Spatial Vision (M2) Flashcards
What refers to how the visual system responds to patterns of light and dark across space?
spatial vision
What do low-contrast acuity charts tell the doctor about the patient?
know less than normal but not a measure of contrast sensitivity for the patient
What allows for Vernier acuity to be so “hyperacute”?
responses to different stimuli overlap or blur occurs
What acuities are impaired by strabismic amblyopia? 1. Which are not impaired? 2
- Vernier and optotype acuities
2. grating acuity
What is the type of hyperacuity that is the ability to use the slightly different images in the two eyes to see in depth? 1. Is this better or worse than Vernier hyperacuity? 2
- stereopsis
2. slightly worse
What are the limits on grating resolution acuity?
- Nyquist limit
- optical blur
- light level
- position on retina
- rods vs. cones
- infants vs. adults
What are the disorders that affect Vernier acuity?
- refractive amblyopia
2. strabismic amblyopia
For human CSF, what value is usually the peak sensitivity?
5 cycles/degree
What are the differences in brightness (and color) of an object with respect to other objects in the field of view called?
contrast
What visual disorders can lead to reduced CSF?
- cataracts
- corneal conditions (especially LASIK)
- multiple sclerosis
- Parkinson’s
- cortical vision impairment
- albinism
Which comes faster for infants: Vernier acuity or resolution acuity?
Vernier acuity (4-6months)
What is the reason for low spatial frequency roll-off?
bright bars stimulate whole receptive field so lateral inhibition from the surround cancels excitation in the center
Is the logMAR or Vernier acuity better in the visual periphery? 1. In the fovea? 2
- logMAR better
2. Vernier
How many arc sec is the minimum Vernier acuity?
10 arc sec
For sine-wave grating, what is the contrast referred to? 1. What is the formula for this? 2
- Michelson or grating contrast
2. grating contrast =(Lmax - Lmin)/(Lmax + Lmin)
What is a discrimination that is finer than the spacing of the rods and cones or by widely-spaced detectors?
hyperacuity
What is the overall ability of infant vernier acuity?
it is poor but not that poor once their poor contrast perception is taken into account
What is one disorder that does not affect Vernier acuity very much but does affect resolution and optotype acuity?
cataracts
What does pre-cataract surgery logMAR predict about post-op logMAR?
doesn’t predict post-op logMAR as well as a pre-op hyperacuity
What is the shape of the contrast threshold for sine waves?
u-shaped
What are the well known low-contrast letter charts?
- Pelli-Robson chart
2. Bailey-Lovie chart
How many arc sec is the minimum resolution acuity?
30 arc sec
What are the ways to tell if cataract surgery is going to be helpful to the patient?
- helpful if no other ocular pathology (but sometimes hard to tell if it’s there)
- use hyperacuity to see if beneficial because poor hyperacuity before the surgery implies some ocular pathology other than catract
What is the numerator of the Snellen fraction? 1. The denominator? 2
- distance at which test was taken
2. distance at which the smallest optotype patient can resolve subtends 5 arcmin