visual perception nbeo.txt
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At what age should you be seeing 20/100 (6 cycles/degree)?
What is the expected VA at birth?
20/600 (1 cycle/degree)
When are children expected to be seeing 20/20?
What is the expected VA at 1 yr?
20/50 (12 cycles/degree)
What does Lax criteria mean?
High sensitivity and high false positives
What does strict criteria mean?
High specificity and high false negatives
What does sensitivity mean?
- Probability of a test giving a positive result given that the signal(disease) is present
- Disease present =positive
What does specificity mean?
Probability of a test giving a negative result when signal(disease) is not present
What is a false positive?
Saying there is a signal when there really isn't
What is a false negative?
Not saying there is a signal, when really there is
At what nanometer is photopic vision most sensitive?
At what nanometer is scotopic vision most sensitive?
What is Abney's law?
Different lumens from different wavelengths being summed together as total lumens
What are lambert surfaces?
Surfaces that scatter light equally in all directions
How sensitive is photopic vision?
How sensitive is scotopic vision?
twice as sensitive as photopic
What is special about 650 nm wavelength?
- At this wavelength, there is no difference between photopic and scotopic sensitivities
- Dusk, both photopic and scotopic is being used
What is the Purkinje shift?
After 650nm, shorter wavelengths become brighter in scotopic vision and visa versa
What is Weber's Law?
- How well we pick out a spot of light on a dark background
- Light adaptation
- Rod saturation
What is ricco's law?
Any number of photons within a given set diameter photopic or scotopic will appear as only one light
What is bloch's law?
- Regardless of number of photons is a given time, it will appear as one single light
- Photopic 10ms
- Scotopic 100ms
What is the stiles-crawford effect?
The angle at which light strikes cones strongly affects the light
What is dicromacy?
- Missing one of three cones
what is anomalous trichromacy?
Have all 3 pigments, but one is weaker
what does an acquired blue/yellow defect typically mean?
Outer retinal disease
What does an acquired red/green defect typically mean?
- Inner retinal disease
- Optic nerve
- Visual pathway
What is color saturation?
How vivid the color is
How do you determine MAR?
- 600/snellen denominator
- Divide cycles by degree by 30 to get snellen form
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