Opthalmology Flashcards
describe the extracranial visual pathway
optic nerve converges and receives impulses from photoreceptors
this optic nerve leaves bony orbit and enters cranial cavity
describe the intracranial visual pathway
optic nerve from each eye meets at optic chiasm
fibres from the medial half of each retina cross over to contralateral optic tract
fibres from lateral half of each retina remain ipsilateral
these fibres meet at LGN
What is the lateral geniculate nucleus (LGN)?
projection of thalamus that meets with the optic nerve
what fibres make up left optic tract?
retinal fibres:
left lateral and
right medial fibres
what fibres make up right optic tract?
retinal fibres:
right lateral and
left medial
where do the optic tracts meet and synapse in the thalamus?
lateral geniculate nucleus (LGN)
What do axons from the LGN do and where do they go?
axons from the LGN carry visual info via pathway called optic radiation
Describe upper optic radiation
fibres carried from superior retinal quadrant
travels through parietal lobe to Primary visual cortex (PVC)
Describe lower optic radiaiton
fibres carried from inferior retinal quadrant
travels through temporal lobe (Meyers loop) to Primary visual cortex
when info at PVC then brain processes this info
Which cells process high intensity light?
cone cells
Which cells process low intensity light?
rod cells
What is lens structure and function?
muscle which refracts light to fall onto retina
Function of aqueous & vitreous humour?
aqueous: supplies nutrients to eyeball - anterior
vitreous: transmits light, nutrient supply - posterior
Function of cornea?
mainly responsible for light refraction
initial refraction onto lens, which then refracts it onto retina
What is the choroid layer?
middle layer between the sclera (outer) and retina (inner)
contains melanocytes to absorb colour
What is the retina?
inner layer which contains photoreceptos
How does light focus on the retina?
as light moves from air to eye
passes through cornea, aqueous humour, lens, vitreous humour
then passes through an entire neural layer
to excite the photoreceptors that are next to the
pigmented layer
What is the fovea and why is VA high here?
centre of macula where visual acuity is the highest due to high no of cone cells
What is the macula?
part of retina at back of eye which contains high no of rod + cone cells
allows us to see fine details in centre of visual field
What are some causes of acute red eye?
subconjunctival haemorrhage
keratitis
conjunctivitis
What are the extrinsic eye muscles and functions?
lateral rectus - moves eye laterally
medial rectus - moves eye medially
superior rectus - upwards
inferior rectus - downwards
superior oblique - down and out
inferior oblique - up and out
Which cranial nerves innervate the extrinsic eye muscles?
lateral rectus - VI abducens
medial rectus - III oculomotor
superior rectus - III oculomotor
inferior rectus - III oculomotor
superior oblique - IV trochlear
inferior oblique - III oculomotor
LR6 SO4 R3
Which CN innervates the levator palpabrae superioris muscle (eyelid)?
CN III - Oculomotor
What happens when light enters the eye? Describe the entire process.
it passes retina (nerves) unaffected
travel straight to choroid
bounces back onto retina
light falls on rods and cones
these photoreceptors pick up the light and send signals to bipolar cells
bipolar cells relay to ganglion cells
send the nerve along the surface of the retina to optic nerve
optic nerves meet at optic chiasm
signal then enters thalamus then goes to visual cortex
what are common causes of blepharitis?
S aureus
rosacea
pollen allergy
seborrheic dermatitis
what is 1st line treatment for blepharitis?
The patient’s symptoms and examination findings suggest anterior blepharitis, likely with a staphylococcal infection.
The NICE guidelines recommend chloramphenicol ointment as the first-line treatment for this condition, to be used for six weeks.
Chloramphenicol is effective against a broad spectrum of bacteria, including Staphylococcus species, commonly associated with blepharitis.
chalazion vs hordeolum
chalazion - blockage of meiboman gland that appears on the inside of the eyelid, usually surfacing as a bump. - firm, non-erythematous, mobile, inner eyelid - warm compress, resassurance, goes away spontaneously
An eye stye (or hordeolum) - smaller pimple-like bump that appears on the upper or lower eyelid due to a blocked oil gland. It is typically near the eyelash and lives on the outside of the eyeli
What is keratitis and what is the most common bacteria that causes it?
inflammation of the cornea = corneal ulcer
causes:
Pseudomonas and S. aureus - Pseudomonas v common in ocular presentation
What are viral causes of Keratitis?
HSV 1 - cold sore
VZV - part of shingle
z
What are symptoms of keratitis?
red, sticky, painful eye
gritty sensation in eye
significant photophobia
some vision loss
contacts can make it worse
Why can contacts cause keratitis?
