Macropsia is a neurological condition affecting human visual perception, in which objects within an affected section of the visual field appear larger than normal, causing the person to feel smaller than they actually are. Macropsia, along with its opposite condition, micropsia, can be categorized under dysmetropsia. Macropsia is related to other conditions dealing with visual perception, such as aniseikonia and Alice in Wonderland Syndrome (AIWS, also known as Todd's syndrome). Macropsia has a wide range of causes, from prescription and illicit drugs, to migraines and (rarely) complex partial epilepsy, and to different retinal conditions, such as epiretinal membrane. 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. However, this theory has been under much scrutiny.
Causes
Structural defects
In cases where macropsia affects one eye resulting in differences in the way the two eyes perceive the size or shape of images, the condition 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 photoreceptor cells. and surgical re-attachment for macula-off rhegmatogenous retinal detachmentThere is evidence that a lesion appearing in the posterior area of the ventral occipitotemporal visual pathway can cause macropsia. This lesion can be due to an ischemic cell death after an acute posterior cerebral infarction.
Medications
The most prevalent research on prescription drugs with side effects 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; it is implied in the article that the level of intensity was based on the patients accounts of her macropsia episodes, and that no external diagnosis was used. Hoyler points out notable similarities among the different reported cases of zolpidem-induced disorganization. The similarities were that 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. It is believed that zolpidem-related macropsia is more prevalent in women because plasma zolpidem concentration is 40% higher in women, a concentration that further increases in anorexic women. 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
There are 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. One of these studies was conducted on Japanese adolescents who reported visual episodic illusions with macropsia and showed that illusions are three times more likely to occur in association with migraine. The illusions were most prevalent among girls between the ages of 16 and 18. It is unlikely that macropsia in Japanese adolescents could be due to epileptic seizure since only 0.3% of Japanese adolescents have epilepsy. The differences in visual phenomena, such as macropsia with slow motion versus macropsia without slow motion, may result from different areas of the brain being affected by migraine. Anxiety and headaches accompany the episodes of visual distortion associated with epilepsy. While Valproic acid has been used to treat this type of seizure, anti-seizure medications appropriate for focal-onset seizures, like oxcarbazapine, have also been used successfully in the treatment of epilepsy-related macropsia.
Hypoglycaemia
Endogenous hypoglycaemia can result in number of visual disturbances and sometimes macropsia. 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 objects, coinciding with other symptoms of Alice in Wonderland Syndrome. Additionally, it has been observed that Epstein-Barr patients who cite hallucinations display abnormal MRI scans. The MRI may show swelling of the cerebral cortex, transient T2 prolongation, and transient lesions. Unlike in MRI's, no abnormalities have been reported in CT scans. It is thus recommended that an Epstein-Barr patient who cites visual hallucinations have an MRI scan. Macropsia may appear either before the onset, or after the resolution, of all clinical symptoms associated with the illness. The duration of the disturbances have been shown to range between two weeks and seven months. 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 photoreceptor cells 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 macropsia. 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. The New Aniseikonia Test (NAT) can quantify the degree of macropsia or micropsia independently in the vertical and horizontal meridians. The test consists of red and green semicircles on a black background with a white round fixation target. The size of the red semicircle is held constant while the green semicircle is varied in size in 1% increments. The patient wears a pair of red/green goggles so that one eye is tested at a time, and the patient attempts to determine when the semicircles are the same size. This is termed the reversal threshold and the size difference between the semicircles is reported as the degree of aniseikonia. A positive value indicates that the object was perceived bigger and thus corresponds to macropsia, and conversely a negative value indicates micropsia. 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 be more research on the subject of macropsia.