Diabetic Retinopathy Treatment Care

I recently had a doctors appointment and their was a sign in the exam room saying that if you are a diabetic to please remove your socks and shoes. Why do diabetics have to remove their shoes and socks? I don’t know much about diabetes and I am curious.

Earlier today I read an article about shoes and the different problems with different kinds of shoes.
I can’t find it anymore, which is why I didn’t post the link.
But in the article, it said that someone with diabetes or would likely eventually get diabetes should never go without shoes; whether inside or outside their house.
Why would that be? Thanks for any help in understanding this.