Eyesight can deteriorate gradually over time, and it can be difficult to realise it has fallen below the minimum standard. For instance, as we grow older our eyes become less able to react quickly to changes in light and we start to have difficulty with colours and contrasts in poor light. Between the ages of 15 and 65 years the time it takes to recover from glare increases from 2 to 9 seconds. This could be one reason why some people find driving at night more difficult