Ophthalmology Flashcards
What are the layers of the eyeball?
Fibrous coat
Vascular coat
Sensory coat
What are the components of the fibrous coat?
Sclera
Cornea
What are the components of the vascular coat?
Iris
Ciliary body
Choroid
What are the components of the sensory coat?
Retina
What is the lens?
A biconvex transparent crystalline lens
Suspended by suspensory ligaments from the ciliary body
Where is the anterior segment and what does it contain?
Infront of the lens
Aqueous humour
Where is the posterior segment and what does it contain?
Behind the lens
Vitreous humour
What is the anterior segment divided into?
Anterior chamber- in front of iris
Posterior chamber- behind iris but in front of lens
Where is the angle of the anterior chamber?
End of sclera but start of cornea
What is the path of aqueous humour?
Reabsorbed via Schlemm’s canal into systemic circulation
Constantly produced and reabsorbed by ciliary body
Trabecular meshwork help aqueous humour drain into Schlemm’s canal
What is the purpose of aqueous humour?
Maintain intraocular pressure
What are the orbital foramen?
Optic foramen
Superior orbital fissure
Inferior orbital fissure
What is the conjunctiva?
Thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera
Does not cover cornea
What are the different parts of the conjunctiva?
Superior fornix
Ocular conjunctiva
Palpebral conjunctiva
Fornical conjunctiva
Inferior fornix
What is the lacrimal apparatus?
Lacrimal gland ducts open into conjunctival sac.
Tears drain through punctae into lacrimal sac.
Sac drains through nasolacrimal duct into inferior meatus of nasal cavity
What are the intrinsic muscles of the eye?
Parasympathetic (III): Ciliaris, Constrictor pupillae
Sympathetic: Dilator pupillae
What are the causes of pupil abnormalities?
Disease of retina
Disease of optic nerve
Disease of III cranial nerve
What are the extrinsic muscles of the eye and their innervation?
Medial rectus- III (oculomotor)
Lateral rectus- VI (Abducent)
Inferior rectus- III (oculomotor)
Superior rectus- III (oculomotor)
Superior oblique- IV (trochlear)
Inferior oblique- III (oculomotor)
Levator Palpabrae Superiorus (LPS)- III (oculomotor)
What is the primary action of the extrinsic eye muscles?
Medial rectus- adduction
Lateral rectus- abduction
Inferior rectus- depression
Superior rectus- elevation
Superior oblique- intorsion
Inferior oblique- extorsion
What is the origin and insertion of recti muscles?
Origin: tendinous ring
Insertion: sclera anteriorly
What is the origin and insertion of the superior oblique muscle?
Origin: lesser wing of sphenoid
Insertion: sclera posteriorly
What is the origin and insertion of the inferior oblique muscle?
Origin: medial part of orbit floor
Insertion: sclera posteriorly
What is the origin and insertion of the LPS muscle?
Origin: roof of orbit
Insertion: upper eyelid
What is strabismus?
Squint- misalignment of the eyes
- Esotropia: convergent
- Exotropia: divergent
What cranial nerves are in the orbit?
Optic (II)
Oculomotor (III)
Trochlear (IV)
Abducens (VI)
What is the arterial supply of the orbit?
Ophthalmic artery (branch of ICA)
- Central retinal artery
- Short posterior ciliary arteries
- Long posterior ciliary arteries
- Anterior and posterior ethmoidal arteries
- Muscular arteries
What is the venous drainage of the orbit?
Superior and Inferior ophthalmic veins which drain into the cavernous sinus
What are the histological layers of the cornea?
- Epithelium- non keratinised stratified squamous
- Bowman’s membrane- basement membrane of corneal epithelium
- Stroma- regularly arranged collagen, no blood vessels
- Descemet’s layer
- Endothelium- single layer
Why is the cornea transparent?
Regular arrangement of collagen in stroma
No blood vessels
Endothelium cell layer has a pump that actively keep aqueous humour out
Why is the cornea an immune privileged site?
Avascularity means foreign antigens from a corneal graft won’t be recognised
What does a gonioscope visualise?
The angle of the anterior chamber
What is the blood supply of the outer retina?
