Unfortunately, it sounds as though the process by which your friend lost vision in his right eye has damaged his optic nerve. This is likely what is called an optic neuropathy or possibly optic neuritis (optic neuropathy much more likely given his age). An optic neuropathy can be caused by an episodic ischemia (lack of blood flow) to the optic nerve, nutritional / alcohol / tobacco abuse or a vasculitis called temporal arteritis (aka giant cell arteritis). Least likely is a hemorrhage in the eye, but this usually does not cause the pupil reactions you described.
Your friend should go see his ophthalmologist right away if he has one or if not, he should go to an ER where he know he will be able to see an ophthalmologist. For the most part, ER doctors will not know how to make heads or tails of your friend's problem. Most importantly if he has been having headaches, scalp tenderness, double vision, episodic vision loss prior to this, cramping in his jaw when he chews his food or talks or other constitutional symptoms such as fevers, weight loss, or night sweats, these could be signs of this vasculitis which can also cause blindness in the other eye, heart attacks and strokes and should be investigated immediately.
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My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must see an eye doctor.