Optic nerve Flashcards
Anatomy: Optic nerve Origin
Retinal ganglion cells on internal retinal surface–> nerve fibre layer–> axons converge on the optic disc, nasal to the macula.
Anatomy: Optic nerve course
axons leave the eyeball–> lamina cribrosa sclerae–> posteromedial in the extraocular muscle cone–> leaves orbit–> optic canal–> enters middle cranial fossa
Anatomy: Optic nerve termination
After a short intracranial course, thejoin to form the optic chiasm.
Anatomy: Optic nerve Misnomer
The optic nerve differs from all other cranial and spinal nerves in that it is not a peripheral nerve, but a central nervous system tract. It has no ability to regenerate if it is damaged.
Anatomy: Optic nerve parts
4 Parts: Ocular bulbar part: 1. Optic Disc Retrobulbar part 2. Intraorbital part 3. Intracanucular part 4. Inter cranial part
Anatomy: Optic nerve blood supply
Retrobulbar part:
internal carotid artery- resistant to vascular occlusions.
Optic disc:
short posterior ciliary aa - susceptible to vascular occlusions.
CLINICAL FINDINGS IN OPTIC NERVE DISEASE
Symptoms
Signs
SYMPTOMS
- Loss of vision: Colour, contrast, brightness
- Retrobulbar pain: optic neuritis.
SIGNS
1. VA↓ if nerve fibres from macula
2. VF defect
3. PUPIL
• Sluggish reaction to light
• RAPD
4. DISC APPEARANCE
• Normal: if the process does not involve the disc.
• Swollen: Raised intracranial pressure (↑ICP) and most processes directly involving the disc.
• Pale: Optic atrophy- nerve fibres lost
> optic cup: chronic glaucoma
- OPHTHALMOSCOPY
- Margin: well defined
- Colour of neuroretinal rim: pink-good capillary flow to the nerve fibers.
- cup/disc ratio: if oval takes the vertical diameters, as the cup tends to enlarge mainly vertically. 0.3
- Venous pulsation in central retinal vein: excludes central retinal venous obstruction.
OPTIC DISC SWELLING
Causes: VIICP
Appearance
CAUSES
- Congenital anomalies:
- Hamartoma
- Passive Swelling
- ↑ ICP (Raised Intracranial Pressure)
- Optic nerve compression
- Systemic hypertension
- Inflammatory
- Papillitis
- Vascular
- AION: Anterior Ischaemic Optic Neuropathy
- CRVO (Central Retinal Venous Occlusion)
- Infiltration
- Neoplasia e.g. glioma, lymphoma.
APPEARANCE
- The disc margin is indistinct.
- Cotton wool spots on and around the disc.
- Hard (true) exudates around the disc.
- Disc hyperaemia with dilated capillaries on the disc. 5.Disc and retinal venous congestion
- Nerve fibre layer haemorrhages on and around the disc.
- Loss of central retinal venous pulsation.
- Blood vessels on and around the disc are partly obscured by nerve fiber layer swelling.
EXCEPTIONS TO THE CLASSICAL APPEARANCE
- Congenital malformations cause indistinct disc margin –> without other signs
- AION: Indistinct disc margin but pale disc and not hyperaemic, and there are no cotton wool spots, haemorrhages or hard exudates.
- CRVO: classical appearance except nerve fibre layer haemorrhages are not confined to the peripapillary area, and stretch out into the periphery.
RAISED INTRACRANIAL PRESSURE (↑ICP)
Visual symptoms
Visual signs
VISUAL SYMPTOMS
1. blurred vision each of which lasts for only a few seconds.
VISUAL SIGNS
1. VA and VF normal.
2. Optic disc swelling, bilateral and symmetrical.
Exception:
- Foster-Kennedy syndrome in which ↑ ICP causes unilateral optic disc swelling.
- Intracranial tumour: ↑ ICP
atrophy of ipsilateral optic nn secondary to pressure on the intracranial part of the optic nerve–> dont swell
↑ ICP–> swelling of contralateral otherwise normal optic disc
OPTIC NEURITIS
Definitions Classification Causes AAII Presentation Complications Management Prognosis
DEFINITION
Inflammation of the optic nerve.
CLASSIFICATION
- Papillitis: inflammation of the optic disc.
- Retrobulbar neuritis: inflammation of the retrobulbar part of the optic nerve.
CAUSES
1. AI: Demyelinating diseases: multiple sclerosis is the commonest cause in adults.
2. Systemic infections:
Viral: influenza, measles, mumps, chicken pox, infective mononucleosis. (> Children)
Bacterial: syphilis, tuberculosis.
3. Idiopathic systemic inflammation: Sarcoidosis
4. Adjacent inflammation
Choroidoretinitis
Orbital cellulitis.
