This document provides information on visual acuity assessment. It discusses the different components assessed, including visual acuity, contrast sensitivity, visual fields, and more. It describes the four types of visual perception and defines visual acuity as the spatial limit of visual discrimination, measured as the minimum resolvable angle. The document outlines the different types of visual acuity that can be measured, such as minimum visible acuity, minimum separable acuity, Vernier acuity, and recognition acuity. It also discusses various visual acuity charts, including Snellen, LogMAR, Landolt rings, and preferential looking tests that can be used with infants and young children.

1. VISUAL ACUITY ASSESSMENT
AYESHA SARFRAZ
ORTHOPTIST
COAVS
KEMU/MHL

2. STRUCTURED VISION ASSESSMENT
 Visual acuity
 Contrast sensitivity
 Visual field
 Face recognition
 Color vision
 Eye movements
 Accommodation
 Refraction

3. VISUAL PERCEPTION
There are four kinds of visual perception
1. Light sense
Scotopic vision
Mesopic vision
Photopic vision
2. Form sense
Perceive shape of objects
3. Sense of contrast
The ability to perceives light changes in luminance between
regions which are not separated by definite border.
4. Color sense
to distinguish between different colors as excited by light of
different wave lengths

4. VISUAL ACUITY
Visual acuity is considered a measure of form sense so it refer to the
spatial limit of visual discrimination.
The visual acuity is defined as the reciprocal of the minimum
resolvable angle measured in minutes of arc for a standard test
pattern.
Visual acuity is the function of the dioptric status if the eye and also of
the retina, the nervous pathway and the central nervous mechanisms.
VISUAL ANGLE
The angle subtended at the nodal point of the eye by the physical
dimensions of an object in the visual field.

5. COMPONENTS OF VISUAL ACUITY
 In clinical practice measurement of threshold of two spatially
separated targets ( a function of fovea centrallis) is termed as
visual acuity.
 The four types of visual acuity that are generally considered
are:
 Minimum visible or detection acuity
 Minimum separable or resolution acuity
 Verneir acuity (hyperacuity)
 Recognition acuity

6. MINIMUM VISIBLE /DETECTION ACUITY
Smallest test object that can just be detected. Under ideal conditions a
dark line of width 0.5 seconds of arc can just be detected.
Detection acuity is not a best descriptor of visual acuity because it is
stimulus bound.
(i.e., by changing the strength of stimulus you can alter the visual
acuity value)
For example
 Sty car balls
 hundred and thousand dot visual acuity
 Catford drum test
 Boek candy bead test

7. MINIMUM SEPARABLE OR RESOLUTION
ACUITY
 Resolution measures the smallest angular separation between
adjacent targets that can be observed. Resolution acuity is
limited by the optical limitations of the eye and the retinal
photoreceptor spacing ; it is usually in 30 seconds of arc.
 The smaller the separation of the acuity prototypes elements
that the person can resolve, the better is the acuity.
 For example
optokinetic nystagmus
preferential looking
visual evoked response
snellen’s test type
landolt c test

8. RECOGNITION ACUITY
 It is the type of acuity measurement normally used clinically on
patient who are old enough to subjectively report on what they
see on typical Snellen acuity letter chart , pictures numbers and
so forth.
 It refers to t he ability to identify a form and its orientation.
 The age at which children can do this varies greatly but starts at
about 2 to 2.5 years. It involves being able to resolve the detail
in the optotype, and on a cognitive level, to identify what the
stimulus is.
 For example,
Kays picture test.

9. VERNIER ACUITY
 It is the measure of the eye’s ability to perceive that
misalignment exists between the elements of the
stimulus when compared with a stimulus without such
misalignment.
 Relative size, orientation and position can be judged with
an accuracy of 3-6 seconds of arc.
 Hyper acuity is limited less by optical and retinal factors
than is resolution acuity and is believed to reflect cortical
processing.
 Stereoacuity may be considered as a type of hyper or
vernier acuity.

