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### 28 Cards in this Set

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 When do you do VA's in the exam? VA's are the first preliminary test except with a chemical burn. Visual Acuity Definition The resolving ability of the eye to see two things as separate What is the "normal" resolving power of the eye? able to detect a gap with in 1'minute of arc (with or without correction) 3 ways to detect VA's 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) what are optotypes? test targets based on grid work What is the universal method of measuring VA? Snellen Acuity Chart What are the dimensions of most snellen letters? 5 units high and 4 units wide What is the best snellen letter? E How many minutes of arc does a 20 foot optotype subtend at 20 feet? 5' minutes of arc (its details subtend 1 minute) what would a 30 foot letter subtend at 20 feet? 20/20='5 so... 5/20=?/30 answer=7.5 What would a 20/200ft letter subtend at 20 feet? 20/20='5 min of arc so... 5/20=?/200 answer=50'min of arc How is the snellen fraction related to MAR? Snellen fraction=1/MAR What are some limitations of the snellen acuity chart? -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. What is the snellen fraction? test distance/distance at which the smallest letter read subtends 5' minutes of arc record VA as the smallest line of letters that not __ letters were missed two What is the general correlating VA's with refractive error? 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 where does 1M letter subtend 5' minutes of arc? 1 meter when would you use teller acuity cards? infants and non-responsive patients when would you use the LEA chart? on children When would you use the HOTV chart? on amblyopes when would you use the feinbloom chart? on low vision patients how would you measure near vision for a low vision patient? Bailey-Lovie Chart are there any ever any reasons not to take VA's? NO! Always attempt it! what are some clues that you may be dealing with a malingerer? -rapid drop off -exagerated difficulty -near and distance do not correlate when should you do a pin hole acuity? when "entering acuities" are 20/40 or worse. (entering acuities means with correction if that makes it better) if an eye is not correctable to 20/20 what should you do? Try and figure out why working from the front of the eye to the back When would you use the BAT brightness acuity test? when you suspect that acuity would be worse in a glare situation. (Cataract looks bad but VA is okay) Can justify cataract surgery How are you considered legally blind? 20/200 or worse in the best eye OR less than 30 degrees of visual field in widest meridean of the better eye.