Ok. The fact that he can still see at the distance with his glasses out of that eye tell me that there is, most likely, nothing serious going on with his retina.
The sudden need for reading glasses in this eye could be due to a change in his refractive error. Once again, since he can see clearly with the glasses, I do not think that anything real concerning, or of an emergency nature, is going on.
Taking him to his primary care MD will not be of much value for this issue. I suggest you get him in to see an ophthalmologist
(eye MD) early next week for a complete eye exam. Also, make sure to bring in his distance glasses and the "new" reading glasses that seem to be working for him so that the doctor can check out his vision with these in place.
Is there anything else you would like to discuss at this point or have all your questions been answered to your satisfaction?
I hope this information was helpful for you. But I do work for tips so I want to make sure you are happy with me before rating me. If you have another question on this or a related issue feel free to fire away. And please let me know if the rating system gives you any troubles.
Thanks in advance,
Dr. Rick MD FACS