11. VISUAL ACUITY CHARTS
 Visual acuity can be measured in several different
ways and various different notations for recording it.
 Different charts used for the measurement of visual
acuity are
 Snellen VA chart
 Log MAR chart
 The Landolt ring or C
 The Checkerboard test
 Illiterate E chart
 The sheridan-Gardiner test

12.  The Cambridge Crowding cards
 Stycar test
 Ffooks’s test
 Script letters
 Pictorial charts
 The Cardiff acuity

13. SNELLEN CHART
 There are two main standards at present (Snellen
and Log MAR), both based on the reading of letter
charts.
Snellen notation is described as the testing distance
over the distance at which the letter would subtend
5 minute of arc vertically.
 So each limb subtends 1minute of arc.

14. SNELLEN CHART

15. ADVANTAGES;
 Widely available
 Snellen notation of VA is universally understood.
 Can be produced in a smaller format

16. DISADVANTAGES;
 Less repeatable and discriminative
 Unequal number of optotypes in each line, there is
more crowding at the bottom of the chart than at
top.
 The spacing between letters and rows shows no
relationship to height and width of letters.
 Progression between lines is irregular
 Statistical analysis of results is precluded so little use
in modern day research.

17. RECORDING
 The Snellen fraction is defined as:
Test distance
The distance at which the letters subtend 5’ of arc
Test distance can be in meters (metric) or feet
(imperial).
VA can be in decimal or conventional imperial
notation.

18. VA NOTATION
The two most common notations to record visual acuity in is
meters and in feet.
* *

19. % CORRECT AT THRESHOLD:
S 70.6
O 71.0
C 71.4
D 79.5
K 82.1
V 84.6
R 86.3
H 89.3
N 91.6
Z 94.0

20. SLOAN
 Next to come out after Snellen
• Same number of letters on each line (on some!)
• Gap between each letter is one letter size
• Each letter about same difficulty
DISADVANTAGE
 Change in minimum angle of resolution still varies
from line to line.

22. Log MAR CHART;
 Log of minimum angle of resolution (log MAR)
 Five letters in each line.
 Each letter assigned a value of 0.02 (.1/5).
 0.1LogMAR progression of letter size.
 Inter-letter on each line is equal to the letter width.
 Inter-row spacing equal to letter height of lower row.

23.  Can be used in conjunction with a scoring system.
 Better suited for research and statistical analysis.
 Better crowding phenomenon in logMAR chart.

24. LogMAR Chart

26. 6/60 H V Z D S
6/48 N C V K D
6/38 C Z S H N
If only those in yellow were read correctly, how would you record
their vision?
6/60-2/+2
6/60 H V Z D S
6/48 N C V K D
6/38 C Z S H N
What if this what they then read with singles…

27. There area also other ways to record your findings:
Some examples of the traditional ways vision results are
sometimes recorded are as follows:
VA cc 20/20
20/40 cPH 20/20
DVA sc 20/100 PH ni, sing ni
20/20
NVA sc 20/100, c+1.00 ni
20/20
DVA CF@ 50cm
20/40 PHni
•DVA= distance
visual acuity
•NVA= near visual
acuity
•PH= pinhole
•Sing= single letter
presentation
•NI= no
improvement

28. VISUAL ACUTY:
 Effect of culture and learning
 Mood and attention span are variable
 Child may b able to understand procedure
 Children have good memory and memorize charts
quickly
 Some time they want to over perform
 Testing with single optototype should not be used
 Method used for checking VA should be mentioned

29.  Level of interest or cooperation obtained from the
child should be mentioned
 Child should be encouraged and pushed to real limits
of resolving power
 In case of younger children instead of making them
to read through whole chart, staircase method
should be used to utilize limited attention span
 A difference of one line performance between two
examinations is not significance

30. GET MOST IMPORTANT INFORMATION
FIRST
 Near vision binocularly with correction
 Distance vision
 Uniocular
 Without glasses

31. HOTV CHART
 Measures recognition acuity
 Calibrated to the snellen parameters
 Children from 3-5 years
 Matching cards

32. Pointing
Card
• Often more difficult for the kids to name in
comparison to the LH shapes and therefore have to
point on a matching card.
• This increases unreliability.
H O
T V

33. •Also available in
near (this is near).
•Boxes on either
side simulate
crowding.
•These boxes are
not present on
distance tests and
instead look like
other ETDRS
chart.

34. LH (LEA) SYMBOLS
 Heart (loose tooth, valentine, butterfly), house (barn),
circle (tire) and square
• Easier for younger kids to name than HOTV where they
often have to point and this can increase unreliability.
• Logarithmic
• Crowding Effect
• Comes with matching card
 *Problem: one in four chance of getting it right!

