One of the rat terrier puppies has a problem!

I feel sorry for the rat terrier puppy which you have got, who suffers from this problem. Generally the pup open his/her eyes in a time period of two weeks, so if the rat terrier is just a week old then I would recommend you to not take any tensions since it is normal.
If the problem persist for a longer period of time, until the time of one month then you should be concerned with forcefully open the rat terrier’s eye and see anything like pus is present in the eyes of the terrier, if yes then it would be fine to apply boric acid on the corners of the eyes. But if nothing happens then the rat terrier should get vet assistance. The pus around the eye can sometimes cause serious eye infection which can result in, worst cases in even blindness of the pup, so please give the pet medical assistance at the earliest. I hope the information provides you with some help. Good luck.