If your glasses are on your face, then obviously you will be aware of their temperature, but if you lay them down, make sure you think about how cold or hot they could get. A dashboard can get boiling hot in direct sun in the summer, or very cold on a frosty day. A shelf above a radiator can also get hot, and extreme heat could damage your glasses. Photochromic lenses will lose the power to react if they get very hot, and anti-reflection coatings have been known to craze across the surface. Plastic frames or frame parts such as end tips can bend and distort, and if the frame front warps the lens may fall out.

If you accidentally get a photochromic lens hot, it may work again after a while, but it will take time to go back to normal. Crazed coatings mean a whole new lens, as coatings are difficult to remove, and the process will probably damage the lens anyway. Warped frames need to be returned to the supplier, for adjustment and correct positioning of lenses.

If your specs get really cold, this can cause problems too. Rimless lenses have been known to crack if fluctuating temperature makes the lens material expand and contract. Usually they split straight across the hole where the screws are drilled through. Never leave them in the car on a chilly night!

The most annoying issue is probably specs steaming up, and as any spec wearing cook knows this can be pretty hazardous! It’s no fun to open the oven door and put yourself in danger of dropping a boiling hot dish on your foot! Make sure your specs fit properly and do not rest on your cheeks, as this will stop air flowing behind them. Keep the frame shallow and small if this is an issue for you. There are anti-fog sprays on the market, just take care not to scratch your lenses as you apply them.