I went to an optometrist recently who wrote me a prescription for eyeglasses but I don't understand any of it or how to shop for glasses. I don't understand how to filter on eyeglass sites for things like OD, OS, etc? I see two lines, OD and OS. In both lines, there are columns like balance, sphere, cylinder, axis, add, prism,base (last 2 appear twice). and BC. My results look like this  
   


 | Balance | Sphere | Cylinder| Axis
---|---|----|----|----
OD:|  | -1.00 | D.S. | 
OS:|   | -0.50| -0.75 | 126
  
  
All the other columns are blank. I'm an idiot I know, just never bought glasses before.