Vision, Ocular: The process in which light signals are transformed by the PHOTORECEPTOR CELLS into electrical signals which can then be transmitted to the brain.Vision, Low: Vision considered to be inferior to normal vision as represented by accepted standards of acuity, field of vision, or motility. Low vision generally refers to visual disorders that are caused by diseases that cannot be corrected by refraction (e.g., MACULAR DEGENERATION; RETINITIS PIGMENTOSA; DIABETIC RETINOPATHY, etc.).Vision Disorders: Visual impairments limiting one or more of the basic functions of the eye: visual acuity, dark adaptation, color vision, or peripheral vision. These may result from EYE DISEASES; OPTIC NERVE DISEASES; VISUAL PATHWAY diseases; OCCIPITAL LOBE diseases; OCULAR MOTILITY DISORDERS; and other conditions (From Newell, Ophthalmology: Principles and Concepts, 7th ed, p132).Vision Tests: A series of tests used to assess various functions of the eyes.Color Vision Defects: Defects of color vision are mainly hereditary traits but can be secondary to acquired or developmental abnormalities in the CONES (RETINA). Severity of hereditary defects of color vision depends on the degree of mutation of the ROD OPSINS genes (on X CHROMOSOME and CHROMOSOME 3) that code the photopigments for red, green and blue.Vision, Binocular: The blending of separate images seen by each eye into one composite image.Visual Acuity: Clarity or sharpness of OCULAR VISION or the ability of the eye to see fine details. Visual acuity depends on the functions of RETINA, neuronal transmission, and the interpretative ability of the brain. Normal visual acuity is expressed as 20/20 indicating that one can see at 20 feet what should normally be seen at that distance. Visual acuity can also be influenced by brightness, color, and contrast.Night Vision: Function of the human eye that is used in dim illumination (scotopic intensities) or at nighttime. Scotopic vision is performed by RETINAL ROD PHOTORECEPTORS with high sensitivity to light and peak absorption wavelength at 507 nm near the blue end of the spectrum.Vision, Monocular: Images seen by one eye.Blindness: The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of EYE DISEASES; OPTIC NERVE DISEASES; OPTIC CHIASM diseases; or BRAIN DISEASES affecting the VISUAL PATHWAYS or OCCIPITAL LOBE.Color Perception Tests: Type of vision test used to determine COLOR VISION DEFECTS.Color Perception: Mental processing of chromatic signals (COLOR VISION) from the eye by the VISUAL CORTEX where they are converted into symbolic representations. Color perception involves numerous neurons, and is influenced not only by the distribution of wavelengths from the viewed object, but also by its background color and brightness contrast at its boundary.Contrast Sensitivity: The ability to detect sharp boundaries (stimuli) and to detect slight changes in luminance at regions without distinct contours. Psychophysical measurements of this visual function are used to evaluate visual acuity and to detect eye disease.Visually Impaired Persons: Persons with loss of vision such that there is an impact on activities of daily living.Visual Fields: The total area or space visible in a person's peripheral vision with the eye looking straightforward.Eyeglasses: A pair of ophthalmic lenses in a frame or mounting which is supported by the nose and ears. The purpose is to aid or improve vision. It does not include goggles or nonprescription sun glasses for which EYE PROTECTIVE DEVICES is available.Visual Perception: The selecting and organizing of visual stimuli based on the individual's past experience.Sensory Aids: Devices that help people with impaired sensory responses.Vision Disparity: The difference between two images on the retina when looking at a visual stimulus. This occurs since the two retinas do not have the same view of the stimulus because of the location of our eyes. Thus the left eye does not get exactly the same view as the right eye.Retinal Cone Photoreceptor Cells: Photosensitive afferent neurons located primarily within the FOVEA CENTRALIS of the MACULA LUTEA. There are three major types of cone cells (red, blue, and green) whose photopigments have different spectral sensitivity curves. Retinal cone cells operate in daylight vision (at photopic intensities) providing color recognition and central visual acuity.Photic Stimulation: Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.Amblyopia: A nonspecific term referring to impaired vision. Major subcategories include stimulus deprivation-induced amblyopia and toxic amblyopia. Stimulus deprivation-induced amblyopia is a developmental disorder of the visual cortex. A discrepancy between visual information received by the visual cortex from each eye results in abnormal cortical development. STRABISMUS and REFRACTIVE ERRORS may cause this condition. Toxic amblyopia is a disorder of the OPTIC NERVE which is associated with ALCOHOLISM, tobacco SMOKING, and other toxins and as an adverse effect of the use of some medications.Psychophysics: The science dealing with the correlation of the physical characteristics of a stimulus, e.g., frequency or intensity, with the response to the stimulus, in order to assess the psychologic factors involved in the relationship.Sensory Thresholds: The minimum amount of stimulus energy necessary to elicit a sensory response.Refractive Errors: Deviations from the average or standard indices of refraction of the eye through its dioptric or refractive apparatus.Mesopic Vision: The function of the eye that is used in the intermediate level of illumination (mesopic intensities) where both the RETINAL ROD PHOTORECEPTORS and the RETINAL CONE PHOTORECEPTORS are active in processing light input simultaneously.Fovea Centralis: An area approximately 1.5 millimeters in diameter within the macula lutea where the retina thins out greatly because of the oblique shifting of all layers except the pigment epithelium layer. It includes the sloping walls of the fovea (clivus) and contains a few rods in its periphery. In its center (foveola) are the cones most adapted to yield high visual acuity, each cone being connected to only one ganglion cell. (Cline et al., Dictionary of Visual Science, 4th ed)Eye Diseases: Diseases affecting the eye.Opsins: Photosensitive proteins in the membranes of PHOTORECEPTOR CELLS such as the rods and the cones. Opsins have varied light absorption properties and are members of the G-PROTEIN-COUPLED RECEPTORS family. Their ligands are VITAMIN A-based chromophores.Strabismus: Misalignment of the visual axes of the eyes. In comitant strabismus the degree of ocular misalignment does not vary with the direction of gaze. In noncomitant strabismus the degree of misalignment varies depending on direction of gaze or which eye is fixating on the target. (Miller, Walsh & Hoyt's Clinical Neuro-Ophthalmology, 4th ed, p641)Lighting: The illumination of an environment and the arrangement of lights to achieve an effect or optimal visibility. Its application is in domestic or in public settings and in medical and non-medical environments.Depth Perception: Perception of three-dimensionality.Pattern Recognition, Visual: Mental process to visually perceive a critical number of facts (the pattern), such as characters, shapes, displays, or designs.Retina: The ten-layered nervous tissue membrane of the eye. It is continuous with the OPTIC NERVE and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the CHOROID and the inner surface with the VITREOUS BODY. The outer-most layer is pigmented, whereas the inner nine layers are transparent.Ophthalmology: A surgical specialty concerned with the structure and function of the eye and the medical and surgical treatment of its defects and diseases.Macular Degeneration: Degenerative changes in the RETINA usually of older adults which results in a loss of vision in the center of the visual field (the MACULA LUTEA) because of damage to the retina. It occurs in dry and wet forms.Retinal Pigments: Photosensitive protein complexes of varied light absorption properties which are expressed in the PHOTORECEPTOR CELLS. They are