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28 Cards in this Set
- Front
- Back
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When do you do VA's in the exam?
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VA's are the first preliminary test except with a chemical burn.
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Visual Acuity Definition
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The resolving ability of the eye to see two things as separate
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What is the "normal" resolving power of the eye?
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able to detect a gap with in 1'minute of arc (with or without correction)
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3 ways to detect VA's
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1. Minimal detectable resolution (can obj be distinguished from background)
2. Minimum separable angle (group of points or lines are separable and distinct) *3. Recognition resolution (most used by clinicians) |
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what are optotypes?
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test targets based on grid work
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What is the universal method of measuring VA?
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Snellen Acuity Chart
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What are the dimensions of most snellen letters?
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5 units high and 4 units wide
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What is the best snellen letter?
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E
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How many minutes of arc does a 20 foot optotype subtend at 20 feet?
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5' minutes of arc (its details subtend 1 minute)
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what would a 30 foot letter subtend at 20 feet?
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20/20='5
so... 5/20=?/30 answer=7.5 |
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What would a 20/200ft letter subtend at 20 feet?
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20/20='5 min of arc
so... 5/20=?/200 answer=50'min of arc |
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How is the snellen fraction related to MAR?
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Snellen fraction=1/MAR
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What are some limitations of the snellen acuity chart?
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-letter sizes between lines do not change by a constant ratio.
-between row and between letter spacing is not proportional to letter size. -legibility for optotypes varies between different size levels. |
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What is the snellen fraction?
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test distance/distance at which the smallest letter read subtends 5' minutes of arc
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record VA as the smallest line of letters that not __ letters were missed
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two
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What is the general correlating VA's with refractive error?
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for every .25D of refractive error accounts for approximatly one line of visual acuity. if the patient has cylinder take the spherical equivilant.
-count from 20/20 -works up to 2D extra line if cyl is oblique |
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where does 1M letter subtend 5' minutes of arc?
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1 meter
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when would you use teller acuity cards?
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infants and non-responsive patients
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when would you use the LEA chart?
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on children
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When would you use the HOTV chart?
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on amblyopes
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when would you use the feinbloom chart?
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on low vision patients
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how would you measure near vision for a low vision patient?
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Bailey-Lovie Chart
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are there any ever any reasons not to take VA's?
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NO! Always attempt it!
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what are some clues that you may be dealing with a malingerer?
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-rapid drop off
-exagerated difficulty -near and distance do not correlate |
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when should you do a pin hole acuity?
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when "entering acuities" are 20/40 or worse.
(entering acuities means with correction if that makes it better) |
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if an eye is not correctable to 20/20 what should you do?
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Try and figure out why working from the front of the eye to the back
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When would you use the BAT brightness acuity test?
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when you suspect that acuity would be worse in a glare situation. (Cataract looks bad but VA is okay)
Can justify cataract surgery |
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How are you considered legally blind?
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20/200 or worse in the best eye OR less than 30 degrees of visual field in widest meridean of the better eye.
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