When you see the term "BAL" written on your prescription, it stands for Balance. You will generally have this term written for the prescription of an eye that does not have good visual function or for a prosthetic eye. It is the doctor's way of writing that the lens for this non-seeing eye needs the same thickness as the other lens - so that they essentially provide a balanced look.
When entering in your prescription during Zenni's order process, for the eye prescription that has a BAL or balance you will want to copy the same exact numbers as the better seeing eye. Both eyes should have the same prescription so they have equal weight and thickness. Please note that you will only enter this if your doctor has not given you other instructions.
It is also strongly recommended that you select impact resistant lenses, such as Polycarbonate or Trivex, for your prescription since you require extra protection for the better seeing eye.