1365: "Heterochromia"
Interesting Things with JC #1365: "Heterochromia" – One eye blue. The other, brown. Or green. Or gray. A rare twist of genetics leaves behind a quiet visual dissonance... and a beautiful biological mystery.
Curriculum - Episode Anchor
Episode Title: Heterochromia
Episode Number: #1365
Host: JC
Audience: Grades 9–12, college intro, homeschool, lifelong learners
Subject Area: Biology, Human Anatomy, Genetics, Medical Science, Visual Arts
Lesson Overview
Students will:
Define heterochromia and its three primary types using anatomical terminology.
Compare congenital versus acquired heterochromia and identify causes for each.
Analyze the biological mechanisms behind melanin distribution in the iris.
Explain how cultural perceptions of heterochromia have evolved over time.
Key Vocabulary
Heterochromia (heh-teh-roh-KROH-mee-uh): A condition where a person has different colored eyes or varied pigmentation in a single eye.
Melanin (MEL-uh-nin): A natural pigment found in skin, hair, and eyes; responsible for coloration differences.
Sectoral (SEK-tur-uhl) heterochromia: A form where one eye shows a segment of a different color.
Anisocoria (an-eye-so-KOH-ree-uh): A condition where the pupils are of unequal sizes, often mistaken for heterochromia.
Congenital (kun-JEN-ih-tuhl): A trait or condition present from birth, often due to genetic or developmental factors.
Narrative Core
Open: The story hooks listeners by describing the eerie feeling of noticing mismatched eyes across a room.
Info: Introduces heterochromia as a rare condition, breaking down its types and biological causes involving melanin.
Details: Explains both congenital and acquired heterochromia, touching on causes like injury, disease, and medication. Also corrects the misconception surrounding David Bowie.
Reflection: Shares cultural interpretations from medieval Europe to Turkish traditions and veterinary studies in animals.
Closing: “These are interesting things, with JC.”
Close-up of a human eye with central heterochromia—green and golden-brown colors radiate from the pupil. Banner above reads: “Interesting Things with JC #1365 – HETEROCHROMIA.”
Transcript
You’re standing across the room from someone... and something’s off. You don’t know why at first. Then it hits you. One of their eyes is blue. The other... brown. Or green. Or gray. Not just light playing tricks, two different colors.
It’s called heterochromia. And it’s beautiful.
Heterochromia iridum means "different colored irises." It’s rare. Fewer than 200,000 people in the United States are believed to have it. Most cases are congenital, meaning a person is born with it. It’s caused by a difference in melanin, the pigment that gives color to your skin, hair, and eyes. Brown eyes have more melanin, blue eyes have less. When melanin doesn’t spread evenly across the iris, the colors can split.
There are three types. Complete heterochromia means each eye is a different color. Sectoral heterochromia shows up as a slice or wedge of different color inside one eye. And central heterochromia creates rings, usually golden or hazel, around the pupil, surrounded by another color. That one’s often mistaken for hazel, but it’s something else entirely.
The condition can show up in newborns, but may fade with age. Infant eye color isn’t stable at birth... melanin levels can change in the first year. That’s why heterochromia detected early might disappear later... or appear later. Around 75 percent of newborns with blue eyes will develop a different color by age one.
Acquired heterochromia is a different matter. It can be caused by blunt trauma, bleeding inside the eye, chronic inflammation, or neurological conditions like Horner syndrome. Certain medications used in glaucoma treatment, especially latanoprost or bimatoprost, can increase melanin production and darken the iris over time. Laser eye procedures, and even tumors inside the eye, have also been known to trigger pigment changes.
And not every case is true heterochromia. David Bowie is the most famous example. His left pupil was permanently enlarged after a fight at age 15. It made the eye appear darker, but the irises were the same color. The condition is called anisocoria, unequal pupils. It affects about 1 in 5 people, but usually not as dramatically.
Now here’s the contrast. In animals, this doesn’t raise eyebrows. Huskies, Australian shepherds, and border collies carry the trait genetically. In white cats, especially those with the W gene, heterochromia is common and often paired with partial deafness in the ear on the blue-eyed side. That’s a real anatomical link... blue-eyed cats with one deaf ear have been studied in veterinary medicine since the 1970s.
The Angora cat, or Ankara kedisi, from Turkey’s capital Ankara (AHN-kar-uh), is one of the oldest naturally occurring breeds with consistent heterochromia. In Turkish tradition, the odd-eyed white Angora was seen as a national treasure. One cat named “Van Kedisi” was even kept at the presidential palace.
People haven’t always been so kind. In parts of medieval Europe, a person with mismatched eyes might be accused of witchcraft, or worse. There were folktales that said one eye looked into our world, and the other into the next. It wasn’t science... it was suspicion.
