here are some layouts for eye charts which i created using three different images of a boom box. i have used black ink (only) to create these images they decrease in detail. i have done this by using less layers of ink therefore the last image is more fainter then the first.
I have looked at a wide range of eye charts, it is a nice simple way to show detail and hierarchy of information within your illustrations.
the layout of the chart is restricted, however even though there is limitations there is still ways that you can be creative with how the images are positioned. here are some more interesting ideas below