What Does the Lancaster Red-Green Test Map Out?

Eyes that can't move in unison result in blurred or double vision.

Human sight is binocular, that is both eyes record an image from slightly different angles and your brain puts the two versions together to create a single sharp image. When your eyes cannot focus on the same point simultaneously, this process is disrupted.

History

Walter Brackett Lancaster, M.D., developed the Lancaster red-green test in 1939 to measure the deviation when a person's eyes do not align with each other, called heterophoria. Dr. Lancaster studied how the muscles around the eye affect vision and his test allows simultaneous yet separate measurement of the two eyes' misalignment.

Uses

The Lancaster red-green test measures strabismus, a condition in which both eyes cannot focus on the same point at the same time, such as cross-eye. The test measures the eye in nine specific positions to determine which muscles are weak and need correction. It also is used to confirm cases of mild myasthenia gravis, an autoimmune disease causing transmission fluctuations between nerve and muscle.

Performing the Test

The patient receives an intravenous dose of edrophonium chloride, a drug that temporarily improves muscle strength, and wears goggles with one red lens and one green lens. The test-giver shines a green light in one of the nine diagnostic positions and the patient aligns a red light on top of it. Measurements are taken of the positions of each eye while the patient performs the test.

References

• American Orthoptic Journal: The Lancaster Red-Green Test
• Merriam-Webster Dictionary: Heterophoria
• NIH Archives: Walter Brackett Lancaster Obituary
• Wiley Online Library: The Laboratory Diagnosis of Mild Myasthenia Gravis
• Women's Health: What Is Myasthenia Gravis?
• NIH: Myasthenia Gravis Fact Sheet: How is Myasthenia Gravis Diagnosed?

Resources

• North American Neuro-Ophthalmology Society: Fourth Nerve Palsy