OPSINS conjugated with VITAMIN A-based chromophores. Chromophores capture photons of light, leading to the activation of opsins and a biochemical cascade that ultimately excites the photoreceptor cells.Cataract: Partial or complete opacity on or in the lens or capsule of one or both eyes, impairing vision or causing blindness. The many kinds of cataract are classified by their morphology (size, shape, location) or etiology (cause and time of occurrence). (Dorland, 27th ed)Visual Pathways: Set of cell bodies and nerve fibers conducting impulses from the eyes to the cerebral cortex. It includes the RETINA; OPTIC NERVE; optic tract; and geniculocalcarine tract.Space Perception: The awareness of the spatial properties of objects; includes physical space.Sensory Deprivation: The absence or restriction of the usual external sensory stimuli to which the individual responds.Form Perception: The sensory discrimination of a pattern shape or outline.Electroretinography: Recording of electric potentials in the retina after stimulation by light.Rod Opsins: Photosensitive proteins expressed in the ROD PHOTORECEPTOR CELLS. They are the protein components of rod photoreceptor pigments such as RHODOPSIN.Scotoma: A localized defect in the visual field bordered by an area of normal vision. This occurs with a variety of EYE DISEASES (e.g., RETINAL DISEASES and GLAUCOMA); OPTIC NERVE DISEASES, and other conditions.Presbyopia: The normal decreasing elasticity of the crystalline lens that leads to loss of accommodation.Orientation: Awareness of oneself in relation to time, place and person.Discrimination (Psychology): Differential response to different stimuli.Adaptation, Ocular: The adjustment of the eye to variations in the intensity of light. Light adaptation is the adjustment of the eye when the light threshold is increased; DARK ADAPTATION when the light is greatly reduced. (From Cline et al., Dictionary of Visual Science, 4th ed)Motion Perception: The real or apparent movement of objects through the visual field.Visual Cortex: Area of the OCCIPITAL LOBE concerned with the processing of visual information relayed via VISUAL PATHWAYS.Vision, Entoptic: Visual sensation derived from sensory stimulation by objects or shadows inside the eye itself, such as floating vitreous fibers, tissues, or blood.Fixation, Ocular: The positioning and accommodation of eyes that allows the image to be brought into place on the FOVEA CENTRALIS of each eye.Glare: Relatively bright light, or the dazzling sensation of relatively bright light, which produces unpleasantness or discomfort, or which interferes with optimal VISION, OCULAR. (Cline et al., Dictionary of Visual Science, 4th ed)Eye Movements: Voluntary or reflex-controlled movements of the eye.Light: That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.Cataract Extraction: The removal of a cataractous CRYSTALLINE LENS from the eye.ReadingRetinoscopy: An objective determination of the refractive state of the eye (NEARSIGHTEDNESS; FARSIGHTEDNESS; ASTIGMATISM). By using a RETINOSCOPE, the amount of correction and the power of lens needed can be determined.Myopia: A refractive error in which rays of light entering the EYE parallel to the optic axis are brought to a focus in front of the RETINA when accommodation (ACCOMMODATION, OCULAR) is relaxed. This results from an overly curved CORNEA or from the eyeball being too long from front to back. It is also called nearsightedness.Optometry: The professional practice of primary eye and vision care that includes the measurement of visual refractive power and the correction of visual defects with lenses or glasses.Lenses: Pieces of glass or other transparent materials used for magnification or increased visual acuity.Blindness, Cortical: Total loss of vision in all or part of the visual field due to bilateral OCCIPITAL LOBE (i.e., VISUAL CORTEX) damage or dysfunction. Anton syndrome is characterized by the psychic denial of true, organic cortical blindness. (Adams et al., Principles of Neurology, 6th ed, p460)Refraction, Ocular: Refraction of LIGHT effected by the media of the EYE.Retinal DiseasesColor: The visually perceived property of objects created by absorption or reflection of specific wavelengths of light.Retinal Rod Photoreceptor Cells: Photosensitive afferent neurons located in the peripheral retina, with their density increases radially away from the FOVEA CENTRALIS. Being much more sensitive to light than the RETINAL CONE CELLS, the rod cells are responsible for twilight vision (at scotopic intensities) as well as peripheral vision, but provide no color discrimination.Flicker Fusion: The point or frequency at which all flicker of an intermittent light stimulus disappears.Photoreceptor Cells, Vertebrate: Specialized PHOTOTRANSDUCTION neurons in the vertebrates, such as the RETINAL ROD CELLS and the RETINAL CONE CELLS. Non-visual photoreceptor neurons have been reported in the deep brain, the PINEAL GLAND and organs of the circadian system.Dark Adaptation: Adjustment of the eyes under conditions of low light. The sensitivity of the eye to light is increased during dark adaptation.Eye: The organ of sight constituting a pair of globular organs made up of a three-layered roughly spherical structure specialized for receiving and responding to light.Ocular Physiological Phenomena: Processes and properties of the EYE as a whole or of any of its parts.Fluorescein Angiography: Visualization of a vascular system after intravenous injection of a fluorescein solution. The images may be photographed or televised. It is used especially in studying the retinal and uveal vasculature.Perceptual Masking: The interference of one perceptual stimulus with another causing a decrease or lessening in perceptual effectiveness.Retinitis Pigmentosa: Hereditary, progressive degeneration of the neuroepithelium of the retina characterized by night blindness and progressive contraction of the visual field.Cone Opsins: Photosensitive proteins expressed in the CONE PHOTORECEPTOR CELLS. They are the protein components of cone photopigments. Cone opsins are classified by their peak absorption wavelengths.Touch: Sensation of making physical contact with objects, animate or inanimate. Tactile stimuli are detected by MECHANORECEPTORS in the skin and mucous membranes.Visual Prosthesis: Artificial device such as an externally-worn camera attached to a stimulator on the RETINA, OPTIC NERVE, or VISUAL CORTEX, intended to restore or amplify vision.Night Blindness: Failure or imperfection of vision at night or in dim light, with good vision only on bright days. (Dorland, 27th ed)Evoked Potentials, Visual: The electric response evoked in the cerebral cortex by visual stimulation or stimulation of the visual pathways.Eye Injuries: Damage or trauma inflicted to the eye by external means. The concept includes both surface injuries and intraocular injuries.Phosphenes: A subjective visual sensation with the eyes closed and in the absence of light. Phosphenes can be spontaneous, or induced by chemical, electrical, or mechanical (pressure) stimuli which cause the visual field to light up without optical inputs.Size Perception: The sensory interpretation of the dimensions of objects.Glaucoma: An ocular disease, occurring in many forms, having as its primary characteristics an unstable or a sustained increase in the intraocular pressure which the eye cannot withstand without damage to its structure or impairment of its function. The consequences of the increased pressure may be manifested in a variety of symptoms, depending upon type and severity, such as excavation of the optic disk, hardness of the eyeball, corneal anesthesia, reduced visual acuity, seeing of colored halos around lights, disturbed dark adaptation, visual field defects, and headaches. (Dictionary of Visual Science, 4th ed)Fundus Oculi: The concave interior of the eye, consisting of the retina, the choroid, the sclera, the optic disk, and blood vessels, seen by means of the ophthalmoscope. (Cline et al., Dictionary of Visual Science, 4th ed)Optic Neuritis: Inflammation of the optic nerve. Commonly associated conditions include