THE VISUAL PATHWAY AND STATE SOME OF THE COMMON VISUAL DEFECTS

 The visual pathway is the rout by which retina stimuli are transferred to the occipital cortex of the brain. It encompasses the retina, optic nerve, optic chiasm, optic radiations and optic visual centre of the occipital lobe.

Understanding the anatomy of optic nerve and visual pathway is the key to appreciating how various focal lesion of the brain cause visual defect.

 

Here are the common visual defects:

-          Optic nerve lesion tend to cause ipsilateral monocular blindness.

-          At the optic chiasm, fibres from the nasal half of the retina corresponding the temporal visual field descussate lesions compressing the chiasm such as pituitary adenonias, therefore cause bitemporal hemianopia.

-          Lsion to the optic radiations result in contralateral quadrantanopia. These affecting Meyers loop result in upper quadrantinopia.

Lesions affecting the calcarine salcus of the occipital lobe tend to cause homonymous hemianopia with sparing of the macula.