Screening programs: Are there more advantages than disadvantages to having eye tests for all preschool children?

It is important to find out whether children have vision problems, but not enough research has been done to be able to determine the benefits and harms of routine eye tests in preschool children.

Specialists believe that people’s eyesight mainly develops in the first 5 years of life, and that poor eyesight later on in life could be prevented if it is detected and treated early enough. This could also prevent problems affecting the child’s social development and performance at school. That is why, in 2008, an extra routine screening test was introduced in Germany for all preschool children who are covered by statutory health insurances. This test is called “U7a” in the German health care system, and its main aim is to detect vision problems. It is offered in addition to the already existing health screening programs for children in Germany (the so-called “U-Untersuchungen”), and is aimed at infants who are between 34 and 36 months old.

However, whether or not children benefit from screening tests for vision problems depends on many factors:

• If the eye problem can be corrected, or early detection makes it easier for parents and their child to manage the problem, screening can be helpful. If not, early detection would make parents and children worry unnecessarily.
• Early treatment should have more benefits for the child than treatment later on in life.
• There has to be a test with which doctors can reliably diagnose vision problems.

For screening tests to be reliable, they have to do two things: On the one hand, they should detect poor eyesight in as many children who have it as possible, so that they can be treated early on. On the other, they should not wrongly conclude that a child with normal vision has vision problems. A false alarm like this could lead to unnecessary and possibly harmful treatment. Experts call this kind of mistake a “false-positive” test result. Yet if the screening test fails to detect vision problems in a child who actually has poor eyesight, this could wrongly make parents believe that there is no problem. Such “false-negative” screening test results could delay diagnosis and treatment.

Generally speaking, eye tests do not hurt and are not dangerous. Various approaches are used to test people’s vision. These mainly include eye charts, like those used for driving tests, and physical examinations to determine the alignment of the eyes.

Amblyopia – a common vision problem in children

In some children only one eye focuses properly. This is known as amblyopia or “lazy eye” and happens if the eyes send two different images to the brain, for instance because they have different refractive powers. The refractive power is the ability of the eye to bend light in such a way that it falls on the retina at exactly the point of sharpest vision (the macula). If the light is bent too little or too much, vision is blurred. The problem with amblyopia is that the “good” eye compensates for poor vision in the other. This means that the weaker eye is used less and eyesight becomes worse in that eye, which could lead to a permanent vision problem. You can read about how the eye works here.

Children often develop amblyopia because they are farsighted in one eye and nearsighted in the other, or because they have a squint. It is not exactly clear how many children have amblyopia in Germany, but experts estimate that it could affect as many as 4 to 6 out of 100 children (4 to 6%). This problem can also affect both eyes, although that is rare.

Amblyopia cannot be fixed instantly using prescription glasses or other kinds of corrective eyewear, but there are treatment options. Depending on what is causing it, amblyopia can be treated using special glasses with lenses of different powers for each eye, an eye patch (occlusive therapy), or both. Sometimes doctors also prescribe eye drops with, for example, atropine in them. This drug temporarily blurs vision in the “good” eye, which means that the weaker eye has to work harder to see properly. Sometimes amblyopia gets better on its own but it is not clear how common this is. You can read more about amblyopia and the treatment options in our fact sheet .

How the benefits of vision screening were evaluated

To find out whether screening for vision problems like amblyopia has benefits, the German Institute for Quality and Efficiency in Health Care (IQWiG) – together with other German and international researchers – evaluated all of the studies that have looked at screening programs like this.

The researchers were particularly interested in the following questions:

• Does early diagnosis of poor eyesight in children make it more likely that treatment will be successful?
• Does early treatment have an effect on the personal, academic and professional development of children?
• Are there eye tests that are reliable enough to be used in screening programs?
• Do some children have unnecessary treatment as a result of screening programs?

The best way to determine the advantages and disadvantages of screening programs is by looking at research that has compared a group of children who had eye tests with a group of children who did not have eye tests. These children should be monitored for a long period of time to see how effective the program was. Trials like this involve a lot of effort and there are not many of them. So the researchers also looked for studies in which diagnostic procedures or treatments were used independently of screening programs.

