Sunglasses and optical frames are available in different sizes to suit a wide range of face shapes. If you look at the temples of a pair of glasses you already own, you will likely find two or three numbers.

The first number (usually between 48 and 58) indicates the lens width in millimetres. The higher the number, the wider the lens. The second number (between 15 and 25) refers to the bridge width, or the distance between the two lenses. The final number (between 135 and 150) indicates the temple length.

If you have ever worn glasses that do not sit comfortably behind your ears, you may want to opt for a temple length of at least 145 mm.