The Eyes Flashcards
Which walls of the orbit are weakest and why
Inferior wall - formed by maxilla. Presence of maxillary sinus means the inferior wall is thin
Medial wall - formed by ethmoid bone. Is very thin as it has air cells within the bone
Name some of the openings in the orbtial apex and what structures enter into and out of the orbit
Optic canal - optic nerve and ophthalmic artery
Superior orbital fissure - CN III, IV, VI, Va, superior ophthalmic vein
Inferior orbital fissure - infraorbital nerve (branch of CN Vb), inferior ophthalmic vein
What is the blood supply to the orbit and eye
Main artery supply is ophthalmic artery - central retinal artery pierces dura surrounding optic nerve to enter with it into the eye
Ophthalmic veins drain venos blood into cavernous sinus, pterygoid plexus, facial vein
What is the nervous innervation to the eyes
General sensory - CN Va
Special sensory - CN II
Motor function - CN III, IV and VI
What are the layers of the eye
Sclera - outer
Choroid/Middle
Retina - inner
How is the eyeball position maintained
Suspensory ligament
Exra-ocular muscles
Orbital fat
Describe the sclera
Outer protective layer
Is tough and fibrous
Provides attachment for extraocular muscles, gives shape to eyeball and is continuous with dural sheath covering optic nerve
Is covered by the conjunctiva
Describe the conjunctiva
Thin transparent layer of cells that covers the eyeball, except for the cornea
Covers the sclera and lines inside of eyelids forming conjunctival sacs
Blood vessels run through the conjunctiva to supply blood to sclera
Describe the middle layer of the eyeball
RIch, vascular area of the eyeball
Includes choroid, ciliary process and iris - the uvea
Ciliary body connects choroid with the iris and consits of ciliary process and muscle
Describe the retina
Inner layer of the eye and consists of photosensitive and non-photosensitive parts (pigmented layer)
Pigmented layer lies between choroid and neurosensory layer of retina. Cells contain melanin which help absorb scattered light that has passed into the eye to focus light onto the retina (macula)
Neurosensory layer senses light and is where photoreceptors (rods and cones) are found
Describe the differences between rods and cones
Cones are responsible ofr high visual activity and colour vision. Are concentrated in the macula - fovea is found in centre of macula where only cones are found
Rods - responsible for vision in low intensity light and do not discern colours. Most abdunant towards peripheral parts of retina
What are the chambers of the eye and what is found in each
Vitreou chamber - vitreous humour found within
Anterior chamber - aqueous humour
Posterior chamber - aqueous humour
Aqueous humour important in supporting shape of eye and in nourishing lens and cornea
Aqueous humour drains through irido-corneal angle into canal of Schlemm via trabecular network
Describe the iris
Thin contractile diaphragm with a central appeture, the pupil, for transmission of light
Gives eye colour
Sphincter and dilator pupillae form iris and control size of pupil
Describe the lens
Transpartent biconvex structure enclosed in a capsule
Recieves nutrients from aqueous humour
Edges attach to ciliary body by circular suspensory ligament
Contraction of ciliary muscle alters tension in suspensory ligament allowing for changes in shape of the lens and its refractive power
Becomes fatter to allow focusing of near-objects
How do cataracts develop
Proteins degrade as we age causing the lens to become cloudy and less transparent resulting in cataracts
What structures help refract light towards the macula
Cornea and tear film - main refractor but cannot cope with near-objects
Lens
Aqueous humour and vitreous humour
Describe the accomodation reflex
Pupillary constriction occurs to ensure light from near-object passes through centre of the lens
Eye convergence ensures both retina focus on one object
Contraction of ciliary muslce causes lens to beocme more biconvex by loosening circular suspensory ligaments
Lens becomes more biconvex to allow for better focusing of near-objects on the retina
Why do patients develop presbyopia
Because as patients age, lens becomes more dense, less elastic and more difficult to change shape
This means ability to accommodate and focus on near-objects is impaired
What does the eyelid consist of and what glands are found in it
Eyelid consists of skin, subcutaneous tissue, tarsal plate and muscle
Meibomian gland - secretes oily substance onto edges of lid to help prevent evaporation of tear film and tear spillage. Bocked = meibomian cyst
Sebaceous glands - assocaited with lash follicle. Can be blocked causing Syles - painful, white head and red eyelid
What is the orbital septum and what is its function
Orbital septum is a thin sheet of fibrous tissue originating from orbital rim that blends with tarsal plates
Orbital septum and tarsal plates separate subcutaneous tissue of eyelid and orbicularis oculi from intra-orbital contents
Describe the lacrimal apparatus
Consists of lacrimal gland, ducts and canaliculi
Glands secrete lacrimal fluid -> enters conjunctival sac through lacrimal ducts -> passes into lacrimal lake
Fluids drains into canaliculi -> lacrimal sac -> passes into nasal cavity via nasolacrimal duct
Obstruction of drainage system causes epiphora
What muscles move the eyelid, what are their movement and what are they innervated by
Orbicularis oculi - closes eyelid. Innervated by facial nerve
Levator palpebrae superioris - opens eyelid. Innervated by oculomotor nerve
Superior tarsal muscle - sympathetic nervous system
What muscles are responsible for eyemovements and what are they innervated by
Extra-ocular muscles
Superior, inferior, medial and lateral rectus
Superior and inferior oblique
Oculomotor innervates superior, inferior and medial rectus and inferior oblique
Lateral rectus - abducens nerve
Superior oblique - trochlear nerve
Where do the extraocular muscles arise
Recti muscles originate from common tendinous ring
Oblique muscles originate from bony walls of orbit
What are the actions of the recti muscles
Medial rectus - adducts eye
Lateral rectus - abducts eye
Superior rectus - elevates, slightly intorts, slightly adducts eye
Inferior rectus - depresses, slightly extorts, slightly adducts eye
What are the actions of the oblique muscles
Superior oblique - intorts, depresses, slightly abducts eye
Inferior oblique - extorts, elevates, slightly abducts eye
Describe how muscles are tested during the clinical examination of extraocular muscles
When eyes abducted:
- Elevation = superior rectus
- Depression = inferior rectus
When eyes adducted:
- Elevation = inferior oblique
- Depression = superior oblique
Describe the steps in the clinical examination of the eye
IVA FORM
I - inspection
VA - visual acuity - snellen chart
F - visual fields
R - reflexes
O - opthalmoscope
M - eye movements
