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New contact lens materials, solutions expand options for dry eye patients
Contact Lenses and Eyewear
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Dry eye affects an estimated 12 million individuals in the United States, and the disorder has generally been considered a contraindication to contact lens wear. On a normal eye with adequate lacrimal patency, the physical presence of a contact lens can induce both physical and physiological changes that stimulate dry eye signs and symptoms. The underlying concern in a true dry eye patient is that a contact lens would exacerbate the condition.
Advancements in material chemistry, lens replacement modalities and care systems have made it possible to offer an alternative to spectacles for the dry eye patient. In addition to the ability to correct ametropia, in some cases, a contact lens may have a therapeutic benefit by acting as a bandage and providing protection against further desiccation. Contact lens design and material selection is focused on maintaining corneal and conjunctival physiology, limiting dehydration and considering all factors that can disrupt tear film architecture or exacerbate inflammation, such as components in lens care regimens.
Dry eye differentiation
Disruption of any of the three layers of the tear film can result in signs and symptoms of dry eye disease. The National Eye Institute has classified dry eye disease into two categories: aqueous layer deficiency and evaporative deficiency. This can be further simplified as either not enough tears are produced or what are produced disappear 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 then leads to excessive evaporation, eventually resulting in ocular inflammation.
Pathologic dry eye
The most serious form of dry eye is 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, as well as individuals taking ocular or systemic medications that affect tear-film stability or production. Exposure keratopathy secondary to lagophthalmos, Bell’s palsy or neurotrophic disease are also causes of true dry eye.
Evaporative dry eye is typically the result of ocular surface disease, blink disorders and conditions that affect lid/globe congruity. These include conditions that cause lipid or mucin layer deficiency, such as meibomianitis, blepharitis, ocular rosacea, goblet cell loss from vitamin A deficiency, Stevens Johnson syndrome, pemphigoid, trachoma and chemical burns. Pathologic causes of a decrease in tear production include Sjogren’s syndrome, vitamin A deficiency, age-related hyposecretion, lacrimal gland excision or damage as a result of sarcoidosis or cancer, sensory motor loss, and conjunctival scarring conditions, such as pemphigoid and burns.
In addition, there are several classes of systemic medications that can compromise tear-film production. Finally, chronic allergic conjunctivitis and collagen vascular disorders such as scleroderma, lupus and rheumatoid arthritis can also cause dry eye disease. From a diagnostic standpoint, pathologic cases are typically the only form of dry eye that have a definitive correlation between objective testing and subjective symptoms. These highly symptomatic individuals have reduced tear break-up time, tear production deficiency (as measured by the Schirmer’s test) or ocular surface damage in the form of conjunctival or corneal staining observed with rose bengal, sodium fluorescein or lissamine green.
Marginal dry eye
A second form of dry eye observed in non-contact lens wearers is commonly referred to as marginal dry eye. These individuals have symptoms of dry eye; however, objective testing often is inconclusive and does not reveal definitive signs of the disorder. The marginal dry eye patient frequently complains of dry eye symptoms that manifest late in the day and increase in severity during the evening hours.
Symptomatic dry eye
Finally, there is the symptomatic dry eye observed in contact lens wearers that has been given several different names including contact lens-induced dry eye or contact lens-induced sicca syndrome. Both by subjective complaint and physical findings, the “dry eye” contact lens patient differs significantly from the true dry eye patient. Most often, the contact lens patient has neither complaint of ocular dryness nor clinical signs of dry eye when not wearing lenses, but finds that symptoms of dryness limit his or her ability to comfortably wear lenses.
Silicone hydrogels, specialty designs
Silicone hydrogels have many advantages for the dry eye patient regardless of the cause of dry eye. These are low-water content, high-oxygen permeable materials for which evaporation and dehydration appear to be significantly less of a problem than with conventional hydrogels. PureVision (36% water, Bausch & Lomb, Rochester, N.Y.) and Focus Night & Day (24% water, CIBA Vision, Duluth, Ga.) are reported to provide relief for many patients suffering from dryness symptoms with conventional soft lenses. As such, they may make sense for the true dry eye patient.
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 and associated inflammatory responses. Likewise, the successful use of silicone hydrogel lenses in some patients with dryness symptoms may be attributable to the increased oxygen.
