Definition: What is meant by an angle of vision?
The angle of vision is the angle at which a viewed object is perceived. The reciprocal of the angle of vision is the visual acuity (Visus) and therefore, among other factors, a measure of the legibility of writing.
How can the angle of vision be calculated?
In order to measure visual acuity, a test person must determine the orientation of the gap in a so-called Landolt ring (a circular ring with a gap or opening as a standard optotype or vision mark for vision tests). The angle of vision can be calculated from the size of the gap in the ring and the viewing distance. The observation distance results in an angle of vision (å), the reciprocal of which is the measure for visual acuity (S = 1: å). A visual acuity (Visus) of 1 equates to recognition of the gap under an angle of vision å = 1'.
Good to know: The unit of the angle of vision å is specified in angular minutes. An angle of one degree can be divided into 60 angular minutes (1' = 1/60°).
