Visual Acuity Flashcards
What is the definition of legal blindness?
Best-corrected visual acuity of 20/200 or less in the better eye, or a visual field of no more than 20 degrees
Amblyopia
Lazy eye. Neurological development disorder that present with deficits in spatio-temporal vision processing.
20/20 vision assumes how many minutes of arc?
1 minute
What would “perfect” vision actually be recorded in snellen and minutes of arc?
20/10 and 30 seconds of arc.
What is the optimal pupil size?
3mm
Large pupils experience reduced ________ so resolution is limited by _______
Reduced Diffraction, Limited by Aberrations
Small pupils experience reduced _________ so resolution is limited by _________
Reduced Aberrations, Limited by Diffraction
Where is the concentration of rods in the eye greatest?
15 degrees from the fovea
Where is the concentration of cones in the eye the greatest?
on the fovea
How fast do cones regenerate photopigments?
5 - 10 minutes
How fast do rods regenerate photopigments?
30-50 minutes
What is the current standard for VA charts?
LogMAR spacing, Sloan optotypes, at a distance of 4m
What is the formula for optotype size in relation to test distance?
Height (mm) = tan (min of arc/60) x distance (mm)
For Snellen, how many letters need to be read correctly in order to record that baseline?
3 or more
For LogMAR charts, when do you stop recording a patient’s score?
If he/she misses 4 out of 5 letter on a given line
What is a Landolt C VA chart?
Has a series of rings with a 1 min arc gap. Guess position of gap
When is Tumbling E VA chart used?
Sometimes with children, illiterate patients
How do you convert from logMAR to snellen?
MAR = 10 ^(logMAR value)
How do you convert from snellen to logMAR?
20/MAR = x then take the log10 of MAR
True/False. Patients typically do better on logMAR when compared to snellen.
True
What’s on both sides of an ICO Near Vision Card?
One side = logMAR
Other side = Lea symbols
What’s on both sides of a Lighthouse Near Vision Card?
One side = Words
Other side = Numbers
What’s on both sides of a Runge Near Vision Card?
One side = logMAR moving horizontally
Other side = True snellen
How do you record low vision?
M-units: 20/20 equivalent @ 40 cms is 0.4M
Define Amplitude of Accomodation
Maximum amount a patient can accommodate
How do you record the Push-Up Method?
Measure the distance of “sustained blur” and take 100 / distance (cms).
What is Hofstetter’s Formula?
For Push-Up Method: Minimum Amp = 15 - (Age/4)
For 3-year-olds, what Lea card do you use?
10/20
For 4-year-olds and beyond, what Lea card do you use?
10/16
Ametropia
Refractive error
Emmetropia
Zero refractive error
Myopia is corrected with + or - lenses?
-
Hyperopia is corrected with + or - lenses?
+
Define Presbyopia
Cannot resolve detail at close distances
