How to restric viewing to author + another role

We are using WP Types for an ordering portal. The two most important people are the author of posts (i.e. the customers) and the admin (i.e. the managers of ALL orders).

How do we apply an wpv-if statement to restrict the content to the AUTHOR + ADMIN-ROLE only?

Currently all customers can view other customers orders/posts if they hit the URL (while being logged in).

Thanks!