How to Assess Human Visual Function Flashcards

1
Q

What is visual function?

What are some visual functions (8)?

A

Things that are done as part of seeing.

Perceiving Fine Spatial Detail

Perceiving Differences in luminance

Perceiving differences in wavelength of light

Perceiving information in the periphery

Adjusting to bright light

Adjusting to low light

Depth Perception

Motion Perception

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2
Q

How do we assess the following visual fucntions:

Perceiving Fine Spatial Detail

Perceiving Differences in luminance

Perceiving differences in wavelength of light

Perceiving information in the periphery

Adjusting to bright light

Adjusting to low light

Depth Perception

Motion Perception

A

Perceiving Fine Spatial Detail ——> Via Testing Visual Acuity

Perceiving Differences in luminance —–> Via Testing Contrast sensitivity

Perceiving differences in wavelength of light—–> Via Testing Coloiur Vision

Perceiving information in the periphery—–> Via Testing Visual Fields

Adjusting to bright light—–> Via Testing Light Adaptation

Adjusting to low light —–> Via Testing Dark Adaptation

Depth Perception —–> Via Testing Stereopsis

Motion Perception —–> Via Tests such as Flicker Fusion Rate Test

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3
Q

What is the visual impairement associated with the following visual functions:

Perceiving Fine Spatial Detail

Perceiving Differences in luminance

Perceiving differences in wavelength of light

Perceiving information in the periphery

Adjusting to bright light

Adjusting to low light

Depth Perception

Motion Perception

A

Perceiving Fine Spatial Detail —–> ‘Blurred Vision’

Perceiving Differences in luminance —–> ‘Hazy/Dim Vision’

Perceiving differences in wavelength of light —–> ‘Colour blindness’

Perceiving information in the periphery —-> ‘Loss of peripheral Vision’

Adjusting to bright light —–> ‘Glare’ or ‘Photophobia’

Adjusting to low light —–> ‘Night Blindness’

Depth Perception —–> e.g. ‘Amblyopia’

Motion Perception —–> ‘Motion Blindness’

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4
Q

True or false- Different eye diseases are associated with affecting particular sets of visual functions

A

True

e.g. e.g., AMD —> acuity & contrast

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5
Q

Why is every and any list we could make on ALL visual functions always going to be an oversimplification?

A

Often different functions are highly overlapping (e.g., Visual Fields & Contrast Sensitivity). And often each function can be subdivided into a many subfunctions (e.g., Acuity à Resolution Acuity, Recognition Acuity) thus any list we make is always going to be an oversimplification.

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6
Q

What are the different tests we can use to measure VA?

A
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7
Q

What are the different tests we can use to measure Contrast Sensitivity?

A
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8
Q

What are the different colour vision tests?

A
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9
Q

What is a disadvantage of Ishihara plates or the cambridge colour Test?

A

Relies on the patient having good enough Visual acuity in order to read the letter/number.

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10
Q

What are the different ways in which we can test Visual Fields?

A
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11
Q

What do we measure in visual function tests?

A

THRESHOLDS

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12
Q

What is a detection threshold?

A

The weakest stimulus that can be detected X% of the time (e.g., 50%, 75%, 95%, etc. – exact value varies between different tests, and not always clearly defined)

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13
Q

What are suprathresholds?

What may suprathreshold tests be used for?

A

Not every clinical test actually measures a threshold.

Some (‘suprathreshold’) tests are just pass/fail at a single stimulus level.

These may be suitable for crude applications (e.g., screening), but not for staging disease severity or monitoring progression.

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14
Q

What are the three ways of measuring a threshold?

A

Method of constant stimuli - you present the stimuli in a random order and each time you are asking whether they can see the stimuli or not (in this method you exhaust all degrees of the stimuli- thus it is the gold standard but incredibly slow thus used for research).

Method of limits - you present the easiest stimuli first and slowly it gets harder for the patient to see the stimuli up till the point where they say they can’t see the stimuli ( this is good as it is like a game for patients).

Method of adjustment- the stimuli would be on a scale and the patient would twiddle a knob until the point that they can’t see the stimuli ( tend not to use as much in practice).

[Note not every test will fit into one of these categories - new tests use a merge of all three ideas]

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15
Q

When measuring thresholds why do we repeat?

A

With any Method, responses must generally be repeated to ensure accuracy. Any single response cannot be 100% trusted due to a variety of factors, including:

  • Intrinsic noise in the visual system (false positives and false negatives)
  • Lapses in concentration (false negatives)
  • ‘Lucky guesses’ (false positives)
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16
Q

Why is measuring threshold hard?

A

Because it involves a complex balance between many, often competing practical considerations:

  • Speed
  • Accuracy
  • Reliability
  • Bias
  • Ease of use
  • Validity
  • Cost
  • Etc.
17
Q

What is step size and how is it a practical consideration when designing a threshold test?

A
18
Q

How is Test Duration a practical consideration when designing a threshold test?

A
19
Q

What are criterion effects and how is it a practical consideration when designing a threshold test?

A
20
Q

How is a response method a practical consideration of designing a threshold test?

A
21
Q

How is the stimulus a practical consideration of designing a threshold test?

A
22
Q

What does it mean for a test to be sustainable?

A

I.e. that it will still work in say 20 years time

23
Q

What makes a good test ?

A
24
Q

What is the difference between functional and structural measures of Visual function?

A
25
Q

What is Functional vision?

A
26
Q
A