Can you explain what you mean by prisms in your vision?Is it on one eye or both eyes?How long does it last?Is this the first time?Customer :A combination of sharp geometric, angular prism effect, left eye only, rather large area in letter "C" shape generally, peripheral, seems to have gone away now so lasted about 30 minutes. I have had this perhaps once or twice before with headache (migraine I think) but that was always following very stressful, tired physical state. I had just woken up after 7 hours of sleep.Dr. James :Yes, migraines can be preceded by visual auras such that you are describing. A headache doesn't always follow such events.Another cause is called a PVD.You have a thick gel material in the middle of your eyes. Over time as it liquefies, this gel material collapses on itself and pulls away from the wall of the eye. In the process it can stimulate the retina -- causing the flashes that you see.It is recommended that you see your ophthalmologist to look at the retina to make sure there are no problems such as a retinal hole or tear. In most cases, there are no problems, but this exam in precautionary and allows for preventative treatment of any lesions that are found.If you notice a sudden increase in floaters, flashes of light (like a lightening storm), or a shadow/veil in the periphery of your vision, this can be worrisome for a retinal detachment. You would need to contact your ophthalmologist promptly in that case.Customer :Ok, Thanks so much for this information. Is this particular prism effect (absolutlely clear (not dark, shadow type) effect something that sounds familiar?Dr. James :Yes, it sounds similar to what is described in people who are having a PVD.You can also get a prism effect with cataracts which is a clouding of your lens inside your eyes. These prism like effect are more predictable however since it is related to the opacities of your lens.Customer :Very interesting. And is there anything that I should or should not be doing at this point, other than making an appt with opthalmologist? Like drinking coffee, playing tennis, etc...Dr. James :No need to make any changes except be aware of those warning signs of a retinal detachment. Normal activities should be OK.Customer :Thanks so much, and have a nice day. Your answer was so helpful and informative.