Flashcards in Eyes Deck (21)
What is the DVLA requirements for minimal eyesight?
Acuity - 6//10
Visual field - <20 degrees
What is inflammation of the cornea called?
What three substances form tears and what secretes them?
Mucus - conjunctival goblet cells
Water - Lacrimal gland
Lipids - Meibomian gland
Describe how aqueous humour drains from the eyes?
Leaves the anterior chamber and travels through the trabecular mesh-work and leaves via the canals of schlem
What is normal intra-ocular eye pressure?
What do rod and cone cells synapse onto?
Rod - On bi-polar cell
Cone - On and Off bi-polar cell
Photons hit the photoreceptor cells and hyper-polarise them. G-protein rector activation (Opsin which is Vit A bound) isomerises leading to Transducin enzyme activating the enzyme phospodiesterase, this hydrolyses cGMP and lowers its level which in turn blocks sodium channels
On the lateral geniculate nucleus describe how macula and peripheral fibres synapse?
Macula fibres - Medial
Peripheral fibres - Lateral
Describe the optic radiations?
Upper retinal fibres travel directly posterior
Lower retinal fibres travel temporally (Meyer's loop)
Define low vision?
Visual field loss of <20 degrees
A lesion of the macula will cause what field defect?
Unilateral central scatoma with distortion
Acute optic nerve lesion will cause what field defect?
Unilateral central scatoma
In the pupillary light reflex, where does the optic tract synapse?
Pre-tectal nucleus (bypassing the lateral geniculate)
Fibres are then sent to the Edinger/Westphall
Describe the relative afferent pupillary defect?
Shine a light in affected eye = No constriction in either pupil, shine light in normal eye and both pupils will constrict (consensual and direct response), shine light in affected eye again and both eyes dilate
What is RAPD indicative of?
Optic nerve (CN II damage)
Describe the pupils of patients with afferent defects against those with efferent defects at rest?
Afferent problems - both pupils same size at rest
Efferent problems - both pupils different size at rest
Describe what can efferent defects?
Failure to constrict - CN (III) palsy/acute glaucoma
Failure to dilate - Horner's syndrome/ Uvitis
Describe medical conditions that may bring about painful sudden loss of vision?
Acute (open-angled) glaucoma
Optic nerve neuritis
Describe medical conditions that may bring about painless sudden loss of vision?
Macular degeneration WET