Timothy C. Hain, MD, Most recent update: October 7, 2017
The Lancaster Red-Green test is one of several methods of quantifying optical alignment (Lancaster, 1939). It is a subjective test, where different images are presented to each eye. It is a member of the "screen" tests used to map out ocular deviation, which also include the Hess test, as well as tests described by Lees and Weiss. (Roodhooft, 2007)
The original version of the red-green test was performed by placing red-green glasses on the patient, and providing the patient and examiner each with either a red or green light that could be projected on a screen. The examiner moves one target, and asks the patient to move their light on top of the target light.
The red/green glasses caused the patient to see a different target with each eye. If the eyes are aligned, then the two targets are "on top" of each other. The relative amount of deviation of the red and green light corresponds to the relative angle between the two eyes.
When bars are used rather than dots, the Lancaster test can be used to quantify relative torsional position as well as horizontal/vertical.
Patterns of Lancaster Test Results from original paper(Lancaster W B, 1939) Left hyper deviation (same in all eye positions) Left inferior Rectus Tilt test in right superior oblique
Variant Lancaster tests:
Awadein (2013) compared a computerized Lancaster test to a conventional Lancaster test, found reasonable agreement.
Other screen tests:
The Hess test was proposed much earlier than the Lancaster test, but it is very similar. There is a tangent screen, with red lines and red spots at 9 cardinal points. The patient wore red-green spectacles, and was asked to place the green spot on various red spots on the screen, which was 0.5 meters distance.
The way that Hess advocated reading this was to make a diagram of the deviations. The red spots are already connected by lines. The green spots were also connected to form a quadrilateral figure, and Hess published a series of charts of the results in cases of certain types of ocular paralysis. Pattern recognition of the quadralateral is used to diagnose particular types of palsies.
- The Lancaster (or Hess tests) see below provide a wealth of information about ocular alignment. They are semiquantitative, and force the examiner to explore all fields of gaze. They can provide data about relatively obscure ocular problems such as torsional phoria or tropias.
- One wonders why Lancaster chose red/green rather than red/blue, as red/blue are separated to a greater extent in the spectrum, and would presumably experience less "bleed".
- The method of showing results chosen by Lancaster, to us, seems a bit difficult. Lancaster comments in his original article, in a somewhat critical way, the simpler Hess method (see below).
- These techniques only explore foveal vision. They do not shed any light on local problems in the visual spatial mapping, such as might occur in astigmatism.