Sunglasses, as probably won't have escaped the more observant reader, have been rather fashionable for some time now. About 79 years to be precise, for 'twas in 1929 that a Sam Foster - and not, as may have been supposed, a Mr Ray Ban - sold the first pair of Foster Grant sunglasses on the boardwalk in Atlantic City, New Jersey.

What a journey. And don't be surprised if, for instance, Katie Holmes's next pair become a matter of national concern, because shades have now acquired a socioeconomic relevance.

Suddenly, you see, shoving on a pair of sunnies isn't merely a frivolous response to various stress triggers, such as finding yourself without access to eye make-up or being in a lift with Anna Wintour.

Au contraire. Wearing sunglasses has become a considered response to the numerous environmental and financial depredations that rain down upon us. By environmental, I don't just mean the whole ozone thingy, but the troublesome business of eye contact and whether or not it is wise to make any when you are seated opposite a stranger on public transport. Thanks to the tireless efforts of celebrities such as George Michael and P. Diddy, it is now acceptable, albeit still a little crazy-looking, to sit in the dark wearing some kind of sun-shield over your eyes.

Sunglasses also reveal oceans about the current plight of women: not content with dieting to size zero, they are guaranteeing their virtual disappearance behind ever huger frames. It's a scientific fact (call it Olsen's law) that the skinnier the woman, the bigger her specs.

Although a ritzy, customised pair in Harvey Nichols will set the devil-may-care customer back £400 (the average spend in the country at large, by contrast, is £15), even that, as Jo Jeffreys, a spokeswoman for the store, points out, is a trifle compared with the price of what, until about six minutes ago, used to be called an It Bag. So buying yet another pair becomes not an indulgence but a frugal response to the credit crunch.

When you also consider just how infinitely greater the ratio of logo and bling to square centimetre of functioning product is on sunglasses compared with any other status item, and how donning the right style can knock three dress sizes off you, the answer to fashion's burning question - what's after the It Bag? - becomes glaringly apparent.

None of which is lost on designers. Eyewear now accounts for 20 per cent of turnover at Yves Saint Laurent. Sales at Harvey Nicks are still on an upward trajectory. Oddly, celebrity “designers” have been uncharacteristically shy about cashing in on the last great underexploited territory of the human body, perhaps because the handful of factories responsible for most of the world's output of top-dollar sunglasses are already at full capacity.

So far only Victoria Beckham has her own line, but presumably it's only a matter of time before Kelly Osborne unleashes her Literary Collection on the world (the white heart-shaped ones that she has been espousing this year aren't the result of a dare, apparently, but an homage to Nabokov's Lolita, by way of the Kubrick movie) and Britney Spears launches a Morning After range.

I can wait for these collections if you can. In the meantime, the most compelling reason of all for donning a pair of shades is that right now they are the only token of summer on which you can sensibly rely.

In step with the super-rich

The Sunday Times Rich List is, overall, lacking in fashion's heavy hitters. Those who are there tend to hail from the high street rather than the schedules of London Fashion Week. Funny, that.

But shoe moguls perform disproportionately well. Five make it, including Tamara Mellon, of Jimmy Choo, Linda Bennett, of L.K. Bennett, and Lance Clark, of Clark's.

A recent survey by Olay tells us that the 1,500 women it polled buy an average of eight pairs of shoes a year. An even more recent survey of Gwyneth Paltrow shows us that since she has started to teeter along the world's red carpets in a selection of increasingly high nose-bleeders, her hair has miraculously shed several droopy feet, her skirts have shrunk and her facial muscles have rediscovered the smile option. Mystery of the zillionaire shoe moguls solved.

Buy this

Never knowingly has this page passed up an opportunity to hammer home the point that one can be both clever and mad about clothes. Look at Zadie Smith. Look at Nigella. Look at Nancy Mitford. Look at ... oh, this could go on all day. The point - and it's a very exciting one indeed - is that you can now display both your design and your literary credentials in one go, solving many gift problems into the bargain. And it is a bargain. For a mere £10, novels by the likes of Muriel Spark, Elizabeth Taylor and Barbara Pym, each one bound in a print by Celia Birtwell, Cath Kidston or Barbara Hulanicki, can be purchased to adorn walls, tables and strategically open bags. Oh and you can read them too. From Virago, on sale tomorrow at Waterstone's.

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