The risks of using expired eye drops include ineffective treatment of vision or other eye problems, inflammation and irritation of the eyes and, in the worst cases, infection. The specific effects depend on what the drops are intended to treat and how much time has passed since their printed expiration date. Most patients report little to no side effects from using drops that have past their prime, but a lot of this depends on whether the drops have ever been opened. Partially used bottles that have expired are often more dangerous and have more risks than those that are still sealed in their original packaging, though it should be noted that ophthalmologists do not ever recommend using eye medications that have passed their expiration date.
There are two main types of eye drops: prescription and over-the-counter. Both versions will expire at some point, and their expiration dates are usually set at least in part according to how long the chemical suspension is expected to be effective. Manufacturers typically print an expiration date on the labeling or packaging of the bottles that can be a year or more in the future, but in most cases the shelf life is about four weeks from the moment they are opened. Oxygen exposure can cause the drops to become unstable, and over time can lead to evaporation. The liquid may look about the same a few months in, but may actually contain different proportions of active and inactive ingredients than intended.
This risk is particularly serious for prescription products that are formulated to treat conditions like glaucoma, chronic dry eyes, or allergies. Using old eye drops might not treat these conditions at all, or might treat them only partially. Partial treatment can make ailments last longer and sometimes actually get worse over time.
Irritation and inflammation can also happen with drops that are unstable or weakened. This is most common with prescription drops, but is also possible with even basic saline solutions depending on how long they have been expired. Once the composition of the medication changes, it is no longer ideal for the surface of the eyeball. Higher levels of chemicals, salts, or other additives can cause redness and swelling.
The eyes are some of the moistest parts of the outside of the body, and as such they can be a breeding ground for bacteria. Patients are usually instructed slowly squirt the drops onto the eyeball, usually just beneath the lid. The dropper is never meant to touch the surface of the eye or its fluids, but contact is nonetheless made in many cases. It can be very difficult to squeeze droplets into one’s own eye without accidentally touching the dropper to the surrounding fluid.
Once contact has been made fluids are able to commingle on the dropper, and may even drop back into the main solution chamber. This doesn’t usually present problems right away — which makes use before the expiration date okay in most cases — but over time, the mixture can begin breeding bacteria and contaminating the solution.
Reintroducing a contaminated dropper to the sensitive eye area can result in serious consequences. Bacterial infections in the eye are often accompanied by swelling, inflammation, and itching. Medical attention is almost always required, too, since the nature of most infections is to spread; left untreated, things can penetrate deep into the eyeball, possibly impacting vision, or can spread across the face.
Healthcare professionals generally recommend that people get rid of expired eye drops and replace them with new products. There is little sense introducing eyes to liquid that is ineffective at best and contaminated at worst. Expired eye medicines, particularly those that were bought over the counter, usually can be thrown away in the household trash; these solutions are typically mild, and are unlikely to pose risks to the environment or to other people's health.
Depending on the contents of the medication, however, simply throwing away eye drops can be dangerous. Many pharmacies will accept expired medications for disposal, and most will least advise patients about safe practices for getting rid of specific compounds.