How to Assess Human Visual Function Flashcards
What is visual function?
What are some visual functions (8)?
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
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
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
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
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’
True or false- Different eye diseases are associated with affecting particular sets of visual functions
True
e.g. e.g., AMD —> acuity & contrast
Why is every and any list we could make on ALL visual functions always going to be an oversimplification?
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.
What are the different tests we can use to measure VA?
What are the different tests we can use to measure Contrast Sensitivity?
What are the different colour vision tests?
What is a disadvantage of Ishihara plates or the cambridge colour Test?
Relies on the patient having good enough Visual acuity in order to read the letter/number.
What are the different ways in which we can test Visual Fields?
What do we measure in visual function tests?
THRESHOLDS
What is a detection threshold?
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)
What are suprathresholds?
What may suprathreshold tests be used for?
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.
What are the three ways of measuring a threshold?
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]
When measuring thresholds why do we repeat?
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)
What is step size and how is it a practical consideration when designing a threshold test?
How is Test Duration a practical consideration when designing a threshold test?
What are criterion effects and how is it a practical consideration when designing a threshold test?
How is a response method a practical consideration of designing a threshold test?
How is the stimulus a practical consideration of designing a threshold test?
What makes a good test ?
What is the difference between functional and structural measures of Visual function?
What is Functional vision?
