Visual acuity
Capacity for seeing distinctly the details of an object
Detection
Minimum distinguishable
Ability to detect a point stimulus against uniform background
Resolution
Minimum separable
Detection of separation of 2 lines or points
Localization
Vernier acuity
Ability to detect misalignment of opposing lines
Recognition
Minimum legible
Ability to detect minimum detail with knowledge and identification of the form
Optimal pupil size
2-3mm
Numerator of Snellen
Test distance of patient from chart
Denominator of Snellen
Distance at which detail subtends 1’ or letter subtends 5’
Distance a normal eye can see the smallest letter read