Micropsia

Micropsia is a rare visual perception disorder in which patients perceive objects or the outside world smaller than it actually is (reduction in the perceived size of a form) ¹. Micropsia is often transient and is usually only present for several hours or days post-stroke (e.g., temporo-parietal infarction) ². In rare occasions, micropsia symptoms can last longer ¹.

Micropsia is the most common form of metamorphopsia ³. Objects can be perceived smaller in one hemifield only ⁴, but it is more common that both visual fields are equally affected ¹.

Micropsia is the most common visual distortion, or metamorphopsia. Metamorphopsia is a syndrome in which the shape of objects appears distorted. It can be permanent, affect parts of the visual field, and may have a retinal, cortical, or even subcortical origin. In some instances, however, metamorphopsia may be restricted to faces, either permanently or transiently when associated with epilepsy.

• Convergence-accommodative micropsia is a physiologic phenomenon in which an object appears smaller as it approaches the subject ⁵
• Psychogenic micropsia can present itself in individuals with certain psychiatric disorders ⁵
• Retinal micropsia is characterized by an increase in the distance between retinal photoreceptors and is associated with decreased visual acuity ⁵
• Cerebral micropsia is a rare form of micropsia that can arise in children with chronic migraines ⁵
• Hemimicropsia is a type of cerebral micropsia ⁶ that occurs within one half of the visual field ⁷.

Micropsia causes

Micropsia can be caused by optical factors (such as wearing glasses), by distortion of images in the eye (such as optically, via swelling of the cornea or from changes in the shape of the retina such as from retinal edema, macular degeneration, or central serous retinopathy), by changes in the brain (such as from traumatic brain injury, stroke, epilepsy, migraines, prescription drugs, and illicit drugs), and from psychological factors. Dissociative phenomena are linked with micropsia, which may be the result of brain-lateralization disturbance ⁸.

Micropsia is also commonly reported when the eyes are fixating at (convergence), or focussing at (accommodation), a distance closer than that of the object. Specific types of micropsia include hemimicropsia, a form of micropsia that is localized to one half of the visual field and can be caused by brain lesions in one of the cerebral hemispheres.

Micropsia potential causes:

• Stroke: Damage to the occipito-temporo-parietal brain region has been found to be related to micropsia ⁹. More specifically, a lesion affecting Brodmann area (BA) 19 has been found to cause hemimicropsia ⁴. However, details about the lesion localization in cases of whole-field micropsia remain unclear ¹⁰.
• 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 ¹¹. 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. Micropsia often occurs as an aura signalling a seizure in patients with medial temporal lobe epilepsy ¹². Most auras last for a very short period, ranging from a few seconds to a few minutes ¹³.
• Drug use: Micropsia can result from the action of mescaline and other hallucinogenic drugs ¹⁴. Although drug-induced changes in perception usually subside as the chemical leaves the body, long-term cocaine use can result in the chronic residual effect of micropsia ¹⁵. Micropsia can be a symptom of Hallucinogen Persisting Perception Disorder, in which a person can experience hallucinogenic flashbacks long after ingesting a hallucinogen. A majority of these flashbacks are visual distortions which include micropsia, and 15-80% of hallucinogen users may experience these flashbacks ¹⁶. Micropsia can also be a rare side effect of zolpidem, a prescription medication used to temporarily treat insomnia ¹⁷.
• Psychological factors: Psychiatric patients may experience micropsia in an attempt to distance themselves from situations involving conflict ¹⁸. Micropsia may also be a symptom of psychological conditions in which patients visualize people as small objects as a way to control others in response to their insecurities and feelings of weakness. In some adults who experienced loneliness as children, micropsia may arise as a mirror of prior feelings of separation from people and objects ¹⁹.
• Alice in Wonderland syndrome: Alice in Wonderland syndrome, named for Lewis Carroll’s titular character, is a disorder characterized by transient episodes of visual hallucinations and perceptual distortions, during which objects or body parts are perceived as altered in various ways (metamorphopsia), including enlargement (macropsia) or reduction (micropsia) in the perceived size of a form ²⁰. Such episodes are of short duration (generally less than an hour), variable frequency (up to several times per day), and unpredictable onset ²¹. Several studies have assessed the neurological underpinnings of the visual distortions of acute-stage Alice in Wonderland syndrome (ie, while individuals were experiencing frequent periods of visual distortion) but none during actual episodes of visual hallucinations. No frank structural brain abnormalities have been linked to viral-onset Alice in Wonderland syndrome, based on studies using both computed-tomography (CT) and magnetic resonance imaging (MRI) scans ²². Findings from psychophysiological studies of micropsia following viral infection appear consistent with dysfunction in posterior visual cortical regions, although findings are mixed. Across three studies, 6 of 13 people with Alice in Wonderland syndrome were found to have abnormal electroencephalogram (EEG) patterns over parieto-occipital and occipital electrode sites ²⁰. Other reports failed to find abnormal EEG in individuals with the disorder (in five of five cases) ²⁰. Abnormal visual evoked potentials (VEP) recorded in response to a reversing black and white checkerboard have been reported in children with Alice in Wonderland syndrome ²¹. Blood perfusion of brain tissue using single-photon emission computed tomography (SPECT) has been reported for 9 cases of Alice in Wonderland syndrome, providing a mixed picture of the disorder ²². While normal perfusion was reported in one case, the other eight showed a varied pattern of hypoperfusion (abnormally low cerebral blood flow) across distinct neural regions. One case demonstrated right hemisphere occipital hypoperfusion, with two additional cases demonstrating bilateral occipital hypoperfusion ²³. Hypoperfusion in the right parietal cortex was reported for five cases, whereas left parietal hypoperfusion was not found in any of the nine cases ²⁴.
• Epstein-Barr virus infection: Micropsia can be caused by swelling of the cornea due to infection by the Epstein-Barr virus (EBV) ²⁵ and can therefore present as an initial symptom of EBV mononucleosis, a disease caused by Epstein-Barr virus infection.
• Retinal edema: Micropsia can result from retinal edema causing a dislocation of the receptor cells. Photoreceptor misalignment seems to occur following the surgical re-attachment for macula-off rhegmatogenous retinal detachment. After surgery, patients may experience micropsia as a result of larger photoreceptor separation ²⁶ by edematous fluid ²⁷.
• Macular degeneration: Macular degeneration typically produces micropsia due to the swelling or bulging of the macula, an oval-shaped yellow spot near the center of the retina in the human eye. The main factors leading to this disease are age, smoking, heredity, and obesity.
• Central serous chorioretinopathy: Central serous chorioretinopathy is a disease in which a serous detachment of the neurosensory retina occurs over an area of leakage from the choriocapillaris through the retinal pigment epithelium (RPE). The most common symptoms that result from the disease are a deterioration of visual acuity and micropsia.

There is still controversy about the theories explaining micropsia. It has been put forward that micropsia is caused by a disturbance in the underlying mechanism responsible for size-constancy ⁴. The principle of size constancy entails the perception of an object as being equally large, irrespective of the viewing distance. If this underlying mechanism would be disturbed in patients with micropsia, scientists would expect them to perceive objects smaller at greater viewing distances. However, Ceriani et al. ¹ did not find support for this hypothesis in their study. Their patient with micropsia perceived objects smaller than they were in reality, regardless of the viewing distance. This indicates that it is more likely to be a higher-order processing problem, especially when both hemifields are affected ²⁸. Ceriani et al. ¹ explained the micropsia in their patient with another theory of Bender and Teuber ²⁹, in which it was suggested that the unilateral brain damage causes a conflict in what is perceived by the damaged right hemisphere versus what is perceived by the intact left hemisphere. This misbalance or rivalry in the visual perceptual network somehow causes a “micropsic bias” ¹. However, details about the underlying mechanism for this bias remain unknown. Thus, much is still unknown and a thorough examination of cases with micropsia is needed ¹⁰.

Micropsia symptoms

Micropsia causes affected individuals to perceive objects as being smaller or more distant than they actually are ¹.

The majority of individuals with micropsia are aware that their perceptions do not mimic reality. Many can imagine the actual sizes of objects and distances between objects. It is common for patients suffering from micropsia to be able to indicate true size and distance despite their inability to perceive objects as they actually are. One specific patient was able to indicate the dimensions of specific objects with her hands. She was also able to estimate the distances between two objects and between an object and herself. She succeeded in indicating horizontal, vertical, and 45 degree positions and did not find it difficult to search for an object in a cluttered drawer, indicating that her figure-ground discrimination was intact despite suffering from micropsia ¹.

