Intermittent apperceptive agnosia, eleven syllables slide off the tongue with the deceptive effortlessness of too-frequent explanation. It's a brain thing, a white matter thing, a near cousin of migraines and epilepsy, but mutually inclusive with neither. It's not an eyeballs thing, not an optic nerve or retina thing. The pupils dilate. They trace movement that the brain doesn't communicate to my conscious awareness. They focus. They navigate upward for something approximating eye contact but not quite achieving it with anybody I have not kissed, anybody whose face I have not minutely scrutinized with fingertips and patience.

It isn't constant; there are hours and days of uninterrupted vision, crisp and high-resolution. These are utterly rare, precious, and frenzied with the mania of wasting no moment. I read books with ink on paper and pixels on screens. I create and edit digital art. I memorize sheet music in exhaustive detail, and I cut my own hair. I stare too much at my husband, who does not like to be watched so closely. I admire the rippling silky grace of my cat, the articulate angles of my own hands, the stark monochromatic loveliness of piano keys. I stand in rooms deliberately darkened and gaze at black cloth, because they are blacker than the foggy charcoal of every other day. I watch sunrises behind purple sunglasses, then delight at how green the world becomes when I take them off. Green is usually the colour I miss the most, and then true black, and then mirrors.

Then the aura begins at the margins of my field of view, a steady loss of resolution, definition of forms, brilliance of colour, differentiation between brightness and darkness. Twenty minutes elapse slowly; if I am driving, I pull off the road and make a call for pick-up. If I am working, I put on my earwig and enable the text-to-speech screen reading software on the work computers. I have enough time, always, to render myself harmless and efficient, to disguise the fact that everything is eigengrau instead of colours and shapes. I proceed with my day, sometimes eight or twelve hours of visual static, other times a week or month of unrelenting lightlessness. Today is the seventeenth without seeing, this time, and a good friend drives me to work and drops me off at the end of my shift, having a similar work schedule and living not too far from me. These logistical considerations are a matter of course; I compensate the costs of fuel in his car, and I teach him to play piano. The light and clarity return later, as slowly as they departed, the randomly-firing nerve signals coalescing from something resembling CRT snow into forms which have meaning and familiarity. Sometimes the fields of vision return at different speeds for each eye, resulting in a cartoonishly flat and sketchy world, until binocular sight is restored for a day or an hour.

My day begins an hour before midnight. I wake to a blaring alarm, and I walk to my wardrobe, pulling on the blue jeans I set out the night before. In the closet, the collar of a work polo is distinctive from other blouses; the lapel is embroidered with a logo. The pastels are near the front of the closet to my left; maroon and black are to the back and right. I select the nearest shirt and the bra with no lace; I know it to be flesh-toned and invisible under this particular blouse. I have paired black bras with pale shirts before, realizing the faux pas only too late, so now I buy them for both texture and colour, to make selection go faster before work.

I navigate - that's the language for this, not 'walk' or 'go,' but 'navigate' - to the bathroom, toes and left hand fingertips first to avoid doors left standing open and inattentive cats napping on the kitchen floor. At my mother's house, every animal knew one command and followed without hesitation: "Move." Move out of the main path through the house, or risk being lightly but unintentionally punted, or having your toes trodden-upon. My current cat is less obliging and has a slightly irrational trust of my navigational capabilities; frequently he trips my husband in unlit rooms; frequently he tangles my feet with an affectionate side-rub, and I have to hop over him and hope for the best. Once at the bathroom, I pull my hair into a tight pony-tail or bun, since these are the easiest styles to verify I did correctly: fly-away hairs are easy to detect. I don't wear make-up, but that is a matter of preference and not only inconvenience. I slip on shoes, grab lunch from the kitchen, give my fellow a kiss, and run out to my waiting ride.

The night shift is quiet. I complete my duties methodically; I know where everything is, and my coworkers know not to move work materials out of place during their shifts. Sometimes the power goes out; I don't need a flashlight to find the circuit breakers. I operate the computers entirely by keyboard, ignoring the mouse; I'm faster this way even when I'm having a good vision day. I walk to the hospitality room to heat up soup for my supper during break time; I hear the telltale whine of a television left on and muted, so I turn it off. Everywhere I go in this building, if a door is opened, I hear it and know where it is. People ask if I get scared working here at night. They wouldn't understand that nothing short of a cat can sneak up on me, that my darkness is not a thing I fear, but a familiar and unthreatening presence which in itself feels very nearly alive. My darkness is knowing everybody as voices and cologne and the air currents stirred by animated body language, but finding faces unfamiliar and void of significance. My darkness is spatial reasoning and three-dimensional isometric mental mapping. My darkness is an unrelenting visceral drive to be hypercompetent and above reproach. My darkness is never helplessness, but it is the extreme social advantage of being underestimated by everybody, and always exceeding expectations. It is refuge in audacity and necessary fearlessness, the amygdala coerced to fall silent forever. Maybe it's hubris.

My shift ends some hours after sunrise, and the sun is piercingly, tangibly bright, my pupils contracting hard and fast as I walk to where my ride waits in the employee parking area. Sometimes I get headaches from obliviously having bright or blinking lights in my field of vision, but I always notice the sun; its light is unmistakable. My sunglasses are for UV protection and headache prevention, not for making my blindness apparent to others; the lenses leave my eyes visible to onlookers, who will notice nothing unusual about me. I prefer it this way, to be a person first, all other preconceptions factored out of the equation. My ride honks once as soon as I emerge from the building, and I navigate quickly to his car. I don't use a cane on familiar territory; counting my steps is adequate here. The agnosia still allows a very low-level obstacle avoidance as long as I have my eyes open, even if I can't consciously see anything, so it is very rare for me to collide with stationary objects. My brain still manages to surprise me with the things it reflexively reacts to, without my conscious thought or sight. A few times I've caught a tennis ball that I didn't know had been thrown at me until after I caught it.

On the drive home, I think about the way my vision works, when it works at all. My world is snapshots and projector slides. You might think that people don't really change all that much from one day or month to the next, but there is a melancholy shock to seeing a face shaven which last had a full beard, even if you have been kissing the stubble for weeks. Every good vision day is a one-sided reunion, white hairs on my mother's head, creases and smile lines on faces I imagine immortally youthful. The briefest images stay embedded long in my memory, because I take everything in so studiously, gazing briefly on nothing and nobody. I know my lifespan is no greater than any other, but I feel like I carry in my visual memory a timelessness and weight of meaning that I cannot share or express to anybody else around me. I look at photographs of events I attended, see myself smiling for the camera, and have no visual memory of these events, despite incontrovertible two-dimensional proof of my presence at them. There is this doppelganger present in every part of my life, this physical body which can be seen by others, photographed, documented, and she is the person in those images. I am just the disembodied voice and ears and senses of smell-taste-touch, the spatial awareness, the synaesthetic recall of how wild onions tasted sharp and alert when cut by a lawn mower. I was there, but nobody saw me, and my double posed in my place. It's her face my husband sees when he thinks of me, and not the face I feel from the inside when I kiss him and abrade this face on whiskers and gentle cynicism.

We arrive at my home, and I exit the car and walk up the back porch of my house. The house key has a distinctive profile, the first tooth longer and sharper than the others, easy to find among several others on its fob. I can smell humidity and heaviness in the air, the musty smell of sycamores predicting one of summer's heavy rainstorms.

I cast off my work clothes, shower in haste, and slip into bed to nap several hours before giving afternoon piano lessons based on memorized sheet music. The curtains are drawn tightly, so that I won't be kept awake by light I cannot see.