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Strabismus 106 > Contrast Sensitivity > Flashcards

Contrast Sensitivity Flashcards

1
Q

81 year old patient
VA: R: 0.020 (6/6-1) L: 0.040 (6/6-2) etdrs chart
NVA: R: 6/6 L: 6/6 reduced Snellen chart
BEO: N5 read fluently Moorfields bar reading book

Tells you she struggles with her vision especially at night and can’t see food on her plate or read well.

What’s this patient’s diagnosis?

A

Reduced Contrast Sensitivity

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2
Q

What’s the definition of contrast?

A

The difference in luminance of adjacent field or objects

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3
Q

What is contrast sensitivity?

A

The ability to detect objects at low contrast

Contrast sensitivity defines the threshold between the visible and invisible

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4
Q

What is visual acuity?

A

The ability to resolve a pattern into spatially separate elements

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5
Q

Why is contrast sensitivity important?

A
  • Driving (especially at night)
  • Reading
  • Navigation
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6
Q

How do we measure contrast?

A

Difference in Luminance / Average Luminance

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7
Q

What’s the contrast threshold?

A

The least amount of contrast necessary to allow detection

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8
Q

How do we measure contrast sensitivity?

A

1 / Contrast Threshold

A measure of the ability to detect patterns and objects at varying contrast levels

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9
Q

What frequency do we use to measure contrast sensitivity?

A

Can be measured using gratings of varying spatial frequency

Spatial frequency - cycles per degree at nodal point of eye e.g. 5 cpd is a higher spatial frequency than 2 cpd

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10
Q

What does it mean that spatial frequencies are in units of cycles per degree of visual angle?

A

It implies that the visibility of details at a particular frequency is a function of viewing distance

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11
Q

When measuring contrast sensitivity, we use a range of what 2 levels?

A
  • Spatial Frequencies
  • Contrast Threshold
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12
Q

What is contrast sensitivity function (CSF)?

A

Contrast sensitivity function(CSF) is the curve that defines the lowest contrast level that you can detect for each spatial frequency tested.

A graph is plotted setting out contrast threshold for each spatial frequency.

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13
Q

What is the critical spatial frequency?

A

Grating can’t be detected even at maximum contrast (Critical spatial frequency)

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14
Q

Can a patient have normal VA but reduced contrast sensitivity?

A

Yes

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15
Q

What information does contrast sensitivity give us?

A

Measuring contrast sensitivity provides additional information on the quality of vision - things like cataracts, glaucoma, age-related macular degeneration and retinitis pigmentosa can reduce CS

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16
Q

What did Xiong et al (2020) find about contrast sensitivity and ocular disease?

A
  • Cataract and Glaucoma, poor VA and reasonable CS.
  • AMD and RP (Retinitis Pigmentosa) poor VA correlated with poor CS.
17
Q

Can contrast sensitivity help in detecting and monitoring ocular diseases?

A

Yes

18
Q

What might contrast sensitivity be useful in monitoring?

A
  • Optic neuritis (Retrobulbar neuritis)
  • Optic nerve compression (e.g in graves orbitopathy = thyroid eye disease)
  • Optic pathway glioma
  • Cataract
  • Glaucoma
  • Macular disease
  • Retinitis pigmentosa
  • Amblyopia
19
Q

What might we see in reference to the contrast sensitivity in anisometropic & stimulus deprivation amblyopes?

A

Contrast sensitivity reduced at all spatial frequencies tested.

20
Q

What might we see in reference to the contrast sensitivity in strabismic amblyopes?

A

Contrast sensitivity reduced for high spatial frequencies only.

21
Q

In amblyopes, can contrast sensitivity improve?

A

Contrast sensitivity may improve during amblyopia treatment, however not to the same level as normal subjects even without improvement to VA.

22
Q

What can contrast sensitivity in low vision predict?

A
  • Predicts persons mobility
  • Indicates which eye will give the better reading performance
  • Explains why some patients cannot attain sufficient reading speeds despite reasonable visual acuity and provision of appropriate magnification
23
Q

What charts are there of clinical contrast sensitivity?

A
  • Pelli-Robson contrast sensitivity test
  • Bailey-Lovie LogMAR low contrast chart
  • The Mars Letter Contrast Sensitivity Test
  • Test chart 2000 (Thompson)
  • American optical contrast sensitivity test
  • Vistech vision contrast test system
  • CSV1000E Contrast Chart
24
Q

How does the Pelli-Robson chart work?

