In the Palazzo Pitti in Florence hangs a painting by Raphael of the Renaissance humanist, poet, scholar, orator and prelate Tommaso Inghirami. He’s pictured at his desk, garbed almost entirely in red, in a typical pose of contemplation, gazing upwards, but look closely at his right eye and you will notice something amiss: there is too much white, as if his eyeball were a shelled egg, its minute pupil dabbed as an afterthought. Inghirami lived with strabismus – a misalignment of the eyes, possibly caused by his fall from a mule – and his right eye is almost turned to look behind him, lizard-like. Were one to trace his gaze from those two eyes, extending outwards to see where he was looking, you would draw two lines into infinity, lines that would never cross. Inghirami saw two things at once.

I had not heard of Inghirami and his misaligned eyes until I fell backwards – not from a mule, but in a skiing accident several years ago, cracking the back of my skull against the compact winter ice of a Vermont resort. I had played rugby until the age of 16, and knew how it felt to have a knee or elbow to the head, but this blow possessed its own character: unsettling, strange and electric. I remember thinking, as I got up from that icy slope, that this fall would exact some price, though back then I did not know its currency.

Concussions are so commonplace that they often cease to inspire much concern or sympathy, but it is worth recalling the origin of the word, the Latin concussio, meaning “a shaking, or earthquake”. To shake the brain is not the same as to shake the liver or ligament, and sufferers of concussions often exhibit a bewildering array of symptoms: severe headaches, light sensitivity, oculomotor dysfunction and anxiety – a range that reflects the complicated nature of the brain and its functions. At its mildest, a concussion causes a headache; at its most extreme it can alter perception and cause death.

For weeks it felt as if the ground beneath me had shifted. I cowered in my Philadelphia flat, blinds down, ears plugged. Outside my flat, construction workers dug a hole in the pavement, and I wanted to beg them to stop: it seemed that every vibration and noise of the city somehow seeped into my head, unfiltered by any shield or carapace. I slept and slept, and, when I didn’t sleep, I massaged my head obsessively, trying to fix what lay within, stroking the shell to settle the yolk. By week eight, things had settled sufficiently, though I noted with alarm that reading had become difficult, even unpleasant.

When we read, we do not usually note the movement of our eyes across the page; it should feel effortless, as smooth as drawing a blade through water, and yet this is an illusion: we in fact shoot our eyes across the page or screen in rapid movements called saccades, before pausing and taking in what we have seen (in so-called fixations). In my case it was as if a veil had been lifted on the workings of my eye muscles, the start-stop mechanism laid bare. Instead of skimming through text, I strained, as if trying to push a viscous liquid through a membrane. I would, much later, discover that my fall had caused a misalignment in my eyes – the very condition from which Inghirami suffered (though my own misalignment was, thankfully, much less severe).

After my fall there followed a difficult two years during which I struggled to read without headaches, eye strain, light sensitivity and near catastrophic mood shifts. The very thought of reading, associated with pain and distress, began to repel me, and I shunned any text, from lines of poetry to the phrases on motorway billboards. You cannot simply decide not to read: as advertisers know, the impulse to read text is instinctive, and I sought to limit its irresistible allure; I eschewed books, newspaper articles and foreign films whose subtitles, rapidly changing against a screen, caused intense pain. I ceased visiting libraries and bookshops, and instead of talking about books, I talked about concussions, a source of frustration for myself and those around me. Like dreams, concussion symptoms tend to make most sense to those who experience them.

During my day, I would usually have read a great deal. Although I rarely say this phrase aloud, I am a writer, and this loss of ability affected not only my routine and work, but also my sense of self; a concussion is an earthquake, a shaking, but it also involves an unbidden shift in foundations. In the place of text, I tried substituting clay, a material that I had often valued as a metaphor for words: I thought of throwing clay as trying out ideas; pulling clay as actual writing; trimming clay as editing, firing clay as printing a manuscript. I started going to a pottery studio every day, and had earthy ideas that I would become a potter, but it is hard when the thing you use to make sense of something, clay, moves from the periphery to the centre of your gaze. Clay is not text, and my elevation of the material only emphasised its difference and inadequacy. There was also the small difficulty that I did not throw particularly good pots.

Strabismus is a common condition (one source estimates that it may affect up to 4% of the adult population), and I sought consolation in the accounts of sufferers such as the comic actor Marty Feldman, and Sartre, who developed strabismus after he caught an infection when he was three. But it was to Inghirami’s portrait that I returned again and again, layering my own desires and insecurities on to Raphael’s oil painting and the biography of this Renaissance humanist. How had a man who was clearly so impaired managed to become the pope’s librarian? In severe cases of strabismus, where the brain receives two images, one eye may become redundant, yet reading must still have been a great challenge for Inghirami. (Sartre would write all over the page, and suffered tremendously from his eye problems.)

I studied the portrait, noting not the man, but the objects around him: his pen, inkwell, notebook and book. Inghirami read and wrote not long after the invention of the first printing press; paper was scarce and expensive, and it is not a stretch to say that his reading habits would have differed enormously from even the most disciplined and monkish writer today. If I were honest with myself, I was an overly casual reader, a skimmer, just like many of my generation (perhaps it’s no coincidence that the word “skim” only migrated from dairy to text as late as the 1930s). In truth I was not quite as impaired as I thought; much of my pain and discomfort was tied to the rate at which I passed my eyes over my laptop’s screen. How we read, how we use our eye muscles, matters just as much as what we choose to read.

These days I read well enough. At the beginning of this year, an Edinburgh-based optometrist did what no other specialist had thought to try: he tested my eyes for vertical misalignment, in addition to horizontal, and ordered me a pair of prismatic lenses, which bend light to ensure my vision is aligned. I no longer need have such a restrictive textual diet, though I do try to read carefully, respecting my eye muscles and their silent labour. After he survived his accident, Inghirami commissioned a painting of his fall as an ex voto, an expression of gratitude to God. I’m not sure whether Inghirami’s God exists, but this piece is my own ex voto to my optometrist.