Anatomy Flashcards
What makes us the uvea
Iris
Ciliary body
Choroid
Describe the function of rod cells
They are sensitive to low levels of light
Used mainly in night vision and peripheral vision
Describe the function of cone cells
Used for detailed and colour vision
What is the macula
Area of the retina with the highest concentration of cones
In a retinal image the thicker vessels are arteries - true or false
FALSE - they are veins
Name the extraocular muscles
Superior. inferior, lateral and medial rectus
Superior and inferior oblique
Which cranial nerves help with control of the eye
2 - optic 3 - oculomotor 4- trochlear 5- trigeminal 6- abducens 7 - facial
Which cranial nerves are involved in the blink reflex
Trigeminal - efferent part
Facial - afferent part
What is emmetropia
Normal vision
no refractive error in eye
What is hypermetropia
Long sightedness
The eyes are smaller than average so light is focussed behind the retina
Will need positive lenses to bring the light forward to retina
What is myopia
Short sightedness
Larger than average eyes so light is focussed in front of retina
Needs negative lenses to move focus back
What is presbyopia
lens gradually stiffens with age (usually starts around 40)
Can’t change shape to adjust focus
List the bones of the bony orbit
Frontal bone Sphenoid bone Orbital plate of the ethmoid bone Zygomatic bone Maxilla Lacrimal
What passes through the optic canal
The optic nerve
What forms the edge of the bony orbit
The orbital rim and margin
Which bones of the bony orbit are most likely to fracture
Medial wall and inferior wall
(ethmoid, lacrimal)
Thin bones
What is an orbital blowout
Fracture of bones in the bony orbit - thinnest ones (medial wall and floor)
usually caused by a blow to the face
Can damage the infraorbital neurovascular bundle
Eyeball can be extruded
What passes through the infraorbital foramen
Infraorbital artery and nerve
What is the function of the eyelid
Protects the eyes
What do the eyelids contain
Tarsal plate - keeps shape
Glands - secrete lipids
Orbicularis oculi
LPS muscle
What is the function of the levator palpabri superiorus
Muscle that elevates the upper eyelid
What is ptosis
Closed eye
Indicator of a third nerve palsy
What is the function of the orbicularis occuli
Circular muscle that closes the eye when it contracts
What is the function of the conjunctiva
A defensive barrier that covers the eye
Reflects back from eye to inner surface of eyelid
What is the cornea
The clear part of the eye that we look through
Responsible for refraction - lets light into the eye and focuses it onto the retina
What nerve supplies the lacrimal gland
CN VII - facial nerve
Parasympathetic supply
Describe how tears are formed
Produced in the lacrimal gland
Blinking washes tears over eye
They are pushed towards medial angle
Drain into the lacrimal puncta then the canaliculi
Will reach the lacrimal sac and eventually down the nasolacrimal duct and out the nose
What makes up the fibrous outer layer of the eye
sclera and cornea
What is the function of the iris
Controls diameter of pupil
It is a coloured muscle!
