March 30, 2014
It seems like I’m hearing more and more patients describe light streaks occurring in their eyes. It could just be chance though. The way they describe these effects pretty much tells me what’s happening (helps me diagnose) and rarely is it anything serious (there are other vascular problems that could cause strange vision problems like a TIA). What patients are telling me about is their ophthalmic migraines whether the patient knew what it was or not. The strange thing is we usually think of the word migraine as causing pain in our head but the eye doesn’t have any pain when this happens. It’s interesting that the cause of this visual phenomenon is thought to be the same cause as the headache type migraine…a vascular fluctuation.
But there are other conditions that can cause light to seem to be inside the eye and not outside. There’s one called a pressure phosphene. You can create these on your own anytime you want. Just press on your eye. It’s easiest to press on the temporal side and then notice the dark circular spot that appears in the nasal part of your vision but it works both ways. That effect has even been used to estimate the intraocular eye pressure and there’s even a simple instrument that is made to do that but it’s accuracy is questionable. You can do this with your eyes open or closed. You can also rub your eyes and get other visual patterns. What’s happening is the photoreceptors are being stimulated, not by light, but by mechanical pressure which then makes those photoreceptors send a signal to your brain as if there was light, or at least an interesting visual pattern…not like a flashlight kind of light.
What is really pretty cool is what the astronauts have described as flashes. As an aside, to be considered an astronaut in the US you have to go up at least 50 miles but that may not be high enough to get cosmic flashes. The astronauts that have orbited the earth have described some really interesting visual phenomenon that has been attributed to cosmic particles that pass through practically anything and can cause a lot of problems with equipment. Astronauts from the Apollo program and more recent ISS orbiter have noticed this. Here’s a quote from astronaut Don Pettit,
“When a cosmic ray happens to pass through the retina it causes the rods and cones to fire, and you perceive a flash of light that is really not there. The triggered cells are localized around the spot where the cosmic ray passes, so the flash has some structure. A perpendicular ray appears as a fuzzy dot. A ray at an angle appears as a segmented line. Sometimes the tracks have side branches, giving the impression of an electric spark. The retina functions as a miniature Wilson cloud chamber where the recording of a cosmic ray is displayed by a trail left in its wake.”
There’s also a certain area above the atmosphere where the astronauts orbit called the South Atlantic Anomaly. When they reach that area they get more cosmic radiation compared to the rest of the orbit apparently due to a change in the magnetic field surrounding the earth. Of course this radiation is being studied but one of the odd ones is with the Phantom Torso and before that there was the the Apollo Light Flash Moving Emulsion Detector (ALFMED).
If you see flashes of light yourself, the likelihood of it being innocuous (harmless) is pretty good. But then, there’s a small chance it’s a retinal problem that needs to be treated which is why patients with any complaint of flashes should be dilated to rule out the bad stuff.
Here are a few links to some of the astronaut web pages that are kinda interesting to read:
And here are a couple of images of what some might “see” when they have a visual migraine: