Aha! Got you, you irritating phenomenon.

Everyone who wears glasses will know the feeling where you suddenly realise the world in front of you is rather more blurred than it needs to be, and you take your glasses off and clean them and your eyesight has improved by an order of magnitude when you put them back on.

Recently - over the past few weeks - I've been finding I'm doing that more than average. A lot more than average. Practically every morning, at least on weekdays. There always seems to be a load of opaque gunk over one lens. I've wondered why, but only idly, and then I just slid glasses-cleaning into my morning routine alongside brushing my teeth and thought no more about it.

Yesterday evening, in that half-asleep state where concepts slide back and forth and try connecting to each other in outlandish ways, I suddenly had an insight, and an experiment overnight has confirmed it. The reason my glasses always have gunk on them in the morning is because the case I store them in overnight is grubby. Jackpot!

Now all I need to do is get a new one. I wonder where you can buy those. I'm pretty sure mine came with the glasses themselves...