Go to your optometrist and get your prescription, base curve and eye diameter readings. Even if you have 20/20 vision, you will still need your base curve and eye diameter.
Go to 9mmsfx.com or Extremesfx.com.
Browse through the catalog of contact lenses until you find the appropriate lenses for your costume. Each site has photographs of what the contact lenses will look like in your eye.
Choose the prescription, or power/strength, of your contact lenses in the designated box.
Choose the base curve of your eye.
Choose your eye diameter. If you didn't receive this from your doctor, you can use a tape measure or ruler to measure your eye diameter in millimeters.
Choose Add to Cart and continue the purchasing process. Have your credit card information available.