What is the function of the ciliary body
Controls iris, shape of lens and secretion of aqueous humour
What is the function of the choroid
Nutrition and gas exchange
Sits behind the retina
Where is the anterior segment
In front of the lens
Describe the divisions of the anterior segment
Anterior and posterior chamber
Anterior is found between cornea and iris
Posterior is found between iris and suspensory ligaments
What is contained in the anterior segment of the eye
Aqueous humour
Where is the posterior segment located
Behind the lens
2/3 of the eye
What is contained in the posterior segment of the eye
Vitreous humour
What can an excess in aqueous fluid lead to
Glaucoma
Raises intraocular pressure
What secretes aqueous humour
Ciliary processes in the ciliary body
Describe the path of aqueous humour through the eye
Secreted in ciliary body
Circulates in the posterior chamber to nourish lens
Then passes through pupil to nourish cornea It is then reabsorbed into scleral venous sinus at the iridocorneal angle
What is the arterial supply to the eye
The ophthalmic arteries
It is a branch of the internal carotid artery
It branches itself into the ciliary arteries and the central artery of the retina
List the venous drainage of the eye
Superior ophthalmic vein
Inferior ophthalmic
Drain into the cavernous sinus
Also drains anteriorly to the facial veins
What is the danger triangle
Area across the nose and upper lip
If there is an abscess here it can drain backwards into the cavernous sinus and lead to sinus thrombosis
What is the fovea
centre of the macula
small depression
area of most acute vision
What is the optic disc
Point of optic nerve formation
Where blood vessels and nerve enter/exit
Also has the blind spot
List the layers of the retina from posterior to anterior
Photoreceptors
Ganglion cells
Axons of the ganglion
Why is the optic disc the blind spot
There are no photoreceptors in the optic disc
Where is light from the right visual field processed
Left primary visual cortex
Opposite is true
Where is light from the lower visual field processed
Upper part of the primary visual cortex
Opposite is true
What does the superior orbital muscle pass through
A pulley
The trochlear
List the action of the recti eye muscles
lateral rectus – pulls eyeball laterally
medial rectus – pulls eyeball medially
superior rectus – up and in
inferior rectus - down and in
List the actions of the oblique eye muscles
superior oblique – down and out
inferior oblique - up and out
List the innervation to the eye muscles
Lateral rectus - abducens nerve (CN6)
Superior oblique - trochlear nerve (CN4)
Rest of the muscles are CN3 (oculomotor)
What areas does CNV1 give sensory supply to
Upper eyelid
Cornea
Conjunctiva
Skin of the root, bridge and tip of the nose
What areas does CNV2 give sensory supply to
Skin of the lower eyelid
Skin over the maxilla
Skin of the ala of the nose
Skin/mucosa of the upper lip
What areas does CNV3 give sensory supply to
Skin over the mandible (except the angle) and temporomandibular joint
Describe the sensory limb of the blink reflex
Action potential conducted from cornea via CNV1
Then to the trigeminal ganglion along CNV
To pons
Describe the motor limb of the blink reflex
Action potentials conducted CNVII
To eyelid part of orbicularis oculi
Describe the route of sympathetic axons
Thoracolumbar outflow
Leaves brain and passes down spinal cord
Exits spinal cord with T1-L2
Travel to the sympathetic chains
Pass into the spinal nerves via anterior and posterior rami
Pass into the splanchnic nerves to supply organs
Which nerves synapse in the superior cervical ganglion
Presynaptic sympathetic axons from the CNS
Exit at T1 level and ascend in the sympathetic trunk
Synapse in the ganglion
Describe the path of the post-synaptic neurons as they level the superior cervical ganglion
Enter the internal and external carotid nerves
Pass onto surface of the internal and external carotid arteries
Carried to the organs of the head with arteries
What carries sympathetic nerves into the orbit
The ophthalmic artery
Delivers fibres to the eye itself
How do parasympathetic axons leave the CNS
Via cranial nerves III, VII, IX and X
And the sacral spinal nerves
(Craniosacral outflow)
Which structures in the orbit are supplied by parasympathetic nerves
Eye
Lacrimal glands
Which parasympathetic nerve is responsible for changing the shape of the iris and lens
Fibres from CNIII
Oculomotor
Describe the path of the oculomotor nerve
Leaves brain between the midline and pons
Passes through the cavernous sinus
Exits via the superior orbital fissure
Divides into superior and inferior division
What does the superior division of the oculomotor nerve supply
