Automatic adjustment to the shape of the lens of the eye in order to bring objects into focus as the viewing distance varies.
Rare, inherited vision disorder in which a person has little or no ability to see color. People with achromatopsia also commonly experience some vision loss, especially in bright light, to which they are extremely sensitive. The severity of achromatopsia varies. Although there is no cure or treatment for this disorder, people with achromatopsia can manage its symptoms. For example, they can wear sunglasses or tinted contact lenses to cope with bright light. They can use magnifiers and other devices for low vision to help them read, and telescopes to help them see distant objects.
Decreased or absent ability to visually recognize or identify shapes, objects or people.
A visual-cognitive disorder characterized by inability to recognize and identify familiar visual stimuli (objects, faces, letters, places, etc.) by vision only, despite sufficiently available visual and cognitive capacities. (This term does
not apply to difficulties with assigning labels/names to visual stimuli (Visual anomia).
A condition in which the individual can only see things when they are not moving.
Difficulty in the naming of letters or words.
Impaired vision in one or both eyes, with no anatomical cause, due to the impaired development of vision as a sequel to untreated optical (refractive) errors, impaired image formation due to an eye disorder such as cataract, or impaired eye alignment (strabismus). Also known as a lazy eye.
Difference in refractive errors between the two eyes.
Inability to name objects or to recognize the written or spoken names of objects.
A defect into the visual field.
Lack of awareness of and insight into an obvious functional impairment because the subject is unable to detect the mismatch between assumed/expected function and the real functional status. Anosognosia typically occurs in about 30% of subjects with hemiplegia and (visual) neglect (mainly after right-hemisphere injury) or homonymous hemianopia (irrespective of the side of brain injury).
Is due to surgical removal of the lens, because of cataract. Ahpakia is corrected either by using intraocular lenses, contact lenses or cataract spectacles.
Difficulty performing learned purposeful actions despite the requisite physical capacity. This can affect simple movements (e.g. gestures) on command after verbal instruction or by imitation (ideomotor apraxia) or complex movements (e.g. preparing a cup of tea, dressing) (ideational apraxia). The latter form is explained as loss of the action plan (impairment of Procedural memory).
Apraxia of gaze
Disorder of the attention due to the bilateral damage to the posterior parietal (dorsal stream) territory of the brain, leading to lack of movements.
Evaluation of functioning i.e. more than the measurement of a few functions.
A type of refractive error that focuses light at different points in front of or behind the retina rather than a single point, and results in blurred vision at all distances, due to the subtle asymmetric, non-spherical shape of the cornea.
Loss of the tissue due to wasting.
Results from bilateral posterior parietal injury and associated disconnection of fronto-parietal fiber tracts. A neuropsychological condition characterized by marked limitation in the number of entities that can be seen at the same time leading to restriction of the Field of attention, Oculomotor (ocular) apraxia and Optic ataxia. The syndrome can vary in severity from mild to severe; the resulting impairments are omission of parts of the surroundings, difficulties with intentionally shifting gaze to locations of interest or to external stimuli and impaired visual guidance of grasping movements and movement of other parts of the body. In addition, those affected exhibit Spatial disorientation and have difficulties with reading, writing, copying, dressing, etc.
Use of both eyes together so that the separate images from each eye (which are slightly different) are interpreted by the brain as a single image. At its highest form - stereopsis - an impression of depth can be obtained by the brain superimposing two slightly dissimilar pictures of the same objects.
Absence of vision. Total blindness is complete absence of vision and is rare.
Slight awareness of, or reflex reaction to, moving targets, lights and colors in an area of apparently absent visual field.
The capacity of the brain to adapt its functions to altered environmental (or task) conditions by experience (Environment-dependent plasticity) and Learning (Practice-dependent plasticity) and to compensate for functional alterations of the brain, e.g. after injury or in pathophysiological states (Functional compensation).
Fluid filled cavities in the middle of the brain. The nerve fibers of the optic radiation run close to the wall of the lateral ventricle and are thus vulnerable if there are circulatory disturbances in the highly vascular ventricles walls.
The area at the base of the brain that, along with the midbrain above it, carries the nerves fibers running in both directions between the brain and the body and receives and processes input from the cranial nerves, including those that serve hearing and eye movements.
Is a region of the Cerebral cortex, which is defined by its structure and organization of cells (so-called cytoarchitecture). Brodmann areas were originally defined and numbered by the German neuroanatomist Korbinian Brodmann who in 1909 described 47 different cortical areas.
The capacity of the visual system to see in the central visual field.
Central fixation target
A target placed in the center of a visual field test.
A timekeeping brain structure that ensures that control of emotion by the frontal lobes, movement of the body processed by the parietal lobes, and vision processed by the occipital lobes are synchronized and coordinated.
Profound impairment or absence of vision due to bilateral damage to the visual pathways posterior to the lateral geniculate bodies that may be accompanied by damage to other regions of the brain that serve vision. Also known as cortical blindness.
The layer of grey matter that covers the outside of the brain and consists of six layers of neurons. Regional differences in the cytoarchitectonic characteristics led Brodmann to the categorization of the cerebral cortex into distinct areas (Brodmann’s areas).
Lack of oxygen supply to the brain, which can be brought about by impaired blood flow or impaired oxygenation due to severe respiratory disorders.
Loss or impairment of motor function caused by damage or abnormal development of the brain before, during or immediately after birth.
Cerebral visual impairment (CVI)
Visual impairment due to the damage or disorder of the visual pathways and visual centers in the brain, including pathways serving visual perception, cognition, and visual guidance of movement.
Chiasma means crossing. In anatomy it means crossing of the optic nerves.
Inherited non-progressive condition in which the person confuses colors either in red-green or blue-yellow axis.
Cognitive visual dysfunction
Disordered function of the brain related to the damage of the visual-associative areas and / or their incoming pathways leading to misinterpretation of the visual world either with respect to where things are or what they are.
One type of sensory cells in the outermost layer of the retina. Cone cells are numerous in the central retina (fovea). They function in daylight and twilight, absorb light energy and produce the reactions that leads to perception of colors. They do not function in scotopic condition.
Inability to name colors due to the neurological dysfunctions.
Existing at or before birth.
The way that a foreground (an object) stands out from its background. Contrast is not a property of visual edges on the retina but of visual edges in space. This is important in allowing us to vary the learner’s visual world in order to enhance contrast.
The ability of the visual system to distinguish the difference in brightness between two adjacent surfaces.
The ability to turn the eyes inward as an object approaches them.
Pertaining to the cerebral cortex.
Vision is sometimes worse when crowded by other information e.g. words on the page too close together or patterns behind an object. Children can be assessed for crowding difficulties with different tests and tools.
Refers to the gain in sensitivity as the eye remains in the dark. It is a relatively slow process, taking around 40 minutes to complete. Where the ability of the eyes to adapt to the dark is slower, this is likely to be associated with poorer contrast sensitivity. Should the learner suddenly exhibit poorer dark adaptation than is usual for that learner, you may want to request further examination.
It measures what is the smallest object that a child notices on a contrasting background.
A measure of a child´s level of development according to social, emotional, intellectual and physical growth.
Mental of physical disability arising as a consequence of a disorder of development.
Paralysis or weakness of the lower limbs.
The pathway between the occipital and posterior parietal lobes that maps surroundings and brings about visual guidance of movement. Sometimes known as the “where” pathway, it functions at a subconscious level.
Dorsal stream dysfunction
Condition in which the function of the dorsal stream is disrupted, causing impaired visual guidance of movement and limiting the number of entities that can be seen in crowed scenes.
A condition in which impaired perception of movement is relative and not absolute.
A language-based learning disability that can be associated with difficulties in reading, spelling, writing and sound-symbol association.
Looking slightly above, below or to one side of an object in order to place a visual image onto an optimum area of the visual field of viewing.
Along with its magnetic counterpart, magnetoencephalography (MEG), this procedure noninvasively records brain activity from the surface of the scalp to provide an indirect evaluation of the brain function.
Condition in which the light coming from a distant object to the eye is focused accurately on the retina to make a crisp, focused image without the need for refractive correction.
Disorder of the brain due to disease, causing damage and malfunction.
A group of conditions in which disturbance of the electrical activity of the brain results in impairment and disorder in a range of brain functions, including consciousness, movement, sensation and vision.
A condition in which one eye is horizontally turned inward; also known as convergent strabismus (US) or convergent squint (UK). Results in a lack of stereopsis.
Higher-order mental skills that are used to control and coordinate cognitive abilities and behaviors to achieve a particular goal.
A condition in which one eye is horizontally turned outward; also known as divergent strabismus (US) or divergent squint (UK). Results in lack of stereopsis.
Extrastriate visual areas
Visual cortical areas outside the Striate (primary) visual cortex; also called prestriate cortex or visual association areas.
The identification of an individual’s face on the basis of specific and characteristic facial features, enabled by repeated identification of the same face.
The ability to discriminate an object from its surroundings; also called figure-ground perception.
The ability to maintain the eyes focused on a target.
The ability to judge the shape, size, texture, etc. of an object by vision or touch; also called form discrimination.
The functional centre of the retina with the most numerous and tightly packed cone cells. This gives the sharpest vision.
Areas of the front of the brain, part of which (the prefrontal cortex on both sides, and the front portion of the frontal lobes) serves the executive functions of thinking, planning and controlling behaviors.
Skills that students with multiple disabilities learn that provide them with the opportunity to work, play, socialize and take care of personal needs to the highest attainable level.
The way in which a person uses available visual skills and abilities in typical tasks of daily life. How well an individual processes the visual information in his or her environment in order to go about daily tasks.
Functional visual impairment
Damage to the visual system that impedes the ability to learn or perform usual tasks of daily life, given a child’s level of maturity and cultural environment.
Is the impairment in using eye movements in a purposeful action, despite the intact capacity to carry out the eye movements.
Immediate mental construct of an overall (global) scenario formed from a collection of separate elements.
A stimulus that consists of regular parallel light and dark elements.
Movement that involves the large muscles of the body such as those in the arms and legs (e.g. crawling, running, or jumping).
Lack of perception of one half of the visual field.
One half of a sensory field.
Weakness on one side of the body.
Paralysis of one side of the body.
Higher visual functions
The combination of visual perception, visual cognition, guidance of movement and the capacity to choose to give visual attention.
A visual field defect which the same half of the field of view is not see by each eye.
A condition due to the impaired of the circulation of the cerebral spinal fluid (CSF), causing increased intracranial pressure, commonly with increased CSF volume expanding the water spaces in the brain (ventricles).
Hyperopia or hypermetropia
A type of refractive error that results in blurred images when the length of the eye from front to back is too short, or the optical power of the eye is insufficient to bring an object into focus. Also known as long-sightedness or farsightedness.
An upward eye turn.
Underdevelopment of the body part.
Lack of oxygen.
Disordered ability to pursue a moving target with the eyes.
Turning of both eyes together in one direction for a variable duration, often with an accompanying head turn. Also paroxysmal deviation.
Insufficient supply of the blood.
An exchange that involves a child´s and a partner’s awareness of the other´s mutual gaze, gesture or language.
The subconscious automatic system in the inner ear and brain stem that is responsible for controlling and maintaining the balance.
Is a recognizable natural or man-made feature used for navigation.
Lateral geniculate body
Small knee-shaped structure deep inside the brain that act as relay stations to convey visual information from the eyes through the brain.
Is a selective type of visual agnosia, which is characterized by the loss of recognition of the significance of letters and/or the integration of letters into words.
Is the capacity of the retina to adapt to increased levels of illumination.
Inability to recognize certain individual letters due to damage to the brain.
Visual impairment that is severe enough to impede the person´s ability to learn or perform usual tasks of daily life but still allows some functionally useful visual discrimination. It covers a range from mild to severe visual impairment, but exclude total blindness.
Magnetic resonance imagining (MRI)
A neuroimaging procedure that shows the anatomical features of the brain in great detail and can be used to study brain structure following injury.
A major pathway of the visual system that primarily transmits visual information in the peripheral visual field to the brain and serves movement perception, as well as facilitating visual guidance of movement.
MDVI – Multiple disabled visually impaired
There is no universally agreed definition of MDVI. As such, there are many different interpretations of the needs of those falling under MDVI. Whilst the network totally agrees with the ICF framework, MDVI Euronet partners have agreed a working definition of: 'A person with at least two disabilities, one of which manifests itself as a visual impairment, which impact significantly on the person's learning potential to such a degree so as to require a customised educational provision.'
The median plane of the body.
Mirror neuron system (MNS)
A system in the brain that facilitate understanding and imitation of the actions of others.
The capacity to see the movement.
A type of refractive error that results in blurred images of the retina when viewing objects in the distance. Also known as nearsightedness or short-sightedness.
Attentional defect, an inability to direct attention, which prevents a person of being aware of part of space around or a part of herself. It may mean loss of attention in one half of the visual field (most often on the left side).
Refers to adaptation of neural pathways and structures which are due to changes in behavior, environment and neural processes as well as changes resulting from injury due to learning processes.
An assessment tool that has been standardized in a way that enables comparison of the results of test takers in relation to a group that has already taken the test.
The position of the eyes in which the oscillations of a person’s nystagmus are least. Often accompanied by a compensatory head posture.
Unintentional or involuntary to-and-fro movement of the eyes.
The understanding that objects still exist when they cannot be seen, heard, touched, smelled or sensed.
Posterior (back) portions of the cerebral cortex in each hemisphere responsible for processing vision and sending visual information to other parts of the brain.
A disorder involving the occipital and parietal lobes of the brain, resulting in impairment of the functions of both structures.
A description of the position of the eyes. If the eyes are out of alignment, strabismus is present.
Ocular visual impairment
Visual impairment caused by a disorder of the eye or optic nerve (but not the brain).
Limited ability to move the eyes fast (saccadic eye movement) from one target to another.
Use of eye movements (Saccades, Fixations) to scan the visual surrounding or a visual stimulus array (scene, object).
Impaired control of the eye movements leading to visual difficulties such as visual fixation or visual tracking problems, ocular alignment and impairment of accommodation.
Impaired accuracy of movement of limbs and body through visual space because visual guidance of movement is impaired.
The X-shaped structure formed by the joining up of the optic nerves, which cross and then become the optic tracts just below and leading into the brain.
Bundle of nerve fibers (axons) from the ganglion cells of the retina. Nerves that transmit visual information from the retina of each eye to the brain.
Optic nerve atrophy
Atrophy means loss of functioning cells. The reason for cell damage may be infection, trauma, tumor or increased intraocular pressure.
A collection of the nerve axons that carry information from the lateral geniculate bodies into the thalamus to the visual cortex in the occipital lobes.
Bundles of nerve fibers that emerge from the back of the optic chiasm on each side that carry visual information to the lateral geniculate body.
Related to the eye movement.
Optokinetic nystagmus (OKN)
Reflex to and fro movement of the eyes in response to moving targets. OKN can be tested horizontally and vertically in response to moving black and white stripes or other repeating targets in the appropriate directions in front of the eyes.
A health care provider who specializes in the measurement of refractive errors and other visual functions, prescribes eyeglasses or contact lenses and (in some countries) diagnoses and manages conditions of the eye.
Letters and symbols used to test visual acuity.
The capacity to know where one is, has been and will be going, as well as the position and location of possession.
A specialist in measurement and management of disorders of the eye movements and binocular vision.
The perception of the relative alignment of objects in relation to the position of viewing. A phenomenon that helps compensate for lack of stereopsis.
Is the ability to simultaneously process several stimuli.
The parts of the brain that integrate incoming sensory information with the execution of body movements and process language (usually on the left side).
A pathway of the brain served by small retinal and brain cells that transmit fine, detailed visual information primarily in the central visual field.
Is the discrimination and identification, respectively, of a set of stimuli arranged in a certain regular form, e.g. contours, figures, objects, faces, words, melodies.
The ability to see, hear or become aware of something through senses.
Perceptual visual dysfunction
A condition in which the brain is unable to process visual information correctly. Sometimes used synonymously with perceptual visual impairment.
Around the time of the birth.
A target placed at the outer edge of a person´s visual field.
Peripheral visual field
The area of vision outside the center of an individual´s gaze.
Damage to the white matter adjacent to the lateral ventricles of the brain.
Periventricular white matter
The white matter near to the ventricles of the brain.
Increased sensitivity to light.
Preferential looking (PL)
Is an experimental method in developmental psychology. An infant is habituated to a particular stimulus; then a second, new stimulus is shown, which differs from the habituated stimulus with respect to a specific feature (e.g. size, color, form). If the infant now looks for longer at the new stimulus, it is suggestive that the infant can discriminate between the two stimuli. Preferential looking is now used routinely to estimate visual acuities in young children and those who are otherwise unable to cooperate with the use of other methods.
Prefrontal cerebral cortex
The anterior part of the frontal lobes of the brain that contributes to initiation and coordination of thoughts and actions.
Birth before 37 weeks’ gestation.
Inability to recognize faces.
Pupil of an eye
The hole in the center of the iris that allows light to enter the eye and, by its change in size, controls the amount of light passing through.
Pursuit eye movements
Smooth eye movements made while following an object. Also known as smooth pursuit movements.
A defect in the visual field that affects a quarter of the visual field, demarcated by vertical and horizontal lines passing through the center of the visual field.
Ability to recognize and distinguish a specific visual target from other similar stimuli; often measured using letter charts.
A focusing inaccuracy within the eye such the light rays do not come into clear focus on the retina, resulting in a blurred image. (In children and young adults the refractive error of hyperopia may be corrected by accommodation and therefore may not lead to a blurred image).
Training to improve skills or behaviors that have been lost or decreased due to disease or injury.
Relative orientation perception
Ability to see subtle differences between orientations.
The inner sensory nerve layer next to the choroid that lines the posterior two-thirds of the eyeball. The retina reacts to light and transmits visual information by means of nerve impulses to the brain.
Retinopathy of prematurity (ROP)
A disorder of the retina related to abnormal vascular development that occurs as a sequel to premature birth. It is arrested in most cases following appropriate screening and treatment.
Sensory cells in the outer layer of the retina. They are highly sensitive to light and thus function best in twilight and scotopic conditions. In daylight their activity is not transmitted through the retina because the function of the cone cells inhibits it. The highest concentration of rod cells is in the peripheral parts of the retina.
Fast eye movements from one fixation to another.
Voluntary eye movements, usually quick movements of both eyes simultaneously, used for tasks such as reading or scanning a scene.
Making a series of visual fixations in order to visually inspect a large area.
A non-seeing area in the visual field.
Inability to see more than one or two items within the visual scene at the same time due to damage to the posterior parietal region of the brain.
A form of cerebral palsy resulting in weakness and stiffness of the lower limbs.
Is the perception of one’s own location in space and its adjustment with reference to objects (Landmark) in the same space.
Perception of spatial properties of visual stimuli, e.g. position, orientation of contours, spatial configuration of figures, objects and scenes.
Fine depth perception that results from the brain´s interpretation of the slight difference between the disparate pictures of the same visual scene provided by the two eyes.
Misalignment of the eyes; eyes do not look on the same direction.
Striate (primary) visual cortex
Is the discrete region in the posterior occipital lobes of the brain that receives input directly from the eyes via the Optic radiations, which serves primary visual functions, e.g. light detection; also labelled Brodmann area 17 or V1 (visual area 1). (When this part of the brain is sectioned, a light brown line, or stria, is observed, from which the term striate is derived).
First cortical area which receives retinal input from the thalamus (geniculo-striate pathway); also called primary visual cortex, Brodmann’s area 17, visual area 1, V1.
The areas of the brain under the temples that analyze the input from the senses. They provide that memory banks that underpin knowledge and recognition.
Is the act of processing text material (letters, numbers); essential prerequisites are an intact central visual field, a sufficiently high visual acuity and contrast sensitivity, accurate form discrimination, ability to integrate letters/numbers to larger elements and regular shifting of fixation in the direction of processing. Text processing is the main basis for understanding of text material.
A structure situated between the cerebral cortex and the midbrain involved in processing and relaying sensory and motor signals to the cerebral cortex. The thalamus plays and important part in bringing about reflex visual attention.
The lower limit of visual acuity measured with each eye separately for the purpose of diagnosis and follow-up of visual disorders.
Disorientation in one´s surrounding. Impairments results from ventral stream damage and problem forming mental map of the environment. Also known as topographic disorientation.
Maintaining fixation on a moving object of interest using pursuit eye movements.
Visual pathway between the occipital and temporal lobes, sometimes known as the “what” pathway, which supports the process of visual recognition. Dysfunction can cause impaired recognition of objects and persons and impaired orientation in surrounding and extended space.
Fluid-filled cavities in the brain.
Vestibular ocular reflex (VOR)
The balance system served by the inner ear accords subconscious knowledge of the vertical and horizontal; these data inform the vestibular system in the midbrain, which automatically aligns the eyes to the horizon in total darkness. Rotation of the head in an unconscious person brings about such righting (doll’s eye) movements if brainstem function is intact.
Lack of vision due to acquired damage to a previously intact visual system.
A measure of the ability of the visual system to see or resolve the component parts of an image as being separate from one another, when tested at maximum contrast.
The ability to focus on specific elements in a visual scene by selecting or by being drawn salient information and filtering out less salient information.
Is observed when discrete boundaries between image components are not seen as distinct, but instead merge into one another. This can be caused by refractive error and disorder of the eyes or visual pathways.
The totality of brain elements serving or supporting vision that serve to map, search, give attention to, recognize and interpret visual input.
The capacity to process what is seen, to think about its significance, and to manipulate and use both incoming image data and remembered imagery in the context of creative thought.
Disorder of the visual perception, visual guidance of movement, and / or visual attention.
Visual evoked potential (VEP)
Computerized recording of electrical activity at the back of the brain used assist in diagnosis and in the estimation of visual acuity and contrast sensitivity.
Area of space visible to the eyes when looking straight ahead.
Measurable components of vision including visual acuity, contrast sensitivity, color perception, visual fields and the perception of movement.
Visual guidance of movement
Mapping of incoming visual information in the mind that is used to guide movement of the limbs and body.
Damage to the visual system that impedes the ability to learn or perform usual tasks of daily life, given a child´s level of maturity and cultural environment. Includes both low vision and blindness.
The time taken to receive and process incoming visual information in the brain.
Visual guided motor behaviors
Behaviors with a major visual-motor component, including reaching for, turning toward, and moving among obstacles toward visual targets.
The ability to remember a visual image or form after viewing.
Coordination of goal-directed motor actions in relation to a visual target.
Inattention to one side of the visual space and / or to one side of the body.
Bundles of nerve fibers that carry visual information to different location of the brain.
Ability to interpret the immediate environment by processing incoming information that is sent from the eyes to the brain.
The brain´s recognition and interpretation of information taken in through the eyes.
The ability to recognize and identify objects, faces, geometric shapes and colors as well as their pictures and images.
Is the process of detecting a target stimulus among distractor stimuli. If the target differs qualitatively from distractors, it pops out, and search time is independent of the number of stimuli in the display (set size); this search type is called a parallel search mode. If the target and distractors are similar, then the subject has to search for the target in a serial fashion (serial search mode).
Visual space perception
Is the sum of abilities to process and comprehend spatial properties of the environment and of objects, i.e. position, distance, direction, spatial relationships between stimuli.
An approach that places a child as a passive observer, in an environment in which selected visual stimuli are presented with the intention of bringing about attention and enhancement of visual development.
Network that produces sight, including both the eyes and the brain.
The capacity to appreciate, understand and map the three-dimensional characteristics of the surroundings, both for subjective appreciation and to facilitate movement through space.
Occipito-temporal route that is specialized for the processing of visual object properties.
Occipito-parietal route that is specialized for the processing of visuospatial information.
Is the ability to actively process information in temporary storage, with a phonological loop for the manipulation of verbal content and a visuospatial scratch pad for retaining of visual information; the central executive coordinates these two ‘slave systems’ and deploys attentional resources between them.
Zihl J. and Dutton G.N. 2015. Cerebral visual impairment in children. Visuoperceptive and visuocognitive disorders. Wien, Austria. Springer.
Lueck A.H. and Dutton G.N. 2015. Vision and the brain: Understanding cerebrl visual impairment in children. United States of America. American Foundation for the Blind.
Hyvarinen L and Jacob N. 2011. What and how does this child see? Helsinki, Finland. VISTEST Ltd.