Individuals experiencing hemimicropsia often complain that objects in their left or right visual field appear to be shrunken or compressed. They may also have difficulty appreciating the symmetry of pictures. When drawing, patients often have a tendency to compensate for their perceptual asymmetry by drawing the left or right half of objects slightly larger than the other. In a case of one person with hemimicropsia asked to draw six symmetrical objects, the size of the picture on the left half was on average 16% larger than the corresponding right half ¹⁴.

Micropsia diagnosis

EEG testing can diagnose patients with medial temporal lobe epilepsy. Epileptiform abnormalities including spikes and sharp waves in the medial temporal lobe of the brain can diagnose this condition, which can in turn be the cause of an epileptic patient’s micropsia.

The Amsler grid test can be used to diagnose macular degeneration. For this test, patients are asked to look at a grid, and distortions or blank spots in the patient’s central field of vision can be detected. A positive diagnosis of macular degeneration may account for a patient’s micropsia ³⁰.

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 ¹⁴.

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 ¹⁴. 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.

Micropsia treatment

Micropsia treatment depends on the diagnosis and treating the underlying cause.

Treatments may involve the occlusion of one eye and the use of a prism fitted over an eyeglass lens have both been shown to provide relief from micropsia in a presumed ocular myasthenia gravis ³¹.

Micropsia that is induced by macular degeneration can be treated in several ways. A study called AREDS (age-related eye disease study) determined that taking dietary supplements containing high-dose antioxidants and mineral supplementation has been shown to reduce the risk of progression in age-related macular degeneration (ARMD) ³².

The daily amounts of antioxidants and zinc in the AREDS formulation is ³³:

• 500 milligrams of vitamin C
• 400 International Units of vitamin E
• 15 milligrams of beta-carotene (equivalent of 25,000 International Units of vitamin A)
• 80 milligrams of zinc as zinc oxide
• 2 milligrams of copper as cupric oxide

Since, high dose zinc supplementation can lead to a copper-deficiency anemia by inhibiting copper absorption at the level of the enterocyte, copper supplementation was added to the AREDS formula ³³. Cigarette smokers should be warned about the small, but real potential risk of lung cancer with high dose beta-carotene supplementation in the AREDS formula. Non-beta-carotene-containing supplements are more appropriate for this subgroup of patients ³⁴.

Based on data suggesting that increasing intake of lutein + zeaxanthin, and omega-3 long-chain polyunsaturated fatty acids (docosahexaenoic acid [DHA] + eicosapentaenoic acid [EPA]) might reduce the risk of developing advanced AMD, AREDS2, a randomized, double-masked control trial was started. AREDS2 was designed to test whether adding lutein + zeaxanthin, DHA + EPA, or lutein + zeaxanthin + DHA + EPA to the AREDS formulation further reduces the risk of progression to advanced age-related macular degeneration. Another goal of AREDS was to test the effects of eliminating beta carotene and reducing the zinc dose from the AREDS formulation. The following are the modifications of AREDS2:

• 10 mg lutein and 2 mg zeaxanthin
• 350 mg DHA and 650 mg EPA
• No beta-carotene
• 25 mg zinc

In AREDS2, lutein/zeaxanthin or DHA/EPA had no additional effect on the risk of advanced age-related macular degeneration. Study participants who took AREDS containing lutein/zeaxanthin and no beta-carotene had a slight reduction in the risk of advanced age-related macular degeneration, compared to those who took AREDS with beta-carotene and no lutein/zeaxanthin. Importantly, former smokers who took AREDS with beta-carotene had a higher incidence of lung cancer. Lower zinc oxide doses (25mg) did not significantly increase the risk of advanced age-related macular degeneration, although a trend to more protection from advanced age-related macular degeneration was noted with higher zinc oxide doses (80mg). Newer formulations replace beta-carotene with lutein/zeaxanthin, but keep the zinc oxide dose the same.

• 500 milligrams of vitamin C
• 400 International Units of vitamin E
• 80 milligrams of zinc as zinc oxide
• 2 milligrams of copper as cupric oxide
• 10 mg lutein and 2 mg zeaxanthin
• No beta-carotene.

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