Introduction to a Hidden Health Risk

Out of sight, out of mind. A new study suggests a common eye condition could be quietly masking one of the only early warning signs of bladder cancer — the 10th leading cause of cancer deaths in the US.

The Condition: Color Blindness

Researchers found people with the visual impairment were more likely to be diagnosed at later stages, when the disease is harder to treat and survival odds nosedive. Around the world, men are much more likely than women to have the eye condition.

Color blindness — also known as color vision deficiency — affects about 1 in 12 men and 1 in 200 women worldwide. It can be caused by several factors, but it’s most often the result of inherited genetic mutations that affect the retina’s light-sensitive cones.

Impact on Health

The most common form of color blindness makes it difficult to distinguish between red and green — which past research shows can make it harder to detect blood in the urine. That’s a major problem because blood in the urine is often one of the only early warning signs of bladder cancer, which is typically painless at first.
Blood in the urine is an early warning sign of bladder cancer that may go unnoticed in people with certain forms of color blindness. GladkovPhoto – stock.adobe.com

Study Findings

Curious whether this could affect patient outcomes, researchers compared the health records of 135 people with both bladder cancer and color blindness with 135 people who had bladder cancer alone. They found that patients with color vision deficiency were more likely to be diagnosed at a more advanced and invasive stage than those with normal vision.

Comparison and Risks

That’s a potential double whammy for men, who are more affected by color blindness and are also four times as likely to be diagnosed with bladder cancer than women. Overall, participants with color blindness had a 52% higher risk of dying within 20 years of their bladder cancer diagnosis compared with the normal-vision group.
Only 11 states require color vision screening for school-aged children, so many cases in the US may never be diagnosed. JU.STOCKER – stock.adobe.com

Broader Implications

Past research has also shown that color blindness can make it harder for people to detect blood in stool — a potential symptom of colorectal cancer, which is rising fast among young Americans. Intrigued, researchers compared colorectal cancer outcomes among patients with and without color blindness, expecting similar results to the bladder cancer group. But notably, they found no statistically significant difference in survival between the two groups.

Expert Insights

They theorized that may be because colorectal cancer often comes with other symptoms — like abdominal pain and changes in stool habits — and because screening is widely recommended for Americans ages 45 to 75, making blood detection less critical. By contrast, there is no comparable recommendation for asymptomatic bladder cancer screening. “There’s much more focus on catching colorectal cancer at an early age and much more public awareness,” Dr. Ehsan Rahimy noted.

Conclusion

The researchers noted several limitations, including that color blindness is often undetected. As a result, some participants may have been incorrectly classified as having normal vision, which could affect the findings. Still, experts say the findings are significant enough to warrant further investigation and may prompt clinicians to be more vigilant with people who have color vision deficiency. Already, Dr. Rahimy has heard from urologists and gastroenterologists who said they had never considered color blindness as a factor in cancer diagnosis. Some said they may begin to ask about it on screening questionnaires. The stakes are high: in 2026 alone, the American Cancer Society estimates that 84,530 new cases of bladder cancer will be diagnosed in the US — and 17,870 people will die from the disease.

FAQs

• Q: What is the common eye condition that could mask an early warning sign of bladder cancer?
  • A: The common eye condition is color blindness, also known as color vision deficiency.
• Q: How does color blindness affect the detection of bladder cancer?
  • A: Color blindness, especially the form that makes it difficult to distinguish between red and green, can make it harder to detect blood in the urine, which is often an early warning sign of bladder cancer.
• Q: Are there any differences in how color blindness affects the detection of other types of cancer, like colorectal cancer?
  • A: Yes, while color blindness can also make it harder to detect blood in stool (a potential symptom of colorectal cancer), the impact on survival rates was not found to be statistically significant for colorectal cancer, possibly due to other symptoms and widespread screening recommendations.
• Q: What is the recommended course of action for individuals with color blindness regarding cancer screening?
  • A: Experts suggest that clinicians should have a low threshold to investigate for bladder cancer in color-blind patients with urinary symptoms, and there may be a need for increased awareness and potentially adjusted screening practices for individuals with color vision deficiency.