Optometric terminology

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A pattern” – a horizontal deviation may be different in upgaze versus downgaze. An “A pattern” deviation shows more eso (or less exo) in upgaze.

Abduction – movement of the eyes away from the nose.

Accommodation – the act of focusing the eyes to provide an image clear enough for interpretation. The stimulus to accommodation may come from blur on the retina, or perceived awareness of the proximity of a target. Accommodation is said to be “stimulated” when looking at near objects, and “relaxed” when looking further away. Accommodation is part of the “identification” system; it tells us the “what is it?” of what we are looking at.
Accommodative amplitude – the range of distance or lens power over which the patient can stimulate focus to maintain clarity. A patient who shows a reduced amplitude is said to have an accommodative insufficiency.
Accommodative flexibility- ease with which accommodation can be changed from one distance to another. A patient who has reduced flexibility is said to have accommodative infacility.
Accommodative Spasm- difficulty releasing (relaxing) accommodation.

Acquired Brain Injury (ABI) refers to damage to the brain acquired after birth. It usually affects cognitive, physical, emotional, social or independent functioning and can result from traumatic brain injury (i.e. accidents, falls, assaults, etc.) and nontraumatic brain injury (i.e. cerebral palsy, stroke, brain tumours, infection, poisoning, hypoxia, ischemia or substance abuse). See also TBI

(Visual) Acuity (VA) – clearness or sharpness of sight, the ability to resolve or discriminate contours and to tell when there is a separation of the contour from its background. In the US, it is usually represented as a fraction, which identifies the size of the smallest letters resolved at the testing distance used. The numerator (top number) represents the testing distance used, typically 20 feet. The denominator (bottom number) has to do with the size of the letter read. For example: 20/20 means that an individual is able to resolve the letter on the 20/20 line of the Snellen chart at 20 feet.

Adduction – a movement of the eyes toward the nose.
Afterimage – a visual sensation that persists after the original light stimulation has ceased.
Alternating – switching from one eye to the other. In relation to strabismus, it means that either eye may fixate while the other eye deviates.
Amblyopia – the visual condition in which there is a low or reduced central visual acuity that cannot be “corrected” by traditional refractive means (eg. glasses or contact lenses), and which is not attributable to disease, injury, or pathology. Amblyopia is said to exist when there is a set level of acuity, typically 20/40 or worse, or when a difference of 2 or more Snellen acuity lines between the eyes is present. Behaviorally amblyopia is looked upon as a dysfunction that hinders a patient’s ability to gather, process, analyze, and respond to visual information in a meaningful way.
According to Ciuffreda, in functional amblyopia (amblyopia ex anopsia) usually one or more of the following conditions is present before the age of six years and accounts for the amblyopic condition: significant anisometropia, constant unilateral esotropia or exotropia, significant isometropia, significant unilateral or bilateral astigmatism, or image degradation. Binocular competition in an amblyopic patient causes adaptations to be made via neural suppression, leading to reduced VA and dysfunctions in such skills as ocular motility, fixation, accommodation, spatial sense, and speed of perception in the amblyopic eye. Vision Therapy has a high rate of success for patients with functional amblyopia to both improve visual acuity and to develop abilities in the visual functional areas (as mentioned above) that are commonly affected by this condition.
Anaglyphs – are used to provide a stereoscopic 3-D effect, when viewed with special anaglyph glasses (each lens a different color, usually red and green or red and blue). Images are made up of two color layers, superimposed, but offset with respect to each other to produce a depth effect. The picture contains two differently filtered colored images, one for each eye. When viewed through anaglyph glasses they produce a unified stereoscopic image
Analytical examination – a comprehensive optometric exam that probes the functioning of the visual system under varying conditions. The findings from this evaluation help the optometrist to understand how vision might be helping or interfering in the patient’s performance, comfort, etc.
Angle Kappa – the angle between the pupillary axis and the visual axis. It is termed “positive” when the pupillary axis is nasal to the visual axis and “negative when the pupillary axis is temporal to the visual axis. A positive angle kappa (displacement toward the nose) of up to 5 degrees is normal.

Aniseikonia – a condition in which the image of an object seen by one eye is different in size and shape from the image seen by the other eye.

Anisometropia – the condition in which unequal refractive states exist between the eyes.
Anomalous Correspondence (AC) – in strabismus, the condition in which an area other than the fovea of the strabismic eye is “matched” with, or “corresponds” to the fovea of the other eye as far as determining location and direction. This provides the patient with some degree of “depth perception,” and avoids double vision and visual confusion.
Anterior Chamber – the space between the iris and the cornea.
Antimetropia – the condition where one eye measures hyperopia, and the other eye, myopia.

Aphasia – a loss of the ability to produce and/or comprehend language, due to injury to brain areas specialized for these functions, such as Broca's area, which governs language production, or Wernicke's area, which governs the interpretation of language. It is not a result of deficits in sensory, intellectual, or psychiatric functioning, nor due to muscle weakness or a cognitive disorder.

Apraxia – a neurological disorder characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements. It is a disorder of motor planning which may be acquired or developmental.

Aqueous Humor – the thin, watery fluid that fills the space between the cornea the iris (anterior chamber).  It is continually produced by the ciliary body, the part of the eye that lies just behind the iris. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape.

Asthenopia – a constellation of symptoms relating to visual discomfort, usually at near, such as blurry vision, watery eyes, itchy eyes, etc.
Astigmatism – the refractive condition in which the light rays from an object are not brought to a single point focus at the back of the eye. Astigmatism is compensated for by the use of lenses with cylinder.
Ataxia –a neurological sign and symptom consisting of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of parts of the nervous system that coordinate movement, such as the cerebellum, the vestibular system, the thalamus, and parietal lobe.

Autonomic nervous system (ANS) – the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These activities are generally performed without conscious control. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition (urination), and sexual arousal. Whereas most of its actions are involuntary, some, such as breathing, work in tandem with the conscious mind. The ANS can be divided by subsystems into the parasympathetic nervous system and sympathetic nervous system. It can also be divided functionally, into its sensory and motor systems.

Bagolini lenses – a pair of finely straited lenses that can be used in diagnosing the status of Correspondence.

Bifocal – a lens which contains two different powers for focusing at different distances. Typically, the bottom part of the lens is for looking at near distances (usually 13 to 16 inches), and the top portion of the lens is for looking further away.

Binocular – also, referred to as “fusion,” refers to the simultaneous perception of information from the right eye and the left eye, organized into a single percept. Binocularity occurs in the brain, and not at the retina. Some of the advantages of Binocular vision are: single vision, stereopsis, enlargement of the field of vision, and compensation for the physiological blind spot.

Normal Binocular vision requires:

  • Reasonably clear vision in both eyes

  • The ability of the retino-cortical elements to function in association with each other to promote the fusion of two slightly dissimilar images i.e. sensory fusion

  • The precise co-ordination of the two eyes for all directions of gaze, so that corresponding retino-cortical elements are placed in a position to deal with two images i.e. motor fusion.

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