Dry Eye & Contact Lenses
A review of the causes, symptoms and cures.
JENNIFER SMYTHE, O.D., M.S., F.A.A.O.; PETER BERGENSKE O.D., F.A.A.O.; AND PATRICK CAROLINE, F.A.A.O.

Ocular dryness remains the most common complication associated with soft contact lens wear. Approximately four out of five lens wearers report symptomatic dryness during some portion of their wearing schedule. As a result, one out of four patients are forced to reduce their wear time; two million individuals abandon soft contact lens wear altogether each year with nearly 50% of these contact lens "dropouts" attributing dryness or discomfort as the primary reason. Keep in mind that the majority of the contact lens wearing population are young, healthy individuals. In this population, true aqueous deficiency or keratoconjunctivitis sicca (KCS) is extremely rare. Thus we have dry eye symptoms in individuals who, for the most part, have adequate tear production. What is the solution?

The first step is to fully appreciate the complex architecture of the 10-µm to 20-µm structure that comprises the tear film and to consider all factors that can disrupt its delicate balance with the ocular system. It's also important to differentiate between all causes of dryness symptoms to develop the most appropriate management strategy with the goal of keeping our patients comfortable in contact lenses.

Figure 1

DEFINING DRYNESS

Disruption of any of the tear film's three layers can result in symptoms of dry eye disease. The National Eye Institute classifies the disease into two categories:

1. Aqueous layer deficiency (not enough tears are produced)

2. Evaporative deficiency (what is produced disappears too quickly).

All too often the clinical presentation is a combination of the two pathogenic pathways; that is, decreased production leads to inefficient spreading of the tear film, which leads to excessive evaporation.

PRESENTING IN THREE FORMS

Optometrists have observed essentially three forms of dry eye in practice: Pathologic, marginal and contact lens induced. We'll start with the most serious.

Pathologic dry eye. Patients exhibiting this form of "true" dry eye have underlying systemic or ocular surface disease that contributes to the disorder. This category also includes patients who have suffered ocular trauma such as physical or chemical burns, and those taking ocular or systemic medications that affect tear film stability or production.

Pathologic causes of a decrease in tear production include Sjögren's syndrome, vitamin A deficiency, age-related hyposecretion, lacrimal gland excision or damage as result of sarcoidosis or cancer, sensory motor loss and conjunctival scarring conditions, and burns. Chronic allergic conjunctivitis and collagen vascular disorders such as scleroderma, lupus and rheumatoid arthritis commonly cause dry eye disease, as does ocular surface disease.

Finally, several classes of systemic medications can compromise tear film production including antihistamines, thiazide diuretics, antidepressants, beta blockers and other antihypertensives. A careful case history is crucial for determining possible culprits that can affect the production of tear film components.

Pathologic cases are typically the only form of dry eye that have a definitive correlation between objective testing and subjective symptoms. These highly symptomatic patients have reduced tear break-up time, tear production deficiency (as measured by the Schirmer test), and/or ocular surface damage in the form of conjunctival or corneal staining.

Marginal dry eye. The second form of dry eye observed in non-contact lens wearers is commonly referred to as marginal dry eye. Though these individuals have symptoms of dry eye, objective testing is often inconclusive and doesn't reveal definitive signs of the disorder. This patient frequently complains of symptoms that manifest late in the day and increase in severity during the evening hours.

Contact lens-induced dry eye. The marginal dry eye observed in contact lens wearers has several different names, including contact lens-induced dry eye (CLIDE) or contact lens induced sicca syndrome (CLISS). The dry eye contact lens patient differs from the true dry eye patient both in subjective complaints and in physical findings.

Most often the contact lens patient neither complains of ocular dryness nor exhibits clinical signs of dry eye when not wearing her lenses. Instead, she finds that symptoms of dryness limit her ability to comfortably wear lenses. In one report, the most frequent complaint of contact lens dry eye patients was dryness, followed by blurry and changeable vision. The true dry eye patient doesn't need contact lenses to stimulate symptoms; complaints are most frequently of dryness and soreness.

	Figure 2

CAUSE AND SOLUTION

The cause of contact lens related dryness has traditionally been attributed to lens dehydration; however, no such correlation has been demonstrated. Other possible causes include hypoxia, tear evaporation and solution sensitivity.