A
  • Identical size letters in groups of 3 (triplet) approx 1.5cpd
  • Each group of 3 letters has same contrast
  • Contrast decreases from 100% to 0.5%
  • Tested at 1m
25
Q

What is the average score on the Pelli-Robson chart for 22yo’s and 70yo’s?

A

Elliot et al (1990)

1.80 log units - mean 22yrs
1.65 log units - mean 70yrs

26
Q

What is the preferred contrast sensitivity chart? (57% UK Orthoptists recommend)

A

Pelli-Robson as it has high repeatability of 92-94%

27
Q

What is the Bailey-Lovie Low Contrast Test? How does it look?

A

It is a contrast sensitivity chart with 10% contrast that can be directly compared with the normal high-contrast chart. Usually there are around 7-11 letters difference.

28
Q

What is the Mars Letter Contrast Sensitivity Test?

A

It’s a hand-held contrast sensitivity chart that’s viewed from 41 - 59cm with a contrast range from 0.04 to 1.92 logMAR.

Each successive letter decreases in contrast by 0.04 logMAR

3 versions with a difference sequence of Sloan letters

Need to wear +2.00DS lens to correct working distance in Presbyopic patients

29
Q

What is the Test Chart 2000?

A

A computerised Contrast Sensitivity Test that presents optotypes on a computer monitor viewed at 1m.
Same as Pelli-Robson but only one triplet presented per line

30
Q

Given the Test Chart 2000 is based off of Pelli-Robson, do they have good agreement?

A

Mars Chart and Pelli-Robson chart show reasonable agreement

Test Chart 2000 and Pelli-Robson chart do not show good agreement. (This could be due to poor performance of liquid crystal display screens at low contrast levels.)

31
Q

What’s the American Optical Contrast Sensitivity Test?

A

There is a demonstration plate and 6 other plates ranging from 0.2 - 6.4cpd and is presented at 57cm.
Average score is <62, Borderline = 78 & Abnormal is >82

32
Q

How is the American Optical Contrast Sensitivity Test conducted?

A
  • Patient instructed to look at border with box and say when ‘stripes’ first seen as plate withdrawn
  • Plate moved slowly (about 20 secs to reveal)
  • Can confirm seen by asking patient to indicate dark ‘stripe’ – can be used in children
  • Score for plate noted
33
Q

How is the Vistech Contrast Test conducted?

A
  • Patient indicates if grating tilted to left or right
  • Test performed at 3m
  • Near chart available
34
Q

What is the CSV1000E Contrast Chart?

A

A contrast sensitivity chart

4 rows of sine-wave gratings

Spatial frequencies of:
3, 6, 12, and 18 cyc/deg

Test at 2.5 meters

35
Q

What contrast sensitivity charts do you use in young children?

A
  • Peek-a-boo Patti / Hiding Heidi
  • Lea symbols
  • Cambridge low contrast grating
36
Q

What is the Hiding Heidi test?

A

A test of contrast sensitivity in young children

Face revealed from covered position and child observed to see if follows / responds to face

‘Know’ patient’s reactions to face / toys prior to testing

Contrast levels: 1.25%, 2.5%, 5%, 10%, 25% & 100%

Mixed spatial frequencies: 9, 3, 1.5 & 0.75 cpd

Preferential looking

Tested at 1m

37
Q

What is the Peek-a-boo Patti test?

A

A test of contrast sensitivity in young children

For testing: typically developing toddlers/young children and older children / adults with learning difficulties.

Pictures of the same size that decrease in contrast between light and dark bands.

The contrast sensitivity is determined by the faintest bands for which the target is visible

12 contrast levels - 3 cards at each level (36 cards total)
Preferential looking technique
Contrast levels 46% to 1%

50 cm, 1.9 cycles per degree (or 6/90, 20/300)
1 m , 3.8 cycles per degree (or 6/45, 20/150)
25 cm, 1.0 cycle per degree (or 6/180, 20/600)

38
Q

What is the Cambridge Low Contrast Gratings?

A

A contrast sensitivity test in young children

39
Q

How is the Cambridge Low Contrast Gratings performed?

A

Grating effect created by dots on one page only, intensity of dots governs contrast (5% to 0.14%)

Tested at 6m, illumination 100cd/m2 (well lit room)
Two pages displayed, one filled with dots – other dots only in stripes (4 cycles/degree), child asked to indicate page with stripe
Proceed until not seen, then go back 4 plates – repeat 3 more times,
then add scores for 4 series and read CS from table (10 to 560)

Normative data published for different age groups.
However, caution due to lack of repeatability over time (Jones et al, 1994)

Strabismus 106 (35 decks)

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