Why your eyes water constantly on chemotherapy

Your eyes are not producing a flood of extra tears. The tears you always made are no longer draining away.

NCI's chemotherapy guide puts it directly: some types of chemotherapy can clog your tear ducts, which can cause blurry vision and watery eyes.

Tear ducts are tiny channels at the inner corner of each eye. They carry tear fluid down into the nose, which is why a good cry leaves you sniffing. When those channels narrow or block, tears have nowhere to go but over the lower lid and down your cheek.

Understanding this changes how the symptom feels. It is a plumbing problem, not an emotional one.

People tend to file this under mildly embarrassing rather than medically relevant, and so they do not mention it.

But NCI links the same clogged ducts to blurry vision. A film of tears sitting across the surface of the eye scatters light. That is enough to make small print harder, screens more tiring and driving at night less comfortable.

If you have been squinting at your phone and blaming your age, the two symptoms may be the same problem.

NCI names contact lens discomfort as something that can happen during chemotherapy.

A lens sits directly on the tear film. When the tear film is disturbed, the lens stops behaving. Many people find glasses simply easier during treatment, and there is no prize for persevering with lenses that hurt.

If you want to keep wearing lenses, that is a reasonable conversation to have with your eye doctor and your oncology nurse, particularly because handling lenses means putting your fingers near your eyes at a time when infection risk may be higher.

NCI's booklet does not give a long self-care list for watery eyes specifically, and we are not going to invent one.

What it does support is telling your team. They know which drugs you are on and whether eye effects are expected with those drugs. They can also tell you whether eye drops are appropriate for you, which is not a decision to make in a pharmacy aisle while on chemotherapy.

A few things are simply sensible while you wait: carry tissues, keep a spare pair of glasses somewhere useful, and do not rub your eyes with unwashed hands.

NCI's booklet does contain a broader instruction that is relevant here: let your doctor or nurse know right away if you notice any nervous system changes.

Vision is part of the nervous system. Sudden vision loss, double vision, a change in colour vision, eye pain, or vision changes that come on quickly are not the same as eyes that have been gently watering for a fortnight. Those warrant a prompt call rather than a note for your next appointment.

For sudden changes in vision, including colour vision, on cisplatin specifically, MedlinePlus lists that among the symptoms to report to your doctor immediately.

At your next visit, describe the pattern. Both eyes or one. All day or worse at certain times. Whether reading has become harder. Whether the watering is enough that it runs down your face in cold air or wind.

That level of detail helps your team separate a drug effect from something else, and it takes about twenty seconds to say.

• Call your care team the same day if your vision changes suddenly, including a change in how you see colour — MedlinePlus lists that among the cisplatin effects to report to your doctor immediately, and NCI's chemotherapy booklet says to let your doctor or nurse know right away about any nervous system changes.
• Call your care team within a day or two if your vision has turned blurry or your eyes are watering more than usual — NCI's booklet asks you to tell your doctor or nurse when either of those happens, rather than waiting for your next scheduled visit.