These organisms may live on the surface of a contact lens or contact lens carrying case. The cornea may become contaminated when the lens is in your eye, resulting in infectious keratitis.
Treatment for keratitis?
bacterial - fluoroquinolone (eg ciprofloxacin) drops hourly for 38h, then 4x day for 5 days
viral - aciclovir drops 6x daily for 2 weeks
What are causes of conjunctivitis?
bacterial -
allergic -
chemical - alkali
Autoimmune -
What are symptoms of viral conjunctivitis?
red sticky eyes
gritty sensation of eyes
URTI symptoms - cough/cold
What viruses can cause conjunctivitis?
- viruses cause 80% of conjunctivtis cases
- ask if recent cold (adenoviruses most common cause)
- very contagious if eye is red + gritty
less common viruses:
EBV
Herpes Simplex
VZV
What bacteria can cause conjunctivitis and how to treat?
staph and strep bacteria
Haemophilius influenzae - bacteria that cause pneumonia
Moraxella catarrhlis - bacteria that cause ear + sinus infections
also v contagious - need chloramphenicol eye drops
What is management of acute bacterial conjunctivitis (<3 day hx)?
According to NICE guidelines, including the initial management involves reassurance that this is a self-limiting condition, typically resolving within 5 to 7 days without the need for treatment. The use of saline to clean away purulent discharge can be advised. Antibiotic therapy, such as chloramphenicol or fusidic acid eye drops, is generally reserved for cases that do not improve or worsen over a period of 3 days, particularly in children under 2 years old.
What are allergic conjunctivitis causes and treatment?
allergen - eg pollen, pet dander, mites
not contagious
what is an enlarged blind spots typically associated with?
swollen optic disc - papilloedema
caused by raised ICP (eg brain tumour, intracranial haemorrhage)
what is strabimus?
when eyes do not line up in the same direction (cross-eyed)
what is orthotropia?
straight alignment of the eyes - no shift in contralateral eye
what is heterotopia?
when you do the cover test, you occlude one eye and observe the contralateral eye for a shift in fixation
shift indicates heterotropia = strabismus
what are the 4 types of strabismus?
esotropia - inward turning
exotropia - outward turning
hypotropia - downward turning
hypertropia - upward turning
what is nystagmus and what does it indicate?
rhythmical, repetitive, involuntary eye movement
indicates vestibular nerve pathology or stroke
what condition is associated with optic neurtis?
multiple sclerosis
what is optic neuritis and symptoms?
inflammation of optic nerve (CN II)
pain at back of eye
pain on moving the eye
what is the clinical relevance of the optic chiasm?
pituitary gland is very close to optic chiasm
so pituitary adenoma (benign) will compress on the optic chiasm
Compression to the optic chiasm particularly affects the fibres that cross over from the nasal half of each retina.
This produces a visual defect affecting the peripheral vision in both eyes, known as bitemporal hemianopia - aka tunnel vision
if there is damage to optic radiation what will occur
homonymous hemianopia
associated with stroke or any damage to this part of the brain
what would optic nerve damage lead to
depending on which side would be anopia
what are the risk factors associated with glaucoma?
diabetes
genetic
family hx
black ethnic origin
risk factors of cataracts
steroids - avoid topical eye steroid
old age
caucasian
sun exposure
diabetes
eye trauma
family history of cataracts
risk factors of AMD?
Older age
Smoking
Family history
Cardiovascular disease (e.g., hypertension)
Obesity
Poor diet (low in vitamins and high in fat)
Which nerves are involved in regulating pupil size?
CN II and III
what condition is RAPD associated with?
MS
palsy associated with CN III
with pupil involvement
vertical diplopia
ptosis
dilated pupil
with CN III palsy, other nerves (superior oblique) overpower, so eye would appear down and out
causes of 3rd nerve palsies?
medical
surgical - PCOM aneurysms - posterior communicating artery presses against the 3rd nerve
dilated pupils
what does 4th cranial nerve supply?
supplies superior oblique - depresses the eye
what does 4th CN palsy present as?
therefore eye will appear higher than the normal
diplopia - double vision
vertical - seeing 2x things side by sie
horizontal - seeing 2x things top & bottom - therefore pt will have trouble going down stairs
also to compensate their neck will be tilted to the side
what muscle does CN VI supply and what does palsy to this area present as?
lateral rectus palsy
therefore to compensate the eye will be deviated medially
