Contact lenses are safe, effective, and worn by roughly 45 million people in the United States alone. But choosing the right type, caring for them properly, and understanding the risks makes a real difference in your comfort and eye health. Here’s what you need to know before you start wearing contacts or if you want to get more out of the ones you already have.
Your Contact Lens Prescription Isn’t the Same as Your Glasses Prescription
You can’t simply order contacts using the numbers from your glasses prescription. Because contact lenses sit directly on your eye instead of about 12 millimeters in front of it, the lens power often needs to be adjusted. For prescriptions stronger than +/- 4.00 diopters, your eye doctor performs a calculation called vertex compensation to account for that difference in distance.
A contact lens prescription also includes measurements you won’t find on a glasses prescription. Base curve (BC) describes the curvature of the back of the lens and needs to match the shape of your cornea. Diameter (DIA) is the width of the lens from edge to edge, ensuring it covers the cornea properly. These can’t be measured with an online calculator. They require an in-office fitting, which is one reason contact lens prescriptions expire and need to be renewed, typically every one to two years.
Soft Lens Materials: Hydrogel vs. Silicone Hydrogel
Most contacts sold today are soft lenses, and they come in two main materials. Traditional hydrogel lenses have higher water content but allow much less oxygen through to the cornea. Early research established that a lens needs an oxygen transmissibility of at least 24.1 to avoid corneal swelling during daily wear, and 87.0 for overnight wear. No hydrogel lens meets the overnight threshold, and some fall short even for daily use.
Silicone hydrogel lenses were developed in the late 1990s to solve this problem. They use silicone-based polymers that let significantly more oxygen pass through while still being comfortable. If you wear your lenses for long hours, silicone hydrogel is generally the better choice for corneal health. Newer versions have also addressed early complaints about stiffness and dryness, with some brands using water gradient technology that keeps the lens surface highly lubricated throughout the day.
Daily Disposables vs. Monthly Lenses
The biggest practical decision is how often you replace your lenses. Daily disposables are single-use: you put in a fresh pair each morning and throw them away at night. Monthly (or biweekly) lenses are reused, stored in solution overnight, and replaced on a set schedule.
Daily disposables carry the lowest infection risk of any soft lens type, with a rate of about 0.52 cases of serious corneal infection per 10,000 wearers per year. Extended-wear lenses used overnight have a rate of 2.52 per 10,000, roughly five times higher. The odds of a severe corneal infection are about four times greater with overnight-wear lenses compared to dailies. Daily disposables also tend to cause less severe disease when infections do occur, likely because there’s no buildup of deposits or bacteria on a lens you never reuse.
Monthly lenses cost less upfront but require cleaning supplies and consistent hygiene habits. If you wear contacts only a few days a week, dailies can actually be cheaper since you’re not opening a monthly lens for occasional use.
Specialty Lenses for Irregular Corneas
Standard soft lenses, including toric lenses designed for mild to moderate astigmatism, work well for most people. But for conditions like keratoconus (where the cornea thins and bulges into a cone shape) or significant corneal irregularity after a transplant, standard lenses often can’t provide clear vision or a stable fit.
Scleral lenses fill this gap. They’re larger rigid lenses that vault over the entire cornea and rest on the white of the eye (the sclera). Because they don’t touch the corneal surface, they work even on highly irregular corneas where smaller rigid lenses won’t stay in place or cause discomfort. In one clinical review, keratoconus accounted for 63% of scleral lens fittings, and post-transplant irregularities accounted for 28%. These lenses also hold a reservoir of fluid against the eye, which helps people with severe dry eye.
How to Clean and Store Reusable Lenses
If you wear reusable lenses, your cleaning routine is the single most important factor in avoiding infection. Poor hygiene accounts for about 33% of contact lens-related corneal infections.
You have two main solution types. Multipurpose solutions clean, rinse, disinfect, and store lenses in one step, making them convenient. Hydrogen peroxide systems use a 3% peroxide solution that’s highly effective at killing microorganisms, achieving 99.9% kill rates against common pathogens within one hour. The peroxide then needs to be neutralized before you put the lens in your eye, either through a built-in catalyst disc (one-step systems) or a separate neutralizing tablet (two-step systems).
Two-step peroxide systems, which maintain peroxide contact for longer before neutralizing, are significantly more effective against tougher organisms like Acanthamoeba cysts, a particularly dangerous cause of eye infection. One-step systems neutralize the peroxide too quickly to be as effective against these cysts. Whichever system you use, never top off old solution in your case. Empty it completely, rinse the case with fresh solution (not water), and let it air dry.
Why Sleeping in Contacts Is Risky
Sleeping in contact lenses is the single riskiest behavior for lens wearers. Overnight use is responsible for about 43% of contact lens-related corneal infections. Roughly one in 500 overnight wearers develops a serious corneal infection each year, with infection rates between 9.2 and 20.9 per 10,000 users depending on the lens type.
The reason is straightforward: your cornea gets oxygen primarily from the air, not from blood vessels. When you close your eyes, oxygen supply drops. Add a contact lens on top and the cornea can become oxygen-starved, which weakens its natural defenses against bacteria. Over time, this can also cause changes to the corneal cells that aren’t reversible, including abnormal blood vessel growth into the cornea and permanent changes to cell shape and size.
Some lenses are specifically approved for overnight wear, and they’re made from high-oxygen silicone hydrogel materials. But even with these lenses, the infection risk remains substantially higher than with daily wear. Eye care professionals generally don’t recommend extended-wear lenses for children and teens because of the increased risk of corneal ulcers.
What Overwearing Does to Your Eyes
Wearing lenses longer than recommended, whether that means too many hours in a day or using a monthly lens for six weeks, disrupts the cornea’s ability to get nutrients and clear waste products from the tear film. About 50% of contact lens wearers experience dry eye symptoms, and overwearing is a major contributor.
Beyond dryness, overwearing causes microtrauma to the corneal surface. Symptoms include pain, tearing, light sensitivity, and reduced tolerance for wearing lenses at all. In more advanced cases, the surface cells of the cornea can start to change, and you may develop small lesions on the upper cornea. Some of these complications reverse when you give your eyes a break. Others, like changes to the deeper corneal cell layers and blood vessel growth, can be permanent. Sticking to the replacement schedule your doctor recommends isn’t just a suggestion from the manufacturer. It’s how you avoid these problems.
Contact Lenses for Children
There’s no hard minimum age for contacts. Kids as young as 8 can wear them successfully, and the FDA has approved a contact lens specifically for slowing the progression of nearsightedness in children ages 8 to 12. That said, about 13,500 children visit the emergency room each year for contact lens-related injuries, making contacts one of the leading device-related reasons for pediatric ER visits.
The most common problems in kids are infections and corneal abrasions, often caused by behaviors like wearing another child’s lenses, using saliva to moisten a lens, or buying decorative lenses without a prescription. Children with seasonal allergies are generally not good candidates, since lenses can worsen itching and burning. The biggest factor in whether a child is ready for contacts isn’t age. It’s maturity and willingness to follow a consistent hygiene routine.
Lenses That Deliver Medication
The FDA has approved the first contact lens that releases medication while correcting vision. Made by Johnson & Johnson, it’s a daily disposable lens containing a small dose of the antihistamine ketotifen, designed to prevent the itchy eyes caused by allergic conjunctivitis. It works like a regular vision-correcting contact lens but delivers the drug gradually throughout the day, eliminating the need for separate allergy eye drops. This is currently the only drug-releasing lens on the market, but it signals a shift in how contacts may be used in the future.