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.
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.
“I’m hopeful that this study raises some awareness, not only for patients with color blindness, but for our colleagues who see these patients,” Dr. Ehsan Rahimy, adjunct clinical associate professor of ophthalmology at Stanford Medicine and senior author of the study, said in a news release.
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.
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.
Curious whether this could affect patient outcomes, Rahimy and his colleagues 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.
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.
“Bladder cancer is a bad disease. If you delay your diagnosis, it will make a difference to your prognosis,” Dr. Veeru Kasivisvanathan, a urological oncologist and surgeon at University College London who was not involved in the study, told Live Science.
When caught and treated before the cancer spreads outside the bladder, the 5-year relative survival rate is 73%, according to the American Cancer Society, based on diagnoses from 2015 to 2021.
Once it travels to distant organs like the lungs, liver, or bones, that number plummets to just 9%.
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, Rahimy and his team 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.
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, Rahimy noted, 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,” he said.
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.
“I would keep a low threshold to investigate for bladder cancer for a color-blind patient with urinary symptoms,” Dr. Masahito Jimbo, a family medicine specialist who studies cancer-screening practices at the University of Illinois at Chicago and was not involved in the research, told ScienceNews.
Already, 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.
“If this study raises awareness and people read this and casually pass it along, I think it’s done its job,” he said.
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.