Somatic motor innervation to the superior rectus and levator palpebrae superioris
What does the inferior division of the oculomotor nerve supply
Somatic motor innervation to the medial and inferior rectus, the inferior oblique
Parasympathetic axons to the ciliary ganglion
What are the functions of the ciliary nerves
Supply autonomic axons to the eye
Controls diameter of iris and shape of lens
Long nerves are sympathetic and somatic sensory (responsible for part of blink)
Short ciliary nerves have both sympathetic and parasympathetic fibres
What occurs in the ciliary ganglion
Synapse of pre and post parasympathetic nerves
List the sympathetic effects on the eye
Open eyes wider
Dilate pupils - get more light in
Focus lens on far objects
Emotional lacrimation - crying
What is the vestibulo-ocular reflex
Eyes move the opposite way to head movement
Stabilizes gaze during head movement
What is the oculocardiac reflex
Reflex bradycardia in response to tension on extraocular muscles or pressure on eye
List the effects of the parasympathetic nerves on the eye
Allows orbicularis oculi to work
Constricts pupil - less light
Focus on near objects
Reflex lacrimation - wash away foreign bodies
Describe the levator palpebrae superioris
Contains smooth and skeletal muscle
Supplied by oculomotor and sympathetic nerves
Responsible for opening the eye
Why do our eyes open wide in the fight or flight response
Sympathetic nerves supplying the LPS are stimulated and the muscle contracts, opening the eye
What is a mydriatic pupil
One that is non-physiologically enlarged
Can be done with chemicals or drugs
What controls the diameter of the pupil
Dilator papillae fibres
Arranged radially around the iris - dilate pupil
Sphincter pupillae fibres constrict the pupil
What is a non-physiologically constricted pupil called
Miotic pupil
Seen in Horner’s
What is a pinpoint pupil a sign of
Opiate drug use
Serious pathological sign
What is a fixed, dilated pupil a sign of
Serious pathology
Pathology of CN3
What is the direct light reflex
Constriction of pupil in the eye when light is shone into it
What is the consensual light reflex
Constriction of pupil when light is shone into the opposite eye
Which nerves are involved in the pupillary light reflex
Sensory info travels up the optic nerve
CNS connection in midbrain
Effector/motor part is by the oculomotor nerve
In the brain, which nuclei are involved in the light reflex
Pretectal nucleus - optic nerve synapses here
Edinger Westphal nucleus - passes signal to CN3
When the ciliary muscle is relaxed what happens
Used for far vision
No parasympathetic input
Suspensory ligaments tighten and lens flattens out
When the ciliary muscle is contracted what happens
Suspensory ligaments relax and the lens goes back to a spherical shape
Allows near vision
Uses parasympathetics
A rounded lens bends more light -true or false
TRUE
What is the accommodation reflex
Change in focus from far to near vision
To do this, the pupils constrict, there is bilateral convergence of eyes (cross eyed) and the lens relaxes
What are basal tears
The tears that clean, hydrate and nourish the cornea
Contain lysozyme - kills bacteria
What are reflex tears
Extra tears in response to mechanical or chemical stimulation
Afferent limb is CN V1 from cornea/conjunctiva (sensory)
Efferent limb is parasympathetic axons originating from CN VII (motor)
What are the functions of the eyelid
Protects the cornea
Spreads the tear film over the eye
Which muscle keeps the eye open unconsciously
Muller’s muscle
collection of muscle fibres within levator palpibrae superiorus that has sympathetic innervation
Where is the mucous layer of the tear film produced
conjunctiva
What is the function of the mucous layer of the tear film
Keeps the other layers stuck to the eye
Where is the lipid layer of the tear film produced
By glands in the eyelids
What is the function of the lipid layer of the tear film
Stops the aqueous phase from evaporating too quickly
Where is the aqueous layer of the tear film produced
Lacrimal glands
Which part of the eye is responsible for refraction
Cornea
The shape of the cornea determines what
whether you need glasses or not
What is the function of the lens
Accommodation = changes shape to allow you to look near or far
The lens naturally sits in what shape
Sphere
What supports the lens of the eye
Zoonules (suspensory ligaments)
What is ametropia
When there is a refractive error present
Light is focused either in front or behind retina
What is anisometropia
When there is a significant difference in the refractive power of each eye
Different prescription L and R
What is an astigmatism
This is when the eye has different refractive powers across it as the eye is more rugby ball shaped
Treated with cylindrical lenses
