WHAT HAPPENED TO YOUR TEST CHART?
Traditional eye charts were designed to test our vision in such a way that we had a standard or benchmark. In this way we could compare our findings with each other.
The way this was done was to have letters drawn on a chart, going from large to small size. Each line had a specific size or height, and they were read at a fixed distance.
At first the measurement was expressed in inches-that’s where 20/20 vision comes from; and the metric equivalent is 6/6. This means that the patient sees an object at 6 metres what a person with normal vision will see at 6 metres.
So if you have a visual acuity of 6/12, it means that you will see an object at 6m what a person with normal vision will see at 12m. Therefore 6/12 vision is half that of 6/6.
In 🇿🇦 South Africa, one needs a minimum visual acuity of 6/12 in each eye with or without spectacles in order to qualify for a driver’s licence, or if the one eye sees less than 6/2, then the other must have a visual acuity of at least 6/9.
We use an electronic chart (which comes complete with a gecko), that is calibrated to work at a distance smaller than 6m. The chart has multiple screens to prevent memorisation, but more importantly it is linked to the testing equipment that allows for a smoother and easier eye exam. It has built in numbers, pictures and symbols for the unlettered, and many other tests that check on the teamwork (called binocularity) of the eyes. A smoother, and sometimes slightly faster exam results in less subjective errors due to fatigue.