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I want to quote Donna H. in full.  

Bec,  The most common cause of headaches in or around the eye or on one side of the forehead is trigger points in the Sternocleidomastoid muscle.   These typically develop as a whiplash symptom, which can be caused not only in auto accidents, but also in falling off a horse on your face, getting punched in the face or getting hit in the face with a baseball or bat, or by anything else that jerks the head back suddenly.   These trigger points may cause symptoms for decades, and may be worsened by stress or unusual positions at work.  A good massage therapist who actually knows how to treat this muscle can stop the headaches.  You can find people who do neuromuscular therapy in the SE US, I don't know about other areas.  

    Another cause of left eye pain can be from the gallbladder.  This is a well known connection in acupuncture.  In light of the fact that gluten does it's worst damage in the duodenum, where you make the hormone that tells the gallbladder when to dump, it stands to reason that a lot of cealics, especially undiagnosed celiacs, would have gallbladder trouble.  I myself have had trouble with my left eye off and on for several years, it sometimes hurts, but mostly gets a bit dim in very dim light, when this happened I'd work my SCM muscle and it would get better.  But a couple of years ago it was particularly painful, and I was practicing for a class in "Visceral manipulation".  I was very surprised to find my gallbladder painful to the touch (we don't usually poke at our gallbladders) , but a few scooping motions as described to drain it removed the tenderness immediately.   It was a couple of months before I realized that my eye pain vanished at about the same time.  
    Hope this is of some help, I'd be very surprised if your pain was not due to one or the other cause.  I treat lots of people for whiplash headaches in my work as a professional MT.                       

I can relate to gallbladder issues, but the muscle spasm didn't seem to fit in my case...But Deborah from Oklahoma sent me this comment:

 I went to a upper cervical chiropractor because I was having some neck problems. When he "adjusted" my neck my headache went away in about 10 minutes. Now, when I have one of those killer eye headaches I go to the chiropractor and they "put my head back on straight" and I feel wonderful in 10 to 30 minutes. It works like a dream for me. 
I told the chiropractor that I had gone to other chiropractors and had not been helped with headaches and he said it was because I hadn't gone to an upper cervical chiropractor. Their theory is that the top vertebra has very little to hold it in place and it may move a degree or less out of vertical. When that happens the nerves that carry electrical impulses up/down the spinal column are pinched. They believe that this can cause numerous problems with the messages between your body and head. They believe that when the top vertebra is out of place the rest of the spinal column will adjust to try to balance your heavy head on top. This can cause pain in your lower back as some of your back muscles are trying to work extra hard. Their theory about your back adjusting to compensate for your heavy head must be right because my daughter had one hip nearly 3/4 ths of an inch higher than the other one. After one treatment which put the atlas (the top vertebra) back into proper position her hips were completely level. They didn't do anything else to her back except work on the top vertebra. 

So massage therapy or chiropractic manipulation might help to relax the muscle.

What Donna wrote about the gallbladder resonated with me, because over the years, I have developed a very unorthodox way to deal with the pain:  saturated fat.  My migraines always linked to bloating and tummy pain.  I remember in desparation eating a mixture of butter and chocolate and sugar in an attempt to stop the pain, and that, combined with a high protein meal, would help me.    I have gotten more sophisticated:  I use coconut milk now, in combination with the fat solubles Vitamin A and K.  It alone doesn't cure the migraine, but it pushes it to the background that I can function.  For me, it's back to that fat thing:  no hydrogenated fats, plenty of the good fats, and plenty of the "fat handlers", vitamin A & K.

There are health claims made for coconut milk.  You can easily look it up using a search engine.  I'm not endorsing these clains, only noting that using it as a source of fat works for me.  On to Part the Third, the recipe for anti-bloat.

Bec Markle

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