STANDARDS ARE NOT FOLLOWED Unfortunately, many existing eye charts on the market do not comply with international standards such as ISO 8596. This results in frequent instances of misleading vision test results and makes it difficult to compare results across different charts and clinics, both nationally and internationally within the healthcare sector.
LACK OF LOGARITHMIC STRUCTURE AND SCALE Although the use of the logarithmic scale, both in the design of eye charts and in the recording of vision test results, has been internationally accepted for over 20 years, we are only now seeing a beginning implementation of this standard. More than 40 countries have committed to using the LogMAR scale, which provides more precise and comparable vision test results across charts and healthcare systems. However, there is an urgent need to enforce this standard, particularly in the EU, where pressure is being placed on member states to require the replacement of eye charts with those built on a logarithmic basis.
MANUFACTURER’S FREE INTERPRETATION When common essential guidelines are not followed and are also not enforced, eye charts are unfortunately produced without regulation. Each manufacturer determines the design and calibration of eye charts in their own way. This leads to significant differences and errors, including in the size of letters and symbols, also known as optotypes. There is a lack of precise weighting between symbol-based and alphanumeric eye charts, a weighting that should ensure consistent vision test results, whether the eye chart is equipped with symbols or, for example, letters.
FALSE SENSE OF SECURITY If you thought everything was fine when the eye chart is CE-marked, unfortunately, you are mistaken. CE marking does not guarantee the correct design and calibration of eye charts. Eye charts, which fall under Class 1 medical devices, only require that the manufacturer approves the product themselves without external, independent evaluation. Most CE-marked eye charts unfortunately suffer from serious flaws. Whether this is due to ignorance on the part of the manufacturer remains uncertain.
GRAPHIC FREE-FOR-ALLUnfortunately, we see many examples of eye charts that are produced under the motto: “Let’s fill the entire board” with evenly spaced rows of letters and symbols down the chart. More and more characters are crammed onto each line as we move down the chart. This goes against all current guidelines, which call for the same number of characters per line and an inverted pyramid layout to accommodate the so-called “Crowding Effect.” Failure to adhere to simple rules makes it impossible to create accurate and comparable testing environments across different manufacturers’ eye charts. This leaves a worrying amount of room for free interpretation of the vision test conducted by the doctor or healthcare staff.
UNREGULATED AND OVERLY FAVORABLE The market for children’s eye charts is particularly unregulated, which can result in figures that do not adhere to the traditional physical laws that have been the foundation for eye chart design for over 150 years. This can lead to inaccurate and overly positive vision test results. We still see children’s eye charts on the market with figures that are up to 200% larger than they should be to deliver accurate vision test results. While it is often necessary to adjust the size of figures that are cognitively harder to distinguish than, for example, letters, what we observe is that these adjustments are often excessive. A good vision test is not one where the child can see all the enlarged figures. A good vision test is one that provides accurate results and ensures that children with vision problems are referred for further examination and treatment.
CONVERSION PROBLEMS The eye charts typically available on the market come only in standard measurements, such as 3 and 6 meters (often loosely translated to 10 and 20 feet), which rarely match the exact distance from the testing position to the wall where the chart is mounted. This often requires conversion of test results, which can lead to significant conversion errors and thus inaccurate vision measurements. In fact, there is no evidence that eye charts must be made to these fixed measurements. As long as the basic rules are not violated, distances can range freely between 3 and 6 meters, provided this is taken into account in the production and placement of the eye chart.
LIMITED PLACEMENT OPTIONS Along with the few available testing distances, the dimensions and depth of the eye chart panel also play a crucial role and further limit placement options in clinics and healthcare facilities. Often, doctors and healthcare professionals cannot conduct tests in the consultation room and must have the test subject go out into the hallway, where there is rarely the necessary calm but plenty of distractions.
INCORRECT HEIGHT PLACEMENT A fixed placement of the eye chart at eye level for adult test subjects can lead to an inappropriate angle when a child is tested on the same chart, even when letters are replaced with figures. This angling leads to incorrect distances between the test subject and the eye chart in relation to the calibrated distance.
INADEQUATE LIGHTING CONDITIONS There are actually requirements for the lighting conditions under which a vision test should be conducted. However, many vision tests are carried out under inadequate and fluctuating lighting conditions. The lack of backlighting on eye charts makes them vulnerable to changing lighting conditions in test rooms, which can lead to greater fluctuations in the vision test results obtained. Even if eye charts are equipped with backlighting, either with a centrally placed bulb or LED strips around the edges, the light is rarely evenly distributed across the entire chart surface and cannot be adjusted or matched to the correct color temperature. All of these factors degrade the testing environment and lead to inaccurate vision test results.