Attempts to associate lens dehydration with comfort have failed to show a causal relationship between the two. Patients who have dryness symptoms tend to have greater dehydration of their lenses than do asymptomatic patients. Use of saline or lubricants can prevent dehydration, but it hasn't been possible to show that a decrease in the amount of dehydration is the cause of improvement in comfort associated with lubricant use. Nevertheless, it's common practice to prescribe lenses less prone to dehydration for patients who have dryness symptoms. Most practitioners believe that lower-water content lenses show less dehydration than higher-water content lenses; however, superiority is best evaluated case by case.

Lens materials that dehydrate significantly less than conventional materials have been developed and perform well in clinical practice. However, the lack of correlation between dehydration and comfort indicates that we can't discount other less quantifiable factors such as lens design, fit and psychological components of comfort.

The silicone hydrogels are low- water content, high permeability materials for which evaporation and dehydration appears significantly less of a problem than with conventional hydrogels. These lenses are reported to provide relief for many patients suffering from dryness symptoms with conventional soft lenses.

In addition to the reduction of dehydration as a contributor to the syndrome, these lenses have surface properties that reduce binding of protein, likely resulting in less preservative uptake. Likewise, the successful use of silicone hydrogel lenses in some patients who have dryness symptoms may be at least as attributable to the increased oxygen as it is to less dehydration.

If low water content is an answer, gas permeable (GP) lenses provide the ultimate. GPs offer the benefits of essentially no evaporation, no preservative uptake and high oxygen transmission. For the contact lens dry eye patient, GPs are a possible successful alternative.

FINDING RELIEF

For many contact lens dry eye patients, the problem becomes worse later in the day, although patients wearing lenses overnight may also complain of dryness upon awakening. Here are some ideas that may help your patients battle feelings of dryness.

On-eye wetting agents. Clinicians and patients alike quickly learn that the simple use of lens rewetting drops at the onset of symptoms is a disappointingly short-lived solution to the problem. Use of rewetting agents at regular intervals (every two to three hours throughout the day) does provide relief to many patients, but this regimen is expensive, particularly when they use the most appropriate formulations (preservative free).

Five o'clock, five-minute soak. All soft lens materials dehydrate in vivo, most likely through evaporation. Unfortunately, rewetting agents only minimally relieve symptoms. It's much more effective to remove the lens for brief immersion in saline or multi-purpose solution, allowing the lens to fully rehydrate. For many, this provides noticeably longer relief of symptoms than rewetting drops. The "five o'clock, five minute soak" is a simple and effective strategy for the patient who has a long evening ahead. (Advise patients who wear lenses overnight to clean and disinfect lenses after any removal before sleeping.)

Solution suspects. When simple rehydration with drops or soaking doesn't work, consider that dryness symptoms may not stem from the effects of evaporation. It's time to suspect other factors -- most notably, lens care solution reactions. You should consider solutions "guilty until proven innocent" because they can cause symptoms of dryness and may sometimes reveal themselves by causing a punctate keratitis, dry spots on the cornea or tarsal plate changes.

The need to balance microbial efficacy with patient convenience challenges makers of modern lens care products. It may be unrealistic to think that we could continually use a solution containing chemicals such as a surfactant (soap for cleaning), a preservative for disinfection and an ingredient to solubolize protein, yet not compromise the delicate balance between the ocular surface and the tear film.

LENS SOLUTION ISSUES

While the exact ingredient(s) in preserved contact lens disinfection systems that is culprit hasn't been clearly identified, specific preservatives have been shown to cause epithelial sloughing and loss of microvilli on the surface of the cornea. For example, lens care regimens with polyaminopropyl biguanide (PHMB) have been indentified as a culprit in causing corneal staining or what could be considered "solution-related keratitis" when used with a variety of lens materials, including HEMA-based hydrogels, silicone hydrogels and GP polymers.

Soft lens patients may display diffuse corneal staining that typically begins in the inferior region of the cornea, then works its way around the periphery, with the central cornea typically being the last region affected (Fig. 1). In GP solution sensitivity reactions, the corneal staining is often confined to the area underneath the lens, especially if the lens is fitted with apical clearance.

Yet absence of significant staining doesn't rule out solution sensitivity. Researchers have documented increasing tarsal plate hyperemia with the use of certain multi-purpose disinfection systems (Fig. 2). Hyperemia is often the first sign of inflammation resulting from increased vascular permeability.

