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© The Children's Mercy Hospital, 2014. 03/14
Megan Sheeley, CO
Visual Acuity
© The Children's Mercy Hospital, 2014. 03/14 2
What you will learn today • History
• Parameters
• Optotypes
• Checking acuity
• Pre-verbal acuity
• Techniques
• Pitfalls
• Pearls
© The Children's Mercy Hospital, 2014. 03/14 3
Forefathers
Herman Snellen Sr
(1834-1908)
Francisco Cornelius
Donders (1818-1889)
© The Children's Mercy Hospital, 2014. 03/14 4
A little bit of History… Snellen devises a standardized measurement
tool to check vision 1862
1867 Monoyer introduces the decimal notation for
acuity measurements
1888 Landolt proposed the broken ring symbol
(Landolt Cs)
1959 Louise Sloan designs a set on non-serif letters
for the acuity chart
1976 Bailey and Lovie design a new acuity chart with
proportional spacing and 5 letters (logMAR)
1982 National Eye Institute combines Sloan and
Bailey-Lovie to produce the ETDRS chart
© The Children's Mercy Hospital, 2014. 03/14 5
A little more history… • Donder was the brains behind creating the visual
acuity measurement
• While writing his book, Refraction and
Accommodation, he realized the need to have a
standard for “sharpness of vision”
• Donder defined the “standard eye” to be able to
recognize letters that are 5 inches high
• He used this “standard eye” to compare his
patient’s vision, which would give the visual acuity
© The Children's Mercy Hospital, 2014. 03/14 6
The Chart…
• Donder asked his
good friend, Herman
Snellen to devise a
measurement tool for
him
• Snellen first used
abstract shapes, but
finally decided that
letters were best
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Parameters
• 20 feet or 6 meters is considered standard when
assessing distance vision
• Requires very little accommodation
• Reported as a fraction
• Illumination in room should not be less than 1/5th
of the illumination of the chart
• Most use computer systems
M&S System
Acuity Pro
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The Fraction….
20/200
Numerator (20) is the distance the patient is
from the object
Denominator is the distance a “normal” eye
can see
Emmetrope can see the letter at 200 feet
Optically handicapped can see at 20 feet
© The Children's Mercy Hospital, 2014. 03/14 9
20/200
E
200 feet
20 feet
20 200
© The Children's Mercy Hospital, 2014. 03/14 10
Optotypes
• Special characters designed specifically
for visual acuity measurement
• Calibrated to the “standard eye”
• Optotypes in a basic row on all charts
subtend 5’ of arc and their detail 1’ of arc
from the testing distance
• Standard distance 20 feet or 6 meters
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Landolt Broken Ring
• aka Landolt C
• Ring that has a gap
• The patient identifies where the gap is located as
the size of the C and the gap are reduced
• Standard optotype for acuity measurement in
most European countries
• Stroke width is the same as the width of the
space, 1/5 of the diameter
© The Children's Mercy Hospital, 2014. 03/14 12
Tumbling E
• Useful for children
• Useful for people who
may not know the
language
© The Children's Mercy Hospital, 2014. 03/14 13
LogMAR
• Logarithm of the Minimum Angle of Resolution
• Letters progress in a geometric progression
• Fixed 5 letters on each line
• Space between lines change in proportion
keeping contour interaction constant
• Used mostly in research settings
• 20/20 or (6/6) = LogMAR 0.00
• 6/60 or 20/200 = LogMar 1.0
© The Children's Mercy Hospital, 2014. 03/14 14
Lea Symbols
• Designed for children who do not know their
alphabet or numbers
• Developed by Leä Hyvarinen, MD, PhD in 1976
while serving her as a fellow at the Wilmer Eye
Institute
• 4 Optotypes: apple, pentagon, square, circle
• Easily recognizable by preschool age patients
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Allen Pictures
• Drawn to Snellen
specifications
• Standardized against adults
with known visual acuities
• Easily recognized pictures
for children who do not
know their alphabet
• Crowding bars can be
added to detect amblyopia
© The Children's Mercy Hospital, 2014. 03/14 16
HOTV
• Designed for children
who do not know the
full alphabet but can
say or match 4 letters
• Similar to Snellen
chart
• Snellen specifications
© The Children's Mercy Hospital, 2014. 03/14 17
Sloan Letters
• Block letters
• Thickness of the lines
equals the thickness
of the white spaces
• Height and width is 5
times the thickness of
the line
© The Children's Mercy Hospital, 2014. 03/14 18
To Crowd or Not to Crowd
• Contour Interaction Bars
Crowding Bars
• Pediatric visual acuity
• Vision acuity can be overestimated if
measured with single optotypes
• Amblyopia
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Monocular Acuity
Either eye can be tested
first
Amblyopic eye
Consistent
Occlusion
Use patch, or tape
Hold the occluder
yourself
© The Children's Mercy Hospital, 2014. 03/14 20
Acuity Testing
• Snellen chart is best
• Age appropriate test
Pictures
Matching
Letters
• Shorten testing
distance if necessary
© The Children's Mercy Hospital, 2014. 03/14 21
Pre-Verbal Acuity
• Rely on objective
techniques
• Observation & good history
• Babies under the age of 3
• Developmentally delayed
• Malingerers
Photo by Denis Libouton/iStockphoto/Thinkstock
© The Children's Mercy Hospital, 2014. 03/14 22
In the beginning… Get a good history
Do the parents think their
child can see?
