What Are the Eye-Related Side Effects of Azathioprine?

Azathioprine has almost no record of harming the eye itself. The eye risks that do exist come from what the drug is meant to do, which is calm the immune system. That can, rarely, leave the eyes open to infection and, after an organ transplant, to growths on the eye’s surface. The same drug is also prescribed to protect eyesight in people with eye inflammation.

Why Azathioprine Rarely Harms the Eye Directly

Medical reviews of arthritis drugs turn up only one reported case of eye harm tied to azathioprine taken by mouth.¹ That case was an infection causing inflammation inside the eye. It took hold because the person’s immunity was lowered.

That sets azathioprine apart from other drugs used in rheumatology. Hydroxychloroquine can build up in the retina, which is why yearly eye screening is advised. Long-term steroids can cause cataracts and raise eye pressure. Azathioprine has no similar built-in screening schedule. If you take steroids alongside it, though, you may still need eye checks because of the steroid. An infection from lowered immunity can start suddenly, so the right approach is to watch for new symptoms rather than wait for a scheduled screening.

Lupus, rheumatoid arthritis and bowel disease can also inflame the eyes on their own, so a new symptom isn’t automatically the drug’s fault, and it’s worth mentioning to your doctor either way. Pain, redness together with blurred vision, or new floaters are the pattern to treat as urgent, because they can signal inflammation or infection inside the eye rather than surface irritation.

Serious Eye Infections From a Weakened Immune System

One woman with lupus and kidney failure developed CMV retinitis, a virus infection of the retina, in both eyes while taking azathioprine plus low-dose steroids.² Doctors are urged to watch for this in people with lupus and kidney failure on that combination.³ Kidney transplant patients on immune-lowering drugs have also developed retinal infections, including a fast tissue-destroying viral infection, 2 to 3 years after surgery.⁴ In one transplant patient, CMV retinitis appeared 7 months after transplant, with bleeding and white patches in the retina.⁵ These infections can appear months or years into treatment, not only at the start. Every reported patient was also taking other immune-lowering medicines or had serious illness.⁶⁷

New floaters, which look like specks, threads or dark spots drifting across your vision, can be an early sign that the retina is inflamed or infected. Flashes of light, or a shadow creeping in from the edge of your vision, can be a sign of retinal detachment. CMV infection of the retina is often painless, so blurred or patchy vision in an eye that looks quiet can still be serious. Any of these in someone on immune-lowering drugs calls for an eye exam the same day, not the next routine appointment, because retinal damage can progress quickly and is often permanent.

At the exam, the eye doctor puts in drops to widen the pupils, which allows a view of the whole retina at the back of the eye. The drops blur near vision and cause light sensitivity for a few hours, so arrange a ride home. Infection often shows up as white or yellow patches, sometimes with bleeding, which is why a dilated exam tells far more than a quick look at the front of the eye. Treatment is typically antiviral medicine, and your eye doctor may work with your prescriber on whether immune-lowering drugs should be adjusted. Don’t stop azathioprine on your own.

Higher Risk of Eye Surface Growths After Organ Transplant

Among organ transplant recipients on immune-lowering drugs, about 1 in 1,000 developed abnormal growths on the eye surface, versus about 1 in 2,000 without.⁸ When transplant recipients were excluded, no clear link remained.⁹ For people treated for eye inflammation, azathioprine probably does not raise overall cancer risk in a detectable way.¹⁰ About 1 in 1,000 is still a small risk, and it applies mainly to transplant recipients on combined immune-lowering treatment.

These growths usually appear as a pinkish, jelly-like or whitish patch on the white of the eye or at its edge near the colored part. They tend to grow slowly. Some people feel only a gritty or irritated sensation, while others notice nothing and the growth turns up at an eye exam. A growth isn’t necessarily cancer, since several harmless conditions look similar. Only an eye doctor can tell, by examining it and sometimes taking a sample. Most surface growths can be treated successfully, often with minor surgery or medicated eye drops, especially when found early.

