spatial acuity (ch.5) Flashcards
detection acuity is the
diameter of the smallest spot of light or width of thinnest line that can just be seen
in detection acuity, the threshold acuity depends primarily on ____ and NOT on ____
depends primarily on contrast/luminance and NOT on the angle of subtense
for black line on white, the threshold = ____ “
0.5”
for a 0.5” line, contrast = ___ %
1 %
2 examples of localization acuity
- spatial-interval acuity
2. vernier acuity
_____ acuity is a type of hyperacuity
localization acuity (spatial-interval and vernier acuity)
when is vernier acuity used?
for extremely small thresholds (about 2-6”)
why is vernier acuity called “hyperacuity”?
because 2-6” is much smaller than the spacing between foveal cones
(Seems impossible based on physical optical setup in eye)
vernier thresholds are ___ with defocus
higher
can localization acuity be trained?
you can train vernier acuity in periphery to a small (certain) degree
clinical application of localization acuity
forsee PHP (preferential hyperacuity perimetry)- use in mac. degen. patients- (turning into wet form?)
what is resolution acuity?
smallest spatial separation that is discriminable
resolution threshold is:
about 30” (0.5’)
resolution acuity is also known as
minimum angle of resolution (MAR)
how is resolution acuity clinically implemented?
as grating acuity (sine wave gratings, multiple lines)
what is a device to measure resolution (grating acuity) in disease?
inferometer (used to bypass the optics of the eye)
how does the inferometer work?
it uses the principle of interference (most commonly used in people with opacities)
which does blur affect more: letter acuity or grating acuity?
blur affects letter acuity more
what is spurious resolution
moderate to severe defocus does not reduce thresholds as much as with letters (you can have phase reversal)
what type of optotype (letters) is in the ETDRS charts?
sloan
what type of optotype (letters) is in the bailey lovie charts?
british
true Snellen fraction’s numerator is=
test distance
true Snellen fraction’s denominator is =
‘foot letter’ size
what is the ‘foot letter size’?
distance at which that letter subtends 5 minutes of arc
a 20 foot letter subtends 5’ at ___ ft
20ft
critical detail/ “MAR”/ stroke width =
1/5th of the total letter height
1’