35. LEA SYMBOLS
 Uses four shapes
 Ranges from 3/15- 3/1.2
 No cultural limitations
 Resolve into each other
 Child unaware if getting it wrong
 Flexible formats available
 Card games
 Large coloured tactile shapes

36. LEA SYMBOLS

37. Available for
distance,
low vision
and near
testing.

38. FOLLOWS A FACE
• reflex present between 6 weeks and 2 months of age
• take off your glasses
• definitely present at 4 months of age or problem
• write: fix and follows face/ light/ toy of ? size

39. HEIDI PADDLES
 Show monocularly starting with largest one.
 Can be adapted as preferential looking test using a
blank.
 Record as:
f & f small/ medium/ large Heidi

41. FIXATION PATTERN
Central, Steady, Maintained = CSM
 If a strabismus is present: will they let either eye turn
equally?
 If yes- acuity likely equal.
 Recorded as: “alternates freely”

42. INDUCED TROPIA TEST
 Use induced tropia test for orthotropic (straight)
patients.
 So far you have observed that their fixation is CSM.
 This is the next step to determining whether or not
they have better vision in one eye than the other.
 Performed on straight patients only!

43. CANDY BEADS
 1mm candy beads used.
 Have to be 4 to 6 months of age to have any pincher
control.
 Good to display reduced vision in one
eye(amblyopia) to parents.

44. PREFERENTIAL LOOKING TESTS
 Teller Cards
 Keeler FCPL cards
 Lea Symbol grating paddles
 Cardiff Cards
 Uses square wave gratings and measure in cycles per
degree.

45. LEA SYMBOLS GRATING PADDLES

46.  Caliberated for a specific distance usually at1 meter
 Four paddles
 Six different frequencies

47. TELLER ACUITY CARDS
TAC are recommended to test visual acuity in
infant from birth to approximately 1 year of
age.

48. TELLER ACUITY CARDS

49. KEELER CARDS
 Uses principle of preferential looking
 Circular pattern of square wave grating

50. KEELER ACUITY CARDS

51. CARDIFF CARDS
 Use to measure visual acuity in children from 1 to 3
years
 Uses principle of vanishing optotype
 11 sets of cards are available
 Acuity values ranging from 20/400- 20/20
 An excellent way to determine minimum separable
acuity in a child

52. CARDIFF ACUITY CARDS

53. CATFORD DRUM TEST
 This consists of a black spot of varying size on an
white oscillating back ground held one third meter
away from the child. This induce a to and fro pursuit
movement.

54. STYCAR BALLS
 This test equipment consists of white balls of varying
sizes corresponding to various levels of visual acuity
and black felt carpet. The child is seated 10feet away
facing the carpet and the balls are slowly rolled on
the carpet. A following movement of the eyes and
the head indicates that the child can see the ball.

55. 100’S & 1000’S
 In this test the child is presented small color colored
sweets on the palm of the examiner’s hand. A child
with vision will try to pick them up. This sort of test
can also be performed with cake decorations. The
size of these edible objects can be made smaller and
smaller to get a quantitative assessment of the
vision.

56. SHAPE RECOGNITION TESTS
 Kay's pictures
 Lea Symbols
 Illiterate Es
 Sheridan-Gardner
 Snellen

57. PICTURE TEST
There are two form of this test available.
 Allen cards
in this test the child is handed a card with different
pictures of common objects on it. Then he is shown a
picture and asked to match it with the corresponding
chart on the card. The size can vary giving a
quantitative assessment.

59. DISADVANTAGES
 Best possible is 20/30.
 Often not equivalent to acuity indicated giving falsely
 HIGH acuity.
 Stylized symbols and difficult to interpret.
 No actual pointing card, use near card as substitute.

60.  Beale Collin's
In this test Snellen’s equivalents are presented in
pictures at a distance of six meters and the child is
asked to identify pictures.

