This needs evaluation, first by a an ophthalmologist and if he refers to a neurologist.Sudden blurring, fogging, or diminution or loss of vision needs answer. This can be because of eye causes or neurological causes. Ischemia is the most common mechanism of acute visual dysfunction, and it can affect any aspect of the visual system. Ischemia reduces delivery of oxygen and other important nutrients to tissues, causing metabolic compromise of cells. Functional deficit may be temporary or permanent, depending on the degree of damage.
There can be other reason too, which can only be ascertained by the examination. Read here;
Your follow up questions are welcome.
Dear J M Harrod,
I am so happy for keeping me updated. The good news is that it is something which would be self limiting and would heal spontaneously. With this check up and medical opinion, we all will have no anxiety at all.
Wishing a very speedy recovery to your son.