HI Bowman I am not a doctor. I am in the position of say an aircraft / automotive engine mech, who can visually / mentally diagnose almost any particular problem with an engine without knowing the metallurgical characteristics etc of the materiel's involved. In light of this I suggest that you consider the following.
A) Apparently the Medical personnel have not found the source of your problem in 7+ years in spite of many, many tests by very competent persons.
B) From what you have posted, your problem is inconsistent in having brief periods of sight returned.
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Referring to (A), none of the tests / examinations etc. show anything unusual. So theoretically, we can rule out a physical reason for your problem. - barring blood or fluid pressure.
The upper right limb of your bow striking you in the left Temporal region would carry quite a bit of kinetic energy, enough for local damage, but not enough to effect the Brain in general since it wasn't of the type and magnitude of a slower heavier impact, such as a fist or club.. While it could have caused extensive local damage, you have not mentioned anything about any fractures or concussions, only severe pain.. So the likely hood of it effecting both optical nerves is slight. Furthermore you have had intemittent sight since, including now. This would tend to eliminate scar tissue involvement also, unless the medical personnel removed it.
So we are back to Fluid pressure. What has your blood pressure been on an average, especially when you have these pain attacks and loss of vision? The bleeding from the eyes is interesting along with the cold apparently effecting your vision. Normally when one is subjected to extreme cold, the body literally retires the blood from the superficial areas, skin, etc., in order to protect the critical areas such as internal organs and brain. So there could be a lower pressure in the eye,, but? At the moment I would tend to rule out Macular Degeneration since a normal examination would have shown this up, plus it is a steadily degenerating condition, no momentary periods of increased vision..
So I am back to the point of auto-suggestion, being triggered by any of many things. There are many people living that have a permanent blindness or other physiological / psychological problems that can, and have been eliminated by competent Psychotherapists. While these problems are basically mentally induced, they are just as much physical as any other cause in their effects.
So I again reccomend that you talk to your doctor about his recommendation for a quality Med certified Hypnotist. If he is not open to talks, and many are still behind in this procedure, ask another, or even better, ask a MED. Certified Hypnotist if she / he believes that they could be of any benefit. check your local telephone book or call your Hospital. for referrals.
In my past experiments I have found that I can easily control fluid pressure, yes blood pressure and heart beat also, as well as pain, discomfort, anxiety, or even bad habits.
I probably can even eliminate the horribly addictive Internet vice, hehhee/ ,.
Tropical Tramp
p.s. apology.to the room for a temp. change in the thread, but it just may keep our bowguy with us and to allow him to finish up his search.
p.p.s You never have stated if your sight just goes black or opaque? Important.
(Plus I live too far away to simply pop in there any old time.) 