autoimmune disorders such as MULTIPLE SCLEROSIS, infections, and granulomatous diseases. Clinical features include retro-orbital pain that is aggravated by eye movement, loss of color vision, and contrast sensitivity that may progress to severe visual loss, an afferent pupillary defect (Marcus-Gunn pupil), and in some instances optic disc hyperemia and swelling. Inflammation may occur in the portion of the nerve within the globe (neuropapillitis or anterior optic neuritis) or the portion behind the globe (retrobulbar neuritis or posterior optic neuritis).Proprioception: Sensory functions that transduce stimuli received by proprioceptive receptors in joints, tendons, muscles, and the INNER EAR into neural impulses to be transmitted to the CENTRAL NERVOUS SYSTEM. Proprioception provides sense of stationary positions and movements of one's body parts, and is important in maintaining KINESTHESIA and POSTURAL BALANCE.Optical Illusions: An illusion of vision usually affecting spatial relations.Psychomotor Performance: The coordination of a sensory or ideational (cognitive) process and a motor activity.Retinal Degeneration: A retrogressive pathological change in the retina, focal or generalized, caused by genetic defects, inflammation, trauma, vascular disease, or aging. Degeneration affecting predominantly the macula lutea of the retina is MACULAR DEGENERATION. (Newell, Ophthalmology: Principles and Concepts, 7th ed, p304)Convergence, Ocular: The turning inward of the lines of sight toward each other.Illusions: The misinterpretation of a real external, sensory experience.Distance Perception: The act of knowing or the recognition of a distance by recollective thought, or by means of a sensory process which is under the influence of set and of prior experience.Diabetic Retinopathy: Disease of the RETINA as a complication of DIABETES MELLITUS. It is characterized by the progressive microvascular complications, such as ANEURYSM, interretinal EDEMA, and intraocular PATHOLOGIC NEOVASCULARIZATION.Cues: Signals for an action; that specific portion of a perceptual field or pattern of stimuli to which a subject has learned to respond.Microspectrophotometry: Analytical technique for studying substances present at enzyme concentrations in single cells, in situ, by measuring light absorption. Light from a tungsten strip lamp or xenon arc dispersed by a grating monochromator illuminates the optical system of a microscope. The absorbance of light is measured (in nanometers) by comparing the difference between the image of the sample and a reference image.Accommodation, Ocular: The dioptric adjustment of the EYE (to attain maximal sharpness of retinal imagery for an object of regard) referring to the ability, to the mechanism, or to the process. Ocular accommodation is the effecting of refractive changes by changes in the shape of the CRYSTALLINE LENS. Loosely, it refers to ocular adjustments for VISION, OCULAR at various distances. (Cline et al., Dictionary of Visual Science, 4th ed)Contact Lenses: Lenses designed to be worn on the front surface of the eyeball. (UMDNS, 1999)Retinal Detachment: Separation of the inner layers of the retina (neural retina) from the pigment epithelium. Retinal detachment occurs more commonly in men than in women, in eyes with degenerative myopia, in aging and in aphakia. It may occur after an uncomplicated cataract extraction, but it is seen more often if vitreous humor has been lost during surgery. (Dorland, 27th ed; Newell, Ophthalmology: Principles and Concepts, 7th ed, p310-12).Models, Neurological: Theoretical representations that simulate the behavior or activity of the neurological system, processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.Afterimage: Continuation of visual impression after cessation of stimuli causing the original image.Photoreceptor Cells: Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.Orthoptics: The study and treatment of defects in binocular vision resulting from defects in the optic musculature or of faulty visual habits. It involves a technique of eye exercises designed to correct the visual axes of eyes not properly coordinated for binocular vision.Photoreceptor Cells, Invertebrate: Specialized cells in the invertebrates that detect and transduce light. They are predominantly rhabdomeric with an array of photosensitive microvilli. Illumination depolarizes invertebrate photoreceptors by stimulating Na+ influx across the plasma membrane.Visual Field Tests: Method of measuring and mapping the scope of vision, from central to peripheral of each eye.Hemianopsia: Partial or complete loss of vision in one half of the visual field(s) of one or both eyes. Subtypes include altitudinal hemianopsia, characterized by a visual defect above or below the horizontal meridian of the visual field. Homonymous hemianopsia refers to a visual defect that affects both eyes equally, and occurs either to the left or right of the midline of the visual field. Binasal hemianopsia consists of loss of vision in the nasal hemifields of both eyes. Bitemporal hemianopsia is the bilateral loss of vision in the temporal fields. Quadrantanopsia refers to loss of vision in one quarter of the visual field in one or both eyes.Macula Lutea: An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. (From Cline et al., Dictionary of Visual Science, 4th ed)Nystagmus, Optokinetic: Normal nystagmus produced by looking at objects moving across the field of vision.Asthenopia: Term generally used to describe complaints related to refractive error, ocular muscle imbalance, including pain or aching around the eyes, burning and itchiness of the eyelids, ocular fatigue, and headaches.Saccades: An abrupt voluntary shift in ocular fixation from one point to another, as occurs in reading.Models, Psychological: Theoretical representations that simulate psychological processes and/or social processes. These include the use of mathematical equations, computers, and other electronic equipment.Eye ProteinsEye Injuries, Penetrating: Deeply perforating or puncturing type intraocular injuries.Nystagmus, Pathologic: Involuntary movements of the eye that are divided into two types, jerk and pendular. Jerk nystagmus has a slow phase in one direction followed by a corrective fast phase in the opposite direction, and is usually caused by central or peripheral vestibular dysfunction. Pendular nystagmus features oscillations that are of equal velocity in both directions and this condition is often associated with visual loss early in life. (Adams et al., Principles of Neurology, 6th ed, p272)Time Factors: Elements of limited time intervals, contributing to particular results or situations.cis-trans-Isomerases: Enzymes that catalyze the rearrangement of geometry about double bonds. EC 5.2.Optic Atrophy: Atrophy of the optic disk which may be congenital or acquired. This condition indicates a deficiency in the number of nerve fibers which arise in the RETINA and converge to form the OPTIC DISK; OPTIC NERVE; OPTIC CHIASM; and optic tracts. GLAUCOMA; ISCHEMIA; inflammation, a chronic elevation of intracranial pressure, toxins, optic nerve compression, and inherited conditions (see OPTIC ATROPHIES, HEREDITARY) are relatively common causes of this condition.Attention: Focusing on certain aspects of current experience to the exclusion of others. It is the act of heeding or taking notice or concentrating.Pupil: The aperture in the iris through which light passes.Ophthalmologic Surgical Procedures: Surgery performed on the eye or any of its parts.Optics and Photonics: A specialized field of physics and engineering involved in studying the behavior and properties of light and the technology of analyzing, generating, transmitting, and manipulating ELECTROMAGNETIC RADIATION in the visible, infrared, and ultraviolet range.Corneal Diseases: Diseases of the cornea.Dominance, Ocular: The functional superiority and preferential use of one eye over the other. The term is usually applied to superiority in sighting (VISUAL PERCEPTION) or motor task but not difference in VISUAL ACUITY or dysfunction of one of the eyes. Ocular dominance can be