Ophthalmology Part 2 Flashcards
What is Visual acuity?
It is the ability to resolve (‘see’) a gap between two objects. This is also known as spatial resolution
How it visual acuity measured?
Standard 6m Snellen Chart. This is recorded as 6/x. Where 6 is the distance the test is preformed and X is the number of the line of the smallest text that was seen
What are the advantages of using the LogMAR for testing visual acuity?
- Crowding phenomena means the letters are equal for each line, unlike snellen.
- Letters change by size by equal logarithmic steps.
- Score easier to analyse than snellens
What is classified as ‘blind’ or severe sight impairement?
Any score worse than 3/60
What is sight impaired or ‘partical sight’ classified as?
Anthing from 3/60 to less than 6/.60
What is classified as driving vision?
Better than or equal to 6/12
What is the afferent and efferent nerves involved in the pupillary reflex?
Afferent - Optic nerve,
Efferent - Occulomotor nerve
What is the pupil pathway?
Information from optic nerve goes to LGN, then to pretectal nuclei which sends bilateral information to the edinger-westphall nucleus which is a PSNS nuclei. Info then runs to ciliary ganglion and then via ciliary nerves to the muscles of the iris. This results in a consensual response
What are the causes of a Relative Afferent Pupillary Defect? (RAPD)
- Asymmetrical disease of retina or optic nerve.
- Retinal detachment,
- Optic neuritis,
- Anterior ischaemic optic neuropathy (AION),
- Tumour pressing on the optic nerve
What can some of the causes of an abnormal fundal reflex test be?
Corneal scars, cataract, vitreous bleeds, retinal tumours or retinoblastoma
What would an abnormal fundal reflex look like?
A difference in the brightness or colour between the eyes, displaced corneal dot thing
What does this show?
A normal optic disk
What does this show?
Swollen optic disk
What does this show?
New Vessels in an Optic disk. Can be due to severe diabetic retinopathy
What does this show?
Cupped optic disk
What does this show?
Pale optic disk
What are some of the causes of a swollen disk?
- Genuine Swelling
- Optic Neuritis,
- Raised Intracranial pressure ( SOL, IIH (idiopathic intracranial hypertension)or hydrocephalus),
- Pseudo swelling which can be due to small discs or calcium deposits ‘drusen’
What are three key elements when examining the optic nerve head?
Margin, colour and cup
Describe features of a 3rd cranial nerve palsy
- Vertical diplopia.
- Eye turned downwards and out,
- Pupil dilated and ptosis,
- Can be associated with an aneurysm so needs urgent brain imagine and angiogram
Describe features of a 4th cranial nerve palsy
- Oblique diplopia,
- Head tilted away from side of lesion,
- Diplopia worse away from the side of the lesion,
- Common after head injury however if bilateral could be congenital.
Describe features of a 6th cranial nerve palsy
- Horizontal diplopia which is worse in far distances.
- Worse towards side of palsy if unilateral.
- If bilateral then concerned that an increase in intracranial pressure is present.
What are some of the world wide causes of blindness?
Cataracts, macular degeneration, glaucoma, trachoma (main infectious cause, caused by chlamydia), diabetic retinopathy, refractive error
Describe the pathophysiological steps of diabetic eye disease
Chronic hyperglycaemia results in glycosylation of protein/ BM which causes loss of pericytes, a reduction in O2 transport causing tissue hypoxia. Vascular formative factors produced but new blood vessels are weak and leaky so it can result in haemorrhage, retinal detachment and glaucoma and loss of sight.
