The Refraction group includes a number of tests and stimuli to assist the clinician in determining the near refractive error / reading ADD.


The test are selected from the Refraction Options list.


Duochrome rings and Duochrome dots


These tests display rings and dots against a red and green background.  Due to the inherent chromatic aberration of the eye, the red and the green light is focussed at different points along the visual axis.  This can be used to fine tune a near refractive correction / near ADD by adjusting the refractive correction until the rings on the red and green appear to be matched in contrast.



The size of the duochrome rectangle can be adjusted depending on the patient's visual acuity using the Size tracker bar or the mouse wheel.


NOTE:  It is important that the red and green rectangles are well-matched in terms of brightness.  This can be adjusted from the Calibration options.


Cross Cyl rings and dots


These tests display rings or dots against a white background which are useful for fine tuning the near prescription or performing a cross-cylinder test.



The size of the rings and dots can be adjusted depending on the patient's visual acuity using the Size tracker bar or the mouse wheel.


Cross Cyl Add test


This test displays fine vertical and horizontal lines as shown below:



This test is sometimes know as the Fused Cross Cylinder (FCC) test and is used to fine tune a near refractive correction.


There are several variants of this test.  However, a popular method is the following:


  • Place a cross-cylinder lens in front of the patient axis 90/180
  • Add +0.50D a sphere.
  • Ask the patient whether the horizontal or vertical lines appear darker and clearer. If they report that the lines are equal or horizontal, add plus lenses until the vertical lines are now the blackest or clearest. This is the desired endpoint. If the patient reports that the lines are vertical, on the other hand, add minus lenses until the lines are equal or horizontal. This is the desired endpoint in this situation. 


The size of the target can be adjusted depending on the patient's visual acuity using the Size tracker bar or the mouse wheel.


Fan and Block test


The Fan and Block test is a well-established and well-documented test for establishing the axis and magnitude of astigmatism.





The angle of the arrow (in Fan mode) and the blocks (in Block mode) may be change using the Angle tracker bar or using the mouse wheel.