modified by visual input and NEUROTROPHIC FACTORS.Hearing Disorders: Conditions that impair the transmission of auditory impulses and information from the level of the ear to the temporal cortices, including the sensorineural pathways.PrintingAdaptation, Physiological: The non-genetic biological changes of an organism in response to challenges in its ENVIRONMENT.Tomography, Optical Coherence: An imaging method using LASERS that is used for mapping subsurface structure. When a reflective site in the sample is at the same optical path length (coherence) as the reference mirror, the detector observes interference fringes.Lens Implantation, Intraocular: Insertion of an artificial lens to replace the natural CRYSTALLINE LENS after CATARACT EXTRACTION or to supplement the natural lens which is left in place.Rhodopsin: A purplish-red, light-sensitive pigment found in RETINAL ROD CELLS of most vertebrates. It is a complex consisting of a molecule of ROD OPSIN and a molecule of 11-cis retinal (RETINALDEHYDE). Rhodopsin exhibits peak absorption wavelength at about 500 nm.Anisometropia: A condition of an inequality of refractive power of the two eyes.Astigmatism: Unequal curvature of the refractive surfaces of the eye. Thus a point source of light cannot be brought to a point focus on the retina but is spread over a more or less diffuse area. This results from the radius of curvature in one plane being longer or shorter than the radius at right angles to it. (Dorland, 27th ed)Retinal Ganglion Cells: Neurons of the innermost layer of the retina, the internal plexiform layer. They are of variable sizes and shapes, and their axons project via the OPTIC NERVE to the brain. A small subset of these cells act as photoreceptors with projections to the SUPRACHIASMATIC NUCLEUS, the center for regulating CIRCADIAN RHYTHM.Diplopia: A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include REFRACTIVE ERRORS; STRABISMUS; OCULOMOTOR NERVE DISEASES; TROCHLEAR NERVE DISEASES; ABDUCENS NERVE DISEASES; and diseases of the BRAIN STEM and OCCIPITAL LOBE.Choroidal Neovascularization: A pathological process consisting of the formation of new blood vessels in the CHOROID.Field Dependence-Independence: The ability to respond to segments of the perceptual experience rather than to the whole.Ocular Motility Disorders: Disorders that feature impairment of eye movements as a primary manifestation of disease. These conditions may be divided into infranuclear, nuclear, and supranuclear disorders. Diseases of the eye muscles or oculomotor cranial nerves (III, IV, and VI) are considered infranuclear. Nuclear disorders are caused by disease of the oculomotor, trochlear, or abducens nuclei in the BRAIN STEM. Supranuclear disorders are produced by dysfunction of higher order sensory and motor systems that control eye movements, including neural networks in the CEREBRAL CORTEX; BASAL GANGLIA; CEREBELLUM; and BRAIN STEM. Ocular torticollis refers to a head tilt that is caused by an ocular misalignment. Opsoclonus refers to rapid, conjugate oscillations of the eyes in multiple directions, which may occur as a parainfectious or paraneoplastic condition (e.g., OPSOCLONUS-MYOCLONUS SYNDROME). (Adams et al., Principles of Neurology, 6th ed, p240)Audiovisual Aids: Auditory and visual instructional materials.Photometry: Measurement of the various properties of light.Laser Coagulation: The use of green light-producing LASERS to stop bleeding. The green light is selectively absorbed by HEMOGLOBIN, thus triggering BLOOD COAGULATION.Vitrectomy: Removal of the whole or part of the vitreous body in treating endophthalmitis, diabetic retinopathy, retinal detachment, intraocular foreign bodies, and some types of glaucoma.Raptors: BIRDS that hunt and kill other animals, especially higher vertebrates, for food. They include the FALCONIFORMES order, or diurnal birds of prey, comprised of EAGLES, falcons, HAWKS, and others, as well as the STRIGIFORMES order, or nocturnal birds of prey, which includes OWLS.Sickness Impact Profile: A quality-of-life scale developed in the United States in 1972 as a measure of health status or dysfunction generated by a disease. It is a behaviorally based questionnaire for patients and addresses activities such as sleep and rest, mobility, recreation, home management, emotional behavior, social interaction, and the like. It measures the patient's perceived health status and is sensitive enough to detect changes or differences in health status occurring over time or between groups. (From Medical Care, vol.xix, no.8, August 1981, p.787-805)Lenses, Intraocular: Artificial implanted lenses.Refractive Surgical Procedures: Surgical procedures employed to correct REFRACTIVE ERRORS such as MYOPIA; HYPEROPIA; or ASTIGMATISM. These may involve altering the curvature of the CORNEA; removal or replacement of the CRYSTALLINE LENS; or modification of the SCLERA to change the axial length of the eye.Movement: The act, process, or result of passing from one place or position to another. It differs from LOCOMOTION in that locomotion is restricted to the passing of the whole body from one place to another, while movement encompasses both locomotion but also a change of the position of the whole body or any of its parts. Movement may be used with reference to humans, vertebrate and invertebrate animals, and microorganisms. Differentiate also from MOTOR ACTIVITY, movement associated with behavior.Questionnaires: Predetermined sets of questions used to collect data - clinical data, social status, occupational group, etc. The term is often applied to a self-completed survey instrument.Light Coagulation: The coagulation of tissue by an intense beam of light, including laser (LASER COAGULATION). In the eye it is used in the treatment of retinal detachments, retinal holes, aneurysms, hemorrhages, and malignant and benign neoplasms. (Dictionary of Visual Science, 3d ed)Light Signal Transduction: The conversion of absorbed light energy into molecular signals.Reaction Time: The time from the onset of a stimulus until a response is observed.Automobile Driving: The effect of environmental or physiological factors on the driver and driving ability. Included are driving fatigue, and the effect of drugs, disease, and physical disabilities on driving.Darkness: The absence of light.Hyperopia: A refractive error in which rays of light entering the eye parallel to the optic axis are brought to a focus behind the retina, as a result of the eyeball being too short from front to back. It is also called farsightedness because the near point is more distant than it is in emmetropia with an equal amplitude of accommodation. (Dorland, 27th ed)Corneal Opacity: Disorder occurring in the central or peripheral area of the cornea. The usual degree of transparency becomes relatively opaque.Differential Threshold: The smallest difference which can be discriminated between two stimuli or one which is barely above the threshold.Leber Congenital Amaurosis: A rare degenerative inherited eye disease that appears at birth or in the first few months of life that results in a loss of vision. Not to be confused with LEBER HEREDITARY OPTIC NEUROPATHY, the disease is thought to be caused by abnormal development of PHOTORECEPTOR CELLS in the RETINA, or by the extremely premature degeneration of retinal cells.Perceptual Disorders: Cognitive disorders characterized by an impaired ability to perceive the nature of objects or concepts through use of the sense organs. These include spatial neglect syndromes, where an individual does not attend to visual, auditory, or sensory stimuli presented from one side of the body.Cornea: The transparent anterior portion of the fibrous coat of the eye consisting of five layers: stratified squamous CORNEAL EPITHELIUM; BOWMAN MEMBRANE; CORNEAL STROMA; DESCEMET MEMBRANE; and mesenchymal CORNEAL ENDOTHELIUM. It serves as the first refracting medium of the eye. It is structurally continuous with the SCLERA, avascular, receiving its nourishment by permeation through spaces between the lamellae, and is innervated by the ophthalmic division of the TRIGEMINAL NERVE via the ciliary