18 March, 2014
As I mentioned previously, I recently fell off my bicycle, onto my head. This had a number of negative effects, a broken arm and a severe concussion amongst them. Though by far the most troubling (and currently persisting) injury has been to my Trochlear Nerve. I’d never heard of it before, and I suspect neither have you, but it is a nerve which travels from the back of the brainstem to control some of the muscles of the eye.
It’s long and thin and easily damaged by a blow to the head. It’s the only nerve which comes out of the back of the brainstem, an evolutionary ‘feature’ which can be traced back to the first vertebrates about 525 million years ago. A ‘feature’ which is fine if you’re a fish, but less so if you’re a large-brained, bipedal primate, who likes to ride a bicycle.
The practical result is that my eyes no longer converge properly, producing a form of double vision known as tortional diplopia.
It has a non-medical name as well.
The first definition is pretty accurate, both eyes are awry, tilted, misaligned. The second is a bit less flattering and better describes my post-concussive state, rather than the effect on my vision. The etymology of the word is unclear, though one can understand how someone with their eyes pointing outwards (in extreme cases of trochlear nerve damage) may look like a cockerel. Perhaps it’s the association of a blow to the head with the confusion of concussion which leads to the second definition. Spinning, non-aligned eyeballs certainly feature heavily in the lexicon of cartoons, a visual shorthand for the effect of being struck in the head.
In practice it means the information being delivered by my eyes together is unusable.
So, I’ve taken to wearing an eyepatch, which, aside from granting me licence to become a pirate, introduces a number of practical difficulties.
In the land of the blind…
Firstly, it significantly reduces my field of vision from nearly 180 degrees, down to about 90.
This means my daughter, who is frequently at my side, has become invisible. It’s only since blocking one eye that I’ve become aware of how often I glance down to check on her.
We are training each other to swap sides.
I am also experimenting with a pair of ‘broken hipster’ glasses, with one lens painted black. They’re quite effective, but I’ve yet to wear them outside the house.
Obviously, the biggest problem with losing the use of an eye is the loss of depth perception. In the last few weeks, I’ve certainly bumped into a few things, and mis-judged the distance when pouring a glass of wine, but my mistakes are becoming less frequent.
The real difficulty lies with the accurate alignment of objects at the <1cm range - fine motor control problems like threading a needle, or painting a picture...
the last millimetre
The last few millimetres between brush and canvas are crucial, misjudge it and you end up with a splodge where you wanted a delicate line.
I’m re-training myself as a (hopefully temporarily) one-eyed painter. It’s forcing me to slow down, to consider that interface between paint and canvas a little more carefully, to read the sensation through my fingers as much as my eye.
It’s early days, but I’ve tried a couple of canvases, and strangely, I’m quite pleased with both the process and the results. I’ll keep you posted.
The prognosis of the condition is irritatingly vague – ‘most people spontaneously recover within about 10 months’, so hopefully it will resolve, but in the meantime I must be patient and enjoy looking at the world with a fresh eye.
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