An engraving (cut) in the contact lens determines if the lens is inside-out. The engraving can be in the form of numbers or letters. It makes handling of contact lenses easy and prevents application of a contact lens the wrong way.
For example, when you place the contact lens on your finger and look from the side, you should see numbers “1–2–3” in the correct way. If the lens is inverted, you will see the numbers “1–2–3” in mirror image.