Does the Farnsworth D-15 Match the HRR Test for Detecting Colour Vision Deficiency? A Comparison Against the Anomaloscope Reference Standard
This study demonstrates that while the HRR test exhibits high sensitivity and excellent agreement with the anomaloscope for classifying red-green colour vision deficiency types, its severity grades do not reliably predict D-15 test outcomes or distinguish between dichromats and anomalous trichromats.
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Color is not just a matter of beauty; for many people, it is a matter of safety and daily function. Some individuals are born with a condition where their eyes cannot distinguish between certain shades of red and green. This is not a total blindness to color, but a subtle shift in how their eyes process light, making it difficult to tell a ripe strawberry from a green one, or to read a traffic light correctly. While this condition rarely threatens eyesight itself, it can block people from careers in aviation, the military, or electrical work, where spotting a specific color is critical. To find out who has this condition and how severe it is, doctors use a few different tools. One is a simple test with colored plates, where the patient must find hidden numbers or shapes. Another is a test where they must arrange colored caps in a smooth order. The most precise tool, however, is a specialized machine that lets the patient mix two lights until they look exactly the same. This machine is considered the gold standard, but it is expensive and rare, so doctors often rely on the simpler tests. The question remains: do these simpler tests tell the whole story, or do they miss the nuances that the machine catches?
A researcher at King Saud University set out to answer this by bringing together one hundred and eight people who were already known to have red-green color vision deficiency. These participants, mostly men between the ages of seventeen and seventy-one, sat down for a single session where they took three different tests. First, they used the Hardy–Rand–Rittler test, which consists of a series of colored plates designed to screen for the problem and sort it into two main types: one where the eye struggles with red (protan) and one where it struggles with green (deutan). Next, they took the Farnsworth D-15 test, which asks them to arrange fifteen colored caps in a circle based on how similar the colors look. Finally, they used the special machine, known as an anomaloscope, to get a precise measurement of their color vision. The goal was to see how well the plate test and the cap arrangement test agreed with the machine, and whether the severity grades given by the plates could predict how many mistakes a person would make on the cap test.
The results showed that the plate test is an excellent screener. Nearly all of the participants, about ninety-seven percent, failed the initial screening plates, meaning the test successfully caught almost everyone with the condition. In contrast, the cap arrangement test was much stricter; only about sixty-five percent of the group failed it, which is expected because that test is designed to find people who would struggle with real-world color tasks, not just to find the condition itself. When the researchers looked at whether the plate test could correctly identify the type of defect, it performed remarkably well. In ninety-two percent of cases, the plate test agreed with the machine on whether the person had a red or green problem. This level of agreement is so high that it suggests the plate test is a reliable way to sort the type of color blindness without needing the expensive machine.
However, the story becomes more complicated when looking at how severe the problem is. The researchers found that people who were graded as having a very mild or mild problem on the plate test almost always passed the cap arrangement test. This means that if a person gets a low score on the plates, they likely do not need to take the second, more difficult test. But for those with medium or severe grades, the connection was not so clear. About half of the people who had the most severe form of color blindness, where they see only two primary colors instead of three, were graded only as "medium" on the plate test. Furthermore, a significant number of people with medium or severe grades on the plates still managed to pass the cap arrangement test. This indicates that the severity scores on the plates do not perfectly predict how a person will perform on the cap test, nor do they always separate the most severe cases from the less severe ones.
The study concludes that while the plate test is a powerful tool for finding color vision deficiency and sorting it into the right category, its severity ratings should be interpreted with caution. It is a reliable first step, but it does not always tell the full story of how a person will handle color in daily life. For those with the mildest forms of the condition, the second test may be unnecessary, but for those with medium or severe grades, the results can be unpredictable. The findings suggest that doctors should not rely solely on the severity grade from the plates to determine a patient's functional ability, as the two tests measure slightly different aspects of how the eye sees the world.
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