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.
Retinoschisis is an eye disease characterized by the abnormal splitting of the retina's neurosensory layers, usually in the outer plexiform layer. Most common forms are asymptomatic, some rarer forms result in a loss of vision in the corresponding visual field.
In visual physiology, adaptation is the ability of the retina of the eye to adjust to various levels of light. Natural night vision, or scotopic vision, is the ability to see under low-light conditions. In humans, rod cells are exclusively responsible for night vision as cone cells are only able to function at higher illumination levels. Night vision is of lower quality than day vision because it is limited in resolution and colors cannot be discerned; only shades of gray are seen. In order for humans to transition from day to night vision they must undergo a dark adaptation period of up to two hours in which each eye adjusts from a high to a low luminescence "setting", increasing sensitivity hugely, by many orders of magnitude. This adaptation period is different between rod and cone cells and results from the regeneration of photopigments to increase retinal sensitivity. Light adaptation, in contrast, works very quickly, within seconds.
Macular edema occurs when fluid and protein deposits collect on or under the macula of the eye and causes it to thicken and swell (edema). The swelling may distort a person's central vision, because the macula holds tightly packed cones that provide sharp, clear, central vision to enable a person to see detail, form, and color that is directly in the centre of the field of view.
The Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula, as well as the optic nerve and the visual pathway to the brain.
A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision.
A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. Visual field testing can be performed clinically by keeping the subject's gaze fixed while presenting objects at various places within their visual field. Simple manual equipment can be used such as in the tangent screen test or the Amsler grid. When dedicated machinery is used it is called a perimeter.
Optic pit, optic nerve pit, or optic disc pit is a congenital excavation of the optic disc, resulting from a malformation during development of the eye. Optic pits are important because they are associated with posterior vitreous detachments (PVD) and even serous retinal detachments.
Choroidal neovascularization (CNV) is the creation of new blood vessels in the choroid layer of the eye. Choroidal neovascularization is a common cause of neovascular degenerative maculopathy commonly exacerbated by extreme myopia, malignant myopic degeneration, or age-related developments.
David Anthony Newsome M.D. FARVO was a scientist, ophthalmologist, inventor, and author. He studied the treatment of age-related macular degeneration and proposed the usefulness of zinc supplements to slow the rate of vision loss from age-related macular degeneration.
Laser coagulation or laser photocoagulation surgery is used to treat a number of eye diseases and has become widely used in recent decades. During the procedure, a laser is used to finely cauterize ocular blood vessels to attempt to bring about various therapeutic benefits.
Distorted vision is a symptom with several different possible causes.
The sharpness of our senses is defined by the finest detail we can discriminate. Visual acuity is measured by the smallest letters that can be distinguished on a chart and is governed by the anatomical spacing of the mosaic of sensory elements on the retina. Yet spatial distinctions can be made on a finer scale still: misalignment of borders can be detected with a precision up to 10 times better than visual acuity, as already shown by Ewald Hering in 1899. This hyperacuity, transcending by far the size limits set by the retinal 'pixels', depends on sophisticated information processing in the brain.
Vitreomacular adhesion (VMA) is a human medical condition where the vitreous gel of the human eye adheres to the retina in an abnormally strong manner. As the eye ages, it is common for the vitreous to separate from the retina. But if this separation is not complete, i.e. there is still an adhesion, this can create pulling forces on the retina that may result in subsequent loss or distortion of vision. The adhesion in of itself is not dangerous, but the resulting pathological vitreomacular traction (VMT) can cause severe ocular damage.
Microperimetry, sometimes called Fundus related perimetry, is a type of visual field test which uses one of several technologies to create a "retinal sensitivity map" of the quantity of light perceived in specific parts of the retina in people who have lost the ability to fixate on an object or light source.
Geographic atrophy (GA), also known as atrophic age-related macular degeneration (AMD) or advanced dry AMD, is an advanced form of age-related macular degeneration that can result in the progressive and irreversible loss of retina which can lead to a loss of visual function over time. It is estimated that GA affects >5 million people worldwide and approximately 1 million patients in the US, which is similar to the prevalence of neovascular (wet) AMD, the other advanced form of the disease.
Occult macular dystrophy (OMD) is a rare inherited degradation of the retina, characterized by progressive loss of function in the most sensitive part of the central retina (macula), the location of the highest concentration of light-sensitive cells (photoreceptors) but presenting no visible abnormality. "Occult" refers to the degradation in the fundus being difficult to discern. The disorder is called "dystrophy" instead of "degradation" to distinguish its genetic origin from other causes, such as age. OMD was first reported by Y. Miyake et al. in 1989.
