Floaters or eye floaters are sometimes visible deposits within the eye's vitreous humour, which is normally transparent, or between the vitreous and retina. They can become particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Each floater can be measured by its size, shape, consistency, refractive index, and motility. They are also called muscae volitantes, or mouches volantes. The vitreous usually starts out transparent, but imperfections may gradually develop as one ages. The common type of floater, present in most people's eyes, is due to these degenerative changes of the vitreous. The perception of floaters, which may be annoying or problematic to some people, is known as myodesopsia, or, less commonly, as myodaeopsia, myiodeopsia, or myiodesopsia. It is not often treated, except in severe cases, where vitrectomy (surgery), laser vitreolysis, and medication may be effective.
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, by distortion of images in the eye, by changes in the brain, and from psychological factors. Dissociative phenomena are linked with micropsia, which may be the result of brain-lateralization disturbance.
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.
Moore's lightning streaks are lightning type streaks (photopsia) due to sudden head or eye movement in the dark. They are generally caused by shock waves in the vitreous humor hitting the retina or traction on the retina from fibers in the vitreous humor. The implication is that the vitreous is softer than normal, generally this is not a cause for alarm provided they are momentary, occur only in the dark, are due to sudden head movements (acceleration) and do not occur along with many new tiny black floating specks in the vision. Professional advice should be sought in cases of doubt, as retinal detachment, a serious condition, also can cause flashes in the eye.
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 phosphene is the phenomenon of seeing light without light entering the eye. The word phosphene comes from the Greek words phos (light) and phainein. Phosphenes that are induced by movement or sound may be associated with optic neuritis.
This is a partial list of human eye diseases and disorders.
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a surgical emergency.
Entoptic phenomena are visual effects whose source is within the human eye itself.
A posterior vitreous detachment (PVD) is a condition of the eye in which the vitreous membrane separates from the retina. It refers to the separation of the posterior hyaloid membrane from the retina anywhere posterior to the vitreous base.
An aura is a perceptual disturbance experienced by some with epilepsy or migraine. An epileptic aura is actually a minor seizure.
Coats' disease is a rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Coats' disease can also fall under glaucoma.
Scintillating scotoma is a common visual aura that was first described by 19th-century physician Hubert Airy (1838–1903). Originating from the brain, it may precede a migraine headache, but can also occur acephalgically, also known as visual migraine or migraine aura. It is often confused with retinal migraine, which originates in the eyeball or socket.
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.
Retinal migraine is a retinal disease often accompanied by migraine headache and typically affects only one eye. It is caused by ischaemia or vascular spasm in or behind the affected eye.
White dot syndromes are inflammatory diseases characterized by the presence of white dots on the fundus, the interior surface of the eye. The majority of individuals affected with white dot syndromes are younger than fifty years of age. Some symptoms include blurred vision and visual field loss. There are many theories for the etiology of white dot syndromes including infectious, viral, genetics and autoimmune.
Vitreous hemorrhage is the extravasation, or leakage, of blood into the areas in and around the vitreous humor of the eye. The vitreous humor is the clear gel that fills the space between the lens and the retina of the eye. A variety of conditions can result in blood leaking into the vitreous humor, which can cause impaired vision, floaters, and photopsia.
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).
