Thursday, April 04, 2013

amaurosis fugax

Yesterday, about 5 o'clock, sitting at my desk. Go to stretch, arms behind me, pulling on my shoulder, started to greyout (I don't know a better term for this - whatever you call the visual consequence of ocular hypotension) just a bit - which is normal for me when I stretch after having sat still for too long - and instead of resolving the greyout continues. My field of view starts to fade in blotches, but I can still see - I realize that it's just in one eye. I close one, then the other, and now I know that the view from my left eye is fading.

I jump up and run to Eli's office, and by this time, my left eye view is almost completely blank, except for a space around the fovea, maybe 5° wide and 2° high. This makes sense - the foveal blood supply comes from the choroid, not the apparently blocked ophthalmic artery. The blankness is plainly visible as a flat gray. This is different from the scotoma of the migraine aura, which is as visible as the space behind my head. The boundary between the visible center and the blankness is shimmering, flickering, like the smoldering edge of slowly burning paper. Eli gets his ophthalmoscope to try and see what's happening, and the superior field starts to fade back into view.

It's then stable for about a minute, the inferior field is blank gray, and there's a smoldering horizontal boundary between the superior and inferior fields. I see some strange parafoveal phosphenes, like super-high contrast arcs. Eli is shining a light in my eye, and I'm shocked to realize that this bright light is totally failing to punch through the grayness. I wave my hand in the scotoma and though I can't see it, I feel like I can sense the motion.

The inferior nasal field returns, very subtly, so that I just realize it's back without noticing much about how it returns. It's patchy but quick - then the inferior temporal field returns. After this point, I can't find any other blind areas; everything has returned. In fact, I can't find any obvious differences between the two eyes, though at this time Eli is urging me to go to the ER to get examined. My heart is pounding and my head is starting to hurt. For the next 10-15 minutes, as I'm on my way to the hospital, I can see my pulse with the left eye, but then no more, and everything is back to normal.

Eli gets me in to see someone at MEEI, and I'm examined by an ophthalmology resident. The doctor pronounces this a case of ocular migraine, which as far as I understand means "we don't know, but everything looks ok".

Typical Wednesday afternoon. Hey, April is here!

**edit @ 16:21**

While I don't like the 'migraine' label, I guess I can't deny that there might be something to it. It is unknown what the proximal cause of a migraine is, though it's definitely associated with cortical spreading depression in the brain, the physiological correlate of a migraine aura; the current consensus seems to be that the CSD produces substances that inflame tissues in the brain, which then is perceived as pain, and which fits with the experience of headache beginning partway through the aura.

But what causes the CSD? One sure way to cause it is to deprive an area of cortex of blood - stroke causes CSD even in areas of cortex that still have blood supply but happen to be nearby the ischemic areas. So it could be that the aura/CSD is caused by a very local, transient ischemia. The ischemia can't be very large or long-lived because there don't tend to be other symptoms accompanying the well-described auras.

I would be happy if I could confirm that this episode is somehow related to the migraines, i.e. that I experienced a spasm of the ophthalmic artery of the same sort that I usually experience on a much smaller scale, and deeper in my brain, immediately preceding a migraine aura. I also do not feel much affection for this experience, in contrast to the fascinating auras - I hope this does not happen repeatedly, because I don't think it can be good for the retina to periodically starve it of oxygen.

No comments:

Post a Comment