Visual Acuity Terminology

Question 1

visual acuity

Answer 1

the criterion for an adequate refraction

movement of lenses to allow patients to see as well as they can

Question 2

detection acuity

Answer 2

the visualization of an object on a background different from the object itself

Question 3

resolution acuity

Answer 3

the ability to just recognize a lateral misalignment on a frontal plane; the most accurate type of acuity

Question 4

recognition acuity

Answer 4

the determination of a threshold of recognition of two or more targets or objects on a contrasting background; ex: Snellen chart and LogMAR

Question 5

contrast sensitivity

Answer 5

minimum contrast which is required to distinguish that there is a bar pattern rather than a uniform grey. This is measured by test gratings of equal width; bright and dark bars in a sine-wave pattern

Question 6

20/20 in contrast sensitivity

Answer 6

30 cycles per degree

Question 7

visual acuity numerator

Answer 7

distance of testing situation or where the patient stands

Question 8

visual acuity denominator

Answer 8

distance at which the letters subtend 5’ of arc at the nodal point of the eye or the letter the patient reads

Question 9

20/20

Answer 9

patient was standing 20 feet from the target and the smallest letters identified would subtend 5’ of arc of the visual field if it was viewed from 20 feet

Question 10

1’ of arc

Answer 10

the human eye is structurally capable of resolving 1’ of arc detail

Question 11

size of Snellen letter

Answer 11

indicates at what distance the letter subtend 5’ of arc

Question 12

VA for newborn

Answer 12

subjective, pupils react to light

Question 13

VA for 3 month old

Answer 13

subjective, fix and follow in both eyes

Question 14

VA for elder w/ cataract

Answer 14

subjective, finger counting at 1 ft

Question 15

optokinetic drum

Answer 15

objective and subconscious, based on principle of optokinetic nystagmus (beating of the eyes)

Question 16

catford

Answer 16

objective and subconscious, test based on varying sizes for optokinetic nystagmus

Question 17

VA sc

Answer 17

visual acuity without correction

Question 18

VA cc

Answer 18

visual acuity with correction

Question 19

height of 20/20 letter

Answer 19

8.73 mm

Question 20

hardest VA letter

Answer 20

B- no break/contrast

Question 21

easiest VA letter

Answer 21

L

Question 22

human pupil average

Answer 22

3-4 mm in diameter in light illumination

Question 23

smaller pupil

Answer 23

less spherical and chromatic aberration, until less than 2mm size

Question 24

pinhole acuity

Answer 24

has a pinhole 1mm in diameter, pinhole occluder limits light to only parallel rays

Question 25

Stiles Crawford effect

Answer 25

basis of 1 mm pinhole, direct light through the center of the pupil resorts in clearer vision

Question 26

amblyopia

Answer 26

diminished visual acuity without structural abnormality of the eyes or visual pathway, uncorrectable by optical means, 20/30 or worse

Question 27

desired patient endpoint

Answer 27

clear, comfortable, binocular vision