nerves and those of the surrounding conjunctiva which together form plexuses. (Cline et al., Dictionary of Visual Science, 4th ed)Cebidae: A family of New World monkeys in the infraorder PLATYRRHINI, consisting of nine subfamilies: ALOUATTINAE; AOTINAE; Atelinae; Callicebinae; CALLIMICONINAE; CALLITRICHINAE; CEBINAE; Pithecinae; and SAIMIRINAE. They inhabit the forests of South and Central America, comprising the largest family of South American monkeys.Optic Nerve: The 2nd cranial nerve which conveys visual information from the RETINA to the brain. The nerve carries the axons of the RETINAL GANGLION CELLS which sort at the OPTIC CHIASM and continue via the OPTIC TRACTS to the brain. The largest projection is to the lateral geniculate nuclei; other targets include the SUPERIOR COLLICULI and the SUPRACHIASMATIC NUCLEI. Though known as the second cranial nerve, it is considered part of the CENTRAL NERVOUS SYSTEM.Pseudophakia: Presence of an intraocular lens after cataract extraction.Aphakia: Absence of crystalline lens totally or partially from field of vision, from any cause except after cataract extraction. Aphakia is mainly congenital or as result of LENS DISLOCATION AND SUBLUXATION.Retinaldehyde: A carotenoid constituent of visual pigments. It is the oxidized form of retinol which functions as the active component of the visual cycle. It is bound to the protein opsin forming the complex rhodopsin. When stimulated by visible light, the retinal component of the rhodopsin complex undergoes isomerization at the 11-position of the double bond to the cis-form; this is reversed in "dark" reactions to return to the native trans-configuration.Eye Enucleation: The surgical removal of the eyeball leaving the eye muscles and remaining orbital contents intact.Macular Edema: Fluid accumulation in the outer layer of the MACULA LUTEA that results from intraocular or systemic insults. It may develop in a diffuse pattern where the macula appears thickened or it may acquire the characteristic petaloid appearance referred to as cystoid macular edema. Although macular edema may be associated with various underlying conditions, it is most commonly seen following intraocular surgery, venous occlusive disease, DIABETIC RETINOPATHY, and posterior segment inflammatory disease. (From Survey of Ophthalmology 2004; 49(5) 470-90)Esotropia: A form of ocular misalignment characterized by an excessive convergence of the visual axes, resulting in a "cross-eye" appearance. An example of this condition occurs when paralysis of the lateral rectus muscle causes an abnormal inward deviation of one eye on attempted gaze.Papilledema: Swelling of the OPTIC DISK, usually in association with increased intracranial pressure, characterized by hyperemia, blurring of the disk margins, microhemorrhages, blind spot enlargement, and engorgement of retinal veins. Chronic papilledema may cause OPTIC ATROPHY and visual loss. (Miller et al., Clinical Neuro-Ophthalmology, 4th ed, p175)Vitreous Body: The transparent, semigelatinous substance that fills the cavity behind the CRYSTALLINE LENS of the EYE and in front of the RETINA. It is contained in a thin hyaloid membrane and forms about four fifths of the optic globe.Retinal Artery Occlusion: Sudden ISCHEMIA in the RETINA due to blocked blood flow through the CENTRAL RETINAL ARTERY or its branches leading to sudden complete or partial loss of vision, respectively, in the eye.Ophthalmoscopy: Examination of the interior of the eye with an ophthalmoscope.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Retinal Hemorrhage: Bleeding from the vessels of the retina.Hand: The distal part of the arm beyond the wrist in humans and primates, that includes the palm, fingers, and thumb.Parrots: BIRDS of the large family Psittacidae, widely distributed in tropical regions and having a distinctive stout, curved hooked bill. The family includes LOVEBIRDS; AMAZON PARROTS; conures; PARAKEETS; and many other kinds of parrots.Activities of Daily Living: The performance of the basic activities of self care, such as dressing, ambulation, or eating.Eye Diseases, Hereditary: Transmission of gene defects or chromosomal aberrations/abnormalities which are expressed in extreme variation in the structure or function of the eye. These may be evident at birth, but may be manifested later with progression of the disorder.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Electrooculography: Recording of the average amplitude of the resting potential arising between the cornea and the retina in light and dark adaptation as the eyes turn a standard distance to the right and the left. The increase in potential with light adaptation is used to evaluate the condition of the retinal pigment epithelium.Postural Balance: A POSTURE in which an ideal body mass distribution is achieved. Postural balance provides the body carriage stability and conditions for normal functions in stationary position or in movement, such as sitting, standing, or walking.Intravitreal Injections: The administration of substances into the VITREOUS BODY of the eye with a hypodermic syringe.Prevalence: The total number of cases of a given disease in a specified population at a designated time. It is differentiated from INCIDENCE, which refers to the number of new cases in the population at a given time.Optic Nerve Diseases: Conditions which produce injury or dysfunction of the second cranial or optic nerve, which is generally considered a component of the central nervous system. Damage to optic nerve fibers may occur at or near their origin in the retina, at the optic disk, or in the nerve, optic chiasm, optic tract, or lateral geniculate nuclei. Clinical manifestations may include decreased visual acuity and contrast sensitivity, impaired color vision, and an afferent pupillary defect.Signal Detection, Psychological: Psychophysical technique that permits the estimation of the bias of the observer as well as detectability of the signal (i.e., stimulus) in any sensory modality. (From APA, Thesaurus of Psychological Index Terms, 8th ed.)Eye Protective Devices: Personal devices for protection of the eyes from impact, flying objects, glare, liquids, or injurious radiation.National Eye Institute (U.S.): Component of the NATIONAL INSTITUTES OF HEALTH. It conducts and supports research on the causes, diagnosis, and treatment of diseases of the eye and visual system. It was originally part of the National Institute of Neurological Diseases and Blindness. The National Eye Institute was established in 1968.Face: The anterior portion of the head that includes the skin, muscles, and structures of the forehead, eyes, nose, mouth, cheeks, and jaw.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Photorefractive Keratectomy: A type of refractive surgery of the CORNEA to correct MYOPIA and ASTIGMATISM. An EXCIMER LASER is used directly on the surface of the EYE to remove some of the CORNEAL EPITHELIUM thus reshaping the anterior curvature of the cornea.Touch Perception: The process by which the nature and meaning of tactile stimuli are recognized and interpreted by the brain, such as realizing the characteristics or name of an object being touched.Choroid Neoplasms: Tumors of the choroid; most common intraocular tumors are malignant melanomas of the choroid. These usually occur after puberty and increase in incidence with advancing age. Most malignant melanomas of the uveal tract develop from benign melanomas (nevi).Aging: The gradual irreversible changes in structure and function of an organism that occur as a result of the passage of time.