Fenestrated blood vessels of the choroid
What is the blood supply of the inner retina?
Branches of central retinal artery
What is the fovea centralis?
Area of maximum visual acuity
Packed with cones, no rods
What are the layers of a tear film?
Layer 1- mucinous layer
Layer 2- aqueous layer
Layer 3- oily layer
What is refraction?
Bending of light when it passes from one optical medium to another
How does a sharp image form on the retina?
Light waves from an object bend at the cornea and bends more at the lens
Therefore, forms an inverted image of the object sharply focused at the retina
What rays reach the eyes for distant objects?
Parallel
What rays reach the eyes for close up objects?
Divergent
Need to be bent a lot more than parallel rays to bring them to focus on the retina
What is accommodation?
Capacity of our eyes to change focus from distant objects to close objects
- Lens changes shape
- Pupils constrict
- Eyes converge
What does a thicker lens allow?
More powerful so able to focus on close objects
What is myopia?
Short sighted
Rays focused in front of retina
Bending power of cornea and lens is too much for that eyeball
What is hyperopia?
Long sighted
Rays focused behind retina
Using accommodative power all the time for far off things, so no power left to see close objects
What is astigmatism?
Close and distant objects appear hazy
Multiple focal points
What is presbyopia?
With age the lens gets less mobile/elastic
Seeing near objects becomes difficult
What is phototransduction?
Conversion of light energy to an electrochemical response by photoreceptors (rods and cones)
Where is visual pigment?
In the outer segment of rods and cones
Outer segment contains stacks of lamella which are made up of cell membrane.
Integrated into cell membrane is visual pigment
What is the visual pigment in rods?
Rhodopsin
What is the visual pigment in cones?
Cone opsins S, M and L
- Blue, Green, Red
What is visual pigment regeneration?
Activated pigment compounds need converted back to normal
Done by vitamin A
What is your visual field?
Everything you see with one eye (including periphery)
What is the visual pathway?
Optic nerve → crosses over at chiasma → optic tract → synapses at LGB → optic radiation reaches occipital lobe (Primary visual cortex)
What are the 2 parts of the retina in the visual pathway?
Nasal retina
Temporal retina
What is amblyopia?
Lazy eye
What is diplopia?
Double vission
What is Horner’s syndrome
Anisocoria due to damage to sympathetic innervation to pupil
What is anisocaria?
Different pupil sizes
What is ptosis?
Drooping of eyelids on affected side
What is anhidrosis?
Loss of sweating on affected side
What are common orbit disorders?
Blow out fracture
Proptosis- eyeball protruding out
Infection spread through emissary veins
What are common eye movement disorders?
CN VI palsy
CNIII palsy
CN IV palsy
What are common lids and conjunctivae disorders?
External stye (hordeolum externum)
Internal stye (hordeolum internum)
Conjunctivitis
Corneal ulcers
Corneal dystrophies
What are cataracts?
Lens opacification
What causes cataracts to develop?
- Embryological fibres never shed and get compacted in the middle.
- No blood supply to lens
- Absorb harmful UV rays
- Damaged lens fibres
What is the treatment for cataracts?
Surgery
What is glaucoma?
Intraocular pressure raised above 21mm of mercury
Eyes optic nerve damaged due to raised intraocular pressure
What is the triad of signs for glaucoma?
- Raised IOP
- Visual field defects
- Optic disc changes on ophthalmoscopy
What is the treatment for glaucoma?
Eye drops to decrease IOP
Laser trabeculoplasty
Trabeculectomy
What is angle closure glaucoma?
Acute, painful onset
IOP severly raised
Anterior chamber (AC) shallow and angle is closed
What are methods for lowering IOP?
- IV infusion with or without oral therapy- carbonic anhydrase inhibitors
- Analgesics, antiemetics
- Constrictor eye drops- pilocarpine
- If no contraindication beta blocker drops
- Steroid eye drops (dexamethasone)
What is uveitis?
Inflammation of uvea (vascular layer of eye)
What are the types of uveitis?
Anterior- iris
Intermediate- ciliary body
Posterior- choroid