Sunglasses that block UV light help protect the eye surface outdoors, and wraparound styles also cut light entering from the sides. A wide-brimmed hat shades the eyes from overhead sun. Transplant recipients should mention any new spot, patch or persistent irritation on the eye at check-ups instead of assuming it is harmless.

Does Azathioprine Cause Dry Eye

In people with inflammatory bowel disease, dry eye affected about 56% of those on another bowel drug alone and 62% when azathioprine was added, a difference too small to show a real effect.¹¹ Dry eye in these patients seems tied to the disease more than the drug. Some eye clinics do list azathioprine as possibly reducing tear production, though strong proof is lacking.¹²

Lupus, rheumatoid arthritis and inflammatory bowel disease can each come with dry eye, so a person on azathioprine often has dryness because of the illness it treats. Dryness that began before the drug was started, or that resembles what you had during flares, is one clue that the underlying condition may be the cause.

Preservative-free artificial tears can be used several times a day and are gentler than preserved drops if you use them often. At screens, take regular breaks and blink fully, because we blink less while concentrating and tears evaporate faster. A humidifier helps in dry indoor air, especially in heated or air-conditioned rooms.

Dryness with sharp pain or light sensitivity needs an exam. Discharge or sudden redness may signal infection. Don’t stop azathioprine because of dryness without talking to your prescriber.

Why Eye Doctors Prescribe Azathioprine

Among people starting on more than 10 mg of prednisone daily, about 1 in 3 got down to 10 mg or less within six months on azathioprine.¹³ By 12 months nearly half had reached that, and about 1 in 10 stopped prednisone.¹⁴ Success typically came in about 5 months, between mycophenolate at 4 and methotrexate at 6.5 months.¹⁵ It is also used, alongside other drugs, for severe surface scarring disease after Stevens-Johnson syndrome.¹⁶ Expect a slow start, not quick relief.

Steroids are usually continued at first because azathioprine works slowly, so the earliest weeks are not a test of whether it is working. Steroid doses are then lowered in steps, and only while the inflammation stays quiet; a flare may mean slowing or pausing the reduction. Regular eye checks measure how much inflammation is present, which is how doctors judge progress when you may feel no different. Benefits can keep building beyond six months, so stopping early because nothing seems to have changed can waste a treatment that might still be working.

Lowering steroid use matters for the eyes because long-term steroids can cause cataracts and raise eye pressure. The infection warning signs still apply, so floaters, blurred vision or eye pain should be reported promptly even when the inflammation seems well controlled.

Blood Tests That Predict Side Effect Risk

TPMT is an enzyme that breaks down azathioprine, and your doctor may order a TPMT test before you start.¹⁷ People with low predicted TPMT had about 3 times the odds of low white blood cells.¹⁸ In one bowel disease group, 29% of those carrying a TPMT variant developed low white cells versus 3% without.¹⁹ Low white cells make infections, including eye infections, more likely.

It’s worth asking whether you were tested before starting, since the result guides the starting dose. A normal result doesn’t remove the need for blood checks.

Blood counts are usually checked frequently in the first months after starting or changing the dose, then less often once things are stable. If white cells fall, the usual response is to lower the dose or pause the drug, which is why the checks are worth keeping.

Because a low count can develop between scheduled tests, report fever, a sore throat or unusual infections promptly. A low blood count combined with new eye symptoms is a reason for urgent care, since infections are harder to fight when white cells are low.

Azathioprine in Pregnancy and Babies’ Eyes

Mice given 4 to 13 times the highest human dose during early development had more cleft palate, open-eye and bone defects.²⁰ Those doses far exceed what people take, and the findings alone can’t say what happens in people. Human experience helps here: azathioprine is often continued in pregnancy for bowel disease when benefits outweigh risks.²¹

Tell your doctor before you try to conceive, so a plan can be made in advance rather than after a positive test. Don’t stop azathioprine on your own; discuss any decision with the specialist who prescribes it.