Units of measurement

Visual acuity does not increase linearly!

– but rather logarithmically – in relation to the size of the visual elements.

When visual acuity is tested, a logarithmic scale is used to graduate the size of the letters or symbols on the chart so that they become smaller and smaller in a logarithmic progression.

The logarithmic scale makes it possible to evaluate visual acuity in a more sensitive way and to detect even small changes in visual acuity. This is particularly important in clinical practice, where accurate measurements of visual acuity are essential for proper screening and assessment of vision-related problems.

The "old" measurement units are still also on the charts from ISOeyes.

The transition from the old registration method to the new one is easier to understand.