This article might be helpful, it says, "A dog born blind will have little trouble accepting the condition, but a newly blinded dog
may become depressed. He will need extra loving attention to overcome the emotional impact of his new condition."
It is possible that his lying around might be a symptom of depression, but I would certainly ask the vet about it. Also, there are some good tips on how to help.
How to care for a blind dog - by Carol Smock