They found 5 trials that looked at a complete screening program. They also analyzed seven trials that did not look at screening programs but provided information that could help determine whether it is better to have treatment earlier rather than later. There were 27 studies on the accuracy of various eye tests. 

Results of research about screening programs

Three of the 5 trials on screening programs indicated that treatment could possibly be more successful in children who participate in screening programs. The other 2 trials did not find any differences between children who had routine eye tests and children who did not, or children who had other tests. However, there were problems with all of the trials. In one case almost half of all the children could not be tested after the trial had been completed. This means that, for many of the children in the trial, it is not clear whether the screening tests detected vision problems. Another problem is that most of the trials were carried out in countries that already routinely offer eye tests. This means that a lot of the children had probably already had an eye test independently of the trials, which could distort the results of the research.

Due to the problems with the trials, it is not yet clear whether it would be beneficial to have routine eye tests for all preschool children. One main problem is that adverse effects of screening tests were hardly looked at.

Early versus later treatment

Three trials looked at how the timing of treatment for children with amblyopia, a squint or other vision problems influences visual acuity (being able to see details clearly). The treatment in these trials consisted of either glasses, glasses with an eye patch, or surgery to correct a squint. In the best quality trial, 4-year-old children with a vision problem were randomly allocated to one of two groups. In one of the groups children were treated immediately after the eye test, and in the other group they were treated one year after the test. The trials showed that there were no proven disadvantages associated with having treatment later. Two other trials found that children who were treated earlier could see somewhat more clearly. However, because the treatment groups in these trials were not similar enough to be easily compared, the results are less reliable. Some aspects other than sharpness of vision were investigated too, including three-dimensional vision, but the findings here were contradictory.

Even if carried out as late as adolescence, treatment for amblyopia could still be successful. This is what a comparison of two trials involving children between the ages of 3 and 7 and teenagers between the ages of 13 and 17 suggested. It was found that treatment was not noticeably less effective in people who were first treated for amblyopia in their teens than it was in people who were first treated at a much younger age. This is surprising news. Up until now it was believed that treatment would only be successful if carried out early in life, and that it was therefore not worth having treatment later on. This belief was not confirmed by the trials. Instead, it has become clear that the natural progression of minor vision problems is not yet fully understood.

Only one of the trials looked at the adverse effects of early treatment. It found that about 1 out of 10 children who have a squint (12%) had unnecessary surgery. Also, the children who had treatment earlier were more likely to need a second operation.

Because of these mixed results, the group of researchers concluded that it is not yet possible to determine an ideal age at which to have treatment for amblyopia. 

Accuracy of eye tests for children

The researchers found 27 studies on the accuracy of eye tests. The tests they looked at included eye charts to measure visual acuity, tests carried out using instruments and eye tests to determine whether both eyes move together and work as a team (binocular vision tests). They found that all of the tests had weaknesses. For example, the eye charts and instrument-based eye tests very often caused false alarms. On average, they wrongly diagnosed poor eyesight in 11 and 23 out of 100 children with normal vision respectively.

Some studies found that the eye tests were more reliable. But there were no tests that were able to reliably detect both normal eyesight and poor eyesight in children. One problem is that most of the tests are less accurate in younger children than they are in older children. A clearer diagnosis would probably be possible if several tests were carried out one after the other. So far there has been no research on what combination of tests would be useful.

Overall, the researchers concluded that there is not enough evidence to assess the advantages or disadvantages of having routine eye tests in addition to the existing screening programs.

If you think that your child may have poor eyesight, it could be important to have things checked out by an eye doctor, regardless of whether your child has already had a routine eye test or not. You can find more information about amblyopia and research on the treatment options here.


Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

Note

This health information is a summary of a scientific report published by IQWiG. It is not an assessment of the right to have health care services reimbursed by statutory health insurance funds in Germany. By law, decisions about the reimbursement of diagnostic and therapeutic procedures can only be made by the German Federal Joint Committee (G-BA). The Federal Joint Committee takes IQWiG reports into consideration in its decision-making process. You can find information about the decisions of the German Federal Joint Committee on its English-language website, www.english.g-ba.de.

© IQWiG (Institute for Quality and Efficiency in Health Care)