Stereoscopic vision assessment

Stereoscopic vision is assessed using two specially developed tests: the "Fly" stereotest and the TNO test.

Using pictures viewed through special glasses, these tests check whether the child has stereoscopic vision. The FLY test is designed for the youngest patients, using child-friendly imagery to facilitate engagement. The child is shown a picture of a fly through the glasses and asked to reach out and grab its wing — which, in the presence of stereoscopic vision, will appear three-dimensional, as if alive, like a 3D cartoon.
The TNO test is more complex and consists of several cards containing "hidden" coloured shapes that can only be identified by someone with three-dimensional vision — that is, when both eyes are able to combine two different images into a single unified percept.