OPTIC PATHWAY LESIONS

OPTIC PATHWAY LESIONS:

Before the Optic chiasm - The visual field loss is seen on the same (ipsilateral) side as the lesion.

Fig 1 – lesion of right optic nerve gives a Right Monocular loss - Can be caused by – trauma, Multiple sclerosis

Fig 2 – lesion at optic chiasm – Can be caused by a pituitary tumour, craniopharyngioma, suprasellar meningioma

 

After the optic chiasm - The visual loss is seen on the opposite (contralateral) side of the lesion because the optic nerves have already crossed over at the optic chiasm.

 

Fig 3 - lesion at the right optic tract gives a left homonymous hemianopia. Can be caused by vascular disease, head injury, cerebral tumour.

Each eye has a left and a right visual field. In a left homonymous hemianopia the left visual field of both the right eye and left eye is lost but the lesion is of the right optic tract.

 

Fig 4 - lesion at the left optic radiation gives a right upper homonymous quadrantanopia. Can be caused by stroke, Space occupying lesions

Each eye has a left and right visual field. In a right upper homonymous quadrantanopia the right visual field ofboth the right eye and left eye is lost.  The lesion is of the left temporal radiation (remember that Temporal produces a Top quadrantanopia).

Fig 5 - lesion of the parietal radiation will result in a lower homonymous quadrantanopia.

 

Fig 6 – Lesion at the right occipital lobe/pole. Gives a left homonymous hemianopia with macular/ central vision sparring. Can be caused by stroke in posterior circulation

 

Quick Summary Table

Defect	Location
Loss of vision in one eye	Ipsilateral Optic Nerve
Bitemporal Hemianopia	Optic chiasm
Binasal hemianopia	Optic chiasm
Left homonymous hemianopia	Right optic tract / radiation
Right homonymous hemianopia	Left optic tract / radiation
Homonymous quadrantopia	Contralateral optic radiation Upper – temporal region Lower – parietal region
Scotoma	Occipital region