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Duochrome test

Duochrome test

A duochrome test is a test commonly used to refine the final sphere in refraction (under-correction and over-correction), which makes use of the longitudinal chromatic aberration of the eye. Because of the chromatic aberration of the eye, the shorter wavelengths (green) are focused in front of the longer red wavelengths. It is assumed that best vision is attained when the yellow wavelengths are focused on the retina.

TOC

Testing

The person is asked to compare the clarity of the letters on the green and the red side. If the letters of the green side are clearer +0.25 D sphere is added and if the letters on the red side are clearer -0.25 D sphere is added. With optimal spherical correction, the letters on the red and green halves of the chart appear equally clear.

Because this test is based on chromatic aberration and not on color discrimination, it is used even with people having color vision deficiency.

The eye with overactive accommodation may still require too much minus sphere in order to balance the red and green. Cycloplegia may be necessary.

The duochrome test is not used with patients whose visual acuity is worse than 20/30 (6/9), because the 0.50 D difference between the two sides is too small to distinguish.

References

References

  1. (2015-03-16). "Can the Red-Green Duochrome Test Be Used Prior to Correcting the Refractive Cylinder Component?". PLOS ONE.
  2. Chukwuyem, Ekele C.. (2025). "Subjective Refraction Technique: Duochrome Test". StatPearls Publishing.
  3. (2020-09-30). "Investigation of the unfused cross cylinder test as an alternative method for the determination of spherical distance refraction end points". African Vision and Eye Health.
  4. Myron Yanoff, Jay S. Duker. (2009). "Ophthalmology". Mosby Elsevier.
Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

diagnostic-ophthalmology medical-tests
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