Various types of visual acuity and how they differ

Minimum Visible Acuity

Smallest object one can detect (ability to separate object from the background) - Ultimately the measure for contrast

Minimum Resolvable Acuity

Smallest angle between objects that one can detect (finest black/white stripes that can be distinguished)

Minimum Recognizable Acuity

Smallest angle that one needs to recognize a feature or object (Eye chart)

Minimum Discriminable Acuity

Smallest angle needed to detect a change in a feature (What angle is needed to detect that to lines are misaligned?)