Do they follow faces?
Toys? Bottles?
Do they notice
crossing/drifting?
Systemic/Developmental?
Any family history of eye
problems?
© The Children's Mercy Hospital, 2014. 03/14 23
Tests • Fix & Follow
Face
Lighted toy
Monocular/Binocular
• Central Steady Maintain
Light Reflex Central
Nystagmus
Maintain with 12BD
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• Eye crossing?
• Does patient use
that eye?
• Can patient abduct
the right eye?
• Amblyopia?
ESOTROPIA
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• Why?
• What happens when
you tilt the head in
the opposite
direction?
• Do parents notice
head position?
• Has it always been
there?
• Old photos?
Head posture
© The Children's Mercy Hospital, 2014. 03/14 26
Normal Pupil?
Vision OK?
Why are they
being seen?
Wake them up
Ptosis
Sleeping
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Tests
Preferential Looking Tests
Teller Cards
Evoked Potential (VEP)
Electrodes placed
occipital lobe
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Pitfalls
Parents
Cooperation
Siblings
Attention Span
ADHD
Autistic
Children!!
© The Children's Mercy Hospital, 2014. 03/14 29
Misunderstood Milestones
• Most children will only be able to identify 1 color
by the age of 3
No treatment for color vision problems
• Letter reversal is normal for a child to do up until
4th-5th grade
Work with school, on task training
• Vision problems will NOT cause debilitating
headaches
At most dull ache that resolves with break
© The Children's Mercy Hospital, 2014. 03/14 30
Take Away Pearls
• Know your tests!
• Explain why you are
doing what you are
doing
• Give the child time to
calm down
• Take breaks
© The Children's Mercy Hospital, 2014. 03/14 31
Take Away Pearls
• Take control of the room
• Gently lay down rules
Hands on lap
Sit up nice and tall
Use your listening
skills
• Talk directly to child
• Get down to child’s level
© The Children's Mercy Hospital, 2014. 03/14 32
AAPOS Techniques for Pediatric Vision Screening (n.d). In AAPOS
retrieved February 2, 2015 from
http://www.aapos.org/client_data/files/2014/1075_aapostechniquesforp
ediatricvisionscreening.pdf
Biography F.C. Donders. (n.d.). Donders Institute. Retrieved on
12/15/2015 from http://www.ru.nl/donders/agenda-news/donders-
lectures/biography-donders/
Herman Snellen (1834-1908). (n.d.). The Foundation of the American
Academy of Ophthalmology. Retrieved 02/12/2015 from
http://museumofvision.org/dynamic/files/uploaded_files_filename_157.
The historical Evolution of Visual Acuity Management. Colenbader,
August M.D. 2001. Retrieved from
http://www.ski.org/Colenbrander/Images/History_VA_Measuremnt.pdf
Visual Acuity. (n.d.). In Wikipoedia. Retrieved February 12, 2015 from
http://wiki.eanswers.com/en/Visual_acuity?ext=t&cid=null
World Health Organization. Consultation on development of standards
for characterization of vision loss and visual functioning. 2003.
Retrieved from http://whqlibdoc.who.int/hq/2003/WHO_PBL_03.91.pdf
Works Cited
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