VA Continued Flashcards
What is a VEP?
visual evoked potentials, looks at the wiring from the central retina to the primary visual cortex
What does VEP not measure?
the perception of what the child is seeing
When do you do a VEP?
in a patient where VA is unable to be obtained (attention or poor responses) or a patient with possible pathology (not obvious)
What are the VEPs from most preferred to least?
patterned reversed, sweep, flash
What is the patterned reversed VEP?
1st choice, black and white alternating stripes or checkerboard squares, detect minor visual pathway abnormalities
What is the sweep VEP?
black and white alternating stripes or checkerboard squares, pattern size/contrast levels change rapidly, clinician can see where good response drops off to determine VA
What is the best VEP for poor attention?
sweep, only need attention for a few seconds
What is flash VEP?
20 degrees, less than 5 ms
T/F checkerboard with more, smaller squares correlates to better VA
true
What is the VEP test distance?
50-150 cm depending on the size of the pattern
What are binocular v monocular considerations for VEP?
binocular summation should be at least 10% more than either OD or OS, if lower than the dominant eye, then interference may be going on and treatment is more critical
What are additional VEP considerations?
attention of patient, placement of electrode, 10% of adult levels at 6 months of age, 200% better than FPL
How to read a pattern reversal VEP
amplitude: N75 to P100 // implicit time (latency) time from stimulus to largest amplitude wave
What is a normal implicit time/latency?
85-120 ms for p wave
What is a Cardiff card?
vanishing optotype with different pictures and vertical presentation
What ages are Cardiff cards good for?
12-36 months aka 1-3 years
What is the Cardiff card test distance?
1m or 50 cm
How does the Cardiff card work?
child will look at the picture over the gray background if they can see it, child could also name the picture
Is the Cardiff card tested monocularly or binocularly?
monocularly if able, otherwise bino
What range of VAs do the Cardiff cards have?
20/160- 20/12.5
What are the approximate Cardiff card age VAs?
1 year- 20/50+, 1.5 to 2 years- 20/25+, 3 years 20/20-20/40
What are preschool acuity considerations?
letter tests are preferred, don’t assume the child knows letters
When should a child ID letters?
end of kindergarten
What are questions to ask yourself about preschool VAs?
Does the child have poor vision? know the letters? understand the task? bored?
How do you occlude for preschool acuity?
pirate patch (fun!), sticky patch, check for peeking, posture squinting
What are Allen pictures?
recognition acuity, pictures (car, phone, bird, cake, hand), child needs to name the pictures
What are criticisms of Allen pictures?
dated, pictures do not blur equally, overestimate the VA, does not go to 20/20
What is the tumbling E?
need to identify the direction of the letter E (up, right, left, down)
What are criticisms of Tumbling E?
directional confusion until 8 yo, up down easier than L/R
What are Lea Symbols/HOTV?
apple, house, circle and square, does not have directional confusion
What is the procedure for Lea symbols?
whole line if child is able (4-5 years), can use matching card, if unable to do the whole line the crowding bars make it more difficult
Why use crowding bars with Lea symbols?
more difficult for amblyopia because they see the 1st and last letters correctly but others hard
What did the HOTV preschool acuity study show?
under 3 VA 20/63+, 3-4 yrs 20/50+, 4-5 yrs 20/40, 5-6 yrs 20/32+
What did the HOTV preschool acuity study show in terms of IOD?
only 6% of normal had intraocular difference of 2+ lines between the eyes
Order of preferred tests in clinic…
pick age/cognitive ability appropriate tests, snellen, lea/hotv, cardiff, FPM (teller or lea paddles)
What age should be able to do one line snellen acuity?
kindergarten
What age should be able to do a whole line Lea/HOTV?
around 4 years
What age should be able to do blocked lea/hotv?
around 3 years, or do matching, single letter may overestimate
What are the two last choice acuities clinically?
cardiff then FPL like teller or lea
What VA test does a school aged child do?
snellen
What VA test does a preschooler do?
HOTV, Lea, cardiff
What VA test does a toddler or nonverbal patient do?
cardiff
What VA test does an infant or nonverbal patient do?
TAC/Lea gratings, CSM, F&F, VEP
