Ophthalmoscopy and Visual Fields Flashcards
What are the 4 parts of the optic nerve?
Intraocular
Intraorbital
Intracanalicular
Intracranial
Where in the skull is the optic canal located?
The greater wing of the sphenoid bone
What is the optic nerve also known as?
CN II
What are the three things to pay attention to when describing the optic nerve when doing an ophthalmoscopy?
Contour (borders of the disc)
Colour
Cup (bright centre of disc)
Describe the normal appearance of the optic nerve?
Clear and well defined borders
Orange-pink colour with a pale centre
Cup to disc ratio should be roughly 0.3
What conditions can cause abnormal contours of the optic nerve?
Disc swelling (e.g. papilloedema) Optic disc drusen
What conditions can cause an abnormal colour of the optic nerve?
Advanced glaucoma
Optic neuritis
Ischaemic optic neuropathy
Compressive lesion
What condition can cause a large cup?
Glaucoma
Which are darker on fundoscopy, veins or arteries?
Veins
What is the cup?
The centre of the optic disc that is devoid of neuroretinal tissue
What is the most common cause of a unilateral swollen disc?
Vascular - e.g. infarcion
What are causes of a swollen disc?
Papilloedema
Disc drusen
What is papilloedema?
A swollen nerve in the context of raised ICP
What is disc drusen?
Swollen disc due to a collection of material in the optic nerve
What are the causes of a pale disc?
Compromised circulation
Demyelination
Drugs (e.g. ethambutol)
Nutritional problems (e.g. B12, folate)
What does myelinated nerve fibres look like?
Bright white area going out from the nerve
What are the clinical features of myelinated nerve fibres?
Changes on visual field test
Enlarged blind spot
What is a homonymous visual field defect?
One affecting the same part of field in each eye (e.g. left field of vision in both eyes)
What is an incongruous visual field defect?
One affecting different parts of the field in each eye (e.g.upper left in right eye and upper and lower left in the left eye)
What is a hemianopic visual field defect?
One that affects half of the visual field
What is a quadrantanopic visual field defect?
One that affects a quarter of the visual field
Where would a defect be if the whole visual field of the right eye is affected?
Right optic nerve, pre-chiasmal
Where would a defect be if the whole visual field of the right eye and the peripheral part of the upper temporal left visual field is affected?
Sometimes the crossing nasal fibre does a small loop into the contralateral optic nerve - defect there
Where would a defect be if the patient has a bitemporal hemianopia?
Optic chiasm
Where would a defect be if the patient has a left homonymous hemianopia?
At any point beyond the chasm on the right hand side of the brain
Where would a defect be if the patient has a left homonymous quadrantanopia?
Nerve fibres going from the chiasm to the visual cortex fan out - so one affecting only some of the fibres
Where would a defect be if the patient has a left homonymous hemianopia that spares central vision?
Defect that spares the macula due to circulation in the occipital cortex
