You need single vision lens replacement if you're either nearsighted or farsighted, but not both. Single vision lenses can also correct for astigmatism.
Not sure if single vision is right for you? An easy way to determine if you need single vision lenses is to look at the ADD column of your prescription. If there are not any numbers in the ADD column of your prescription, then you need single vision lenses and you've come to the right place.