Micropsia | |
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The perception a person can have due to symptoms of pronounced micropsia. See § Comparison with Alice's Adventures in Wonderland, below. Image from that same novel. | |
Specialty | Ophthalmology |
Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. 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, 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. [1]
Micropsia is also commonly reported when the eyes are fixating at (convergence), or focusing at (accommodation), a distance closer than that of the object [2] in accord with Emmert's law. 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.
Related visual distortion conditions include macropsia, a less common condition with the reverse effect, and Alice in Wonderland syndrome, a condition that has symptoms that can include both micropsia and macropsia.
Micropsia causes affected individuals to perceive objects as being smaller or more distant than they actually are. [3]
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 with 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 having micropsia. [3]
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. [4]
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. [5]
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. [6]
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. [4]
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. [4] 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.[ citation needed ]
Micropsia is the most common visual distortion, or dysmetropsia. [7] It is categorized as an illusion in the positive phenomena grouping of abnormal visual distortions. [8]
Of all of the visual distortions, micropsia has the largest variety of causes. [7]
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. [12]
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. [13] Most auras last for a very short period, ranging from a few seconds to a few minutes. [14]
Micropsia can result from the action of mescaline and other hallucinogenic drugs. [4] 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, or HPPD, 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]
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]
Micropsia can be caused by swelling of the cornea due to infection by the Epstein-Barr virus (EBV) [20] and can therefore present as an initial symptom of EBV mononucleosis, a disease caused by Epstein-Barr virus infection.
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 [21] by edematous fluid. [22]
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%. [23]
CSCR 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. [24]
Micropsia is sometimes seen in individuals 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 individual to experience micropsia. Lesions affecting other parts of the extracerebral visual pathways can also cause micropsia. [3]
Treatment varies for micropsia due to the large number of different causes for the condition.[ citation needed ]
Treatments involving 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. [25]
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. [26] Laser treatments also look promising but are still in clinical stages. [26]
Episodes of micropsia or macropsia occur in 9% of adolescents. [27]
10-35% of those with migraines experience auras, with 88% of these patients experiencing both visual auras (which include micropsia) and neurological auras. [28]
Micropsia seems to be slightly more common in boys than in girls among children who experience migraines. [29]
Approximately 80% of temporal lobe seizures produce auras that may lead to micropsia or macropsia. They are a common feature of simple partial seizures and usually precede complex partial seizures of temporal lobe origin. [14]
Central Serous Chorioretinopathy (CSCR) which can produce micropsia predominantly affects persons between the ages of 20 and 50. Women appear to be affected more than men by a factor of almost 3 to 1. [24]
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 have. It has also been suggested that Carroll may have had temporal lobe epilepsy.[ citation needed ]
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, [30] based on the small people that inhabited the island of Lilliput in the novel. [31]
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. [4] 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.[ citation needed ]
Current research is being done on macular degeneration which could help prevent cases of micropsia. A variety of drugs that block vascular endothelial growth factors (VEGFs) are being evaluated as a treatment option. [32] 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. [26]
A hallucination is a perception in the absence of an external stimulus that has the compelling sense of reality. Hallucination is a combination of two conscious states of brain: wakefulness and REM sleep. They are distinguishable from several related phenomena, such as dreaming, which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus is given some additional significance.
Alice in Wonderland Syndrome (AIWS), also known as Todd's Syndrome or Dysmetropsia, is a neurological disorder that distorts perception. People with this syndrome may experience distortions in their visual perception of objects, such as appearing smaller (micropsia) or larger (macropsia), or appearing to be closer (pelopsia) or farther (teleopsia) than they are. Distortion may also occur for senses other than vision.
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. 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. Physiologically, retinal 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.
Visual snow syndrome (VSS) is an uncommon neurological condition in which the primary symptom is that affected individuals see persistent flickering white, black, transparent, or colored dots across the whole visual field.
A scotoma is an area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that is surrounded by a field of normal – or relatively well-preserved – vision.
The visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; in ophthalmology and neurology the emphasis is mostly on the structure inside the visual field and it is then considered “the field of functional capacity obtained and recorded by means of perimetry”.
Palinopsia is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis; it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia.
An aura is a perceptual disturbance experienced by some with epilepsy or migraine. An epileptic aura is actually a minor seizure.
Acephalgic migraine is a neurological syndrome. It is a relatively uncommon variant of migraine in which the patient may experience some migraine symptoms such as aura, nausea, photophobia, and hemiparesis, but does not experience headache. It is generally classified as an event fulfilling the conditions of migraine with aura with no headache. It is sometimes distinguished from visual-only migraine aura without headache, also called ocular migraine.
