Sturm interval

Sturm in·ter·val

(shtūrm),
the distance between the anterior and posterior focal lines in a spherocylindric lens combination.

Sturm in·ter·val

(stūrm in'tĕr-văl)
The distance between the anterior and posterior focal lines in a spherocylindric lens combination.

Sturm,

Johann C., German physician and mathematician, 1635-1703.
Sturm conoid - in optics, the pattern of rays formed after passage through a spherocylindrical combination.
Sturm interval - the distance between the anterior and posterior focal lines in a spherocylindrical lens combination.