contact lenses

Dry Eye: Rewetting Drops vs. Artificial Tears

Understanding the benefits of rewetting drops and tears may prevent CL drop-outs.

BY KENNETH A. LEBOW, O.D., F.A.A.O.
Virginia Beach, Va.

Dry eye is a multi-faceted disease with a variable pathophysiology and inconsistent clinical presentation. One of the factors linked with dry eye is contact lens (CL) wear. Out of the approximately 35 million CL wearers in North America, 50% have reported some dryness-related symptoms.^1-3 One survey demonstrated that roughly 24.1% of CL wearers discontinued lens wear due primarily to reasons of dryness and discomfort.⁴

Upon interaction with the ocular surface, CL characteristics (e.g. oxygen permeability) and mechanics (i.e. contact of the lens with the ocular surface) can affect the patient's overall comfort and satisfaction.

Patients who experience dry eye symptoms rely on ophthalmic solutions, such as rewetting drops and artificial tears, to relieve their discomfort. What patients may not know is that the Food and Drug Administration (FDA) regards these solutions as quite different from one another and, as a result, has established regulations for the use of each.

Here, I discuss CL-induced dry eye and how the FDA's perspective on rewetting drops and artificial tears should guide you in your prescription decisions and patient education.

CL-induced dry eye

The symptoms of CL-induced dry eye — burning, stinging, dryness, scratchiness and soreness — are often very similar to those of clinical dry eye.⁵ Patient questionnaires can provide quick and reliable evaluations of the frequency of symptoms and their impact on the patient's quality of life.⁶

In order to clinically evaluate the objective signs of CL-induced dry eye, first assess:

► ocular surface staining using lissamine green and/or fluorescein,
► tear film break-up time (TFBUT) measured with 1μL to 5 μL of fluorescein,
► the ocular protection index (OPI) — the ratio of TFBUT to inter-blink interval (IBI).

Ocular surface staining TFBUT shorter than five seconds and an OPI score <1 are both indicative of some degree of tear-film instability.

CL wear is particularly associated with ocular surface staining. In fact, one study of 500 hydrogel CL wearers demonstrated at least some degree of staining in 55.7% of participants.⁷

Staining in CL wearers has also revealed ring-like or arcuate patterns on conjunctival staining.^8,9

Investigating the culprits

CL wearers can experience dry eye signs and symptoms as a result of the lens interacting with the tear film and altering the natural flow of tears across the ocular surface. Research shows this disturbance specifically affects the lipid layer and thus increases rates of tear evaporation.¹⁰ Several factors, including lens hydration and oxygen permeability of CL design, are related to the level of lens comfort.

Low-water content CLs have demonstrated an increased ability to resist dehydration when compared with high-water content CLs.¹⁰ Also, the oxygen permeability of CLs is important to protect the ocular surface and is responsible for providing ample oxygen. Thus, in order to combat dryness, CL manufacturers aim to find an optimal balance of oxygen permeability and water content.

Several over-the-counter (OTC) products combat CL-induced- as well as other forms of dry eye.

Rewetting drops relieve symptoms of discomfort during lens wear, and several CL solutions now aim to improve the comfort of the lens as well.

Artificial tears offer relief of ocular dryness and discomfort.

Although rewetting drops and artificial tears may appear very similar, the FDA regulates the manufacture, testing and use of these solutions differently.

Rewetting drops

The FDA classifies rewetting drops as medical devices under the category of "in-eye contact lens solutions."¹¹ The agency defines rewetting drops as solutions intended for use with CLs and as devices designed to interact with CLs. FDA approval of these solutions is contingent on comprehensive chemical, microbiological, toxicological and clinical testing.

In addition, the agency has strict requirements for the packaging and labeling of these solutions.¹¹ Rewetting drops for CLs aim to accomplish their name-sake through reinstating the fluid characteristics between the CL and ocular surface. Ultimately, these drops aim to improve the comfort of the lens on the ocular surface.

Artificial tears

The FDA regulates the approval of lubricant eye drops — or artificial tears — through the monograph "Ophthalmic Drug Products for Over-the-Counter Human Use" (21 CFR Parts 349 and 369) — the recipe book for artificial tears since 1989. It includes descriptions of the active ingredients (and concentrations thereof) and labeling provisions for an ophthalmic OTC drug to be "generally recognized as safe and effective."¹² The FDA considers artificial tears ophthalmic drug products and defines them as "drug products applied to the eyelid or instilled in the eye."

Artificial tears typically contain ingredients that initially provide lubrication to the ocular surface, and several artificial tears aim to provide long-lasting ocular surface protection through scientific mechanisms of action. One such artificial tear contains carboxymethylcellulose (CMC) and glycerin and advertises a mechanism of action providing both lubrication and osmoprotection. Another contains polyethylene glycol (PEG 400), propylene glycol (PG) and gelling agent HP-Guar and relies on the interaction between the solution and natural tears to approximate the glycocalyx and maintain prolonged residence of the demulcents. These mechanisms of action are designed for interaction with the natural ocular environment, but not for interaction with CLs.

The FDA regulations are clear that in order to be used with CLs, an ophthalmic solution must be approved under the regulations for a medical device, and therefore, no lubricant eye drop (artificial tear) has this approval.

Biocompatibility is a large concern, as required testing for the drops designed for use with CLs examines the interaction between ingredients and the CL materials. One material, benzalkonium chloride (BAK) — a preservative found in several artificial tears — has proven toxic to CL materials and could cause detriment, should a patient instill drops during CL wear.¹³

Make this point when explaining to patients the differences between CL rewetting drops and artificial tears. The patient must understand that no matter how similar the ingredients appear, the artificial tears are not approved for use with their CLs.

Artificial tear use while patients aren't wearing their lenses, however, is a possibility for CL wearers. Some artificial tears have shown efficacy in addressing dryness experienced by CL wearers.

Patient care

When CL wearers present complaining of dry, uncomfortable symptoms, assess the clinical signs of ocular dryness and recommend appropriate treatment based on the aforementioned information. When counseling patients, emphasize that artificial tears are not the same as rewetting drops and vice versa. After all, if your patients use solutions with proven efficacy in treating their dryness symptoms, you just might avoid unnecessary dropouts. OM

References available on request.

Dr. Lebow is in private practice in Virginia Beach, Va., specializing in contact lenses. He is a Fellow of the American Academy of Optometry and Past president of the Virginia Optometric Association.