Learning a new word the hard way

I'd be very curious to know how many of you are familiar with the following word: dioptre. Any ideas? Well, dioptre is the measure of the strength of a lens, and whether you know the word may well depend on where you come from. I myself had never heard it before I came to this country ten years ago. In Ireland, where I come from, when you get a pair of glasses they just give you your glasses, they don't tell you that your right eye has a dioptre of minus three and your left a dioptre of minus three and a half, possibly imagining that this is specialist knowledge and of no particular use to the bespectacled layman.

Like I say, I first heard the word dioptre in this country. It was 1992 and I had been in Prague a full two days, when I found myself in a pub with a couple of English guys. We'd had a few (wonderfully cheap) beers when a Czech guy joined our table. He'd just got a new job and was celebrating. Would we join him in a Becherovka, the herbal liquer? It would have been rude not to, and it would have been even ruder to refuse a second. And another couple. I'd arranged to meet a friend flying in that day in front of the National Museum on Wenceslas Square at 9 o'clock. I managed to extricate myself from the pub and get to the meeting place on time, where (to my eternal shame) I fell asleep. Around 11:30 I woke up sitting on the fountain, no sign of my friend, and realised I had no idea when the last metro went. Like a fool I ran across the main road, and down into the metro, where I realised as soon as I had got on, that I was no longer in possession of my glasses.

Somehow, and I'm still not sure how, I made it back to the place I was staying in the suburbs. The next morning I explained my situation to a girl I was staying with, who kindly offered to help me try find my specs, as optimistic an undertaking as it was. We looked (I should say SHE looked) all around the fountain: no glasses. Then as we were crossing the main road, she said stop, I see them. They were right by the kerb, one side perfect, the other totally flattened.

Here's where the mighty dioptre comes in. As I say, I'd never heard of a dioptre, and didn't get it when helpful Czechs asked me what my number was. Are your glasses number two, or three? one man asked me. With images of consumer shortages during the communist era, I - stupidly - imagined they only had three or four types of lens for the whole nation. And was I going to wear such potentially damaging glasses? No way was I. Idiot that I was, I stayed in the country for two months without being able to see, never going to an opticians for fear of primitive Czech optometry. By the way, I had the best summer of my life, though it was a bit of a blur!