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Introduction
Macropsia (also known as megalopia) is a neurological condition affecting human visual perception, in which objects appear larger than normal, and the subject smaller. Macropsia, along with its opposite condition, micropsia, and can be categorized under dysmetropsia. Macropsia is related to other conditions dealing with visual perception, such as aniseikonia and Alice in Wonerland syndrome (AIWS, also known as Todd’s syndrome). Macropsia has a large range of causes, from prescription and illicit drugs, to migraines and (rarely) complex partial epilepsy, to different retinal conditions, such as epiretinal membrane. Physiologically, macropsia results from the compression of cones in the eye. It is the compression of receptor distribution that results in greater stimulation and thus a larger perceived image of an object.

Symptomology
The most obvious symptom of macropsia is the presence of exceptionally enlarged objects throughout the visual field. For example, a young girl might see her sister’s books the same size as she sees her sister. Stemming from this symptom, someone with macropsia may feel undersized in relation to his or her surrounding environment. Patients with macropsia have also noted the cessation of auditory function prior to the onset of visual hallucination, indicating possible seizure either before or after the hallucination. A buzzing sound in the ears has also been reported immediately before macropsia development. Some patients claim that symptoms may be eased if an attempt is made to physically touch the object which appears enormous in size. It is important to note, however, that patients typically remain lucid and alert throughout episodes, being able to recount specific details. A person with macropsia may have no psychiatric conditions. Symptoms caused chemically by drugs such as cannabis, magic mushrooms, or cocaine tend to dissipate after the chemical compound has been excreted from the body. Those who acquire macropsia as a symptom of a virus usually experience complete recovery and restoration of normal vision.

Dysmetropsia in one eye, a case of aniseikonia, can present with symptoms such as headaches, asthenopia, reading difficulties, depth perception problems, or double vision. The visual distortion can cause uncorrelated images to stimulate corresponding retinal regions simultaneously impairing fusion of the images. Without suppression of one of the images symptoms from mild poor stereopsis, binocular diplopia and intolerable rivalry can occur.

Psychological effects
There are a broad range of psychological and emotional effects that the macropsia patient may experience. It has even been stated that macropsia may be an entirely psychological pathological phenomenon without any structural defect or definite cause. He or she may be in an irritable or angry state, or in contrast, a euphoric state. There is evidence that those who experience Alice in Wonderland Syndrome and associated macropsia are able to recount their experiences with thorough detail. There may be no evidence of psychiatric disturbance and, as a result, no psychiatric therapy may be required. Psychological conditions are often caused by macropsia, but do not cause macropsia. Those afflicted may additionally experience extreme anxiety both during and after episodes as a result of the overwhelming nature of his or her distorted visual field. Due to the fear and anxiety associated with the condition, those who previously suffered hesitate to recount the episodes, although retain the ability to do so. Psychologically, a person with macropsia may have feel separation and dissociation from the outside world and even from immediate family. This feeling of dissociation has mostly been noted in child or adolescent patients. The patient may feel that he or she must unfairly contend with hostile and aggressive forces due to the gigantic nature of the surrounding environment. The defense against said forces is usually expressed verbally. The patient may falsely present an outgoing or flamboyant persona, while remaining fearful of people internally. He or she, in an attempt to balance the size distortion, may try to make others feel small in size through insult or hostile behavior. The psychological impact of macropsia on long time sufferers who have had the condition since childhood may be greater and lead to severe ego-deficiencies .It has additionally been proposed that macropsia is a response to biophysiological contraction and has no psychological roots. Thus, when a patient reaches for an enlarged object, he or she is overcoming that physiological contraction. This theory, however, has rarely been proposed.

Prescription Drugs
The most prevalent research on prescription drugs with side affects of macropsia deals with zolpidem and citalopram. Zolpidem is a drug prescribed for insomnia, and although it has proven beneficial effects, there have been numerous reported cases of adverse perceptual reactions. One of these cases discusses an anorexic woman’s episode of macropsia, which occurred twenty minutes after taking 10 mg zolpidem. The same woman later had two more episodes of zolpidem-induced macropsia, after taking 5 mg and 2.5 mg zolpidem, respective to each episode. The intensity of the macropsia episodes decreased with the decreasing amount of zolpidem administered. Hoyler points out notable similarities among the different reported cases of zolpidem-induced disorganization. All the cases were reported by women, the disorganization and agitation followed the first administration of zolpidem, and once zolpidem was discontinued, there were no lasting residual effects. .

Citalopram-induced macropsia is similar to zolpidem-induced macropsia since both types have been observed in relatively few cases, and neither of the drugs’ side effects can be supported by experimental evidence. Citalopram is an antidepressant that inhibits serotonin reuptake. The first case of macropsia thought to be induced by citalopram involves a woman who experienced macropsia after her first administration of 10 mg citalopram. Just as with zolpidem, after the immediate discontinuation of citalopram, there were no further episodes of macropsia.

Illicit Drugs
Temporary macropsia can be induced by a number of other illicit drugs. Various psychoactive drugs, such as LSD, psilocybin mushrooms (magic mushrooms), and marijuana can cause the user to hallucinate and experience macropsia. There are also suggestions that visual distortions such as macropsia can be associated with cocaine use. Episodes of temporary drug-induced macropsia subside as the chemicals leave the body.

