The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina is made up of what are called Rods and Cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.



The cones, each contain a light sensitive pigment which is sensitive over a range of wavelengths (each visible color is a different wavelength from approximately 400 to 700 nm). Genes contain the coding instructions for these pigments, and if the coding instructions are wrong, then the wrong pigments will be produced, and the cones will be sensitive to different wavelengths of light (resulting in a color deficiency). The colors that we see are completely dependent on the sensitivity ranges of those pigments.




People with normal cones and light sensitive pigment (trichromasy) are able to see all the different colors and subtle mixtures of them by using cones sensitive to one of three wavelength of light - red, green, and blue. A mild color deficiency is present when one or more of the three cones light sensitive pigments are not quite right and their peak sensitivity is  shifted (anomalous trichromasy -  includes protanomaly and deuteranomaly).  A more severe color deficiency is present when one or more of the cones light sensitive pigments is really wrong (dichromasy - includes protanopia and deuteranopia).



These tests are utilized to evaluate and measure color discrimination in patients. There are diverse congenital and acquired eye diseases that can cause color deficiency. These exams help to differentiate different pathology.

The Farnsworth arrangement test, or more commonly – the color arrangement test, was originally developed for Navy use by Commander Dean Farnsworth in 1943 at the Naval Laboratory. Based on the combined work of Farnsworth and Deane Judd (1943-1945), in 1947 the Farnsworth Dichotomous Test (D-15) was created. The D-15 test was designed to distinguish the differences in visual ability between color blind or color deficient people, and those with normal color vision.


The test above is a simulation by Daniel Flück (colblindor.com) of the D-15 test originally created by Farnsworth. The test results are based around the lines of confusion. These lines are associated with Protan (red), Deutan (green), and Tritan (blue) color blindness. Using a mathematical formula developed by Vingrys and King-Smith in 1988 to derive your personal color difference vector, a line can be drawn and its angle compared to the three confusion lines. This makes it possible to quantify the type and severity of your color blindness.