In that case, you will need to first order lenses for your right eye and only then for your left eye.
On the product page make sure to uncheck the box next to "Left Eye" and enter your prescription in the "Right Eye" section. Once done, continue by clicking the "Add to Cart" button.
Now that you've done that, just proceed to your left eye's brand page by finding it on the left side navigation bar. Once you get to its product page, make sure to uncheck the "Right Eye" box. Enter your prescription in the "Left Eye"section. When you are finished, click Add to Cart.
Click the shopping cart and make sure that both brands appear there. Once you are sure your order is right, click "Continue Order" to proceed.