How do our eyes focus?

There’s more to it than you might think:

  • Your eyes need to tell the brain that something interesting is out there.
  • Your brain then has to send messages out to control your eyes.
  • Six little muscles on the outside of your eye not only have to co-ordinate with each other, but also have to co-ordinate with the six in the other eye.
  • Lining up both eyes wherever you look allows binocular vision. If they are not lined up you see double.
  • As well as lining up vertically and horizontally, you also need to converge your eyes whenever you look at close objects so you don’t see double of everything as it comes towards you.
  • Once the eyes are both lined up the slightly different view each eye sees allows us to see in 3D (stereovision).
  • At the same time the lens inside each eye needs to be focused on the same point so that it stays clear. This is called accommodation.
  • Convergence and accommodation are usually coordinated in a fairly stable relationship so that each tends to accompany the other.
  • As things move backwards and forwards in space, all these processes have to be constantly updated as you, your head, your eyes or the object moves.

Clever, isn’t it? And all this goes on all day, every day, all your life without you needing to think about it.

What happens if it goes wrong?

Most babies learn to control their eyes in the very first weeks of life, but it is also a system that can easily be disrupted, especially if it happens in early childhood. If the binocular vision system develops abnormally, or is disrupted in later life, it can lead to many common eye problems which affect well over 5% of us all. They include:

  • Squint (strabismus, crossed eyes)
  • Lazy eye (amblyopia)
  • Double vision
  • Eye strain

What is the Infant Vision Laboratory?

Originally set up in 1997 to research babies’ eyesight, the Infant Vision Laboratory researches many aspects of eye focusing, as people of all ages look at things at different distances.

Our particular interest is in ocular convergence (to point both eyes inwards to look at close objects) and accommodation (focusing within the eye to make the object clear).

We research:

  • Typical focusing development across the lifespan
  • The ocular accommodation convergence linkage
  • Accommodation and convergence in strabismus (squint)
  • Eye strain and eye (orthoptic) exercises
  • Accommodation during reading

Some things make these problems more likely, although they can also come on out of the blue. Things that add to the risk of developing problems with binocular vision include being born premature, having developmental problems, needing glasses (especially in childhood), having neurological problems, having abnormalities of the eye muscles, and general health issues such as diabetes, multiple sclerosis or high blood pressure. Some of these things tend to run in families. Eye strain in adults is more common if you do a lot of close work.

We are interested in how the binocular vision system develops, why it sometimes goes wrong, and how the eyes are controlled if something disrupts the images reaching the brain.

What have we found?