10 reasons why we must look at vision charts with new eyes:

10 reasons to why You should replace Your eye charts!

    Unfortunately, many existing vision charts on the market do not meet international standards such as ISO 8596. This results in frequent cases of misleading vision test results and makes it difficult to compare results across different charts and clinics, both nationally and internationally in the healthcare sector.

    Although the use of the logarithmic scale, both in the construction of vision charts and in the recording of vision test results, has been internationally accepted for over 20 years, we are only now seeing an incipient implementation of this standard. More than 40 countries have committed to using the LogMAR scale, providing more accurate and comparable vision test results across charts and health systems. However, there is an urgent need to enforce this standard, especially in the EU, where pressure is being put on member states to require the replacement of sight charts with logarithmic ones.

     When common essential guidelines are not followed nor enforced, sight charts are unfortunately produced unregulated. Each individual manufacturer determines the design and calibration of vision charts in their own way. This leads to significant differences and errors, including in the size of letters and figures, also known as optotypes. There is a lack of precise weighting between figure-based and alphanumeric vision charts, a weighting that would otherwise ensure uniform vision test results, regardless of whether the vision chart is equipped with figures or e.g. letters.

    If you thought that everything was fine when the vision chart is CE-approved, you are sadly mistaken. CE marking does not guarantee correct design and calibration of vision charts. Vision charts that belong to class 1 medical devices only require the manufacturer to approve the product itself without an external, impartial assessment. Unfortunately, most CE-marked vision charts suffer from serious faults. Whether this is due to ignorance on the part of the manufacturer is uncertain.

    Unfortunately, we see many examples of vision charts that have been produced according to the slogan: "Let's fill the whole chart out" with equally wide rows of letters and figures down the chart. There is room for more and more characters per line, the further we get down the chart. It goes against current guidelines on all levels, which require the same number of characters per line and location in an inverted pyramid to accommodate the so-called “Crowding Effect”. Failure to adhere to simple rules of the game makes fair and comparable test environments impossible across different manufacturers' vision charts. And that leaves a worrying room for free interpretation of the vision test the doctor or healthcare staff carries out.
    The children's vision chart market is particularly unregulated, which can result in figures that do not adhere to the traditional laws of physics that have underpinned the design of vision charts for over 150 years. This can cause inaccurate and excessively positive vision test results. Thus, we continue to see vision charts for children on the market with figures that are up to 200% of the size they should properly be in order to deliver correct vision test results. The size of figures, which are cognitively more difficult to distinguish from each other than e.g. letters, but what we see is that there is far too much screwing up. A good vision test is not where the child can see all the enlarged figures. A good vision test is a test that gives accurate vision test results and ensures that children with problems are referred for further examinations and treatment.

    The vision charts that are typically available on the market only come in standard measurements such as 3 and 6 meters, (which are often loosely translated to 10 and 20 feet), which rarely match the exact distance from the test position to the wall where the chart is mounted. This often requires conversion of test results, which can result in significant conversion errors and thus inaccurate vision test measurements. There is actually no evidence to attribute that charts should be performed precisely on these fixed targets. Without violating basic rules, distances can be freely between 3 and 6 meters, as long as this is taken into account in the production of the sight chart and in the location of the sight chart.

    Together with the few available vision test distances, the dimensions and depth of the vision chart panel also play a decisive role and further limit the placement options in clinics and healthcare. Often the doctor and healthcare staff cannot offer tests in the consultation room, but must have the test person out in the corridor, where there is rarely the necessary calm, but plenty of distractions.

     A fixed placement of the vision chart at eye level for adult testers can lead to an inappropriate angle when a child is to be tested on the same chart, even when the letters are replaced by figures. The angulation leads to incorrect distances between the test person and the vision chart compared to the calibrated distance.

    There were actually requirements for the lighting conditions under which a vision test should be carried out. However, many vision tests are performed under insufficient and fluctuating lighting conditions. Lack of background lighting on vision charts makes them vulnerable to changing lighting conditions in test rooms, which can cause greater fluctuations in the vision test results obtained. If vision charts were to be equipped with background lighting, either with a centrally located bulb or LED strips around the edge, the light is rarely evenly distributed over the entire surface of the chart, cannot be regulated or adapted to the correct color temperature. All relationships there  degrades the test environment and leads to incorrect vision test results.