The US Food and Drug Administration this month announced that it has issued warning letters to eight companies selling unapproved eye drops. They're in violation of the law, the FDA says, because they're marketed as being able to treat health conditions like cataracts and pink eye without being properly vetted for safety. Some of the companies also didn't meet safety inspection requirements. 

It's part of the FDA's "ongoing effort to protect Americans from potentially harmful ophthalmic products," the agency said in a news release Sept. 12. Unrelated to the FDA's current warning letters and the companies they were issued to, there was a recall of a couple of different eye drops earlier this year over possible contamination with a dangerous bacteria, which resulted in at least four deaths. 

Monitoring the quality and safety of eye drops is a big deal because products that you put directly into your eye "bypass some of the body's natural defenses," according to the FDA.

Here's what you should know about eye drop safety, including which products have been marketed illegally and how to find the right drops for you.

What eye drop companies received warning letters from the FDA? 

Companies including CVS Health and Walgreens Boots Alliance (which owns Walgreens pharmacy chains) have been called out by the FDA. Once the FDA sends a company a warning letter, the company has 15 business days to respond to or address the agency's concerns.  

In addition to CVS Health Pink Eye Relief Drops and Walgreens' Allergy Eye Drops, Stye Eye Drops and Pink Eye Drops, products from Boiron, DR Vitamin Solutions, Natural Ophthalmics, OcluMed, Similasan AG and TRP Company have been recalled. Information about the exact name or brand of the eye drops can be found through the FDA's news release. If you have any of these products, you should stop using them and contact your doctor if you have concerns.

In a statement, Walgreens said that it's pulling the eye drops addressed by the FDA from its shelves "out of an abundance of caution," and that people who have purchased them can return them for a full refund.

CVS also said it's stopped the sale of its store brand eye drops marketed for pink eye and that customers can get a full refund if returning them. "We're committed to ensuring the products we offer are safe, work as intended and satisfy customers," the company said.

On its website, Similasan said in a statement that the company is "engaging" with the FDA over the agency's concerns to "better understand the issues raised and provide updated documentation around our manufacturing processes."

Boiron, DR Vitamin Solutions/DR Vitamins, Natural Ophthalmics, OcluMed and TRP Company didn't immediately respond to a request for comment.

Read more: 6 Eye Problems That Become More Common As We Age 

Other eye drops or ingredients to avoid 

Some of the eye drops the FDA called attention to this month — the ones from CVS, Similasan and Walgreens — contain silver as a preservative. Over time, silver used in eye drops may cause argyria, the FDA says, which is when tissue permanently turns gray or grayish blue. 

Also in its online statement, Similasan said that its products have been available in the US since 1987 and, to the company's knowledge, there have been "zero cases of adverse events linked to the use of Silver Sulfate as a preservative."

In terms of past alerts from the FDA, brands that made headlines earlier this year due to their recalls (artificial tears from EzriCare's and Delsam Pharma) were found to be contaminated with a drug-resistant bacteria, rather than it being an issue with an active ingredient. Global Pharma Healthcare issued a voluntary recall of these products. 

Also earlier this year, Purely Soothing eye drops and Dr. Berne's eye drops were recalled over sterility concerns and possible contamination. Dr. Berne's Whole Health Products and Pharmedica USA (which made the Purely Soothing drops) voluntarily recalled their products.

If you notice signs of an eye infection, it's important you get medical help right away because of how fast an eye infection can spread and how dangerous it can become. Symptoms can include pain in the eye, the feeling that something's in it, redness, swelling, discharge from the eye, fever with no other cause and blurred vision.

Read more: 4 Tips For Protecting Your Eyes as You Age 

How to find safe and effective eye drops 

If you're using eye drops to treat a medical condition like pink eye, glaucoma, cataracts or chronic dry eye, ask your optometrist or ophthalmologist for their recommendation. They should point you to something that's both effective for your health concerns and vetted for safety. If you're using eye drops that haven't gone through the FDA's process, you might be delaying treatment with an effective product, the agency noted this month.

Generally speaking, it's a good idea for anyone to get a recommendation from a medical professional, simply because you're applying something to one of your most sensitive body parts. But if you're like many people who use eye drops, it might not always be realistic to get a professional recommendation, and you may find yourself perusing pharmacy shelves, online or in person. 

To help narrow down your search, you can check out this list of some of the best eye drops out there. It includes drops made specifically for people with contacts, those with allergies and more. These ones by iVizia were voted best overall.

For more information about eye drops, read on for how to avoid contamination and tips for using eye drops safely.