spatial acuity (ch.5)

Question 1

detection acuity is the

Answer 1

diameter of the smallest spot of light or width of thinnest line that can just be seen

Question 2

in detection acuity, the threshold acuity depends primarily on ____ and NOT on ____

Answer 2

depends primarily on contrast/luminance and NOT on the angle of subtense

Question 3

for black line on white, the threshold = ____ “

Answer 3

0.5”

Question 4

for a 0.5” line, contrast = ___ %

Answer 4

1 %

Question 5

2 examples of localization acuity

Answer 5

1. spatial-interval acuity

2. vernier acuity

Question 6

_____ acuity is a type of hyperacuity

Answer 6

localization acuity (spatial-interval and vernier acuity)

Question 7

when is vernier acuity used?

Answer 7

for extremely small thresholds (about 2-6”)

Question 8

why is vernier acuity called “hyperacuity”?

Answer 8

because 2-6” is much smaller than the spacing between foveal cones
(Seems impossible based on physical optical setup in eye)

Question 9

vernier thresholds are ___ with defocus

Answer 9

higher

Question 10

can localization acuity be trained?

Answer 10

you can train vernier acuity in periphery to a small (certain) degree

Question 11

clinical application of localization acuity

Answer 11

forsee PHP (preferential hyperacuity perimetry)- use in mac. degen. patients- (turning into wet form?)

Question 12

what is resolution acuity?

Answer 12

smallest spatial separation that is discriminable

Question 13

resolution threshold is:

Answer 13

about 30” (0.5’)

Question 14

resolution acuity is also known as

Answer 14

minimum angle of resolution (MAR)

Question 15

how is resolution acuity clinically implemented?

Answer 15

as grating acuity (sine wave gratings, multiple lines)

Question 16

what is a device to measure resolution (grating acuity) in disease?

Answer 16

inferometer (used to bypass the optics of the eye)

Question 17

how does the inferometer work?

Answer 17

it uses the principle of interference (most commonly used in people with opacities)

Question 18

which does blur affect more: letter acuity or grating acuity?

Answer 18

blur affects letter acuity more

Question 19

what is spurious resolution

Answer 19

moderate to severe defocus does not reduce thresholds as much as with letters (you can have phase reversal)

Question 20

what type of optotype (letters) is in the ETDRS charts?

Answer 20

sloan

Question 21

what type of optotype (letters) is in the bailey lovie charts?

Answer 21

british

Question 22

true Snellen fraction’s numerator is=

Answer 22

test distance

Question 23

true Snellen fraction’s denominator is =

Answer 23

‘foot letter’ size

Question 24

what is the ‘foot letter size’?

Answer 24

distance at which that letter subtends 5 minutes of arc

Question 25

a 20 foot letter subtends 5’ at ___ ft

Answer 25

20ft

Question 26

critical detail/ “MAR”/ stroke width =

Answer 26

1/5th of the total letter height

1’