|Site of lesion||Salient features||Common causes|
|• Optic nerve||Ipsilateral blindness, Absent ipsilateral direct light reflex, Absent contralateral consensual light reflex||Optic atrophy, Traumatic avulsion of optic nerve Acute optic neuritis|
|• Saggital (central) lesions of the chiasma||Bitemporal hemianopia||Supra-sellar aneurysms, Pituitary tumours, Craniopharyngioma, Glioma of third ventricle|
|• Lateral chiasmal lesions||Binasal hemianopia||Distention of third ventricle,
– Atheroma of posterior communi-cating arteries
|• Optic tract||– Homonymous heminanopia
– Wernick’s hemianopic pupillary response
|– Syphlitic meningitis
– Tuberculosis and tumours of optic thalamus
– Aneurysms of superior cereb ellar or posterior cerebral arteries
|• Lateral geniculate body||Homonymous hemianopia with sparing of pupillary reflexes||– Syphlitic meningitis
– Tuberculosis and tumours of optic thalamus
|• Optic radiations
– Total fibres
– Lower fibres only
– Upper fibres only
|Homonymous hemianopia (sometimes sparing the macula)
Homonymous upper quadrantinopia (pie-in the sky)
Homonymous lower quadrantinopia (Pie-in the floor)
| – Vascular occlusion,
– Primary and secondary tumours, and
– Anterior parietal lobe lesion
|• Visual cortex||Homonymous hemianopia (usually sparing the macula)||– Vascular occlusion
– Primary and secondary tumour
ABNORMAL PUPILLARY REFLEXES
1. Amaurotic (pupil) light reflex (Total afferent conduction defect): It refers to absence of direct light reflex on the affected side and absence of consensual reflex on the normal side. It indicates blindness due to lesions of the optic nerve or retina. Near reflex is normal and pupils are equal in size in both eyes.
2. Efferent pathway defect: In this situation both direct and consensual light reflexes are absent on the affected side and present on the normal side. Causes of efferent pathway defect include: effect of parasympatholytic drugs like atropine and homatropine, internal ophthalmoplegia and third nerve paralysis.
3. Wernicke’s hemianopic pupil. It is seen in lesions of one optic tract. In this condition ipsilateral direct and contralateral consensual light reflexes are absent when light is thrown on the temporal half of the retina on the affected side and nasal half of the opposite side.
4. Argyll Robertson pupil (ARP): In this condition light reflex is absent while near reflex is present. Both the pupils are small in size, irregular and dilate poorly with mydriatics. It is seen in the lesions of tectum region (neurosyphilis).
5. Tonic pupil (Adie’s pupil): Aunilateral condition in which reaction to light is absent and to near reflex is very slow and tonic. The affected pupil is larger (anisocoria). It may be associated with absent knee jerk and occurs more often in young women (Adie’s syndrome). Adie’s pupil constricts with weak pilocarpine (0.125%) while normal pupil does not. It occurs due to denervation of the postganglionic supply to the musculus sphincter pupillae which may follow a viral infection.
DISEASES OF OPTIC NERVE
• The most common cause is multiple sclerosis.
• The most common field defect in optic neuritis is a relative central or centrocaecal scotoma.
• Earliest sign of optic neuritis is relative afferent pupillary defect (RAPD).
• Leber’s disease is a type of hereditary optic neuritis which primarily affects males around the age of 20 years and is transmitted by female carriers.
• Tobacco-alcohol-amblyopia occuring in heavy smokers and drinkers is characterized by foggy vision associated with bilateral centrocaecal scotomas.
• Methyl alcohol amblyopia results from degeneration of ganglion cells of the retina, due to effect of formic acid and formaldehyde which are metabolic products of methyl alcohol.
• Quinine amblyopia may occur even with small doses in susceptible individuals. Visual loss may be associated with deafness and tinnitus.
• Ethambutol amblyopia may recover completely in most of the cases after immediate cessation of the drug
Anterior ischaemic optic neuropathy (AION)
• Results from the occlusion of short posterior ciliary arteries
• The most common cause is giant cell arteritis
• Characterized by inferior altitudinal hemianopic field defects
Autoimmune optic neuropathy
• Denotes optic nerve involvement in patients with systemic lupus erythematosis (SLE) and other systemic collagen vascular disorders.
• Pathogenesis and features are similar to AION.
• Raised intracranial pressure is the commonest cause of bilateral papilloedema
• Tumour of cerebellum, midbrain and parieto¬occipital region produce papilloedema more rapidly
• Tumour of medulla rarely produce papilloedema
• Foster kennedy syndrome characterized by pressure optic atrophy on the side of lesion and papilloedema on the otherside is a feature of olfactory groove meningioma and frontal lobe tumours.
• Pathogenesis of papilloedema involves stasis of axoplasm in the prelaminar region of the optic disc due to increased tissue pressure within the retrolaminar region.
• Blurring of optic disc margin in papilloedema first of all involves nasal margins, followed by superior and inferior margin and lastly temporal margin.
