For this test, patients are asked to look at a grid, and distortions or blank spots in the patients central field of vision can be detected. A positive diagnosis of macular degeneration may account for a patients micropsia.A controlled size comparison task can be employed to evaluate objectively whether a person is experiencing hemimicropsia. For each trial, a pair of horizontally aligned circles is presented on a computer screen, and the person being tested is asked to decide which circle is larger. After a set of trials, the overall pattern of responses should display a normal distance effect where the more similar the two circles, the higher the number of errors. This test is able to effectively diagnose micropsia and confirm which hemisphere is being distorted.Due to the large range of causes that lead to micropsia, diagnosis varies among cases. Computed tomography (CT) and magnetic resonance imaging (MRI) may find lesions and hypodense areas in the temporal and occipital lobes. MRI and CT techniques are able to rule out lesions as the cause for micropsia, but are not sufficient to diagnose the most common causes. Definition
Micropsia is the most common visual distortion, or dysmetropsia. It is categorized as an illusion in the positive phenomena grouping of abnormal visual distortions. Convergence-accommodative micropsia is a physiologic phenomenon in which an object appears smaller as it approaches the subject. Psychogenic micropsia can present itself in individuals with certain psychiatric disorders.
Retinal micropsia is characterized by an increase in the distance between retinal photoreceptors and is associated with decreased visual acuity. Cerebral micropsia is a rare form of micropsia that can arise in children with chronic migraines. Hemimicropsia is a type of cerebral micropsia that occurs within one half of the visual field. Differential diagnosis
Of all of the visual distortions, micropsia has the largest variety of causes. Migraines
Micropsia can occur during the aura phase of a migraine attack, a phase that often precedes the onset of a headache and is commonly characterized by visual disturbances. Micropsia, along with hemianopsia, quadrantopsia, scotoma, phosphene, teicopsia, metamorphopsia, macropsia, teleopsia, diplopia, dischromatopsia, and hallucination disturbances, is a type of aura that occurs immediately before or during the onset of a migraine headache. The symptom usually occurs less than thirty minutes before the migraine headache begins and lasts for five to twenty minutes. Only 10-20% of children with migraine headaches experience auras. Visual auras such as micropsia are most common in children with migraines. Seizures
The most frequent neurological origin of micropsia is a result of temporal lobe seizures. These seizures affect the entire visual field of the patient. More rarely, micropsia can be part of purely visual seizures. This in turn only affects one half of the visual field and is accompanied by other cerebral visual disturbances. The most common cause of seizures which produce perceptual disturbances such as micropsia and macropsia is medial temporal lobe epilepsy in which the seizures originate in the amygdala-hippocampus complex.