61. KAYS PICTURE TEST
 Crowwded logMAR book
 Used at distance of 3 meters.
 Common pictures of different sizes
 Single, uncluttered
 Cultural limitations
 Range 6/60- 6/3

62. KAYS PICTURE TEST

64. SHERIDAN GARDINER
 Uses seven letters X, U, T, O, H, V
 Uses at a distance of 6 meters
 Range from 6/60-6/3
 Child shown usual Snellen chart
 Child matches letter from 'key' card
 Replaced by logMAR tests instead more scientific
measure of acuity in children

66. ILLITRATE E/ LANDOLT’S C
 Actually designed for people who can not read the
alphabet
 In illiterate E letter E is written
 In Landolt’s C letter C is written
 6 meter distance
 Different position of E and C

68. BROKEN WHEEL CARDS
 Seven match pairs of cards
 Acuity values ranging from 20/20- 20/100 at 10 feet
 Measures minimum separable acuity

69. POST ROTATORY NYSTAGMUS
 Method- perform when you suspect blindness and
have gotten no response to faces or light.
 Mom holds babe, cover one eye, sit on stool
and rotate the stool, observe.
 Vestibular nystagmus occurs when you rotate.
 If you rotate RIGHT you get slow tonic movement in
the direction of the movement and fast refixation to
the left = left beating nystagmus.

70.  Normals- stop nystagmus after 3-5 seconds of
stopping stool.
 Blind- nystagmus continues for 15-30 seconds.

71. OPTOKINETC NYSTAGMUS
 Sighted or non sighted
 Can be used for quatitavie assessment
 Rotating drum of black and white strips
 Smooth pursuit and saccadic response

72. OKN DRUM

73.  OKN Drum- stripes
(Watch speed!! SLOWLY rotate)
 OKN Tape- stripes

74. OPTOKINETIC TAPE

75. SONKSEN SILVER TEST
 Six letters X,O, U, H, V, T
 Linear format
 Matches with letters on key card

76. FFOOKES SYMBOLS
 Shapes of a circle square and triangle
 Patient matches with hand-held corresponding shape

77. Patient holds this up to indicate
what shape they see.

78. LIGHTHOUSE
 Uses pictures as stimuli.
 No crowding, not a lot of choices so increases
chance of getting correct even though guessing.
 The infancy of LH symbols.

80. SJOGREN HAND TEST
 Symbolic pictures of hand in various orientations and
sizes
 The child can identify them if he can see them

81. NEAR TEST
 Lea near vision test
 N Notation
 J notation
 Reduced sheridan gardiner
 Maclure book

82. SLOAN
 Used today on literate patients in this clinic.
 Does have crowding but not logarithmic progression.

84. ROSENBAUM
 variety of visual test objects
 Tumbling E
 #’s
 X’s and O
 Also has vision in Jaegar form:
J1+ is 6/6, J1 is 6/7.5, etc. J10 is 6/60

85. FONDA-ANDERSON
 Print in a variety of sizes and source of this size print
indicated (eg. Phone book, bible).

87. MACLURE READING BOOK
 Different levels of reading ability and different sizes
of print.

90. ELECTROPHYSIOLOGY
 VEP (visually evoked potential)- records brain
response to visual stimuli.
 Can be done on infants because it doesn’t require
any subjective response.
 Uses electrodes on head to record speed of
transmission.
 So good way to assess pathway intact and speed of
pathway.

91.  Disadvantages
 Expensive equipment!
 Need well trained person to perform it
 Generally reproducible but some question as to what
exactly is being recorded (not checking cognitive
vision but does confirm light recognition gets there).

92. SO, THAT’S A LOT OF INFORMATION!

93. Distance Testing Literates
 Preferred test ETDRS
Pre-literates:
 HOTV
 LH
If shape matching/ naming not possible:
 Induced tropia test when straight.
 CSM when manifest- how long do they hold with the eye that was
turned when forced to fix with the turned eye?
 Teller/ Heidi paddles/ if very young do they follow your face

94. RECOMMENDED VISUAL ACUITY TESTS
FOR SPECIFIC AGE GROUP OF CHILDREN
Age range Recommended tests
0-3 months Facial recognition, CSM, Optokinetic nystagmus, visual evoked
potentials.
3-6 months Visually directed reaching, Cat ford drum, preferential looking tests.
6-12 months Worth’s static and rolling balls, hundred and thousands bead test.
1-2 years Kay picture test, Sty car, Cardiff cards
3-5 years Sheridan-Gardiner, landolt’s c broken ring, sonksten silver test
6 years + Snellen, ETDRS logMAR chart, N test, J tests.