Visual hallucinations are common in migraine when the occipital lobe is involved; also in epilepsy when the seizure source lies here.
Hallucinations of occipital origin are elementary - unformed - appearing as patterns (zigzags, flashes) and fill the hemianopic field, whereas hallucinations of temporal lobe origin are formed, complex and fill the whole of the visual field.
Visual illusions also may occur as a consequence of occipital lobe disease. Objects appear smaller (MICROPSIA) or larger (MACROPSIA) than reality. Distortion of a shape may occur or disappearance of colour from vision.
These illusions are more common with non-dominant occipital lobe disease.
Prosopagnosia: the patient, though able to see a familiar face, e.g. a member of the family, cannot name it. This is usually associated with other disturbances of 'interpretation' and naming with intact vision such as colour agnosia (recognition of colours and matching of pairs of colours). Bilateral lesions at occipito-temporal junction are responsible.
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