Today, we know better. Heterochromia is almost always harmless. It doesn’t change how a person sees. It doesn’t affect eyesight or perception. It’s just pigment... just a variance in the instructions our cells follow when building color.
Not every case is the same, and not every example is medical. Some just live with it. Actress Kate Bosworth has one blue eye, and one that’s part blue, part hazel. It’s real heterochromia, sectoral, and visible on every close-up. Same goes for Christopher Walken and Jane Seymour. None of them made it part of their identity. They just showed up with it, and the world noticed.
But if you’ve ever looked someone in the eye... and seen two stories staring back, one from each side... you remember. Sometimes it’s two different colors in two different eyes. Other times, both colors in the same eye. Either way, it stops you, just for a second.
We expect faces to match. Eyes to mirror each other. But every now and then... nature decides not to.
These are interesting things, with JC.
Student Worksheet
What is the biological pigment responsible for eye color differences in heterochromia?
List and define the three types of heterochromia mentioned in the episode.
What is the difference between congenital and acquired heterochromia?
Why is David Bowie’s eye condition not technically heterochromia?
How does heterochromia in animals differ from that in humans, culturally and genetically?
Teacher Guide
Estimated Time: 1–2 class periods (45–60 minutes each)
Pre-Teaching Vocabulary Strategy:
Use visual aids showing different heterochromia types.
Define and pronounce key terms in small groups.
Anticipated Misconceptions:
Students may confuse anisocoria with heterochromia.
May assume heterochromia affects vision.
Discussion Prompts:
Why do you think heterochromia was once feared or seen as magical?
How can science correct myths about rare conditions?
Should physical differences be medicalized or normalized?
Differentiation Strategies:
ESL: Use labeled eye diagrams and bilingual glossaries.
IEP: Provide sentence starters and vocabulary flashcards.
Gifted: Research and present on another rare visual condition.
Extension Activities:
Create a visual art piece inspired by heterochromia.
Interview a vet or doctor about how heterochromia is identified or treated.
Cross-Curricular Connections:
Art: Study the use of eye color in portraiture.
Genetics: Explore gene expression and melanin synthesis.
History: Investigate cultural superstitions tied to body appearance.
Quiz
Q1. What pigment is primarily responsible for eye color?
A. Hemoglobin
B. Melanin
C. Keratin
D. Collagen
Answer: B
Q2. Which form of heterochromia features a ring around the pupil?
A. Complete
B. Sectoral
C. Central
D. Partial
Answer: C
Q3. What condition did David Bowie actually have?
A. Central heterochromia
B. Sectoral heterochromia
C. Anisocoria
D. Cataracts
Answer: C
Q4. Which medication can increase iris pigmentation?
A. Penicillin
B. Ibuprofen
C. Latanoprost
D. Acetaminophen
Answer: C
Q5. In which animal is heterochromia often linked to deafness?
A. Golden retrievers
B. White cats
C. Turtles
D. Parrots
Answer: B
Assessment
Explain how melanin affects eye color and how uneven distribution can result in heterochromia.
Compare heterochromia in humans and animals. What causes it, and how is it perceived in different contexts?
3–2–1 Rubric:
3 = Accurate, complete, thoughtful
2 = Partial or missing detail
1 = Inaccurate or vague
Standards Alignment
U.S. Standards:
NGSS HS-LS3-1: Students can analyze how genetic variation, including heterochromia, results from inherited traits.
CCSS.ELA-LITERACY.RST.9-10.2: Determine the central ideas of a scientific text and summarize relationships among key details.
ISTE 3a: Students plan and employ effective research strategies to locate information on genetic traits.
C3.D2.His.2.9-12: Analyze change and continuity in human cultural practices like views of physical traits.
International Equivalents:
AQA GCSE Biology 4.5.3: Human inheritance, including genetic disorders and traits.
IB MYP Science Criterion A & C: Understanding scientific knowledge and communicating scientific information.
Cambridge IGCSE Biology 2.21: Genetic variation and its causes in organisms.
Show Notes
This episode of Interesting Things with JC delves into the rare but fascinating condition of heterochromia—where the irises of an individual's eyes show differing colors. Through clear scientific explanation and cultural reflection, the episode explores genetic and acquired causes of heterochromia, debunks common myths (like David Bowie's eye), and highlights how humans and animals alike display this trait. In classrooms, it opens rich discussions around biology, anatomy, genetics, and society's perception of physical differences. A valuable lesson for science, art, and social studies educators alike.
References
American Academy of Ophthalmology. (2023). Heterochromia. https://www.aao.org/eye-health/diseases/what-is-heterochromia
MedlinePlus Genetics. (2024). Eye color and melanin production. https://medlineplus.gov/genetics/understanding/traits/eyecolor/
National Eye Institute. (2023). Facts About the Cornea and Corneal Disease. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases
