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32 Cards in this Set
- Front
- Back
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Visual Task Analysis
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A method of applying optometric knowledge to determine the various visual ability and skills necessary for individuals to achieve their potential when they perform particular tasks in life.
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Static Visual Acuity
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Refers to the clarity of eyesight as tested with a video Snellen test chart. *VA tested at 6 m and 40 cm
*VA of 20/15 is preferred for athlethes |
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Contrast Sensitivity
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A measure of visual sensitivity to subtle differences in black/white contrast.
*related to VA and provides qualitative index of an athlete's visual sensitivity to detail |
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Two-Eyed Depth Perception
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A measure of speed and accuracy in judging two-eyed depth and distance information (stereopsis).
*testing is conducted with state-of-the-art high resolution video equipment that is capable of creating 3-D targets which are viewed through special liquid crystal goggles |
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Accommodative Vergence Facility
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Refers to several measures designed to assess the athlete's ability to quickly and efficiently shift visual attention while maintaining clarity and spatial accuracy.
*vergence refers to the process of maintaining singleness of vision at different distances and is related to accuracy of spatial judgement *accommodation is the process of maintaining clarity of vision at different distances |
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Visual Alignment Accuracy
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A measure of any error between the aiming tendency of the two eyes and the true target location.
*measurement made by using a high resolution video monitor and high speed liquid crystal goggles that enable presentation of target to each eye individually while both eyes are open and seeing *a visual alignment error, if stable, is usually compensated by adaptation in the visual perceptual system *such adaptations may deteriorate in high pressure competitive situations or in conditions of extreme fatigue *the presence of an unstable visual alignment error, or a visual alignment error that is not adequately compensated by visual perceptual changes, can result in the athlete making inaccurate judgements about target location |
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Visual Alignment Stability
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An index of the stability of the two-eyed visual-spatial process which provides information regarding WHERE a visual target is.
*visual alignment stability can be influenced by age-related changes in focusing systems, by general health factors, by high stress levels, and by high heterophoria values (heterophoria is a measure of the pointing or aiming tendency of the two eyes) |
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Central Speed of Perception
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A measure of accuracy of processing of visual information which is presented for a brief moment in the center of the visual field.
*athlete is asked to identify series of digits that are presented for 100ms. *may be interpreted as an indicator of "visual quickness" |
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Target Localization Accuracy
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A measure of the accuracy of visual judgement of target location of small targets that are briefly (100ms) presented in the visual field.
*tested by using a laser point and dual constant illumination tachistoscopes *intent of assessment is to reveal any visual perceptual tendencies to localize targets above, below, or to the left or right of the true location |
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Eye-Hand Coordination
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A measure of speed and accuracy of visually-guided hand movements in all areas of the visual field.
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Eye-Hand Reaction and Response Speeds
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Refers to measures of visual reaction and response time consisting of an accurate hand movement in response to a visual stimuli in the center of the visual field.
*reaction time: time required to mentally determine the presence of visual information and to formulate a motor response *response time: total time required to notice the visual target and complete the motor response sequence (hand movement) **reaction time = overall quickness **response time = overall speed |
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Refractive Condition
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the relationship between optical powers and the size and shape of the eyeball (globe) that defines precision of focus of the eye
*measurement of refractive condition always tested at optical infinity (>6m) *lens power specified in DIOPTERS necessary to compensate the AMETROPIC eye to see clearly at optical infinity with no accommodation in play |
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Ametropia:
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any refractive condition other than emmetropia (eg. myopia, hyperopia, presbyopia, astigmatism, etc)
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Emmetripia:
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the optical power of the eye matches the size of the eye so that distant targets are clearly imaged on the retina
*no corrective lens required |
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Hyperopia:
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aka hypermetropia, the optical power of the eye is less than necessary to provide a clear retinal image of distant targets
*"farsighted" *compensated using lens with positive dioptric power (adds power) |
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Myopia:
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the optical power of the eye is excessive relative to the size of the eyeball, causing distant targets to be blurred while targets closer than optical infinity may be seen clearly
*"nearsighted" *compensate using lens with negative dioptric power (reduces power) |
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Critical Points of Refractive Conditions:
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1) refractive condition measurement is always always referenced to optical infinity
2) refractive conditions are caused by a mismatch between optical power and size of eyeball 3) to compensate simple refractive conditions, use plus lens for hyperopia and minus lens for myopia 4) ophthalmic prescriptions are written as the power that COMPENSATES the refractive condition, not the power of the refractive condition per se 5) Most young hyperopes can temporarily compensate for their refractive condition by using accommodation. This process requires energy and can result in eye strain, reduced visual performance and other symptoms 6) An appropriate compensating lens Rx does not stimulate accommodation when viewing a target at optical infinity |
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Monocular Visual Sensitivity
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the ability to see clearly with each eye alone
*proper refractive compensation is necessary to determine best sensitivity *visual acuity *contrast sensitivity *normal ocular health |
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Accommodation Function
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to enable clear eyesight when viewing targets located at different distances from observer
*greater lens power is necessary to see closer targets - D = 1/target distance (m) *primary stimulus to accommodation is retinal image blur *when fixating a distant target, near target is blurred |
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Accommodation Innvervation
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*primary innervation for accommodation is from the parasympathetic nervous system with lesser level of innervation from sympathetic
*parasympathetic activation increases accommodation *sympathetic activation decreases or inhibits accommodation *the innervation of accommodation is monitored by both vergence and pupil through the near triad -near triad=neural interaction between vergence, pupil, and accommodation -when accommodation increases, convergence increases and pupil size decreases |
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Anatomy of Crystalline Lens
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*small lens of variable focusing power
*suspended within the lens capsule, a translucent elastic "bag" *during accommodation, lens diameter decreases and anterior surface curvature increases and lens thickness increases |
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Ciliary Muscle
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*specialized smooth sphincter muscle that encircles the crystalline lens and regulates the power of the lens by varying the elastic forces applied to lens capsule
*ciliary body and muscle move forward slightly during accommodation *primary innervation is from parasym (activation causes increase of accommodation) *limited innervation from sym (activation causes decrease in accommodation) |
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Zonular Fibers
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*microscopic fibers of collagen-based material that serve to connect the crystalline lens capsule to the ciliary muscle
*posterior zonules connect the ciliary muscle to the pars plana region of the ora serrata of the retina *under greater tension when viewing distant targets and accommodation is relaxed *when accommodation is active, ciliary muscle contracts and tension on the zonular fibers is decreased, allowing the lens to become more round |
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Factors that Influence Accommodation
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*stress: reduces ones ability to accommodate efficiently and accurately
*fatigue: reduces one's ability to accommodate efficiently and accurately *drugs: variable effects depending on type of drug may cause hyper- or hypo-accommodation. Most drugs that affect CNS function have some effect of accommodation. Caffeine, at high doses, causes a reduction in accommodative control **when viewing close target, myopes must accommodate less and hyperopes accommodate more** |
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Symptoms of Accommodative Dysfunction
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*slowness in changing focus when looking between targets located at different distances from the individual (reduce accommodative facility)
*blurry vision (especially when looking at near targets) *eyeache (asthenopia) *substitution of letters of similar shape when reading (especially with children) |
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Effects of Added Lenses Upon Accommodation
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Added Negative Lens: (concave)
stimulates accommodation and increases accommodative demand Added Positive Lens: (convex) lenses relaxes (or replaces) accommodation -reading glasses, computer glasses, learning lenses, etc. |
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Measuring Accommodation: Factors
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1) amplitude: maximum accommodative ability
2) facility: speed of change of accommodation 3) posture: habitual tendency to hyper or hypo accommodate |
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Amplitude of Accommodation
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*monocular: true accommodative amplitude must be measured monocularly
*relative binocular: how much can accommodation be changed without affected binocular vision via effect on vergence Positive Relative Accommodation (PRA): the amount in diopters that accommodation can be increased while viewing a target at 40cm before vergence is affected (blurred diplopia) Negative Relative Accommodation (NRA): the amount in diopters that accommodation can be decreased while viewing a target at 40cm before vergence is affected |
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Binocular Accommodative Facility
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How quickly can accommodation be increased or decreased, usually measured by alternately placing plus and minus lenses before the eyes. A measure of SPEED of accommodative control
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Measuring Accommodative Facility
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Lens Rock: if binocular, changes in accommodation relative to changes in vergence
-change the stimulus to accommodation by changing the lens powers through which the subject views a target at 40cm -typically use lens flipper with same power on each side, but one positive and one minus Distance Rock: if binocular, measure real-world facility of accommodation and vergence together -change the stimulus to accommodation by changing the distance between two targets that the patients alternately fixates |
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Measuring Accommodative Posture
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Accommodative Lag or Lead:
the difference between calculated optical demand of a given target distance and the amount of accommodation that the individual responds with. *hypoaccommodation (lag) is expected *hyperaccommodation (lead) sometimes occurs and is generally indicative of inefficient visual function |
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Methods to Measure Accommodative Posture
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1) nearpoint cross cylinder/cross grid technique (subjective)
2) dynamic retinoscopy (objective) |
