Thursday, February 13, 2014

Sore Eyes For Sight

I wrote a while ago with an illustrated guide to how the world looks to me. That has changed recently. Two and a half years after having the strokes, I'm not occluding my left eye. The change is more dramatic for observers than for me: it looks a lot better, but it doesn't by any means 'fix' my sight. 

One of the lingering effects of my brain damage has been diplopia, double vision. My problem is not in the visual cortex (where knocks to the noggin can cause double vision), but in the muscles around my left eye. My brain might want to have my eyes line up correctly, but the neurons that controlled eye movement are gone.

Worse, as other neurons take over the tasks of activation, the muscles themselves have atrophied. My left eyelids have not worked for over two years, and I can feel the difference: they are thinner. So, even as my brain recovers heretofore lost function, my body wants to make life difficult.
To make matters more fun, my double vision is diagonal; there is both horizontal and vertical displacement of the images from each eye. (This might make more sense when you know that three pairs of muscles control the movement of each eyeball, not two nor four.) Add in the oscillopsia in each eye, with independent period, and it's a laugh riot.
What has changed is that my eyes are now stable enough that it is now worth correcting the vertical displacement instead of occluding the left eye. I have double vision, still (and, honestly, that sucks harder than I can describe), but it is more-or-less level. It turns out that vertical displacement is a lot harder to manage than horizontal, a fact I would have been interested to learn two years ago.
Experiments have shown that most people cannot tolerate a vertical displacement of 1 but it takes a horizontal displacement of 12* to have the same effect. This helps me understand why the diagonal diplopia was so debilitating; the Fresnel lens I'm wearing corrects for 3 or 4. I don't remember which. The correction is not 1, it's taken over two years to get this far, and the prism lens will not change for another year at best, so whether it's 3 or 4 doesn't really matter.

The downside, since there has to be one, is that the muscles around my left eye are often working harder. That's a good thing! The headaches that ensue, however, are not.
My double vision is better, despite what the expert said, because I have worked on it every day. That is boring, difficult, and imperceptible day by day, but it is necessary. My vision is still objectively terrible, but it is improving.
* No, I don't know what units are being used, but the difference is an order of magnitude.