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Endophthalmitis: Suppurative inflammation of the tissues of the internal structures of the eye frequently associated with an infection.Optic Atrophy, Hereditary, Leber: A maternally linked genetic disorder that presents in mid-life as acute or subacute central vision loss leading to central scotoma and blindness. The disease has been associated with missense mutations in the mtDNA, in genes for Complex I, III, and IV polypeptides, that can act autonomously or in association with each other to cause the disease. (from Online Mendelian Inheritance in Man, http://www.ncbi.nlm.nih.gov/Omim/, MIM#535000 (April 17, 2001))Psychometrics: Assessment of psychological variables by the application of mathematical procedures.Optic Chiasm: The X-shaped structure formed by the meeting of the two optic nerves. At the optic chiasm the fibers from the medial part of each retina cross to project to the other side of the brain while the lateral retinal fibers continue on the same side. As a result each half of the brain receives information about the contralateral visual field from both eyes.Feedback, Sensory: A mechanism of communicating one's own sensory system information about a task, movement or skill.IndiaPupil Disorders: Conditions which affect the structure or function of the pupil of the eye, including disorders of innervation to the pupillary constrictor or dilator muscles, and disorders of pupillary reflexes.Orbital Diseases: Diseases of the bony orbit and contents except the eyeball.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Optic Lobe, Nonmammalian: In invertebrate zoology, a lateral lobe of the FOREBRAIN in certain ARTHROPODS. In vertebrate zoology, either of the corpora bigemina of non-mammalian VERTEBRATES. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed, p1329)
Low vision assessment: Low vision is both a subspeciality and a condition. Optometrists and Ophthalmologists after their training may undergo further training in Low vision assessment and management.Operation Eyesight Universal: Operation Eyesight Universal is a Canada-based international development organisation, founded in 1963. It works to prevent avoidable blindness and to cure blindness that is treatable.Landolt CGene therapy for color blindness: Gene therapy for color blindness is an experimental gene therapy aiming to convert congenitally colorblind individuals to trichromats by introducing a photopigment gene that they lack. Though partial color blindness is considered only a mild disability and is controversial whether it is even a disorder, it is a condition that affects many people, particularly males.Binocular vision: Binocular vision is vision in which creatures having two eyes use them together. The word binocular comes from two Latin roots, bini for double, and oculus for eye.LogMAR chart: A LogMAR chart comprises rows of letters and is used by ophthalmologists and vision scientists to estimate visual acuity. This chart was developed at the National Vision Research Institute of Australia in 1976, and is designed to enable a more accurate estimate of acuity as compared to other charts (e.Tactical light: A tactical light is a flashlight used in conjunction with a firearm to aid low light target identification, allowing the marksman to simultaneously aim and illuminate the target. Tactical lights can be handheld or mounted to the weapon with the light beam parallel to the bore.Blind People's Association: The Blind People’s Association (BPA) is an organisation in India which promotes comprehensive rehabilitation of persons with all categories of disabilities through education, training, employment, community based rehabilitation, integrated education, research, publications, human resource development and other innovative means.Farnsworth Lantern Test: The Farnsworth Lantern Test, or FALANT, is a test of color vision originally developed specifically to screen sailors for shipboard tasks requiring color vision, such as identifying signal lights at night. It screens for red-green deficiencies, but not the much rarer blue color deficiency.Meridian (perimetry, visual field): Meridian (plural: "meridians") is used in perimetry and in specifying visual fields. According to IPS Perimetry Standards 1978 (2002): "Perimetry is the measurement of [an observer's] visual functions ...Rimless eyeglasses: Rimless eyeglasses, are a type of eyeglasses in which the lenses are mounted directly to the bridge and/or temples. The style is divided into two subtypes: three piece glasses are composed of lenses mounted to a bridge and two separate temple arms, while rimways (also called cortlands) feature a supporting arch that connects the temples to the bridge and provides extra stability for the lenses.Braille technology: Braille technology is assistive technology which allows blind or visually impaired people to do common tasks such as writing, browsing the Internet, typing in Braille and printing in text, engaging in chat, downloading files, music, using electronic mail, burning music, and reading documents. It also allows blind or visually impaired students to complete all assignments in school as the rest of sighted classmates and allows them take courses online.AmblyopiaKorte's law: In psychophysics, Korte's law, also known more completely as Korte's third law of apparent motion, is an observation relating the phenomenon of apparent motion to the distance and duration between two successively presented stimuli. It was originally proposed in 1915 by Adolf Korte.Percolation threshold: Percolation threshold is a mathematical concept related to percolation theory, which is the formation of long-range connectivity in random systems. Below the threshold a giant connected component does not exist; while above it, there exists a giant component of the order of system size.Autorefractor: An autorefractor or automated refractor is a computer-controlled machine used during an eye examination to provide an objective measurement of a person's refractive error and prescription for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye.Photopic vision: Photopic vision is the vision of the eye under well-lit conditions. In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visual acuity and temporal resolution than available with scotopic vision.Macula of retina: The macula or macula lutea (from Latin macula, "spot" + lutea, "yellow") is an oval-shaped pigmented area near the center of the retina of the human eye. It has a diameter of around .Neuro-ophthalmology: Neuro-ophthalmology is an academically-oriented subspecialty that merges the fields of neurology and ophthalmology, often dealing with complex systemic diseases that have manifestations in the visual system. Neuro-ophthalmologists initially complete a residency in either neurology or ophthalmology, then do a fellowship in the complementary field.OpsinStrabismusPlastic headlight restorationStereopsis: Stereopsis (from the Greek στερεο- [meaning "solid", and ὄψις] opsis, "appearance, [[visual perception|sight") is a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision.Retinal regeneration: Retinal regeneration deals with restoring retinal function to vertebrates so impaired.Pediatric ophthalmology: Pediatric ophthalmology is a sub-speciality of ophthalmology concerned with eye diseases, visual development, and vision care in children.Age-Related Eye Disease Study: The Age-Related Eye Disease Study (AREDS) was a clinical trial sponsored by the National Eye Institute, one of the National Institutes of Health in the United States.A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation With Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss.Photopigment: Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and photoreception.Congenital cataractMelanopsin: Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. Two other opsins in the mammalian retina are both involved in the formation of visual images: rhodopsin and photopsin in the rod and cone photoreceptor cells, respectively.ScotomaPresbyopiaCanon EOS 5Biological motion: Biological motion is a term used by social and cognitive neuroscientists to refer to the unique visual phenomenon of a moving, animate object. Often, the stimuli used in biological motion experiments are just a few moving dots that reflect the motion of some key joints of the moving organism.Entoptic phenomena (archaeology): In archaeology, the term entoptic phenomena relates to visual experiences derived from within the eye or brain (as opposed to externally, as in normal vision). In this respect they differ slightly from the medical definition, which defines entoptic phenomena as only applying to sources within the eye, not the brain.Glare (vision): Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. Because of this, some cars include mirrors with automatic anti-glare functions.Grow lightCataract surgerySpalding MethodMonocular estimate method: The monocular estimate method or monocular estimation method is a form of dynamic retinoscopy widely used to objectively measure accommodative response.Tassinari JT.Sustainability marketing myopia: Sustainability marketing myopia is a term used in sustainability marketing referring to a distortion stemming from the overlooking of socio-environmental attributes of a sustainable product or service at the expenses of customer benefits and values. The idea of sustainability marketing myopia is rooted into conventional marketing myopia theory, as well as green marketing myopia.List of optometry schools: The following list of optometry schools covers many countries, although the list is not exhaustive. Internationally, optometry as a profession includes different levels of education.Micromirror device: Micromirror devices are devices based on microscopically small mirrors. The mirrors are Microelectromechanical systems (MEMS), which means that their states are controlled by applying a voltage between the two electrodes around the mirror arrays.Cortical blindnessPurtscher's retinopathy: Purtscher's retinopathy is a disease where part of the eye (retina) is damaged. Usually associated with severe head injuries, it may also occur with other types of trauma, such as long bone fractures, or with several non-traumatic systemic diseases.Blue colour works: A blue colour works () is a paintworks where blue paint for use in glassmaking is produced. Usually the pigment, cobalt blue, needed for this purpose, was manufactured from cobalt-containing ore as in the case of the factories listed below.Flicker (screen): Flicker is a visible fading between cycles displayed on video displays, especially the refresh interval on cathode ray tube (CRT) based computer screens. Flicker occurs on CRTs when they are driven at a low refresh rate, allowing the brightness to drop for time intervals sufficiently long to be noticed by a human eye – see persistence of vision and flicker fusion threshold.Guiding Eyes for the Blind: Yorktown Heights, New YorkNeuropathy, ataxia, and retinitis pigmentosaMicroneurography: Microneurography is a neurophysiological method employed by scientists to visualize and record the normal traffic of nerve impulses that are conducted in peripheral nerves of waking human subjects. The method has been successfully employed to reveal functional properties of a number of neural systems, e.Photovoltaic retinal prosthesis: Photovoltaic retinal prosthesis is a technology for restoring sight to blind patients suffering from degenerative retinal diseases. In retinal degenerative diseases such as Retinitis Pigmentosa and Age-Related Macular Degeneration, patients loss ‘image capturing’ photo-receptors, but, neurons in the ‘image-processing’ inner retinal layers are relatively well preserved.X-linked congenital stationary night blindnessEye injuryPhospheneSubatomic scale: The subatomic scale is the domain of physical size that encompasses objects smaller than an atom. It is the scale at which the atomic constituents, such as the nucleus containing protons and neutrons, and the electrons, which orbit in spherical or elliptical paths around the nucleus, become apparent.Charles D. Phelps: Charles Dexter Phelps (September 16, 1937 – September 13, 1985) was a prominent American medical doctor, professor, and researcher in the field of ophthalmology. The clinical studies he oversaw contributed to significant advances in the scientific understanding and surgical and pharmacological treatment of glaucoma.Optic neuritisExtended physiological proprioception: Extended physiological proprioception (EPP) is a concept pioneered by D.C.List of optical illusions: This is a list of optical illusions.Convergence of measures: In mathematics, more specifically measure theory, there are various notions of the convergence of measures. For an intuitive general sense of what is meant by convergence in measure, consider a sequence of measures μn on a space, sharing a common collection of measurable sets.Auditory illusion: An auditory illusion is an illusion of hearing, the aural equivalent of an optical illusion: the listener hears either sounds which are not present in the stimulus, or "impossible" sounds.Perspective distortion (photography): Perspective correction}}Diabetic retinopathy: ( )Cue stick: A cue stick (or simply cue, more specifically pool cue, snooker cue, or billiards cue), is an item of sporting equipment essential to the games of pool, snooker and carom billiards. It is used to strike a ball, usually the .Chemical imaging: Chemical imaging (as quantitative – chemical mapping) is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time information.http://www.Spasm of accommodation: A spasm of accommodation (also known as an accommodation, or accommodative spasm) is a condition in which the ciliary muscle of the eye remains in a constant state of contraction. Normal accommodation allows the eye to "accommodate" for near-vision.Fairness to Contact Lens Consumers Act: The Fairness to Contact Lens Consumers Act (, 117 Stat. 2025, 2026, 2027, 2028 and 2029, codified at et seq.Optic disc pit: An optic disc pit is a congenital excavation (or regional depression) of the optic nerve head 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.
(1/1648) Brain activation during maintenance of standing postures in humans.
The regulatory mechanism of bipedal standing in humans remains to be elucidated. We investigated neural substrates for maintaining standing postures in humans using PET with our mobile gantry PET system. Normal volunteers were instructed to adopt several postures: supine with eyes open toward a target; standing with feet together and eyes open or eyes closed; and standing on one foot or with two feet in a tandem relationship with eyes open toward the target. Compared with the supine posture, standing with feet together activated the cerebellar anterior lobe and the right visual cortex (Brodmann area 18/19), and standing on one foot increased cerebral blood flow in the cerebellar anterior vermis and the posterior lobe lateral cortex ipsilateral to the weight-bearing side. Standing in tandem was accompanied by activation within the visual association cortex, the anterior and posterior vermis as well as within the midbrain. Standing with eyes closed activated the prefrontal cortex (Brodmann area 8/9). Our findings confirmed that the cerebellar vermis efferent system plays an important role in maintenance of standing posture and suggested that the visual association cortex may subserve regulating postural equilibrium while standing. (+info)
(2/1648) Optical imaging of functional domains in the cortex of the awake and behaving monkey.
As demonstrated by anatomical and physiological studies, the cerebral cortex consists of groups of cortical modules, each comprising populations of neurons with similar functional properties. This functional modularity exists in both sensory and association neocortices. However, the role of such cortical modules in perceptual and cognitive behavior is unknown. To aid in the examination of this issue we have applied the high spatial resolution optical imaging methodology to the study of awake, behaving animals. In this paper, we report the optical imaging of orientation domains and blob structures, approximately 100-200 micrometer in size, in visual cortex of the awake and behaving monkey. By overcoming the spatial limitations of other existing imaging methods, optical imaging will permit the study of a wide variety of cortical functions at the columnar level, including motor and cognitive functions traditionally studied with positron-emission tomography or functional MRI techniques. (+info)
(3/1648) Dynamics of horizontal vergence movements: interaction with horizontal and vertical saccades and relation with monocular preferences.
