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DEFINITION: ability to resolve or see fine
details. |
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Visual Angle: DEFINITION: Angle formed by object
on retina. |
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Types of Acuity: what is meant by acuity depends
upon the stimulus used to measure it. |
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Detection: black bar on white field |
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Resolution: a grating |
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Recognition: e.g. Snellen, where |
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you read letters. |
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Measures of Acuity |
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20/20: can see at 20’ what a normal person
can see at 20’. |
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This is normal, not perfect, vision. |
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20/200: can see at 20’ what a normal
person can see at 200’. |
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Visual angle of the critical feature in a test,
e.g. the width of the bars in a grating. |
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A typical population average is 1 arcmin (1/60
degree). |
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Acuity and Retinal Location: |
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Best at fovea.
Falls off rapidly in periphery.
Is tied to density of cones. |
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We move our eyes because of the limited field
with good acuity. |
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There are 6 eye muscles |
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4 rectus |
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2 oblique |
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Types of Eye Movements |
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Version: Both eyes move together |
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Vergence: Eye move in opposite directions |
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Version |
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Saccades, most common |
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places object on fovea. |
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can be > 400 deg/sec. |
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Takes ~ 200 msec to begin |
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Smooth Pursuit |
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track moving objects |
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relatively slow ~30 deg/sec. |
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Vergence: |
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Convergence (together) and divergence (apart) |
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Allows us to look at closer and farther objects. |
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relatively slow and also takes about 200 msec to
begin |
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Notes