Optotypes for children – a science in itself!

Vision charts for children in many cases have serious faults.

An unregulated market

Charts for children are an unregulated market that leads to incorrect, overly favorable vision test results for children, resulting in a lack of visitation and treatment. Unfortunately, it is entirely up to the manufacturer to determine the compensation that figure-based Optotypes must be equipped with in order to give an eye test result that is appropriate according to the manufacturer's judgment.

 

Research and measurements document the problems

Unfortunately, research shows that there is often no evidence for the compensations that the respective manufacturers equip their figures with. This means in concrete terms that figure-based vision test charts overcompensate to such an extent that many children's vision problems are only discovered when they are old enough to be tested on a chart with letters, Tumbling E and the like!

Charts that give children good vision test results are erroneously presented as "the good" charts.

However, the purpose of an eye test is not to ensure that all children "pass" the eye test, but to uncover whether there are vision problems that call for a visit for further examinations and treatment.

In Denmark, it is particularly the Østerberg chart that has been the culprit.

Of foreign charts, we can mention Kay Pictures, which consistently equips their vision charts with figures (optotypes) which are exactly 200% larger than the corresponding letters on the adult charts. International research and ISOeye's own studies indicate that the compensation factor should rather have been around 122% – i.e. a significantly smaller compensation factor, which would ensure comparable vision test results between Kay Pictures' figure-based charts and ETDRS charts with letters.

The Lea chart does not overcompensate to the same degree, and gives only minor deviations from the vision test result that an ETDRS, Tumbling-E or LandoltC chart gives.

 

The compensation factor

Figures are more complex for the eye to decode and so it actually makes sense to compensate. It is therefore not useful to apply exactly the same rules of the game to different Optotypes.
But there are still a number of "rules of the game" that must be observed.

Based on the charts produced by ISOeyes, studies and tests have shown that comparable vision test results are achieved with a compensation of 122%

It provides the following compensation:

  • On a 3 meter chart, the height of a letter on the 6/6 (Logmar 0,0) line must be 43,63 millimeters
  • On the same 3 meter chart, the height of a figure on the 6/6 (Logmar 0,0) line must be 53,61 millimeters

But why is it necessary to compensate?
– On anatomy and extremities

ISO 8596 prescribes as the National Chart of Health's guidelines that figures on vision test charts must be line drawings and not filled figures as on e.g. The Østerberg chart. This is because line drawings in their construction resemble the anatomy of a letter more than a filled figure does. And when shapes look more like letters, the need for compensation is less. However, there are a few issues that many seem to overlook in their production of vision charts.

  1. Line drawings often become too thin in the line and does not comply with the "5 minute of an arc" basic rule for thickness of the line. The figures thus appear with a thinner outline than letters and thus become more difficult to identify during the visual test. You can of course compensate for this, and this often happens - unfortunately not always with such care that the vision test results are comparable to other vision charts.
  2. The choice of figures and their design, even when we are talking line drawings, is also of great and often overlooked importance. If we look at the letter "K" and put it up against a line drawing of a house, it becomes clear that they are anatomically very different. Where the "K" is open and, so to speak, bristles in all directions, the house is a closed figure. When something bristles – has extremities, it becomes easier for the human eye and brain to decode and remember. Far easier than with a closed figure without notable extremities.
  3. If line drawings are designed so that they partially comply with rules for line thickness and anatomically resemble letters, the need for compensation (magnification) is considerably less, because they are of the same degree of difficulty for the human eye. It's that simple. And only in this way if you give the human brain the same "working conditions" and ensures comparable vision test results.

The further development of vision charts at ISOeyes

ISOeyes has further developed their popular "eyekey" optotype for an even more accurate vision test result.

The goal of screening vision tests must be to be able to carry out accurate and comparable vision tests, in order to be able to decide whether a visit should take place, regardless of which vision test chart the test person is presented with.

ISOeyes has newly developed our popular vision chart for children so that we can now offer a chart with optotypes which anatomically look more like letters than we have previously been able to. In tests with over 206 children, we obtain results that show that our new "Similar" Optotype series provides even better and even more comparable vision test results than our popular "Eyekey" series has delivered. The "Similar" series is precisely characterized by shapes that look more like letters and are not closed in shape. Yes, a single watch stands out, but it also stands alone and cannot easily be confused with others in the series.

Buy the new charts with "Similar" optotypes from your preferred dealer.

Similar – Optotypes used on 3 meter chart

Eyekey – Optotypes used on 3 meter chart