focal interval
Also found in: Dictionary, Thesaurus, Legal, Encyclopedia.
fo·cal in·ter·val
the distance between the anterior and posterior focal points of the eye.
focal interval
The distance between the anterior and posterior focal points of the eyes.
See also: interval
Sturm, interval of
The linear distance between the two focal lines of an astigmatic optical system. Syn. astigmatic interval; focal interval. See oblique astigmatism.