acuity


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acuity

 [ah-ku´ĭ-te]
1. Acuteness (see acute [def. 2]); the level of severity of an illness. This is one of the parameters considered in patient classification systems that are designed to serve as guidelines for allocation of nursing staff, to justify staffing decisions, and to aid in long-range projection of staffing and budget.
2. clearness of the visual perception of an image.
visual acuity the ability to discriminate visually between forms.
 Visual field chart illustrating the divisions of the visual field related to visual acuity. (Courtesy of Josephine C. Moore, PhD, OTR.) From Pedretti and Early, 2001.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

a·cu·i·ty

(ă-kyū'i-tē),
1. Sharpness, clearness, distinctness.
2. Severity.
[thr. Fr., fr. L. acuo, pp. acutus, sharpen]
Farlex Partner Medical Dictionary © Farlex 2012

acuity

Audiology Clarity of hearing Emergency medicine Acuteness, intensity, level of urgency. See Triage OphthalmologySharpness of vision, expressed as a ratio–eg, 20/100, where a subject can see at 20 meters what a person with perfect vision can see at 100 meters.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.

a·cu·i·ty

(ă-kyū'i-tē)
1. Sharpness, clearness, distinctness.
2. Severity.
[thr. Fr., fr. L. acuo, pp. acutus, sharpen]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

acuity

Keenness of sense perception, especially in relation to vision and hearing.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

acuity

sharpness of vision; the resolving power of the eye.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

acuity 

Term derived from the Latin (acutus) meaning acute or sharp: sharpness of vision.
angular visual acuity See monotype visual acuity.
central visual acuity Visual acuity of the fovea and the macular area.
decimal visual acuity Visual acuity expressed as a decimal. The Snellen fraction is reduced, e.g. 6/18 (or 20/60 in feet) = 0.33. If the acuity is given in visual angle, decimal acuity is the reciprocal, e.g. 1/(3 minutes of arc) = 0.33.
dynamic visual acuity Capacity to see distinctly moving objects. Syn. kinetic visual acuity.
kinetic visual acuity See dynamic visual acuity.
letter visual acuity 1. Visual acuity determined with letters on a chart. 2. Visual acuity determined with single isolated letters.
line visual acuity See morphoscopic visual acuity.
minimum separable visual acuity See visual acuity.
monotype visual acuity Visual acuity determined with single isolated optotypes and therefore uninfluenced by neighbouring contours. Syn. acuity, angular visual.
morphoscopic visual acuity Visual acuity determined with a group of optotypes such as, for example, a line of letters or Landolt rings. The result may thus be influenced by neighbouring contours. Syn. line visual acuity. See crowding phenomenon.
near visual acuity Capacity for seeing distinctly the details of an object at near. It is specified in various ways: (1) As the angle of resolution of the smallest resolvable print (in minutes of arc) at a given near distance. (2) As a Snellen fraction, either as one that is equivalent to the distance visual acuity (Snellen equivalent) or more correctly as one which indicates the actual distance (e.g. 16/32 if the distance is 16 inches). (3) As an arbitrary Jaeger notation (e.g. J6). (4) As N notation (using Times Roman typeface) or Points (using any typeface), such as N8 at 40 cm (or simply 8-point), where N refers to near and the number to the amount of points (a point is a unit used by printers to specify print size and is equal to 0.35 mm or 1/72 of an inch). Thus N8 indicates that the overall height is 8/72 inch (or 2.82 mm) or about 4/72 inch (or 1.41 mm) for lower-case letters. (5) As M Units. For the usual font styles (e.g. Times Roman, Century) used in newsprint, 8-point print is usually considered to be approximately equal to 1 M Unit, so 1 M = N8, 2 M = N16, etc. See Bailey-Lovie chart; Jaeger test types.
objective visual acuity Visual acuity measured without the subject's judgement. See visual evoked cortical potential; preferential looking method; optokinetic nystagmus test.
peripheral visual acuity Visual acuity of the peripheral regions of the retina, outside the macula.
resolution visual acuity See visual acuity.
Snellen acuity Visual acuity as measured with Snellen letters.
static visual acuity Acuity determined with stationary test types or test objects. See dynamic visual acuity; test type.
stereoscopic visual acuity The ability to detect the smallest difference in depth between two objects. It is expressed as the difference η between the two angles subtended at any two objects in the field of view by the base line (or interpupillary distance). This threshold angle η (eta) is given by the approximate relationship, in radians
η = PD ✕ ΧD/d2
where PD is the interpupillary distance, d the test distance of the reference object and ΧD the distance between the two objects. (To convert the result into seconds of arc it should be multiplied by 180/π ✕ 60 ✕ 60 = 206265.) The difference between the two angles u1u2 (the difference between the two retinal images) is called binocular disparity or retinal disparity and the difference between the two angles β - α is called the relative binocular parallax (Fig. A5). Stereoscopic visual acuity is extremely fine, varying between 5 and 15 seconds of arc. It tends to decrease with age and it is positively correlated with Snellen visual acuity. Example: suppose ΧD is equal to 2 mm, d is 827 mm and the PD is 64 mm
Syn. stereo-acuity; stereo-threshold. See angle of stereopsis; retinal disparity; Howard-Dolman test; three needle test; vectogram.
Teller acuity cards Test cards used to assess the visual acuity of infants. The set consists of 16 rectangular grey cards, each approximately 26 by 56 cm. Fifteen of the cards contain a high contrast square-wave grating, 12 by 12 cm, each of a given spatial frequency, and located either on the left or the right of a central peephole in the card. The average luminance of the grating is approximately equal to that of the grey background. The spatial frequencies of the gratings range from 0.3 to 38 cpd when viewed from 55 cm. The procedure consists in starting with the card with the lowest spatial frequency (or coarser grating) and proceeding to cards with finer gratings. The observer watches the infant through the central peephole and his or her task is to make a subjective judgment, based on the infant's head and eye movements, of which is the finest grating card that the child can just resolve. The spatial frequency of this last card represents the estimate of the visual acuity. The procedure using these cards is based on the method of preferential looking but it is simpler, quicker and equally reliable. See cycle per degree; preferential looking method.
unaided visual acuity Visual acuity without any correction. Syn. vision; unaided vision.
vernier visual acuity The ability to detect the alignment or otherwise of two lines as in the reading of a vernier scale. This is the finest acuity being of the order of 1-5 seconds of arc depending on the length of the line; the longer the line, the more acute the detection. Syn. aligning power. See hyperacuity.
visual acuity (VA) Capacity for seeing distinctly the details of an object. Quantitatively, it is represented in two ways: (1) As the reciprocal of the minimum angle of resolution (in minutes of arc). This is the resolution visual acuity. Syn. minimum separable visual acuity. (2) As the Snellen fraction. This is measured using letters or Landolt rings or equivalent objects.Average clinical visual acuity varies between 6/4 and 6/6 (or 20/15 and 20/20 in feet). Visual acuity varies with the region of the retina (being maximum in the foveola), with general illumination, contrast, colour and type of test, time of exposure, the refractive error of the eye, etc. See minimum angle of resolution; cycle per degree; Glasgow acuity cards; hyperacuity; isoacuity; optotype; contrast sensitivity; Snellen fraction; Cardiff acuity test; photostress test; Sheridan-Gardiner test; Snell-Sterling visual efficiency scale.
Fig. A5 Stereoscopic visual acuity, η = u 1 − u 2 = β − αenlarge picture
Fig. A5 Stereoscopic visual acuity, η = u1u2 = β − α

