About Our Prescriptions
Eye glass prescriptions contain the information required to create your corrective lenses. You may understand what the Eye Doctor means when she says you are nearsighted or farsighted, but you probably don’t understand the fields on your prescription.
OD and OS (Oculus Dexter and Oculus Sinister) – Simply: Left Eye and Right Eye
OU (Oculus Uterque) – Both Eyes
(Some doctors have adopted RE and LE to clarify Right Eye and Left Eye)
The information for your right eye (OD) comes before the information for your left eye (OS) on a prescription.
Sphere (SPH) – The lens power, measured in diopters (D), needed to correct nearsightedness or farsightedness. A minus sign (–) to correct nearsighted and a plus sign (+) or no sign to correct farsightedness. Spherical means correction needed is equal in all meridians of the eye.
Cylinder (CYL). The lens power for astigmatism. If blank, you have no astigmatism concern. Cylinder means correction needed is shaped so one meridian has no added curvature, and the other meridian contains the maximum power to correct astigmatism. The Axis is the meridian that contains no cylinder power to correct astigmatism. 90 is the vertical meridian of the eye, and 180 is the horizontal meridian.
Add. This is the added magnifying power applied to the bottom part of multi-focal lenses to correct presbyopia.
Prism. This is the amount of prismatic power, measured prism diopters compensates for eye alignment. Prism direction: BU = base up; BD = base down; BI = base in (nose); BO = base out (ear)