Visual Impairment Flashcards
Learn how vision is disturbed
1
Q
How does visual impairment present to a Neurologist?
A
Normally involves a lesion in the visual pathway from the retina to the occipital cortex
2
Q
What is the anatomical path of light through the eye?
A
- Retina to the optic nerve
- Optic nerve to the optic chiasm
- Optic chiasm to lateral geniculate nucleus
- Lateral geniculate nucleus to occipital cortex
3
Q
The retina?
A
- Three neuronal levels: photoreceptors, bipolar and ganglion cells
- Rods: night vision/peripheral movement (In periphery)
- Cones: daytime/colour concentrated in macula
- Macula
4
Q
What is the blood supply to the visual pathway?
A
- The opthalmic artery us the first branch of the internal carotid, gives rise to the central retinal and posterior ciliary arteries.
- Forms the blood supply to the retina and optic nerve.
- Optic radiations are supplied by the middle cerebral artery.
- The posterior cerebral artery supplies the lateral geniculate nucleus and the. occipital cortex
5
Q
Name the lesions of the visual field defects?
A
- Monocular visual loss
- Bitemporal hemianopia
- Homonymous hemianopia
- Homonymous inferior quadrantanopia
- Homonymous superior quadrantanopia
- Homonymous hemianopia with macular sparing
6
Q
Describe an optic nerve lesion?
A
- Impaired vision in one eye
- O/E reduced visual acuity, reduction of colour vision and a central scotoma
- An afferent pupillary defect may be present.
- If lesion is longstanding vision maybe lost in affected eye and optic disc becomes pale.
7
Q
Describe an optic chiasm lesion
A
- Causes bitemporal hemianopia, involving decussating fibres.
- Pressure from a lesion below the chiasm ie a pituitary tumour will cause bitemporal superior quadrantanopia.
- Pressure from above will cause an inferior quadrantanopia
8
Q
Lesions of the optic chiasm include:
A
- Tumours, eg pituitary adenoma, meningioma, craniopharyngioma, or metastatic deposits
- Cerebral aneurysm
- Granulomatous disease, TB, sarcoidosis
9
Q
Optic tract and optic radiation lesions
A
- Cause a contralateral homonymous quadrantanopia.
- Those involving the parietal fibres give an inferior quadrantanopia.
- Those involving the temporal lobe fibres give rise to a superior quadrantanopia
10
Q
Lesions of the optic tract and optic radiation include:
A
- Infarction, such as a lesion of the middle cerebral artery
- Intra cerebral hemorrhage
- Tumours
- Trauma
11
Q
Occipital cortex lesions
A
- Unilateral lesions of the posterior cerebral artery, embolism from vertebrobasilar arterial tree causes a contralateral homonymous hemianopia.
- Bilateral occipital damage gives rise to cortical blindness.
- Visual loss throughout the field in both eyes but preserved pupillary response
- Patient can be unaware of blindness.
12
Q
Differential diagnosis: 1. Temporal pattern 2. Mode of onset 3. Subsequent course Determine if: 1. Transient 2. Persistent
A
Acute Transient Visual Impairment:
- Amaurosis fugax
- Migraine with aura
- Papilloedema
13
Q
What is Amaurosis Fugax
A
- Patient complains of unilateral latitudinal visual loss, shutter coming down. Lasts several seconds followed by recovery.
- Caused by atheroma of ipsilateral carotid artery, causing embolism into central retinal artery and its distal branches.
14
Q
What is migraine with aura?
A
- Visual symptoms - flashing lights, lines etc
- Diagnosis made from history of paroxysmal attacks with headache nausea vomiting.
- Can get focal symptoms eg tingling hands etc
15
Q
What is papilloedma?
A
- Swelling of the optic disc due to raised intracranial pressure.
- Optic nerve covers by meninges, hence covered with subarachnoid fluid.
- Raised intracranial pressure impedes venous drainage and axoplasmic flow.
- O/E visual acuity normal, but blind spot enlarged, restriction of peripheral field of vision.
- Disc is swollen, retinal veins engorged, flame shaped hemorrhages, optic atrophy.
