods do
-they are for nocturnal vision i.e. black and white vision, so give great sensitivity in dim light
-they discriminate shapes and movements distributed along the periphery retina
whats visual transduction
its when light initiates a nerve impulse
whats the structure of a rod cell
-it has an inner segment made up of synapse, nucleus, mitochondria
-outer segment made up of membrane disks
in visual transduction detection of light is carried out on what
the membrane disks
what do membrane disks contain
rhodopsin
what is rhodopsin
its a pigment of the photoreceptor cells in the retina
what does rhodopsin do
its responsible for the first events in the perception of light
what rhodopsin comprised of
-opsin
-retinal
retinal is made from what
vitamin A
which part of rhodopsin is the light sensitive part
retinal
retinal exists in what 2 forms
cis and trans
in the dark retinal is in what form
cis
what happens for retinal to switch to the trans form
it absorbs a photon of light and the shape of the opsin protein changes- a process called bleaching
what is the reverse reaction i.e. from trans to cis like
-its very slow
-it requires an enzyme reaction
- it requires ATP as rhodopsin has to be resynthesised
in visual transduction how does the impulse reach the brain
- there is bleaching of the rhodopsin in a rod cell
- this will alter the permeability of the membrane to Na+
- this will create an nerve impulse that will travel down the sensory neuron in the optic nerve to the brain
what does rhodopsin control
sodium channels
which rhodopsin opens sodium channels
the rhodopsin with cis retinal (absence of light)
which rhodopsin closes sodium channels
the rhodopsin with trans retinal (light)
in visual transduction what happens in the dark
the cannel is open and Na+ flows in which causes rod cells to depolarise (so when in total darkness the membrane of a rod cell is polarised)
what do rod cells release in the dark
neurotransmitter
in visual transduction ,when in the dark, the synapse with bipolar cells is what
an inhibitory synapse (the neurotransmitter stops the impulse)
in visual transduction what happens in the light
- cis retinal is converted to trans retinal and the Na+ channels begin to close
- less neurotransmitter is produced , but if the threshold is reached the bipolar cell will be depolarised
- this will then create an impulse which is then passed to the ganglion cells and then to the brain
what is the outer segment like for rods and cons
R- rod shaped
C- con shaped
where do you find rods and cones and what are they used for
R- are distributed throughout the retina so are for peripheral vision
C- are found mainly in the fovea, so they only detect images in the centre of retina
what is the sensitivity like for rods and cones
R- have good sensitivity
C- have poor sensitivity
what are the types of rods and cones and what vision do they provide
R- is only 1 type and gives monochromatic vision
C- has 3 types (R,G,B) and gives colour vision
what do rods and cones connect to
R- many of them connect to one bipolar cell, which results in poor acuity= poor resolution
C- each con is connected to 1 bipolar cell, which results in good acuity= good resolution
con cells have different what
forms of opsin but have the same retinal
red light stimulates which cones
R cones
yellow light stimulates which cones
R and G cones equally
cyan light stimulates which cones
B and G cones equally
white light stimulates which cones
all 3 cones equally
how are objects in the periphery of our field viewed
they are not seen in colour or detail
whats the pathway of light
ganglion cells- bipolar cells- photoreceptor cells
what is the pathway for visual impulses
photoreceptor cells- bipolar cells- ganglion cells- optic nerve
the optic nerve behind the eyeball is surrounded by what
CSF
behind the eyeball the optic nerve is protected by what
the meninges
what makes up the optic nerve
axons of the retinal ganglion cells
what 3 neurons make up the visual pathway and where do they lie
- bipolar cell which lies within the retina
- ganglion cell synapse in lateral geniculate body
- the 3rd neuron terminates in the visual cortex
the left occipital lobe receives visual images from what
- nasal 1/2 of the right eye
-temporal 1/2 of the left eye
the right occipital lobe receives visual images from where
-nasal 1/2 of the left eye
- temporal 1/2 of the right eye
What’s the importance of the tear film
It maintains the normal environment for the corneal epithelial cells
