Babies are able to open their eyes and see as soon as they're born, but for the first few months they can only focus on what's close to them. So to start with, for example, they can see a toy or face in front of them but anything much further away is a blur. Slowly, the distance that they can see clearly increases, until by about six months they can see across a room.

Many tiny babies also have a squint (their eyes look in different directions), which usually gets better within a few months.

Faces are a good test

Most babies can recognise their parents by about two weeks and start to smile at about six weeks. In these early weeks, most babies are particularly fascinated by faces and will focus on one in front of them - following it with their gaze (they prefer familiar faces).

This gives you a chance to test your baby's sight from the age of six weeks.

• Sit your baby on the lap of someone they're comfortable with
• Crouch down so your face becomes level with your baby's face and about an arm's length away from them
• Your baby should fix his eyes on your face (rather than looking everywhere else)
• Keep looking at your baby but move your head around from one side to another
• Your baby should keep his eyes fixed on your gaze

Alternatively, use a toy moved in front of your baby. They should be able to follow a brightly coloured moving toy held about 20cm (8in) away from them by about six weeks.

It can be difficult to be certain

Small babies are easily distracted and it can be very difficult to test their sight with certainty, so any worries you have are best checked by a professional.

Small babies can seem to take longer than normal for their brain to register what their eyes are seeing, even though there's no problem with their vision. This is more likely in premature babies. After a matter of weeks, their visual sense suddenly kicks in and the problem's resolved.

Serious visual problems are rare at this age, especially if his eyes appear normal, but occasionally they do occur.

A parent's instincts should never be ignored. If you're worried talk to your doctor, especially because your son has now reached ten weeks.

This article was last medically reviewed by Dr Trisha Macnair in November 2007