Focal Length : SPH. Long Distance ?

Question

I have an eye glass lens , it's for far distance uses , the doctor wrote 0.5 under a section SPH. what do 0.5 and SPH. mean? and if there is a unit what it is ?and what is the focal length of this lens ?, if it's possible to know by the (0.5) , thanks ..

Answer 1

0.5 is one half of a diopter. Sph is short for sphere. This means there is no astigmatism. The focal length is 2 meters (about 6.5 feet)