What would you do if you were told you were going blind? Quit your job, cut loose and rush to live out your most lurid fantasies? Nice idea, but your mates are still at work, and wealth doesn't increase in inverse proportion to eyesight, alas. Still, you'd be expected to react, so what would it be: fury, despondency, soul-searching, or would you try to see the funny side?

In the summer of 2006 I was diagnosed with retinitis pigmentosa (RP) – an inherited condition that affects the retina of the eyes, often leading to complete blindness. It was picked up by an optician at a routine sight test after I casually mentioned my exceptional clumsiness after dark (how I'd fail to spot big things like cars and ditches which, I'd noticed, everyone else managed to avoid). That's how RP begins, with night-blindness and accidents, followed by a gradual erosion of peripheral vision and more accidents.

When I told my family, they frowned gravely and muttered terrible portents like "devastating" and "life-changing".

But I didn't feel as though much had changed. I might go blind; I might not. I might walk into the path of a bus; I might hop on it and go on a fantastic journey. The future remained unforeseeable, and the splotches of peripheral vision whose absconding I had barely noticed remained unseen – as well as unseeing. Blindness was already here in a ghostly, imperceptible sort of way; I felt more perplexed than devastated.

My mum, realising that half the genetic flaw causing my eyes to self-destruct came from her, was overcome with guilt. Learning about the randomness and odds-defyingly bad luck inherent in inheritance didn't help. Nor did it help when I stressed that I was not merely unresentful, but grateful to her for having had the particular genetic accident – coding error notwithstanding – that made me.

None of this was funny. I don't remember crying, but I definitely didn't laugh. Now, seven years on, when kindly folk ask – as they do – "How are your eyes?", what am I meant to say: "Still rotting?" Hardly amusing, I grant you, but what else?

There's no natural or comforting response to sight loss. A couple of years back, a Channel 4 documentary-maker leapt to the presumption that I'd want to go on a grand sightseeing expedition to curate a memory-gallery of sights to console myself with in years to come – a proposal I turned down after emailing the blind academic John Hull (PDF).

"The supposition is that the life of a blind person will be retrospective, living in the past," replied the media-wary professor. "But one must affirm one's grasp of life as a present reality, not live in nostalgia."

I also emailed the American memoirist Jim Knipfel – who went blind as a result of RP in his 20s – who explained how he too was approached by a film-maker of a sentimental bent. "Upon meeting me she said, 'Oh, how wonderful it must be to be blind – you're living in a whole new, magical world.'"

What possible response? "My first impulse was to grab a letter-opener and let her find out first-hand what blindness is like. Instead, I warned her that her belief in magic might not survive watching me try to get across my apartment without tripping over anything."

In fairness to these film-makers, it's not easy to depict sight loss in a visual medium – and at least they wanted to try. All too often, blind people are omitted from film and TV for fear of depicting them in an insensitive way or unsettling the audience. This lack of representation is creating a problem for visually impaired citizens of the US, reckons Knipfel.

"Kids no longer grow up with images of bumbling blind people in cartoons and on sitcoms, and so no longer understand the white cane. This move to make everything 'nice' has resulted in an incredibly dangerous situation, as all those people I've run into can attest."

Which is one good reason among many to endorse the daring exceptions, films such as Come As You Are (to be released in UK cinemas on June 7) – a funny, moving and distinctly unsentimental story about three young men, one blind, one paralysed and one who has cancer, who go on a road trip in pursuit of sex.

Knipfel's writing is a masterclass in seeing the funny side when you can't see much else. Now 47, he has honed a knack for dragging readers deep into the awfulness of a situation before bursting the pathos with an acerbic joke. His grimly mirthful memoir Slackjaw – lauded widely, even by the usually reticent Thomas Pynchon – details some of the dire predicaments Knipfel got into as a young man with deteriorating sight. The worst was when, aged 20, he collided with a lamppost so hard that it left him with a brain lesion and permanently reliant on anti-seizure medication. His vision continued to recede and he was registered blind by the time he was 30 – the age I am now – yet he remains relentlessly sardonic and self-mocking. Is that what I should do, take my sight loss less seriously?

"Well, humour has always been my reaction to a world I find absurd," confesses Knipfel, "especially when the people around me seem to take it all so seriously. When I went blind, that seemed as ridiculous as anything else, so I reacted to it in the same way."

But does it help to cope with sight loss, this refusal to take the world seriously? "To be honest, blindness has never really bothered me that much. It's an annoyance – like a head cold or hangnail. The best thing about mixing blindness and humour is that I can now get away with even more than I did before."

I admire Knipfel's insouciance, but it's not for me, I fear. The prospect of worsening sight scares me, and I don't find it easy to make light of the gaucheness it causes. Remember when Gordon Brown, who is blind in his left eye, roused hilarity by appearing to shun a handshake from a policeman on the door of 10 Downing Street? I felt a stab of vicarious embarrassment because I suspected that Brown's failure to spot the officer's outstretched hand had been caused by his limited peripheral vision – it's a mishap that has befallen me several times. OK, such faux-pas are comical, but isn't it just plain cruel to laugh?

"Not at all," insists Knipfel, who wears a fedora because the brim gives a "split-second warning" before his head hits another post. "All of us – blind people, sighted, disabled, mentally ill, whatever race, whatever religion – we all have attributes that can and should be amplified for comic exploitation. We're all fodder!"

It's hardly comforting, the prospect of becoming ever riper-fodder for ridicule, but I suppose it's preferable to being disregarded or patronised. "Damn right. The blind are, for the most part, a fairly hapless group. You deny that and, as I mentioned, before long no one will know what a white cane is or what blindness entails, and that's no good for anyone."

"OK, Jim, I'll do my best," I resolve to email back. "Now if you'll excuse me, I'm off to buy a sombrero. Even if it doesn't save me from handshake blunders or lampposts, at least it'll hide my blushes."

David Bradford tweets at twitter.com/bradford82