User:CharlesWCII/Micropsia

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An illustration depicting the symptoms of micropsia from Lewis Carrol's 1865 novel Alice's Adventures in Wonderland.

CharlesWCII/Micropsia

Micropsia is a neurological condition affecting human visual perception in which objects are perceived to be smaller than they actually are by a subject. Micropsia can be caused by optical distortion of the image in the eye, or because of glasses, but it is most often the result of a neurological dysfunction in people with normal eyes. The condition has a large range of causes, including traumatic brain injury, swelling of the cornea (often caused by the Epstein-Barr virus), epilepsy, prescription and illicit drug use, and migraines. Micropsia is related to other conditions dealing with visual perception including Alice in Wonderland Syndrome, the Epstein-Barr virus, and macropsia, a similar, less common condition with the opposite effect. It is often presented as an initial symptom of mononucleosis. The neurological causes of micropsia include migraines and rarely complex partial epilepsy. 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. Ocular conditions can also result in micropsia. Dissociative phenomena are linked with micropsia, which may be the result of brain lateralization disturbance. Hemimicropsia is a form of micropsia that is localized to one hemisphere of the brain and can be caused by brain lesions.

Signs and symptoms

Micropsia causes sufferers to perceive objects as being smaller or more distant than they are in reality. The condition is a frequent symptom of Alice in Wonderland syndrome and is often referred to as "Lilliput sight," in reference to the small people found on the island of Lilliput in the novel Gulliver’s Travels.

Most sufferers of 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.

Patients who suffer from hemimicropsia often complain that objects in their left or right visual field appear to be shrunken or compressed. Patients 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 the case of one patient 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.

Causes

The causes of Micropsia are varied and include retinal edema, lesions, seizures, macular degeneration, and hallucinogenic drug use.

Micropsia is sometimes seen in patients with brain infarctions. The damaged side of the brain conveys size information that contradicts the size information conveyed by the other side of the brain. This causes a contradiction to arise between the true perception of an object's size and the smaller perception of the object, and micropsic bias ultimately causes the patient to suffer from micropsia.

Micropsia is prevalent among children, specifically between the ages of 5 and 10, and is often caused by the onset of migraines. Micropsia can occur during the aura phase of a migraine attack. 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 migraine sufferers.

Micropsia can result from retinal edema causing a dislocation of the receptor cells. Lesions affecting other parts of the extracerebral visual pathways can also cause micropsia. 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. Apart from epileptic phenomena, micropsia can also result from migraines, or from the action of mescaline and other hallucinogenic drugs.

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. Some studies show that consuming spinach or collard greens five times a week cuts the risk of macular degeneration by 43%.

Diagnosis

Due to the large range of causes that lead to micropsia diagnosis varies from patient to patient. Computed tomography (CT) and Magnetic Resonance Imaging (MRI) visual imaging techniques are employed to find lesions and hypodense ares in the temporal and occipital lobes. These techniques aid in both the determination of the cause of the patient's micropsia and also whether the symptoms will be chronic or not.

A patient suffering from hemimicropsia was evaluated objectively with a controlled size comparison task. For each trial, a pair of horizontally aligned circles was presented on a computer screen, and the patient had to decide which circle was larger. After the first set of trials, the overall pattern of responses displayed a normal distance effect: the more similar the two circles, the higher the number of errors. This test was able to effectively diagnose the patient's micropsia and confirm that only the patient's right hemisphere was distorted.

Treatment

Treatment varies for micropsia due to the large number of different causes for the condition. Most frequently, episodes of micropsia go away with time, however, in the rarer case, micropsia may be chronic.

In patients whose micropsia is associated with migraines, medication used to control migraines often shortens the duration of micropsia.

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 zinc produced significant benefits with regard to disease progression. (This study was the first ever to prove that dietary supplements can alter the natural progression and complications of a disease state.) Laser treatments also look promising but are still in clinical stages.

History and culture

Alice in Wonderland Syndrome, a neurological condition associated with both micropsia and macropsia, is named after Lewis Carroll's famous 19th century novel Alice's Adventures in Wonderland. In the story, the title character, Alice, experiences numerous situations similar to those of micropsia and macropsia. Speculation has arisen that Carroll may have written the story using his own direct experience with episodes of micropsia resulting from the numerous migraines he was known to suffer from. It has also been suggested that Carroll may have suffered from temporal lobe epilepsy.

Micropsia has also been related to Jonathan Swift's novel Gulliver's Travels. It has been referred to as "Lilliput sight" and "Lilliputian hallucination," a term coined by British physician Raoul Leroy in 1909, based on the small people that inhabited the island of Lilliput in the novel.

Current and future research

Current experimental evidence focuses on the involvement of the occipitotemporal pathway in both the perceptual equivalence of objects across translations of retinal position and also across size modifications. Recent evidence points to this pathway as a mediator for an individual's perception of size. Even further, numerous cases suggest that size perception may be dissociated from other aspects of visual perception such as color and movement. However, more research is called for to correctly relate the condition to defined physiological conditions.

Current research is being done on macular degeneration which could help prevent cases of micropsia. A variety of drugs that block vascular endothelial growth factor (VEGF) are being evaluated as a treatment option. These treatments for the first time have produced actual improvements in vision, rather than simply delaying or arresting the continued loss of vision characteristic of macular degeneration. A number of surgical treatments are also being investigated for macular degeneration lesions that may not qualify for laser treatment, including macular translocation to a healthier area of the eye, displacement of submacular blood using gas, and removing membranes by surgery.

Famous Sufferers

• Lewis Carroll

See also

• Alice in Wonderland syndrome
• Convergence micropsia
• Diplopia
• Dysmetropsia
• Hemianopsia
• Macropsia
• Metamorphopsia
• Phosphene
• Scotoma

External links

• What is Micropsia?
• Word a Day: Micropsia
• Medical Dictionary: Micropsia
• Web-Md: Migraines in Children
• KnowledgeRush: Micropsia
• Top 10: Weirdest Diseases You've Never Heard Of