Eye Doctors Still Use This 100-Year-Old Test for Color Blindness

You may have seen them at your ophthalmologist's office: large circular diagrams made up of colored dots. People with normal vision are able to discern a number among the dots of contrasting colors. People who are color blind might see only a field of spots.

These elegant, deceptively modern drawings were published 100 years ago by a Japanese ophthalmologist, Shinobu Ishihara. Thanks to the designs' simplicity and diagnostic accuracy, the Ishihara test is still the most popular and efficient way to identify patients with color vision deficiencies.

Born in Tokyo in 1879, Ishihara studied medicine at the prestigious Tokyo Imperial University on a military scholarship, which required him to serve in the armed forces. After graduating in 1905, he worked for three years as a physician specializing in surgery in the Imperial Japanese Army, and then returned to the university for postgraduate studies in ophthalmology. In his research, Ishihara focused on identifying and recruiting soldiers with superior vision, thereby increasing the overall effectiveness of the military. And that became of prime importance to Japan beginning in 1914.

As World War I spread across Europe, Asia, and the Pacific, the Japanese army asked Ishihara to develop a better way to screen draftees for color vision problems. The most popular method at the time was the Stilling test, invented by German ophthalmologist Jakob Stilling in 1878 as the first clinical color vision test. (Previous tools had asked patients to identify the colors of wool skeins or illuminated lanterns—useful skills for sailors and railway conductors, but an imprecise method for diagnosing vision issues.)

"Though popular, 'the Stilling' retained a distinctly 19th-century flavor, more treatise-like and less diagnostically incisive," according to Eye magazine.

Shinobu Ishihara
Wellcome Images // CC BY 4.0

Japanese army officials requested a new diagnostic tool that was easier to administer and interpret. The test Ishihara began to develop was based, like Stilling's, on the principle of pseudo-isochromatism—a phenomenon in which two or more colors are seen as the same (or isochromatic) when they're actually different. A person with normal vision could easily see the difference, while people with red-green deficiency, the most common form of color blindness, would have difficulty distinguishing those two opposing colors. Those with blue-yellow color blindness, a less common type, would have a hard time discerning reds, greens, blues, or yellows.

Ishihara hand-painted circular designs comprised of small dots of different areas and colors so that variations in the design could be discerned only by color and not shape, size, or pattern. Hidden in the field of dots was a figure of a contrasting color that people with normal vision could see, while those with deficiencies could not. Other plates in the series were designed to show figures that would be visible only to people with deficiencies. When physicians displayed the diagrams, patients said or traced the visible figure within the circle without needing to use ambiguous color names, which standardized the possible results.

The earliest sets of Ishihara plates, produced in 1916, were reserved exclusively for the army's use and featured Japanese characters within the diagrams. In 1917, in an effort to sell the series internationally, Ishihara redesigned it with the now-familiar Arabic numerals and published a set of 16 plates as Tests for Colour Deficiency.

The tests were adopted throughout the world beginning in the early 1920s, and eventually grew into a set of 38 plates. But their popularity almost led to their undoing. Unauthorized publishers printed their own version of the plates to meet demand, throwing the accuracy of the diagnostic colors into doubt. "The plates have been duplicated along with an easily memorized key by cheap color processes in the tabloid press, and exposed in public places, reducing the fifth edition [of the collection] to a parlor game," one psychologist warned in the Journal of the Optical Society of America in 1943.

Despite those obstacles, the tests proved indispensable for both practicing physicians and researchers. Ishihara continued to refine the designs and improve the color accuracy of the images into the late 1950s, while he also served as the chair of the ophthalmology department and then dean of the medical school at Tokyo Imperial University. In addition to Tests for Colour Deficiency, he also published an atlas, textbook, lectures, and research studies on eye diseases. But he is remembered most for the iconic charts that seamlessly blend art and science.

Some Mathematicians Think the Equal Sign is On Its Way Out

Paperkites/iStock via Getty Images
Paperkites/iStock via Getty Images

A growing number of mathematicians are skeptical that the equal sign, traditionally used to show exact relationships between sets of objects, holds up to new mathematical models, WIRED reports.

To understand their arguments, it’s important to understand set theory—a theory of mathematics that’s been around since at least the 1870s [PDF]. Take the classic formula 1+1=2. Say you have four pieces of fruit—an apple, an orange, and two bananas—and you put the apple and the orange on one side of a table and the two bananas on the other. In set theory, that’s an equation: One piece of fruit plus one piece of fruit on the left side of the table equals two pieces of fruit on the right side of the table. The two sets, or collections of objects, are the same size, so they’re equal.

But here’s where it gets complicated. What if you put an apple and a banana on the left side of the table and an orange and a banana on the other side? That’s clearly different from the first scenario, but set theory writes it as the same thing: 1+1=2. What if you switched the order of the first set of objects, so instead of having an apple and an orange, you had an orange and an apple? What if you had only bananas? There are potentially infinite scenarios, but set theory is limited to expressing them all in only one way.

“The problem is, there are many ways to pair up,” Joseph Campbell, a mathematics professor at Duke University, told Quanta Magazine. “We’ve forgotten them when we say ‘equals.’”

A better alternative is the idea of equivalence, some mathematicians say [PDF]. Equality is a strict relationship, but equivalence comes in different forms. The two-bananas-on-each-side-of-the-table scenario is considered strong equivalence—all of the elements in both sets are the same. The scenario where you have an apple and an orange on one side and two bananas on the other? That’s a slightly weaker form of equivalence.

A new wave of mathematicians is turning to the idea of category theory [PDF], which is based in understanding the relationships between different objects. Category theory is better than set theory at dealing with equivalence, and it’s also more universally applicable to different branches of mathematics.

But a switch to category theory won’t come overnight, according to Quanta. Interpreting equations using equivalence rather than equality is much more complicated, and it requires relearning and rewriting everything about mathematics—even down to algebra and arithmetic.

“This complicates matters enormously, in a way that makes it seem impossible to work with this new version of mathematics we’re imagining,” mathematician David Ayala told Quanta.

Several mathematicians are at the forefront of category theory research, but the field is still relatively young. So while the equal sign isn’t passé just yet, it’s likely that an oncoming mathematical revolution will change its meaning.

[h/t Wired]

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.