Eye Flashcards
What forms the roof of the orbit?
Frontal bone
Lesser wing of sphenoid
What forms the floor of the orbit?
Maxillary bone
Palatine bone
Zygomatic bone
What forms the medial wall of the orbit?
Lacrimal bone
Ethmoid bone
Maxillary bone
Sphenoid bone
What forms the lateral wall of the orbit?
Zygomatic bone
Greater wing of sphenoid
What forms the apex of the orbit?
Optic canal
What are the openings into the orbit?
Optic canal
Superior orbital fissure
Inferior orbital fissure
What is the arterial supply to the orbit?
Ophthalmic artery
What is the venous drainage of the orbit?
Superior ophthalmic vein
Inferior ophthalmic vein
Where does the superior ophthalmic vein drain?
Cavernous sinus
Where does the inferior ophthalmic vein drain?
Pterygoid plexus
What provides general sensory innervation to eye?
CN Va
What are the weakest parts of the orbit?
Medial wall + floor
What is an orbital blowout fracture?
Traumatic fracture of medial wall or floor of orbit
What causes an orbital blowout fracture?
Sudden increase in intra-orbital pressure often due to fist or ball hitting eye
What happens in an orbital blowout fracture?
Orbital contents can prolapse and bleed into maxillary sinus
Fracture site can ‘trap’ structures
What are the signs of an orbital blowout fracture?
Loss of upward gaze on affected size History of trauma Periorbital swelling Double vision Anaesthesia over affected cheek
What causes anaesthesia in an orbital blowout fracture?
Infraorbital branch of CNVb runs through floor of orbit
What makes up the eyelids?
Skin Subcutaneous tissue Tarsal plate Orbicularis oculi Levator palpaebrae superioris Meibomian glands Sebaceous glands - associated with eyelash follicles
What do Meibomian glands secrete?
Meibum - an oily substance that prevents the evaporation of the tear film
What do sebaceous glands secrete?
Sweat
What is caused by a blockage of a Meibomian gland?
Meibomian cyst
What is a stye?
Infection due to blockage of sebaceous gland or eyelash follicle
Where do Meibomian glands lie?
Within the tarsal plate
What is the orbital septum?
Thin sheet of fibrous tissue that originates from the orbital rim periosteum and blends with the tarsal plates
What is the role of the orbital septum?
Prevents superficial infection spreading into orbit
What is peri-orbital cellulitis?
Infection occurring within eyelid tissue - superficial to orbital septum
Where does peri-orbital cellulitis effect?
Confined to tissues superficial to orbital septum
What happens to ocular function in peri-orbital cellulitis?
Unaffected
What is orbital cellulitis?
Infection within the orbit - deep to orbital septum
What are the signs of orbital cellulitis?
Proptosis
Exophthalmos
Reduced/painful eye movements
Reduced visual acuity
What is the risk of orbital cellulitis?
Can spread intracranially - via venous system
What is proptosis?
Protrusion of the eyeball
What is exophthalmos?
Appearance of protruding eyes
What are the contents of the orbital cavity?
Eyeball Fat Extra-ocular muscles Nerves Blood vessels Lacrimal apparatus
What is the lacrimal apparatus?
Structures involved in tear film production and drainage
What makes up the lacrimal apparatus?
Lacrimal gland
Lacrimal sac
Lacrimal ducts
What produces tears?
Lacrimal gland
What drains tears?
Lacrimal ducts
- canaliculi
- nasolacrimal duct
What happens with tears?
Blinking washes tear film across front of eye
Drain into nasal cavity
What is epiphora?
Overflow of tears over lower eyelid
What is the role of tears?
Lubricate conjunctiva and cornea
How many layers does the eyeball have?
3
What are 3 layers?
Outer
Middle
Inner
What forms the outer layer?
Sclera
Cornea
What forms the middle layer?
Choroid
Ciliary body
Iris
What forms the inner layer?
Retina
What is the retina?
Inner photosensitive layer lying on an outer pigmented layer
What is the conjunctiva?
Transparent mucous membrane producing mucous and tears
Where does the conjunctiva lie?
Covers sclera, lines inside of eyelids
Where does the conjunctiva not cover?
Cornea
What is the limbus?
Junction of the conjunctiva with the cornea
What is conjunctivitis?
Inflammation of conjunctiva
How do we see?
Light enters eye
Refracted on to a focal point
What structures refract light?
Cornea
Tear film
Lens
Aqueous + vitreous humour
What is myopia?
Short-sightedness
What is hypermetropia?
Long-sightedness
What is the accommodation reflex?
Focusing near objects requires greater refraction of light so eye accomadates
How does the eye accommodate?
Pupil constricts
Eyes converge
Lens becomes more biconvex - contraction of ciliary muscle
What is presbyopia?
Age-related inability to focus near objects
What types of cells are present on the retina?
Rods
Cones
What do rods do?
Active at low light levels
Do not mediate colour vision
Where do rods lie?
Peripheral parts of retina
What do cones do?
High definition
Colour vision
Where do cones lie?
Concentrated in macula
What is the fovea?
Area of only cones
How are visual action potentials generated?
Action potentials generated in response to light via retinal ganglion cells
RGC axons collect in area of optic disc forming optic nerve
Action potentials follow visual pathway to occipital lobe
What can cause blurring of vision?
Transparency of structures anterior to retina
- cataract
Ability of structures to refract light
- astigmatism
- presbyopia
Retina
- retinal detachment
- macular degeneration
- optic neuritis
How is the shape of the eyeball maintained?
Chambers filled with fluid
- anterior and posterior
- vitreous
What fills the anterior and posterior chambers?
Aqueous humour
What is aqueous humour?
Fluid produced by ciliary processes within ciliary body
What is the flow of aqueous humour?
Flows from ciliary body
Posterior chamber
Anterior chamber
Drains through iridocorneal angle
Where does aqueous humour drain?
Via trabecular meshwork into canal of Schlemm
What is glaucoma?
Optic nerve damage secondary to raised intraocular pressure
What is chronic glaucoma also known as?
Open-angle glaucoma
What happens in chronic glaucoma?
Trabecular meshwork deteriorates as we age
Increased intraocular pressure = increased optic disc cupping
Gradual loss of peripheral vision
What is acute glaucoma also known as?
Closed-angle glaucoma
What happens in acute glaucoma?
Narrowing of iridocorneal angle
What is the relevance of acute glaucoma?
Ophthalmological emergency
What are the signs of acute glaucoma?
>55 Acutely painful red eye Irregular oval pupil Blurring of vision N+V
How is acute glaucoma managed?
Drugs to reduce intraocular pressure then surgery
What is astigmatism?
Irregularity of corneal surface