Table A5 Average relative visual acuity in the central region of the retina
eccentricity
(degrees)
acuity
(%)
Snellen fraction
(m) (ft)
01006/620/20
0.5 806/7.520/25
1 666/920/30
1.5 576/1120/37
2 496/1220/40
2.5 416/14.520/48
3 396/1520/50
3.5 376/1620/53
4 356/1720/57
4.5 336/1820/60
5 326/1920/63
6 296/2120/70
7 276/2220/73

Table A6 Relationship between several near visual acuity notations
Snellen equivalent in metres (feet)
25 cm40 cm pointsM units
6/240 (20/800)6/144 (20/480)8010.0
6/192 (20/640)6/120 (20/400)648.0
6/144 (20/480)6/96 (20/320)486.4
6/120 (20/400)6/72 (20/240)404.8
6/96 (20/320)6/60 (20/200)324.0
6/72 (20/240)6/48 (20/160)243.2
6/60 (20/200)6/36 (20/120)202.4
6/48 (20/160)6/30 (20/100)162.0
6/36 (20/120)6/24 (20/80)121.6
6/30 (20/100)6/18 (20/60)101.2
6/24 (20/80)6/15 (20/50)81.0
6/18 (20/60)6/12 (20/40)60.8
6/15 (20/50)6/9 (20/30)50.6
6/12 (20/40)6/7.5 (20/25)40.5
6/9 (20/30)6/6 (20/20)30.4
6/6 (20/20)6/3.6 (20/12)20.25

Table A7 Relationship between several distance visual acuity notations
Snellen
fraction
(m) (ft)
min. angle of resolution (min. of arc)decimal
6/18020/60030.00.03
6/15020/50025.00.04
6/12020/40020.00.05
6/9020/30015.00.07
6/6020/20010.00.10
6/3020/1005.00.20
6/2420/804.00.25
6/2120/703.50.29
6/1820/603.00.33
6/1520/502.50.40
6/1220/402.00.50
6/920/301.50.67
6/7.520/251.30.80
6/620/201.01.0
6/4.520/150.751.33
6/320/100.52.0
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann

a·cu·i·ty

(ă-kyū'i-tē)
1. Sharpness, clearness, distinctness.
2. Severity.
[thr. Fr., fr. L. acuo, pp. acutus, sharpen]
Medical Dictionary for the Dental Professions © Farlex 2012
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