CLINICAL PICTURE
SYMPTOMS
1. Sudden Unilateral Visual loss–> improve 2-3 weeks after the onset
2. Retrobulbar pain only in retrobulbar neuritis. Pain is usually aggravated by movement of the eye.
SIGNS
1. ↓VA
2. VF defect: a central scotoma is the commonest
3. Pupil: Sluggish reaction to light RAPD
4. Ophthalmoscopy:
Papillitis: disc swelling
Retrobulbar neuritis: the disc appears normal
MANAGEMENT
There is no specific management if a treatable cause cannot be found.
COMPLICA TIONS
2° optic atrophy and associated permanent loss of vision.
PROGNOSIS
Visual prognosis after a single episode is usually good.
MS: recurrences are common, and increasingly significant irreversible visual loss tends to occur over a period of years.
ANTERIOR ISCHAEMIC OPTIC NEUROPATHY (AION)
Definition
Causes
Presentation Treatment
DEFINITION
Partial or complete infarction of the optic disc due to posterior ciliary arterial occlusion.
CAUSES
- Arteriosclerosis
- Giant cell arteritis
CLINICAL PICTURE
SYMPTOMS
1. Sudden unilateral painless loss of vision in an elderly patient.
2. Visual loss is typically maximal at the onset.
SIGNS
1. VA: Severe loss: perception of light may be absent.
2. VF defect: This depends on the size and position of the area of infarction.
3.Pupil:
(a) Sluggish reaction to light.
(b) RAPD
4. Ophthalmoscopy: Pale swollen disc.
MANAGEMENT
- Giant cell arteritis:
a) systemic steroids may result in recovery of some vision in the affected eye, and may also prevent involvement of the second eye. 2) An urgent ESR or CRP must be obtained, and if very elevated–> high dose systemic steroids should be started immediately and a temporal artery biopsy arranged. - Arteriosclerosis: There is no effective treatment.
PROGNOSIS
There is generally no visual recovery.
OPTIC ATROPHY
Definition
Causes: VITCCM
Presentation
Management
DEFINITION
Optic nerve axonal loss.
CAUSES
- Congenital
- Traumatic
- Inflammatory
- 2° to optic neuritis
- 2° to widespread retinitis resulting in ganglion cell destruction and axonal loss. - Compression
- Tumours of the orbit, optic canal and parasellar area, eg meningioma.
- Aneurysm of the anterior circulus arteriosus.
- Chronic disc swelling from any cause. - Vascular
- CRAO (Central Retinal Arterial Occlusion)
- AION (Anterior Ischaemic Optic Neuropathy)
- Glaucoma
- Diabetes mellitus
- Arteriosclerosis - Metabolic
- Nutritional amblyopia - Toxix
- Methanol
- Ethambutol
CLINICAL PICTURE
SYMPTOMS
Loss of vision is the only symptom.
SIGNS
1. ↓ VA–> Dependent upon both cause and severity.
2. VF defect –> Proportional to the degree of optic atrophy.
3. RAPD –> Proportional to the degree of optic atrophy.
4. Disc pallor –> Proportional to the degree of optic atrophy.
MANAGEMENT
It is seldom possible to treat the underlying cause effectively. Treatable causes include the following:
1. Tumours and aneurysms causing compression of the nerve can be surgically removed.
2. Meticulous IOP control can stop or slow glaucomatous damage, but cannot reverse it.
3. In nutritional amblyopia a balanced diet supplemented with thiamine, folic acid and vitamin B12 almost always completely reverses the amblyopia provided that it is recognised before significant disc damage occurs.
CLINICAL CLUES IN OPTIC NERVE DISEASE
VA Normal: - Congenital malformations - ↑ICP - Systemic hypertension - Chronic glaucoma Decreased: - Vascular events - Inflammation - Infiltration - Compression
VF Normal: - Congenital malformations - ↑ICP - Systemic hypertension Decreased: - Chronic glaucoma - Vascular events - Inflammation - Infiltration - Compression
Other
1. Congenital malformations tend to produce an unclear disc margin but none of the other signs of disc swelling or atrophy.
2. AION produces a pale swollen disc with no haemorrhages, cotton wool spots or hard exudates.
3. CRVO produces nerve fibre layer haemorrhages out into the periphery.
4. Retrobulbar neuritis tends to produce retrobulbar pain on eye movement.
It does not produce disc swelling unless papillitis is also present.
5. A pale flat disc is characteristic of optic atrophy.
A NOTE ABOUT TERMINOLOGY
Papilloedema: optic disc swelling due to ↑ ICP.
Oedema: increase in the amount of ECF.
Disc swelling: Swelling is intracellular due to ischaemic stasis of axonal transport, and the ECF content of the disc remains normal until late.
There are some conditions in which a significant amount of true optic disc oedema does occur, such as CRVO.
