Many readers who are short-sighted will graphically remember the first time they were given glasses. Before, they could not see the blackboard; after, a new and vivid distant world was instantly revealed. They may also remember suddenly being able to “hear” the teacher better because their facial movements became visible.

Adults usually know when their vision has deteriorated because they remember what they used to be able to see, but children “know” that their vision is normal (to them) because they have never known anything different. So it’s important that children who are not doing well at school have their vision checked.

There are three types of spectacle correction: for long sight (hypermetropia), for short sight (myopia) and for astigmatism, where the focus is blurred because the front of the eye is shaped like a rugby ball rather than a sphere.

Just as people can be different sizes, so can eyes. Infants’ eyes are small, and small eyes are long-sighted. (Many people think that infants are short-sighted. They’re not. Most are long-sighted. The reason why they’re interested in the near world is that they give attention to only one or two things at a time, and the more distant things are, the more there is to see.)

During early childhood, most children don’t need glasses for long sight; the eyes focus (accommodate) because the lens inside the eye becomes more convex. With growth, most eyes gradually develop normal sight.

Two groups of children need glasses for long sight and it is important that they get them. There are those whose long-sightedness is too great to be compensated for by focusing, and those who squint because their long sight makes one eye turn in towards the nose.

The first group is often identified by visual screening at pre-school or nursery school and wearing spectacles gradually improves their vision. These children sometimes choose to take their glasses off when they’re tired, to get blurry vision that may be more restful.

The second group usually starts to squint about the age of two or three, and wearing glasses usually straightens the eyes. It also makes many children less clumsy, because the visual guidance of their movements is more accurate.

If the two eyes have different vision so that one is out of focus, or one eye has been turned in for a while, then that eye can become “lazy” or amblyopic. Wearing spectacles helps to cure the amblyopia, but some children need to wear a patch to regain vision in the lazy eye. The patch stops the good eye hogging the visual brain; it forces the lazy eye to make more brain connections and forces the brain to recognise the image it produces.

Short sight (myopia) is less common in young children but tends to develop in older childhood. The child can see clearly close up but distance is out of focus. Any child who can do near work but has difficulty seeing the whiteboard needs to see an optometrist. Unfortunately, while the eye’s ability to focus can overcome long sight (at least while we are young), it can’t overcome short sight. That’s one reason why there are many more people wearing glasses for short sight than there are for long sight - and short-sighted children tend to need glasses (or contact lenses) all their lives.

Are short-sighted people more introverted and more conscientious than others? Recent work on twins in Australia has shown that this view, long held by doctors and others, is probably wrong. In fact, the researchers found that being short-sighted is associated with being more open and agreeable.

On the other hand, another recent Australian study has confirmed that children who spend their time poring over near work indoors are more likely to be short-sighted than their outdoor-loving peers. Children aged 12 who spend the greatest amount of time outdoors are less likely to be short-sighted, it found - and this appears to be the effect of total time spent outdoors rather than sport per se.

Whatever their character and preferred activities, short-sighted children and others who need to wear glasses should not be mocked. When a child turns up at school self consciously wearing glasses for the first time, it’s important to adopt a positive approach, complimenting the child on their new appearance. In some schools, children who wear glasses can still be bullied. This can be a major reason for their reluctance to wear glasses, or even go to school at all. Nip it in the bud

Professor Gordon N. Dutton is consultant paediatric ophthalmologist at the Royal Hospital for Sick Children in Glasgow

REFERENCES

Van de Berg et al, Myopia and Personality: The genes in myopia (GEM) personality study. Investigative Ophthalmology Visual Science (2008) 49, 882-886

Rose, K.A. et al, Outdoor Activity Reduces the Prevalence of Myopia in Children. Ophthalmology (2008, Electronic publishing ahead of print. See www.ophsource.orgperiodicalsophtha)