Focal seizures are seizures that affect initially only one hemisphere of the brain. The brain is divided into two hemispheres, each consisting of four lobes – the frontal, temporal, parietal and occipital lobes. A focal seizure is generated in and affects just one part of the brain – a whole hemisphere or part of a lobe. Symptoms will vary according to where the seizure occurs. When seizures occur in the frontal lobe, the patient may experience a wave-like sensation in the head. When seizures occur in the temporal lobe, a feeling of déjà vu may be experienced. When seizures are localized to the parietal lobe, a numbness or tingling may occur. With seizures occurring in the occipital lobe, visual disturbances or hallucinations have been reported.
A retinal implant is a visual prosthesis for restoration of sight to patients blinded by retinal degeneration. The system is meant to partially restore useful vision to those who have lost their photoreceptors due to retinal diseases such as retinitis pigmentosa (RP) or age-related macular degeneration (AMD). Retinal implants are being developed by a number of private companies and research institutions, and three types are in clinical trials: epiretinal, subretinal, and suprachoroidal. The implants introduce visual information into the retina by electrically stimulating the surviving retinal neurons. So far, elicited percepts had rather low resolution, and may be suitable for light perception and recognition of simple objects.
Photopsia is the presence of perceived flashes of light in the field of vision.
Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes.
Epiretinal membrane or macular pucker is a disease of the eye in response to changes in the vitreous humor or more rarely, diabetes. Sometimes, as a result of immune system response to protect the retina, cells converge in the macular area as the vitreous ages and pulls away in posterior vitreous detachment (PVD).
Blurred vision is an ocular symptom where vision becomes less precise and there is added difficulty to resolve fine details.
Lesions in the visual pathway affect vision most often by creating deficits or negative phenomena, such as blindness, visual field deficits or scotomas, decreased visual acuity and color blindness. On occasion, they may also create false visual images, called positive visual phenomena. These images can be a result of distortion of incoming sensory information leading to an incorrect perception of a real image called an illusion. When the visual system produces images which are not based on sensory input, they can be referred to as hallucinations. The visual phenomena may last from brief moments to several hours, but they also can be permanent. They are generally associated with other symptoms but occasionally are isolated. Conditions causing these phenomena include disruptions in the visual input along the pathways lesions in the extracortical visual system, migraines, seizures, toxic-metabolic encephalopathy, psychiatric conditions and sleep apnea, among others. The mechanisms underlying positive visual phenomena are not yet well understood. Possible mechanisms may be: 1) defect in the sensory input causing compensatory upregulation of the visual cortex, 2) faulty visual processing in which inputs are normal but lesions result in an inappropriate pattern of cortical excitation, 3)variants of normal visual processing. Of all forms of hallucination, visual hallucinations are the least likely to be associated with psychiatric disorders. For example most patients with visual hallucinations do not have schizophrenia and most patients with schizophrenia do not have visual hallucinations.
Vertiginous epilepsy is infrequently the first symptom of a seizure, characterized by a feeling of vertigo. When it occurs, there is a sensation of rotation or movement that lasts for a few seconds before full seizure activity. While the specific causes of this disease are speculative there are several methods for diagnosis, the most important being the patient's recall of episodes. Most times, those diagnosed with vertiginous seizures are left to self-manage their symptoms or are able to use anti-epileptic medication to dampen the severity of their symptoms.
Illusory palinopsia is a subtype of palinopsia, a visual disturbance defined as the persistence or recurrence of a visual image after the stimulus has been removed. Palinopsia is a broad term describing a heterogeneous group of symptoms, which is divided into hallucinatory palinopsia and illusory palinopsia. Illusory palinopsia is likely due to sustained awareness of a stimulus and is similar to a visual illusion: the distorted perception of a real external stimulus.
Cerebral diplopia or polyopia describes seeing two or more images arranged in ordered rows, columns, or diagonals after fixation on a stimulus. The polyopic images occur monocular bilaterally and binocularly, differentiating it from ocular diplopia or polyopia. The number of duplicated images can range from one to hundreds. Some patients report difficulty in distinguishing the replicated images from the real images, while others report that the false images differ in size, intensity, or color. Cerebral polyopia is sometimes confused with palinopsia, in which multiple images appear while watching an object. However, in cerebral polyopia, the duplicated images are of a stationary object which are perceived even after the object is removed from the visual field. Movement of the original object causes all of the duplicated images to move, or the polyopic images disappear during motion. In palinoptic polyopia, movement causes each polyopic image to leave an image in its wake, creating hundreds of persistent images (entomopia).
Prosopometamorphopsia, also known as demon face syndrome, is a visual disorder characterized by altered perceptions of faces. In the perception of a person with the disorder, facial features are distorted in a variety of ways including drooping, swelling, discoloration, and shifts of position.
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