1. Primary optic atrophy: It results from lesions proximal to the optic disc without antecedent papilloedema. Its common causes are multiple sclerosis, idiopathic retrobulbar neuritis, Leber’s and other hereditary optic atrophy, pituitary tumours, toxic amblyopia and trauma to the optic nerve.
Ophthalmoscopically, disc is greyish white in colour, margins are well defined, lamina cribrosa is visible, retinal vessels and surrounding retina are normal.
2. Consecutive optic atrophy: It occurs following destruction of the ganglion cells secondary to degenerative or inflammatory lesions of the choroid and retina. Its common causes are retinitis pigmentosa, diffuse chorioretinitis, pathological myopia and occlusion of central retinal artery. Its ophthalmoscopic features include: yellow waxy colour, not so sharply defined margins and attenuation of vessels.
3. Postneuritic optic atrophy: It develops as a sequel to longstanding papilloedema or papillitis.
The disc looks dirty white in colour, its edges are blurred, physiological cup is obliterated, lamina cribrosa is not visible, vessels are attenuated and perivascular sheathing is often present.
4. Glaucomatous optic atrophy: It results due to the effect of raised intraocular pressure. It is characterised by deep and wide cupping of the optic disc and nasal shift of the vessels.
5. Vascular (ischaemic) optic atrophy: It results from the conditions producing disc ischaemia (other than glaucoma) such as: central retinal artery’ occlusion, giant cell arteritis, severe haemorrhage, severe anaemia and quinine poisoning. Its ophthalmoscopic features are pallor associated with marked vascular attenuation.
• Pallor of the disc in optic atrophy is not due to atrophy of the nerve fibres but due to loss of vascularity.
• Pallor of the disc can not be correlated with the amount of visual loss.
SYMPTOMATIC DISTURBANCES OF THE VISION
Night blindness (Nyctalopia)
Its common causes are: vitamin A deficiency, tapetoretinal degenerations (e.g., retinitis pigmentosa), congenital high myopia, and Oguchi’s disease.
Day blindness (Hamarlopia)
Its causes are central corneal and central lenticular opacities and congenital deficiency of cones.
(a) Congenital colour blindness: It is an inherited condition affecting males more (3-4%) than females (0.4%). It may be of following types:
(i) Anomalous trichromatic colour viston : In this one of the primary colour i.e., red, green or blue
is defective and the condition is called protanomalous, deuteranomalous or tritanomalous respectively.
(ii) Dichromatic colour vision: Here faculty to percieve one of the three primary colours viz. red, green or blue is completely absent and the condition is called protanopia, deuteranopia or tritanopia respectively.
(iii) Monochromatic colour vision: Here only one primary colour can be appreciated. It is very rare condition.
(iv) Achromatic vision: It refers to total colour blindness. It is an extremely rare condition occurring due to congenital absence of the cones. Therefore, it is associated with day blindness and nystagmus.
(b) Acquired colourblindness: It may follow damage to macula or optic nerve, where red, green discrimination is particularly affected. Acquired blue colour defect may occur in old age due to increased sclerosis of the crystalline lens.
A complete loss of sight in one or both eyes, in the absence of ophthalmoscopic or other marked objective signs.
Amaurosis fugax: A sudden, temporary (lasting 2-5 minutes) and painless monocular visual loss occurring due to a transient failure of retinal circulation.
• Carotid transient ischaemic attacks (TIA)
• Embolization of retinal circulation
• Giant cell arteritis
• Raynaud’s disease
• Prodromal symptom of central retinal artery or carotid artery occlusion
• Hypertensive retinopathy
• Venous stasis retinopathy
• Suprageniculate lesions of visual pathway usually produce visual field defects with macular sparing.
• Optic nerve lesions produce negative scotomas whereas macular lesions cause positive scotoma.
• The chromophobe adenoma is the most common primary intracranial tumour producing neuroophthalmological features.
• Gaze evoked amaurosis is seen in optic nerve sheath meningioma.
• Horner’s syndrome (lack of sympathetic innervation) is characterized by miosis, mild ptosis, mild enophthalmos and anhydrosis of the face on the affected side. Tests to confirm diagnosis of Horner’s syndrome are: dilation lag, and cocaine test (normal pupil dilates while Horner’s pupil does not dilate with topical cocaine).
• The swelling of the optic disc in papillitis rarely exceeds 2-3D.
• Scintilating scotoma is a feature of migraine.
• Unilateral central scotoma is the earliest symptom of compression of optic nerve.
• Hippus (alternate rhythmatic dilation and constriction of pupils) is a feature of multiple sclerosis.
• Erythropsia (red coloured vision) may be experienced by some patients after cataract extraction.
• Pupil sparing, third nerve paralysis suggests a medical cause (diabetes or hypertension). While in surgical causes (aneurysm, tumour) pupil is also invovled.
• The two most common ocular signs of myasthenia gravis are ptosis and extraocular muscle weakness (paralytic squint).
• Neuromyelitis optica (Devic’s disease) may be associated with sudden bilateral blindness.