Eye Flashcards
What are the bones forming the walls of the orbit
Ethmoid Maxilla Zygomatic Lacrimal Frontal Sphenoid
Why are some aspects of the walls vulnerable to fracture
Sinuses next to floor and medial wall causes weakness
What is a blow out fracture
Sudden increase in intra orbital pressure which fractures the floor. This causes prolapse into medullary sinus and tethers the eye from the bottom so cannot look up.
Why with a blow out can you get numbness over the cheek, upper lip and eyelid
Disruption to cutaneous nerve Vb
Where does the eye get its blood suppy
1st branch of ICA
Ophthalmic artery
Gives off central retinal after going through optic canal and this supplies retina and chorioid layer
Ciliary artery feeds choroid layer.
What happens if there is central retinal artery occlusion
Cherry red spot where macula is thinnest as choroid layer is still being perfused by ciliary artery.
Why does infection to eye pose threat of spreading
Ophthalmic veins drain into cavernous sinus, pterygoid plexus and facial vein
What muscle and nerve closes the eye
CN7 palpable part of orbicularis oculi
What muscle and nerve contracts and elevates the eyelid
Levator palpebrae- CN3
What is the function of the meibomian gland
Oily substance to prevent evaporation of tear film.
In tarsal plates
Function of orbital septum
Barrier against superficial infection spreading pre septal to post septal
Where is humour made and when does it go
Maid in ciliary processes in ciliary body. flows posterior to anterior draining through iridocorneal angle via trabecular meshwork into canal of schlemm to venous circulation
Where does vitreous humour fill
Intraocular
Aqueous humour
fills anterior and posterior chambers providing O2 and nutrients to lens and cornea.
What is the function of the lacrimal apparatus
Tear film production and drainage
What is epiphora
Overflow due to obstruction of nasolacrimal duct
What are the 3 layers of the eyeball
Sclera
Choroid
Retina - innermost layer
What is the macula densa
Dense area of photoreceptors- cones for high acuity of colour vision
The thinnest part of retina
Light is focused here
What helps refract light
Tear film, cornea, lens and humour
What helps regulate light entry
Pupil
What causes long sight
Hypermetropic- eyeball to short
What causes short sight
Myopic- eyeball to long
What is the Accommodation reflex
Eye restricts pupil and converge to stay fixed on same point. Lens becomes biconvex- fatter
How does the lens change shape
Contraction of ciliary muscles under parasympathetic oculomotor control leads to fatter. Relaxation means ligaments are pulled tight = lens flattens.
What is the fovea
Place with only cones
What causes blind spot
Optic disc has no photoreceptors
What does pinhole testing do
Sees if there is a refractive error or not
Difference between styes and meibomian cyst
Painful, superficial, blocked sebacceous ? staph VS painless blocked meibomian gland
What is blepharitis
Inflammation of lids, gritty
What is conjunctivitis
Inflammation of conjunctiva viral or bacterial.
What are cateracts
Decrease transparency of structures anterior to retina. Decreases refractive ability.
What is presbyopia
Lens stiffer with age
Less able to change shape
Near objects hard to focus on
What are the two types of glaucoma
Acute vs Chronic
What is the issue in glaucoma
Blockage of drainage of aqueous humour from anterior chamber = increased intraocular pressure.
Explain chronic glaucoma
Open angel
Trabecular meshwork deteriorates with age
Increased intraocular pressure
Disc cupping
Gradual loss of peripheral vision due to ischemia and damage to optic nerve
Explain acute glaucoma
Closed angle
Narrowing of iridocorneal angle
Emergency
Halo- corneal edema
What changes do you see in Papilledema
Disc swelling secondary to raised intracranial pressure
Bilateral
Optic nerve swelling
What changes do you see in glaucoma
Disc cupping
Increased cup to disc ratio caused by high pressures in the eye
Why do we have binocular vision
Wider field of vision
Depth perception
What does misalignment of visual axis cause
Image focuses of different areas of retina. Image cannot be fused = double vision - diplopia
What are the extraocular muscles
S,M,L,I rectus
SO and IO
What is the origin for all but IO muscle
Apex of orbit
Where does the IO muscle arise
Floor of orbital cavity
What is the action of the SO
Intort, depress and slightly abduct
When is the SO most powerful
Medially
What does the IO do
Extort, elevate, abducts
When is the IO most powerful
Medially
What is the action of S recuts
Elevation, slight adduction, slight intorsion
When is S rectus most powerful
Laterally
What is the action of I rectus
Depression, slight adduct, slight extort
When is I retus most powerful
Laterally
Why do we perform a H in eye exam
To isolate muscles to test individually as some share common action but each has a place where it’s more dominant
What is Stabismus
Ocular misalignment- common in children
What is the innervation of LR
CN6
What is the innervation of SO
CN4
What is the innervation of the rectus and IO
CN3
What else does CN3 innervate
Sphincter pupillae muscles and levator palpebrae superioris
In compressive lesion is the pupil spared
No, its involved