Migraine
Past Research has linked macropsia to migraine. Studies conducted on Japanese adolescents who reported visual episodic illusions with macropsia showed that illusions are three times more likely to occur in association with migraine. The illusions were most prevalent amongst girls between ages 16 and 18. It is unlikely that macropsia in Japanese adolescents could be due to epileptic seizure since only .3% of Japanese adolescents have epilepsy. No evidence of drugs was found which eliminates the possibility of the macropsia being drug-induced. It is unlikely for macropsia in adolescent children to be associated with a serious disease. It is usually the macropsia or other visual disturbance which precedes the painful migrainous headaches. The episodes of macropsia can occur as part of the aura in a migraine. These episodes are often brief, lasting minutes. Adolescents who are deemed to have multiple distortions per episode such slow motion vision and macropsia, are even more likely to be sufferers of migraine. Nonmigrainous headaches are not known to be associated with episodic illusions. Even in the absence of migraine, fever or a hypnagocic state can provoke visual illusions which one might claim to be macropsia. A person with macropsia may fail to see the connection between the migraine and the macropsia, since the conditions may not elicit symptoms at the same time. The pathophysiology of the condition is not full understood, but the timing of some episodic occurrences with the headaches suggests that there is a connection between macropsia and the vasoconstrictive phase of a migraine. The differences in visual phenomena, such as macropsia with slow motion verus macropsia without slow motion, may result from different areas of the brain being affected by migraine.

Epilepsy
Macropsia may present itself as a symptom of both frontal lobe epilepsy and temporal lobe epilepsy and help in diagnosis of the disease. Anxiety and headaches accompany the episodes of visual distortion associated with epilepsy. Valproic acid is used to treat the epilepsy and may be effective in ending the macropsia episodes

Hypoglycaemia
Endogenous hypoglycaemia can result in different types of visual disturbances, with macropsia being one of those. This kind of hypoglycaemia is defined as having an abnormally low blood-sugar level due to anything other than the exogenous administration of insulin. Macropsia has been observed in experimental hypoglycaemia and in patients receiving insulin therapy.

Viruses
Patients with both Epstein-Barr virus and infectious mononucleosis have cited an increase in the sizes of perceived object, coinciding with other symptoms of Alice in Wonderland Syndrome. ,. Macropsia may appear either before the onset or after the resolution of all all clinical symptoms associated with the illness. The duration of the disturbances have been showed to range between 2 weeks and seven months. Almost all patients with macropsia due to infection mononucleiosis have full recoveries.Patients with coxsackie virus B1 have reported numerous symptoms of Alice in Wonderland Syndrome, the most common of which being macropsia and micropsia.

Treatment
The most common way to treat aniseikonia due to macropsia is through the use of auxiliary optics to correct for the magnification properties of the eyes. This method includes changing the shape of spectacle lenses, changing the vertex distances with contact lenses, creating a weak telescope system with contact lenses and spectacles, and changing the power of one of the spectacle lenses. Computer software, such as the Aniseikonia Inspector, has been developed to determine the prescription needed to correct for a certain degree of aniseikonia. The problem with correction through optical means is that the optics do not vary with field angle and thus cannot compensate for non-uniform macropsia. Patients have reported significantly improved visual comfort associated with a correction of 5-10% of the aniseikonia.

Physiology Behind The Disease
In cases where macropsia affects one eye resulting in differences in the way the two eyes perceive the size or shape of images is known as aniseikonia. Aniseikonia is known to be associated with certain retinal conditions. Epiretinal membrane has been found to cause metamorphopsia and aniseikonia. Vitreomacular traction caused by the excessive adhesion of vitreous fluid to the retina is related to aniseikonia due to the separation and compression of photoreceptors. Macular edema and surgical re-attachment for macula-of rhegmatogenous retinal detachment can also cause an increased separation of macular photoreceptors resulting in dysmetropsia. Retinoschisis is another eye disease that has been shown to cause aniseikonia.

Macropsia may be a result of optical magnification differences between the eyes, retinal receptor distribution, or the cortical processing of the sampled image. The current hypothesis for the occurrence of dysmetropsia is due to the stretching or compression of the retina leading to the displacement of receptors. Macropsia arises from a compressed receptor distribution leading to a larger perceived image size and conversely, micropsia results from stretching of the retina leading to a more sparse receptor distribution that gives a smaller perceived image size. In the case of macropsia, the greater density of photoreceptors leads to greater stimulation making the object seem larger. In some cases, the effects of macropsia have been shown to be field dependent, in that the degree of visual distortion is related to the visual field angle. Non-uniform stretching or compression of the receptor distribution could explain the field dependency of the macrospia. If the compression forces were closer to the fovea the resulting compression would cause a greater amount of macropsia at lower field angles with little effect at higher field angles where the receptor distribution is not as compressed. Alterations in receptor distribution can be the result of epiretinal membrane, neuroretina detachment and/or re-attachment, or retinoschisis. Macropsia caused by macula-off rhegmatogenous retinal detachment is not symmetrical around the fovea, resulting in differences size changes in the horizontal and vertical meridians. Asymmetry has also been observed with retinoschisis, in which macropsia generally results in the vertical direction while micropsia presents in the horizontal direction.

Future Research
Future research may be performed on the incidence of retinally-induced macropsia through surgery and ways to limit the occurrence. In terms of treatment, the most effective optical correction is still being researched with respect to visual field angles and direction to a target in the correction. The susceptibility of certain age demographics to macropsia is a subject that requires further validation. Overall, there have not been very many reports of macropsia induced by certain drugs, specifically zolpidem and citalopram. Once a larger effort is made to compile such reports, there will inevitably more research on the subject of macropsia.

Famous Sufferers of Macropsia
Edgar Allan Poe Lewis Carroll Käthe Schmidt Kollwitz