Contact Lens Rewetting Drops

Contact Lens Rewetting Drops

Contact Lens Rewetting Drops
Michael A. Ward, MMSc, FAAO

When contact lenses become dry and uncomfortable, rewetting drops can provide relief.

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For patients who suffer from chronic contact lens dryness or simply need to rewet their contact lenses after exposure to a drying environment, contact lens rewetting drops are a safe, convenient way to add moisture and increase comfort. Rewetting drops are often prescribed or patient self-selected in an attempt to alleviate symptoms of dryness and irritation.
   
While the use of contact lens rewetting drops may seem self-explanatory, a short time spent counseling patients on product choice and use can pay dividends in patient comfort and satisfaction. This also provides an opportunity to educate patients about the difference between contact lens rewetting drops and artificial tears.

Assessing A Need
   
Even patients with robust tear films may occasionally need rewetting drops after time in a dry environment, such as on an airplane. However, not all feelings of dryness indicate a dry eye.  Contact lens related dryness symptoms may also result from a tight lens fit or lens care product sensitivity. 
   
In either case, it is a simple matter to pinpoint the real problem. Contact lens fit can be readily assessed at the slit lamp. A tight lens tends to be initially comfortable, but becomes less comfortable as the day progresses. As lens movement slows it may cause a mild peri-limbal injection along with a mild burning sensation. While rewetting drops may be beneficial in soothing feelings of irritation, they do not address the underlying problem. A lens material change, flatter base curve, or smaller lens diameter may be necessary to correct the fit. 
   
Determining whether there is a problem with the patient’s care solution is typically determined by changing to a single use disposable lens or switching the patient to a nonpreserved hydrogen peroxide-based solution, and seeing whether symptoms resolve. If either of these measures solves the underlying problem, the patient’s use of contact lens rewetting drops should significantly decrease. 

Lens Materials/Drop Formulation
   
The specific contact lens material a patient is wearing can affect ocular hydration, as each contact lens material imbibes and absorbs water differently. Silicone hydrogel contact lenses typically have lower water content than HEMA-based contact lenses, however the water in silicone hydrogel lenses is tightly bound to the plastic and, as a result, these lenses tend to dehydrate less than HEMA lenses.
   
For patients who have chronic dryness, I recommend contact lens rewetting drops that contain hyaluronic acid (HA), which can imbibe close to a thousand times its weight in water and is very effective in retarding evaporation. Sodium hyaluronate solutions strongly adhere to the mucin layer of the tear film, creating a persistent water retaining layer that resists evaporation.
   
HA is also “viscoadaptive,” which means that HA drops rapidly thin during blinking and thicken between blinks because of a property called shear-thinning. As a result, HA drops tend to be long lasting. Patients with chronic dryness may get extra benefit from placing a rewetting drop in the bowl of the contact lens or in the eye directly, immediately prior to lens insertion.     

Rewetting Drops vs Artificial Tears
   
It is important to record and monitor all eye drops a patient uses, both prescription and over-the-counter, by name and dosage. Artificial tears (also called lubricating drops) may help to relieve symptoms of dryness or actually make symptoms more profound, depending on the dosage and types of drops chosen.  Contact lens rewetting drops are typically either preservative-free or use rapidly-dissipating preservative solutions that are specifically designed for use over contact lenses. By contrast, artificial tears are designed to be used on the naked eye, and often contain preservatives that can build up in contact lenses and subsequently cause ocular surface cell damage.
   
Benzalkonium chloride (BAK) is the most well-known offender because of its toxic effects on the ocular surface (the FDA does not allow drops containing BAK to be labeled for use with contact lenses), but even dissipating preservatives have the potential to build up on contact lenses. Therefore, I counsel patients who use contact lens rewetting drops more than 4 times a day to choose a nonpreserved version. Gentler preservatives, such as those that dissipate rapidly on the eye, are less of a concern in patients who use daily disposable contact lenses or may require drops infrequently.
   
To make the trip to the drug store less confusing for my patients, I usually recommend a brand, or a couple brands, from which they can choose. I also give my patients these general rules: choose drops that indicate that they are designed for use with contact lenses on the box, or drops that are labeled as preservative-free and come in unit-dose containers. One last point I make to patients is that any rewetting drop labeled for use with soft contact lenses can be used by gas permeable (GP) lens wearers, but not vice versa. The preservatives and constituents in GP contact lens rewetting drops can cause irritation when used over soft contact lenses.

THE BOTTOM LINE
Contact lens rewetting drops are designed to add moisture to a dry lens and increase contact lens comfort. These drops are either preservative-free or contain mild, dissipating preservatives, and some contain compounds such as HA that effectively draw and hold water to the contact lens. It is worth taking the time to ask patients about rewetting drop use, however, as patients who make frequent use of rewetting drops without obtaining more than transient relief may have a problem other than lack of moisture—typically the issue is poor lens fit or a reaction to some component of the lens care solution. These problems can be readily identified, and resolving the underlying problem will typically reduce the need for contact lens rewetting drops.

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Michael A. Ward, MMSc, FAAO, is director of the Emory Contact Lens Service and an instructor of ophthalmology at Emory University School of Medicine in Atlanta, GA.