Metamorphopsia is an illusory visual phenomenon characterized by objects appearing distorted or misshapen in form. As with neglect, these phenomena may be classified as objector person-centered:
- Object-centered: affecting size and spatial relationships Macropsia: objects appear larger than normal
Micropsia: objects appear smaller than normal
Pelopsia: objects appear closer to the observer than actual Porropsia: objects appear farther away from the observer than actual
- Person centered:
Microand macrosomatognosia: body image appears smaller or larger than normal ("Alice in Wonderland" syndrome).
Metamorphopsias are often transient and episodic, occurring for example during migraine attacks, epileptic seizures, with psychotropic drug abuse, and following petechial intraparenchymal hemorrhages. Rarely, they are long-lasting or permanent, for example following brain infarction (most commonly involving the occipito-parietal or temporo-parietal cortex: lesions on the right are more likely than those on the left to give metamorphopsia) or tumors. Retinal disease causing displacement of photoreceptors may produce metamorphopsia: micropsia due to receptor separation in retinal edema, macropsia due to receptor approximation in retinal scarring. Occasional cases of metamorphopsia have been reported with lesions of the optic chiasm, optic radiation, and retrosplenial region. Indeed, it seems that metamorphopsia may occur with pathology at any point along the visual pathway from retina to cortex. Differing patterns of metamorphopsia may assist with clinico-anatomical correlation:
- retinal lesions: ipsilateral monocular
- chiasmal lesions: bitemporal
- occipitoparietal lesions: contralateral homonymous Metamorphopsia may be associated with visual hallucinations.
Shiga K, Makino M, Ueda Y, Nakajima K. Metamorphopsia and visual hallucinations restricted to the right visual hemifield after a left putaminal hemorrhage. Journal of Neurology, Neurosurgery andPsychiatry 1996; 61: 420-421