It sounds like you experienced an acephalgic migraine.A typical migraine headache starts with shimmering lights, often times they surround a blurry area or have dots or jaggedly lines associated with them. They tend to progressively increase in intensity and sometimes march across the visual field causing difficulty with reading. Many times this is then accompanied by nausea, irritability, sensitivity to bright lights and/or loud noises. After the onset of the lights (called scintillating scotomas), the headache typically starts and the light show tends to progressively go away.Many people can have this migraine phenomenon without the headache; it is called an acephalgic migraine. Some people even start having these late in life, or may have had a few much earlier in life that behaved differently and haven't had any for decades and then begin to have them; this is not uncommon. A family history of migraines is often present as well.This is nothing to worry about. It is not a sign of a more serious underlying condition, brain tumor or anything like that. If the episodes become so frequent that they are bothersome there are medicines that can be used to decrease their frequency or stop an episode once it has started.This is something that I, personally, have been dealing with for over 30 years and professionally treating for almost 20 years.Visine is not necessary.....JACUSTOMER-f0dedf1p- :I don't have to actually have head pain to have a migraine? I did have a minor headache this afternoon, but didn't think it was related.What causes the prism ?Dr. Rick :No. As a matter of fact getting the migraine headache almost never happened to me, except for a few years in my 30's when actually went on meds for a bit due to the headaches. In my practice I'd say that about 2 in 10 patients get the headache after the shimming lights.JACUSTOMER-f0dedf1p- :Should I expect to see this happen on any kind of regular basis now?Dr. Rick :That is a great question. It is caused by a lack of blood flow in the part of your brain that runs your vision. It is actually possible to map out the specific areas involved by plotting the shimming light/ c shaped thing you see.It is not a sign of a brain tumor, stroke risk or anything like that....Yes, it very well may recur and, if it does, don't worry.JACUSTOMER-f0dedf1p- :When I had my eyes examined a few years ago by my optometrist , she said I had a sausage effect in the blood vessels of my eyes and should be seen by an ophthalmologist. They said nothing was wrong with my eyes however.Dr. Rick :Here is a good article on the topic from the Mayo Clinic:http://www.mayoclinic.com/health/ocular-migraine/AN01681I am a retina specialist and, it my belief that an optometrist really doesn't have enough training to diagnose abnormal retinal vessels.JACUSTOMER-f0dedf1p- :so I'm basically okay thenDr. Rick :If you did have "sausage" vessels it could be from high BP, diabetes etc....I would suggest that you have your next yearly exam by an MDJACUSTOMER-f0dedf1p- :I have that, my blood pressure is normal and I am not diabetic nor borderline .. we looked into those.Dr. Rick :Yup. Both you and I are basically OK.....well, maybe my daughter would not agree with that statement....but from a migraine standpoint...nothing to worry about :)JACUSTOMER-f0dedf1p- :lol good to know we are both basically okay. Those were the things my optometrist had suggested too. Thanks for listening and reassuring meDr. Rick :Optometerists have been given the "right" to treat eye disease.....but they don't have the training to diagnose it or treat it even if the State gives then a piece of paper that says they can....see an ophthalmologist for a routine eye exam in the future and I bet you will be fine.My pleasure :)JACUSTOMER-f0dedf1p- :I'll just learn to enjoy the colors the next time it happens.Dr. Rick :I must admit the colors are pretty vibrant, eh?I once had to pause during retina surgery during an attack as I had lost part of my visual field and couldn 't see well enough to operate.....but other then that I've never had a problem.JACUSTOMER-f0dedf1p- :crazy brilliant, it was very cool. Wow, that must have startled you. That's how it was for me today.I teach school and I was having trouble discerning the book from the colors and then it just goes awayDr. Rick :ya, we just all stood around in the OR listening to the music for 15 minutes....I never told the patient :)You might find it impossible to read during an event.JACUSTOMER-f0dedf1p- :that's how it was, I was reading to the children and I kept seeing the lights and colors. I just told them my eyes were acting up and they waitedDr. Rick :But you described the visual findings very well.....must be the teacher in you.JACUSTOMER-f0dedf1p- :Thank you for your help. It was much nicer to find this out sitting in my living room. Thank you.Dr. Rick :my pleasure.