In the fields of

optometry Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the Uni ...

and

ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medic ...

, the Lancaster red-green test is a binocular, dissociative, subjective

cover test A cover test or ''cover-uncover test'' is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations. The two primary types of cov ...

that measures strabismus in the nine diagnostic positions of gaze. The test is named after Walter Brackett Lancaster, who introduced it in 1939. __TOC__

Test procedure

The patient wears red-green glasses, and two lights (one red, one green) are used, so that the patient thus sees each light with a different eye. One light is held by the clinician, the other by the patient. The clinician points the light to a screen, requesting the patient to bring the second light to align on top of it. The patient's eye positions are measured while the patient performs the test. Advantageously, monocular occlusion is applied before the test for at least 30 minutes. This largely eliminates the neurologically learned

fusional vergence Fusional vergence is the movement of both eyes that enables the fusion of monocular images producing binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perce ...

tone ("vergence adaptation") that is present in patients who are able to achieve fusion in a limited area of gaze, as is often the case for patients with incomitant strabismus.

Scope

The Lancaster red-green test quantifies comitant and incomitant misalignments. It accurately assesses horizontal and vertical misalignments (

heterotropia Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a ...

heterophoria Heterophoria is an eye condition in which the directions that the eyes are pointing at rest position, when ''not'' performing binocular fusion, are not the same as each other, or, "not straight". This condition can be esophoria, where the eyes ten ...

) as well as torsional misalignments (

cyclotropia Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye (or both) about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each o ...

, cyclophoria) in all nine diagnostic gaze positions. (Comitancy means that there is the same misalignment in all gaze directions. Incomitant misalignment, that is, a different misalignment of the eyes in different gaze directions, is typically present in patients with paralytic, mechanical or restrictive strabismus. The test allows to determine and accurately quantify also latent forms of strabism

). There also exists a computerized version of the Lancaster red-green test.

References

Diagnostic ophthalmology Optometry Physical examination {{Eye-stub