Opthamology 2 - Eye and Vision (special senses) Flashcards
What is visual acuity?
Ability of the visual system to resolve or see the gap between two object (spatial resolution)
How is visual acuity measured?
- Snellen chart (6 metres)
- 6/x - x denotes the number of the line of the smallest text that was seen
What visual acuity is considered ‘blind’ or Severe sight impairment (SSI)?
3/60 (ubake to see first letter on snellen within 3m)
What visual acuity is needed for driving?
6/12 or better
What is the parasympathetic motor element of the 3rd cranial nerve?
Edingar Westphal nucleus
Where does the optic nerve synapse?
Pretectum in superior colliculus gives off information to both Edingar Westphal nuclei - precipitates a response down both nerves causing shpincters of the iris to constrict
What does a swinging light test look for?
Relative afferent pupillary defect - defect in optic nerve of one side
What are the causes of Relative Afferebt Pupillary Defects (RAPD)?
- Optic neuritis
- Anterior ischaemic optic neuropathy (AION) - associated with giant cell arteritis
- Tumour pressing on optic nerve
- Glaucoma
What is a retinal reflection test looking for?
- Assess clarity of ‘media’
- Corneal scars
- Cataract
- Vitreous bleeds
- Retinal tumours
What are the advantages of a retinal reflection test?
Quick and non-invasive
What are most red reflex abnormalities due to?
Cataracts
What does a central dark opacity indicate on a retinal reflection test?
Cataract or corneal scar
What does a white retinal reflection on aretinal reflection test indicate?
Retinoblastoma
What are the 2 types of retinoblastoma?
- Familial - bilaterally (younger)
- Sporadically - unilaterally (older babies)
WHy do retinal structures all move to the side at the fovea?
Make it thinner maximising acuety and photoreceptors are most tightly packed together to give highest acuity
WHat does a pale neuro-retinal rim indicate?
Optic atrophy - toxcitity from drugs, poor diet, optic nerve being pressed on or optic neuritis
What does a enlarged central cup and thinning of the neuro-retinal rim and enlarged cup to disk ration indicate?
Glaucoma
What are new blood vessels growing on the optic disc associated with?
Proliferative Diabetic retinopathy
What is an enlarged cup at the optic disk caused by?
- Glaucoma
- New retinal rim becomes thinned axons from ganglion cells are dying
- Associated with age ethnicity and intraoccular pressure
What can raised intra-occcular pressure be associated with?
Glaucoma
- Can be reversed through eye-drops, laser and surgery
What are the causes of swolen disc?
Pseudo swelling - Small discs - Calscium deposits 'Drusen' Genuine Swelling - Optic neuritis (VA reduced) - Raised ICP (VA normal): SOL, IIH, Hydrocephalus
What is it called when a swollen disc is raised due to raised ICP?
Papilloedema
What are the 3 key elements that should be commented on when examining the optic nerve head?
- Margin, colour, cup size
What are the muscles of the eye?
- 6 extra-ocular muscles
- 2 horizontal recti (medial and lateral)
- 2 vertical recti (superior and inferior)
- 2 oblique (superior and inferior)
What are the 3 types of cranial nerve palsy?
- 3rd CNP
- 4th CNP
- 6th CNP
What is associated with 3rd CNP?
- Vertical diplopia
- Eye is ‘down and out’
- Diplopia every where
- Pupil dilated and ptosis
- Can be associated with an aneurysm - needs urgent brain imaging and angiogram
What is associated with a 4th CNP?
- Oblique diplopia
- Head tilt away from side of the lesion
- Diplopia worse away from the side of the palsy if unilateral (adduction)
- Common after head injury
- Bilateral - might be congenital
What is associated with a 6th CNP?
- Horizontal diplopia
- Worse in far distance
- Worse towards the side of the palsy if unilateral
- Bilateral - concerned that raised ICP is present
What is the worldwide number 1 cause of blindness?
Cataracts
In developed countries what is the main cause of blindness?
Macular degeneration
WHat is the main cause of irreversible blindness in poor countries?
Glaucoma
What is trachoma?
- Chlamydia
- Scarring of conjunctivqa which leads ro the eyelid turning into the cornea and causing corneal scarring
