130 - Visual Disterbance Flashcards
What is hyphaema?
Bleeding between iris and cornea
What protects the eye from trauma/damage?
Orbit bones (they blow out rather than the eye)
Soft tissue - lids + orbital fat
Tears - physically removes debris and contains immunoglobulins - it is antimicrobial
What are the 7 parts of an eye examination?
Examine externally Visual acuity Visual fields fundoscopy Eye movements intraoccular pressure Pupils Red Reflex
Where in the eye has no pain receptors?
The retina
What can happen to the vitreous cavity?
Loss of clarity
Blood
Pus
Uvitus
How does the lens respond to injury?
It goes cloudy
What pathologies related to the optic nerve can cause sudden visual disterbance?
Optic neuritis Papillitis Ischaemic optic neuritis Giant cell arthritis Compression - tumour?
If someone has trouble seeing in the centre of their vision, what may they have?
Age related Macular degeneration.
Blood vessels can grow into the retina and bleeed - ‘wet’, or can be ‘dry’.
Most common cause of blindness and partial sightedness.
What state is the rod/cone cells in in the dark?
Depolarised.
cGMP is produced
The Na/Ca channel is open
What state are rod/cone cells in in the light/
The become hyperpolarised
Describe what occurs in the rod/cones when light is absorbed.
Light hits rhodoopsin, changes retinal from cis to trans form.
This causes the alpha unit to be cleaved from transducin
this converts GDP to GTP
Phosphodiesterase is activated
This changes the cGMP to GMP
This closes the na/Ca channel (but it is still leaky), but the Na/Ca/K exchanger is still open
Ca is removed from the cell
It becomes hypperpolarised
–> LESS glutamate produced
–> Stimulates bipolar cells (some depolarise, some hyperpolarise)
What neeurotransmitter do rod/cones produce?
Glutamate
Does glutamate levels go up or down in light in a rod/cone cell?
Down
What is convergence?
Multiple bipolar cells synapse with just one ganglion - so multiple rods/cons activity is pooled.
east convergence at the fovea, where there is 1:1 synapsing.
What is the 3rd photosensitive cell?
Photosensitive retinal ganglion cells.
What do photosensitive retinal ganglion cells do?
They project to the pineal gland, which controls melatonin production and involved in the diurnal rhythm.
What does the swinging light test diagnose?
RAPD - Relative afferent pupil defect
damage to the afferent nerve from one eye (which travels along the optic nerve (CNII), so light isn’t detected to start the pupil reflex.
Why does shining light in one eye make both eyes pupils constrict?
Despite light being detected individually in each eye, the efferent neurone signalling to constrict the pupils originates from a common central efferent tract - so only one eyes needs to be stimulated for both to react.
What is the pupillary near reflex?
When switching between looking at a near object and a far object the eye reacts by a co-ordinated change in convergence, lens shape and pupil size.
What damage causes light-near dissociaton?
Dorsal Midbrain syndrome - shining a light doesn’t constrict pupils, but eliciting a near response does.
What is Mrydriasis?
Opening of pupils/widening
What drugs can be used to cause mydriasis?
Sympathomimetics - eg. phenyleprine
Anti-muscarics eg. tropicamide
If someone has very dark irises, which drug wouldn’t you use for mydriasis?
Phenyepherine
What do sympathomimetics act on?
alpha 1 receptors - sympathetic NS
What do anti-muscarinics act on?
Bloch action of Ach at muscarinic receptors - block parasympathetic
Which drug would you use to paralyse cillary muscles, and why would you want to do that?
Cyclopentolate - causes cycloplegia (paralysis of cillary muscle) - post op, in trauma, for investigations, in uveitis - stops inflamed muscles rubbing which causes pain.
What could you do to reverse mydriasis?
a Parasymaphimemetic - eg pilocarpine
Wha is used to examine for corneal or conjunctivl damage?
Fleurescein - yellow dye.
What can you use before painful procedure?
An anaesthetic -eg. lidocaine, proxymetacaine
What OTC drug is useful in treating superficial infections?
Chloramphenicol
What are the different sorts of artificial tears you can get?
Hydromellose - acts liek the aqueous layer, jelly like ones like caromers, viscous ointments, surfactant - polyvinyl alcohol.