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Recently, Focus Night & Day received Food and Drug Administration approval for use as a therapeutic contact lens, in part because complications secondary to hypoxia are nearly non-existent with the high-Dk material. The lens can successfully act as a bandage without compromising corneal physiology and even minimize chronic desiccation with conditions that cause exposure keratopathy. Additionally, in cases of filamentary keratitis, the mechanical presence of the contact lens can help disrupt existing filaments and prevent proliferation of new strands.
Newer materials that dehydrate significantly less than conventional designs, such as the Proclear (CooperVision, Fairport, N.Y.) and Extreme H2O (Hydrogel Vision, Sarasota, Fla.), have been developed and perform well in clinical practice. These should be considered in cases where the fit or long-term comfort of a silicone hydrogel is unsatisfactory.
Finally, if significant conjunctival anomalies or lid disruption are present, custom large-diameter hydrogel lenses are available to provide more extensive ocular protection. The Super Nova Sphere and Asphere (Innovations in Sight, Front Royal, Va.), FlexLens Custom Sphere (X-Cel Contacts, Duluth, Ga.) and Kontur Custom (Kontur Kontact Lens Co., Richmond, Calif.) can be specified in diameters up to 22 mm.
Corneal and specialty GP designs
If limiting dehydration is an answer for the dry eye patient, then gas-permeable (GP) lenses offer the ultimate in this regard. GPs provide the benefits of essentially no evaporation, no preservative uptake and high oxygen transmission. For the marginal dry eye patient, corneal GPs can be a successful alternative to hydrogels and should be considered, particularly where other attempts fail.
A recent addition to the GP market is the Hydro2 lens material (Innovisions). The Hydro2 has a low wetting angle (<5), and in the presence of water, solutions or the tear film, the surface becomes hydrophilic. This is not a surface-coated or treated lens. With a simple 12- to 24-hour soak in a conditioning solution, the surface will regenerate if scratched, modified or dried out. The lens manufacturer recommends the use of either Lobob Optimum or Alcon Unique-pH lens care regimens to maintain wettability and optimize the surface characteristics.
Another option for the extreme case of dry eye where extensive keratinization of the ocular surface and loss of lid structure (such as in advanced Stevens Johnson syndrome) cause excessive discomfort is the high-Dk GP scleral shell. Custom large-diameter GP lenses are available from Innovations in Sight and the Boston Scleral Lens Foundation. Because they do not compete with the ocular surface for hydration, these large (15 mm to 24 mm) GP lens designs can provide a dramatic improvement in ocular comfort and external signs.
Lens care issues
When managing a dry eye patient with contact lenses or problem-solving complaints of dryness in any individual, contact lens solutions should be given the same consideration as the lens design or material. It is common practice to specify preservative-free artificial tear preparations for our dry eye patients, and it is prudent to consider preservative-free disinfection systems for these same individuals.
Several studies have shown that lens care regimens preserved with polyaminopropyl biguanide (PHMB) have been identified as causing corneal staining when used with a variety of lens materials including hema-based hydrogels, silicone hydrogels and GP polymers. (Pritchard et al.Contact Lens and Anterior Eye 2003;26:3-9; and Jones et al. Optom Vis Sci 2002;27:12.) Researchers in Denmark have documented increasing tarsal plate hyperemia with the use of some multipurpose disinfection systems. This indicates that specific multipurpose solutions may be an irritant in some cases, as opposed to strictly the presence of a contact lens.
Another element of one-bottle solutions that must be considered suspect in tear-film disruption is the surfactant action of these products. Surfactants, which dissolve lipids and mucins, could potentially cause tear evaporation, disrupt cell membranes and allow preservatives to further react with the surface cells. Therefore, for the true dry eye patient, the classic peroxide-based lens care regimens such as AoSept (CIBA Vision) and Ultracare (AMO) or ultraviolet disinfection (Purilens) provide the least potential for exacerbating or introducing new sources of inflammation. Likewise, preservative-free rewetting drops are also recommended, such as Lens-Plus Rewetting Drops (AMO), Refresh Contacts (AMO), ReNu MultiPlus Preservative Free Lubricating and Rewetting Drops (Bausch & Lomb) and TheraTears preservative-free (Advanced Vision Research).