Duochrome test

It is assumed that best vision is attained when the yellow wavelengths are focused on the retina.

[1] The patient is asked to compare the clarity of the letters on the green and the red side.

With optimal spherical correction, the letters on the red and green halves of the chart appear equally clear.

[2] The eye with overactive accommodation may still require too much minus sphere in order to balance the red and green.

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.