Hess screen test
The Hess screen test was Found by Walter Rudolf Hess in 1908 with subsequent modifications. Hess was a famous neurophysiologist.
Hess screen/Lees screen test give information about the paralysed muscles and the pathological sequelae of the paralysis, like overaction, contracture and secondary inhibitional palsy.
The two charts are compared. The smaller chart belongs to the eye with paretic muscle and the larger to the eye with overacting muscle
Indications of hess screen test
• Hess screen test is commonly used for to diagnose the paralyse squint or strabismus.
• Diagnosis of overacting muscles
Procedure of Hess screen test
The Hess screen 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.