Another element of multipurpose solutions to consider suspect in tear film disruption is the surfactant. Patients are soaking these porous, sponge-like lens materials not only in preservatives on a routine basis, but also in soap. Surfactants, which dissolve lipids and mucins, could cause tear evaporation, disrupt cell membranes and allow preservatives to further react with the surface cells.

A combination of excessive tear evaporation and loss of surface microvilli can lead the observation of dry spots on the cornea or areas of non-wetting. Thus, you should include both NaFl staining and simple lid eversion in contact lens follow-up exams to ascertain the ocular response to both contact lens wear and lens care solutions.

Even in the absence of corneal staining or palpebral hyperemia, you can suspect multipurpose solutions when patients complain of chronic dryness while wearing contact lenses. Thus many patients find relief when you change or eliminate lens care products.

A SOLUTION FOR SOLUTIONS

The simplest solution to these solution-related dryness problems is to eliminate the solutions! Ideally, a trial with single-use lenses is indicated. For those patients for whom this isn't an option, changing the care regimen to a preservative-free disinfection system such as peroxide or UV-C is the best alternative. It may take up to two weeks to purge the residual effects from previous lens care products; often the patient won't notice any immediate relief.

Gradually, however, she will feel improvement and increase her total lens wear time. You should dispense a new pair of lenses with a preservative-free disinfection system whenever possible to speed recovery.

ATTEMPTING TO PRESERVE TEARS

Punctal occlusion, one of the most common nonpharmacological dry eye treatments, is ineffective for many soft lens dry eye patients. Even for true dry eye patients, results are variable. Because the majority of contact lens patients aren't tear deficient, this inefficacy should come as no surprise.

Furthermore, obstruction or delay of tear drainage may exacerbate some problems. Delayed tear clearance may increase concentration of residual solution preservatives in tear film, potentially increasing chances of toxicity. There's been some evidence that punctal occlusion may lead to a decrease in tear production. This may explain the observation that the benefits appear to decrease over a few months in many contact lens wearers who initially show improvement.

Rigid lens patients who experience dryness may benefit from punctal occlusion, because they're more likely to have true dryness. For soft lens wearers, you should attempt rehydration, preservative elimination and change to silicone hydrogel material (to minimize evaporation) before considering punctal occlusion. Success with punctal occlusion in soft lens wearers does occur, but you should make the decision to block tear drainage carefully.

Increasing ambient humidity, by use of a room humidifier for example, can prove effective in reducing the evaporation of tears. Goggles or moisture chamber spectacles are also effective, however impractical.

Practitioners often use soft contact lenses as bandages for injured or post-surgical eyes. Use of a soft lens as a fluid reservoir for the dry eye patient is an appealing concept; in practice, however, lenses tend to dry out in the eye after a short while and are prone to falling out. The presence of a contact lens in the absence of normal tear flow may additionally increase the risk of ocular infection. The therapeutic benefits of a soft contact lens in true dry eye patients is minimal and may exacerbate symptoms.

INFLAMMATION AND DRY EYE

Whatever the cause of dry eye -- tear deficiency, evaporation, allergy or reaction to toxins -- the result is an inflammatory reaction. The contact lens wearer with symptoms of dryness is no exception. This patient shows elevated levels of conjunctival antigens and reduced density of goblet cells -- a pattern typical of chronic allergic conjunctivitis. Just as chronic allergy leads to elevation of local immune response and affects the ocular surface, so does contact lens wear in many instances.

Clinically, we can consider the immense relief that both allergy and dry eye patients obtain with topical corticosteroids as circumstantial evidence that local immune processes are at work when symptoms occur.

Clearly, the use of corticosteroids for treatment of contact lens symptomatic dryness, although potentially effective, is contraindicated in any but the most extreme circumstances. We must concentrate our efforts on eliminating the stimulus to inflammation, rather than blocking the inflammatory process.

Dr. Smythe is an associate professor of optometry at Pacific University College of Optometry in Forest Grove, Ore., and is in private practice in Beaverton, Ore.

Pat Caroline is associate professor of optometry at Pacific University College of Optometry and is associate professor of ophthalmology at the Oregon Health University.

Dr. Bergenske is assistant clinical professor of optometry and is chief of the Contact Lens Service at the Pacific University College of Optometry.