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The Hess Screen Test

Correspondence: Requests for reprints should be addressed to: Gill Roper-Hall, D.B.O.T., C.O., C.O.M.T., St. Louis University Eye Institute, 1755 S. Grand Blvd., St. Louis, MO 63104. e-mail: grh{at}slu.edu

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.

Key words: Hess screen, Lancaster screen, Lees screen, Harms tangent screen, diplopia, confusion, Walter Rudolph Hess