We studied the dynamics of pure vergence shifts and vergence shifts combined with vertical and horizontal saccades. It is known from earlier studies that horizontal saccades accelerate horizontal vergence. We wanted to obtain a more complete picture of the interactions between version and vergence. Therefore we studied pure version (horizontal and vertical), pure vergence (divergence and convergence) and combinations of both in five adult subjects with normal binocular vision and little phoria (< 5 degrees). The visual targets were LED's in isovergence arrays presented at two distances (35 and 130 cm) in a dimly lit room. Two targets were continuously lit during each trial and gaze-shifts were paced by a metronome. The two subjects with a strong monocular preference made vergence eye movements together with small horizontal saccades during pure vergence tasks. The other subjects, who did not have a strong monocular preference, made pure vergence movements (without saccades). These findings, suggest that monocular preferences influence the oculomotor strategy during vergence tasks. Vergence was facilitated by both horizontal and vertical saccades but vergence peak-velocity during horizontal saccades was higher than during vertical saccades. (+info)
(4/1648) Functional micro-organization of primary visual cortex: receptive field analysis of nearby neurons.
It is well established that multiple stimulus dimensions (e.g., orientation and spatial frequency) are mapped onto the surface of striate cortex. However, the detailed organization of neurons within a local region of striate cortex remains unclear. Within a vertical column, do all neurons have the same response selectivities? And if not, how do they most commonly differ and why? To address these questions, we recorded from nearby pairs of simple cells and made detailed spatiotemporal maps of their receptive fields. From these maps, we extracted and analyzed a variety of response metrics. Our results provide new insights into the local organization of striate cortex. First, we show that nearby neurons seldom have very similar receptive fields, when these fields are characterized in space and time. Thus, there may be less redundancy within a column than previously thought. Moreover, we show that correlated discharge increases with receptive field similarity; thus, the local dissimilarity between neurons may allow for noise reduction by response pooling. Second, we show that several response variables are clustered within striate cortex, including some that have not received much attention such as response latency and temporal frequency. We also demonstrate that other parameters are not clustered, including the spatial phase (or symmetry) of the receptive field. Third, we show that spatial phase is the single parameter that accounts for most of the difference between receptive fields of nearby neurons. We consider the implications of this local diversity of spatial phase for population coding and construction of higher-order receptive fields. (+info)
(5/1648) Configuration saliency revealed in short duration binocular rivalry.
Supra-threshold spatial integration was studied by testing the saliency of multi-Gabor element configurations in short duration binocular rivalry (dichoptic masking) conditions. Dichoptic presentations allow for a competition between spatially overlapping supra-threshold stimuli that involve non-overlapping monocular receptive fields in the first stage of visual filtering. Different spatial configurations of Gabor patches (sigma = lambda = 0.12 degree) were presented to one eye (target) together with a bandpass noise presented to the other eye (mask). After a short rivalry period (120 ms) in which a dominance of one eye was established, a probe (a randomly positioned small rectangle of reduced contrast in the target) was presented for additional detection period (80 ms). Probe detection performance was measured (two-alternative-forced choice paradigm (2AFC) by finding the mask contrast leading to 79% correct response. Results show that configuration saliency is consistently expressed as dominance in short-duration binocular rivalry, with similar results obtained for longer durations (200 ms and continuous presentations). We find that textures of high-contrast randomly oriented patches are more dominant than uniform textures where the effect decreases and eventually reverses with decreasing of contrast. For supra-threshold contours, however, we find that smooth collinear contours are more dominant than 'jagged' ones, regardless of phase and contrast. These findings suggest principles underlying early lateral integration mechanisms based on contrast dependent inhibitory and excitatory connections. This mechanism could be based on iso-orientation surround (2D) inhibition and collinear (1D) facilitation, with inhibition being more effective at high contrasts. (+info)
(6/1648) Instability of torsion during smooth asymmetric vergence.
Several categories of torsional eye movements obey Listing's law; however, systematic deviations from this law occur during vergence. Two kinematic models attempt to incorporate these deviations, both of which are supported by experimental evidence; however, they lead to different torsion predictions. These discrepancies have been explained in terms of experimental procedures, but it now seems likely from several recent studies that individual differences in torsion patterns may also be important. This study therefore examines the variation of torsion during a smooth asymmetric vergence task in which a fixation target was moved along the line-of-sight of the right eye at 15 degrees elevation; each of five subjects observed five trials of both inward and outward target motion, repeated in two sessions several weeks apart. There were no significant group differences in left or right eye torsion between trials or sessions, suggesting that monocular torsion patterns were relatively stable over time. When examined more closely, however, the torsion patterns shown by some individuals did vary for inward versus outward target motion. Hence, monocular torsion was idiosyncratic and depended on the direction in which fixation was changing (convergence or divergence). In a binocular analysis, cycloversion varied dramatically between subjects and depended on the direction of target motion; however, this was not the case for cyclovergence. In summary, cyclovergence is relatively stable and depends on where the eyes are looking, whereas cycloversion (and hence monocular torsion) is relatively unstable and depends on how they came to be in that particular horizontal and vertical orientation. These findings help to explain the controversy surrounding the torsional behaviour of the human eye during vergence. (+info)
(7/1648) The influence of large scanning eye movements on stereoscopic slant estimation of large surfaces.
The results of several experiments demonstrate that the estimated magnitude of perceived slant of large stereoscopic surfaces increases with the duration of the presentation. In these experiments, subjects were free to make eye movements. A possible explanation for the increase is that the visual system needs to scan the stimulus with eye movements (which take time) before it can make a reliable estimate of slant. We investigated the influence of large scanning eye movements on stereoscopic slant estimation of large surfaces. Six subjects estimated the magnitude of slant about the vertical or horizontal axis induced by large-field stereograms of which one half-image was transformed by horizontal scale, horizontal shear, vertical scale, vertical shear, divergence or rotation relative to the other half-image. The experiment was blocked in three sessions. Each session was devoted to one of the following fixation strategies: central fixation, peripheral (20 deg) fixation and active scanning of the stimulus. The presentation duration in each of the sessions was 0.5, 2 or 8 s. Estimations were done with and without a visual reference. The magnitudes of estimated slant and the perceptual biases were not significantly influenced by the three fixation strategies. Thus, our results provide no support for the hypothesis that the time used for the execution of large scanning eye movements explains the build-up of estimated slant with the duration of the stimulus presentation. (+info)
(8/1648) An orientation anisotropy in the effects of scaling vertical disparities.
Garding et al. (Vis Res 1995;35:703-722) proposed a two-stage theory of stereopsis. The first uses horizontal disparities for relief computations after they have been subjected to a process called disparity correction that utilises vertical disparities. The second stage, termed disparity normalisation, is concerned with computing metric representations from the output of stage one. It uses vertical disparities to a much lesser extent, if at all, for small field stimuli. We report two psychophysical experiments that tested whether human vision implements this two-stage theory. They tested the prediction that scaling vertical disparities to simulate different viewing distances to the fixation point should affect the perceived amplitudes of vertically but not horizontally oriented ridges. The first used elliptical half-cylinders and the 'apparently circular cylinder' judgement task of Johnston (Vis Res 1991;31:1351-1360). The second experiment used parabolic ridges and the amplitude judgement task of Buckley and Frisby (Vis Res 1993;33:919-934). Both studies broadly confirmed the anisotropy prediction by finding that large scalings of vertical disparities simulating near distances had a strong effect on the perceived amplitudes of the vertically oriented stimuli but little effect on the horizontal ones. When distances > 25 cm were simulated there were no significant differential effects and various methodological reasons are offered for this departure from expectations. (+info)
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