The hess screen test.

The Hess screen test was designed by Walter Rudolf Hess in 1908 with subsequent modifications.(1, 2) Hess was a famous neurophysiologist who was awarded the Nobel Prize in 1949 for his research into the functional organization of the vegetative nervous system.(3, 4) The original test used a black screen on which was marked a square-meter tangent scale. The tangent nature of the coordinate lines converts equidistant points, seen in a virtual sphere like a perimeter, into a two-dimensional chart. The test relies on color dissociation using red/green complementary filters. This maximizes the ocular deviation. A red target is illuminated or projected at the juncture where each tangent line crosses. A green light is projected by the patient and each plot is recorded. The test is repeated for the opposite eye resulting in a chart showing an inner and outer range of ocular rotation for each eye.