VISUAL PATHWAY

Dr.S.SoundariConsultant Ophthalmologist

Dr Agarwal’s Eye HospitalChennai

Optic nerve is an outgrowth of the brain

Its fibers posses no neurolemmal cells

Surrounded by meninges unlike any peripheral nerves

Both the primary and second order neurons are in the retina.

VISUAL PATHWAY

Optic nerve

Intraocular part

Intraorbital part

Intracanalicular part

Intracranial part

OPTIC NERVE LESION &

FIELD DEFECTS

Optic nerve field defects

Central scotoma

Enlargement of blind spot

Arcuate field defects

Altitudinal field defects

Paillomacular bundle

Macular fibres enter the temporal aspect of the disc. Defect can lead to

Central scotoma

Centrocecal scotoma

Paracentral scotoma

Causes for central scotoma

Demylineation[retrobulbar neuritis]

Leber’s hereditary optic neuropathy

Toxins- tobacco,lead,alcohol,methanol

Vitamin B12 deficiency

Enlargement of blind spot

Altitudinal field defect

Ischaemic optic neuropathy

Branch retinal artery occlusion

Inferior retinal coloboma

CHIASMAL LESION &

FIELD DEFECTS

Chiasma

Lower nasal fibres cross low and anteriorly

Upper nasal fibres cross high and posteriorly

Macular fibres also cross in the posterior part of the chiasm.

Location of chiasma

Central fixation -80%- above the sella

Pre fixed chiasm-10%-located anteriorly-

so pitutary tumour involves the optic tract first [lower temporal fields first]

Post fixed chiasm-10%-located posteriorly- so optic nerve gets involved first[upper temporal fields first]

Pitutary adenoma

Visual fields ; bitemporal hemianopia,junctional scotoma,

bitemporal hemianopic scotomaColour vision; early red deficitVisual acuity tends to reduceOptic disc- bow tie atrophy rarely papilloedemaExtraocular movements: cranial nerve palsies,see saw nystagmus,spasm nutans.

hemifield slip- due to the failure of controlling phoria by fusion.

Post fixation blindness.

Pseudo bitemporal hemianopia

Bilateral sectoral retinitis pigmentosa

Tilted disc

Bilateral inferotemporal retinoschsis.

OPTIC TRACT LESIONS &

ITS FIELD DEFECTS

OPTIC TRACT

Carries ipsilateral temporal fibres and controlateral nasal fibres and pupillary fibres.

So right optic tract lesion will cause left homonymous hemianopia

ASSOCIATIONS

Controlateral pyramidal signs.

Incongruous homonymous hemianopia.

Wernicke's hemianopic pupil

Optic atrophy

OPTIC RADIATION AND ITS FIELD DEFECTS

OPTIC RADIATIONS

The corresponding retinal elements lie progressively closer, so congruous hemianopia.

Passes through the temporal lobe and pareital lobe and ends in the visual cortex.

TEMPORAL LOBE

Controlateral congruous homonymous superior quadrantanopia[pie in the sky]

Controlateral hemisensory disturbance

Mild hemiparesis

Paraxysomal olfactory and uncinate fits.

Formed visual hallucinations

Seizures and receptive dysphasia.

Pie in the sky

PAREITAL LOBE

Controlateral congruous homonymous inferior quadrantanopia[pie on the floor]

Visual perception difficulties

Right-left confusion

Acalculia

Assymmetric OKN.[OKN response diminished towards the side of the lesion.]

Pie on the floor

Striate calcarine cortex

Congruous homonymous hemianopias with macular sparing, macular involvement alone.

Formed visual hallucinations.

Anton's syndrome[ denial of blindness]

Riddoch phenomenon

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