Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OT > Contrast Sensitivity > Flashcards

Contrast Sensitivity Flashcards

1
Q

What is the significance to doing contrast sensitivity test

A

evaluates the patients ability to see a range of target sizes at various contrast levels under optimum conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the most common equation that defines contrast

A

Michelson Contrast
contrast = (Lmax - Lmin) / (Lmax + Lmin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the less common equation that defines contrast

A

Weber Fxn
Contrast = (Lt -Lb) / Lb

Lt - luminance of target
Lb = luminance of background

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does visual acuity test in terms of contrast, how ideal is this to the real world ?

A

Measures sharp edges at high contrast
not ideal to real life scenarios

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define contrast sensitivity in terms of threshold

A

CS = 1 / threshold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is threshold

A

the minimum amount of contrast needed to see a letter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the relationship between contrast sensitivity and threshold

A

high threshold = low contrast sensitivity
indirect relationship

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

if a pt has contrast threshold = 10%, find their contrast sensitivity

A

1/ 0.10 = 10

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are the contrast sensitivity and threshold

A

none

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

if a pt has contrast threshold = 50%, find their contrast sensitivity

A

1/ 0.50 = 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does spatial frequency tell us

A

measuring the width of stripes in cycles per degree

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two most common spatial frequency gratings used ?

A

square wave and sine wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is square wave frequency

A

the change between black and white shades are abrupt, producing sharp edges on the graph

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is sine wave frequency

A

where the change in black and white shades are smooth, producing a gradual change on the graph

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is the definition of one cycle

A

one cycle includes one light bar (peak) and one dark bar (trough)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how many stripes per degree appear for each cycle per degree

A

1 cycle = 2 stripes

17
Q

if a pt has A SF of 20cpd, what level of snellen VA does this correspond to

A

20 cpd = 40spd
40 stipes per 60min
1 stripe = 60min/40 stripes = 1.5 min of arc
MAR = 1.5, VA = 1/MAR
VA = 20/30

18
Q

What is the grating acuity limit

A

represents the theoretical maximum VA at 100% contrast

19
Q

which target size is a patient most sensitive to

A

medium size

20
Q

what is type 1 CS loss

A

challenges with HIGH SF, small targets

21
Q

what is the most common reason to have type 1 CS

A

uncorrected myopia

22
Q

What is type 2 CS

A

challenges with LOW and HIGH SF

23
Q

what is the most common reason to have type 2 CS

A

cataract

24
Q

What is type 3 CS

A

unable to see LOW SF, large targets

25
Q

What are the most common reasons to have type 3 CS

A

optic neuritis
MS
parkinson’s disease
dibaetes
POAG
papilledema
alzheimers

26
Q

When contrast sensitivity doubles, what happens to the threshold

A

decreases by 0.30

27
Q

Clinically testing CS with Pelli Robson Chart, what distance should it be performed

A

1 meter

28
Q

what is the clinical goal with CS testing

A

find lowest triplet a pt can see

29
Q

each set of triple is how much of the previous line

A

0.15 log units

30
Q

At what distance is the MARS test for CS performed at

A

0.5m

31
Q

What is the clinical goal for Melbourne Edge test

A

have pt find where the edge is located, all pt needs to see is the different direction of lines

32
Q

What is the relationship between Melbourne edge test and VA

A

independent of VA given pt uses edge detection

33
Q

If a pt has low vision, which test should be used ?

A

Melbourne Edge Test

34
Q

What is the Vistech Chart

A

pt informs you the orientation of a given letter
- testing sine wave gratings at 1.5, 3, 6, 12 and 18 CPD

35
Q

What distance is the Vistech chart performed at

A

3m

36
Q

What are the vectorvision charts

A

similar to vistech charts
- testing sine wave gratings at 3, 6,12, and 18 cpd

37
Q

As we age, what is the relationship with contrast and sensitivity

A

increased age = decreases contrast = decreased high spatial frequency

38
Q

What are the main finding of CS

A
  • detects visual loss that would be missed by testing VA alone
  • gives better assessment of visual performance in the real world
  • highest predictor of falls in elderly
  • great predictor of driving recognition performance

OT (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions