During eye examinations, the refractive power required to correct defective vision is determined without accommodation (the eye's automatic adaptation to various distances).
0.00 D (diopters) = normal vision (emmetropia)
Powers other than 0.00 D (diopters) = defective vision (ametropia)
e.g. sph +2.00 D (diopters) = long-sightedness (hyperopia) – also with presbyopia (gradual loss of ability to focus on near objects with increasing age). Here the term addition (Add) is used
e.g. sph -1.00 D (dioptres) = short-sightedness (myopia) Powers below -6.00 D are classified as high myopia.
cyl 1.00 D (diopters) = cylindrical ametropia (astigmatism) –the eye sees dots as bars or lines