Contrast Sensitivity Flashcards
What is contrast sensitivity?
CS is the ability to distinguish differences in luminance (e.g., ‘shades of grey’). Crudely speaking:
While visual acuity (VA) measures the smallest thing you can see [at 100% contrast]
CS measures the dimmest thing you can see
How is contrast sensitivity measured?
CS is most often measured with Pelli-Robson letter charts. Though other tests exist.
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Why is conrast sensitivity important?
It is important because in real life need to be able to see large, faint objects (i.e., CS), as well as fine spatial detail at high contrast (i.e., acuity)
Name some conditions that can reduce contrast senstivity.
Many conditions affecting eyes and visual pathways can reduce CS, independent of VA. E.g., amblyopia, cerebral visual impairment, cataract, optic neuritis, multiple sclerosis, diabetic macular oedema, glaucoma
True or False - Contrast Sensitivity testing may also be helpful for screening for Parkinson’s or Alzheimer’s disease
True
What is the formal definition of Contrast Sensitivity?
CS is the smallest difference in luminance between a target and a background that a person can detect reliably (e.g., on 90% of trials)
What is perimetry often referred to as?
Visual field testing
In perimetry what is contrast sensitivity refered to as?
Differential Light Sensitivity (DLS)
True or False- Contrast is a relative measure
True - (It’s important to understand the slide)
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The contrast of a stimulus (stimulus contrast) can be expressed in mnay ways including but not limited to; the weber contrast, the micheson contrast and the RMS contrast. When would each of these contrasts be used?
The Weber Contrast would be used to express stimulus contrast for a uniform target
The Michelson contrast would be used to express stimulus contrast for 2 toned targets such as sinosuidal gradings.
The Rms contrast would be used to express stimulus contrast for complex images (targets) with different luminance levels
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True or False- Contrast sensitivity varies with temporal resolution/frequency
False - I literally made this up
True or False - Contrast sensitivity varies with spatial frequency
True
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Why is contrast sensitivity regarded as a function (e.g. Contrast sensitivity function)?
Contrast sensitivity is dependant on spatial frequency thus you can’t just tell someone their contrast sensitivity is a certain value but rather you tell them their function ( in the sense that mathematically a function is an expression/line that is dependant on one or more variables - in this case spatial frequency.
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What unit is spatial frequency recorded in?
Cycles per degree / LogMAR or Snellen fraction ( depending on what the stimulus used was e.g. sinosuidal gratings, logmar or snellen letters respectively).
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What is the range for the peak of CSF in (healthy) adults?
Peak of CSF is generally 2-4 cpd in healthy adults