The Current State of Extended Wear

BY GREGORY J. NIXON, O.D.
DEC. 1997

Practitioners and patients are often skeptical about the safety of extended wear. But new materials and proper instruction, fitting and follow-up may allow more patients to enjoy this pinnacle of contact lens convenience. Overnight wear of contact lenses has experienced both a rich history and a checkered past. Over the past two decades, the use of contact lenses for extended wear has prompted scientists and clinicians alike to learn more about ocular physiology and corneal immunology.

Leaders in contact lens research (such as CIBA Vision and Bausch & Lomb) continue to develop new lens materials that allow greater oxygen transmission and that minimize surface non-wetting, surface deposition and lens adherence. Modern, modified lens designs, as well as frequent lens replacement and patient follow-up schedules may minimize ocular complications.

Despite these efforts, however, incidence of ocular complications such as corneal edema, microcysts, corneal vascularization, corneal infiltrates, acute red eye and infectious keratitis has limited the success and use of the extended wear modality.

EXTENDED WEAR APPREHENSION PERSISTS

Currently, of the 26 million contact lens wearers in the United States, about four to five million are extended wear patients. These numbers reflect a decline in the frequency of practitioners actively promoting the use of contact lenses for overnight wear. In fact, many practitioners have gone so far as to say that extended wear complications cause a significant public health concern. These concerns were somewhat justified in 1989 when the FDA restricted the number of allowable continuous days of wear from 30 days to seven days.

The literature has cited cases of successful extended wear without serious ocular complication, but complicated cases resulting in irreversible damage and decreased best corrected visual acuity have also been documented. Although no one seems to know the number of these unfortunate occurrences, it is low. Needless to say, a great deal of variability exists among the outcomes of extended wear encounters.

As health care providers, it is our duty to identify and understand the variables that put our patients at risk. Most practitioners embark on each extended wear encounter with great discretion. Success with extended wear depends on appropriately selected patients receiving proper instruction, fitting, and follow-up care.

THE RISKS OF EXTENDED WEAR

We know there are a host of ocular complications that accompany the use of contact lenses. However, the most compelling and feared complication is infectious keratitis. Overnight wear has been identified as the principal risk factor for contact lens related infectious keratitis. The risk increases as the number of nights of continuous wear increases.

Research studies have sought to determine the relative risk of different types of lenses utilized in extended wear regimens. With daily wear RGP contact lenses as a reference (relative risk=1.0), it's estimated that soft lenses used on an extended wear basis increase the relative risk of ulcerative keratitis to 4.1. Fortunately, the widespread use of disposable contact lenses has reduced the prevalence of lens deposits, giant papillary conjunctivitis and solution-related complications. In fact, most extended wear soft contact lens wearers in the United States today use disposable lenses on only a one- or perhaps two-week replacement cycle. Studies on disposable lens extended wear have isolated overnight wearing schedules, not the physical entity of disposable contact lenses, as the single factor that increases the risk of complications.

PATHOPHYSIOLOGY OF EXTENDED WEAR COMPLICATIONS

Understanding the mechanisms that cause ocular complications is essential for the development of preventative measures. In the open eye state, the avascular cornea relies on the ambient atmosphere to supply the oxygen required to fuel its metabolic processes. In the closed eye state, oxygen is supplied mainly from the blood vasculature in the palpebral conjunctiva. The diminished oxygen supply to the cornea resulting from continual contact lens wear results in tissue hypoxia. The hypoxic environment impairs the metabolic rate of the corneal epithelium, resulting in decreased mitotic activity and compromised junctional integrity of epithelial cells.

The hypoxia and a decrease in endothelial pump function causes water retention, resulting in stromal and epithelial edema, characterized by striae and microcysts, respectively (Fig. 1).

FIG. 1: MICROCYSTS.

Prolonged hypoxic stress causes endothelial cells to undergo polymegethism (Fig. 2).

FIG. 2: ENDOTHELIAL POLYMEGETHISM.

The combination of tissue injury from surrounding edema on already weakened existing epithelial cells, coupled with the inability of the epithelium to effectively replenish itself, results in epithelial defects that serve as a sight for potential microbial invasion.

Contact lens adherence caused by hydrogel dehydration, RGP decentration or contact adhesion can severely impair the proper tear exchange needed to jettison epithelial metabolic waste from beneath the contact lens surface. The consequence of this tear stagnation is two-fold. Trapped debris can accumulate on the posterior surface of the lens and provide the architecture for opportunistic microbes to adhere. Also, the increased concentration of antigenic substances can trigger an immunological response. This, combined with the prominence of the limbal vasculature secondary to the induced hypoxia, is a major cause of peripheral corneal infiltrates.

Based on what we know about the development of extended wear-induced complications, contact lens selection and fitting methods should aim to maximize oxygen transmission, tear flow and mucin distribution while reducing lens deposits. Doing so will permit the least amount of compromise to ocular physiology.

FITTING CONSIDERATIONS

Patient selection -- Patient selection is probably the most important and most challenging element in limiting extended wear complications. Recommend as extended wear candidates only successful daily lens wearers who have exhibited compliance with appropriate care systems, wearing times and lens replacement schedules.

RGP wearers are preferred due to the added safety profile of RGP lenses. Patients should also exhibit a justifiable motivation for overnight wear due to vocational demands (such as a physician, nurse or firefighter), avocational needs (such as travel or camping events) or quality of life concerns (continual correction of high refractive error, for example).

Discourage contact lens abusers -- those who avoid caring for their lenses -- from pursuing overnight wear. Patients who smoke are also poor extended wear candidates because studies have shown that smoking further increases the risk of infectious keratitis.

Conduct a thorough examination on all extended wear candidates to detect any anterior segment anomalies. Dry eye, corneal vascularization, corneal staining and lid disease all increase the risk of ocular complications which are compounded in extended wear. Educate all potential candidates on the increased risks associated with extended wear. Each candidate must accept the responsibility of strict compliance, and each must adhere to the "look good, feel good, see good" management philosophy. That is, if redness, pain, photophobia, discharge or a decrease in vision occurs, the patient must cease lens wear and seek immediate care. It's a good idea to obtain a signed informed consent statement and to disseminate written information to supplement patient education.

Soft lens fitting -- Although high water content lenses offer better oxygen transmission than low water lenses, they need to be made thicker for structural integrity. High water, ionic lenses are more susceptible to deposition. Therefore, thin, non-ionic, low water content lenses are ideal for low to moderate myopic refractive errors. Higher water lenses may help maximize oxygen transmission in thick lens designs, i.e., plus lenses and high minus lenses.

In order to maximize tear exchange, I recommend using the smallest diameter lens that achieves limbal coverage. Choosing the base curve that will provide adequate centration and maximize movement will be helpful in preventing tear stagnation.

RGP fitting -- Rigid gas permeable contact lenses offer a physical and a mechanical advantage over hydrogel lenses. Extended wear-approved RGP materials exhibit significantly higher Dk/L values. The mechanical tear pump mechanism furnishes an additional mode of oxygen supply to the underlying cornea. The pump also increases tear exchange, removing metabolic waste and preventing entrapment of debris. These factors plus a lower degree of protein deposition make RGPs the lenses of choice in extended wear. Yet, due to initial adaptation and perhaps some practitioner and patient avoidance of rigid lenses, few patients use RGPs for extended wear. Yet, improved comfort is very rapid with RGP contact lenses.

The fitting philosophy of extended wear RGPs does not differ significantly from that employed for daily wear. Aim for a well-centered, lid attached fit with an alignment fluorescein pattern. Heavy blending of peripheral curves will provide a smooth posterior surface that will prevent deposition and epithelial erosion. A wide, moderate edge clearance will enhance tear exchange and prevent lens seal-off.

FOLLOW-UP SCHEDULE

Frequent and thorough follow-up is critical in the proper care of an extended wear patient. Each visit serves as an opportunity to assess and reinforce patient compliance and to detect potential problems before they progress to major complications. As mentioned previously, all extended lens wearers must first exhibit success with daily wear.

Schedule the first extended wear follow-up following the first night of overnight wear. At the examination, assess the fit to ensure proper lens centration and movement. Then evaluate the cornea for striae, microcysts, infiltrates, limbal vascularization and epithelial staining. If these signs are absent, extended wear may continue with repeat examination in one week, two weeks, one month, three months, six months and every three to six months thereafter. Remind patients at each visit to remove their lenses and seek immediate care if they experience any redness, pain, photophobia, discharge, or decrease in vision.

MANAGEMENT OF COMPLICATIONS

Despite careful patient selection, proper fitting and strict compliance with contact lens care and follow-up, complications will still arise. A wide range of variability exists in individual corneal oxygen demands and physiological requirements. A high-demand cornea will be more prone to show signs of hypoxia such as prominent limbal vascularization (greater than 1.0mm from the limbus in more than one quadrant), significant epithelial staining or edema characterized by microcysts and striae. Keep in mind that highly myopic patients may have greater oxygen compromise peripherally due to significant contact lens thickness.

Even when symptoms are absent, these seemingly mild complications represent a significant compromise to corneal integrity and need to be addressed to prevent progression to a more threatening condition. Have patients discontinue lens wear until corneal integrity is reinstated as evidenced by an intact epithelium and absence of edema. A change to a more permeable lens (thinner design or higher Dk/L) or modification of lens fit to promote more lens movement may avert significant compromise to corneal vitality. If not, it may be necessary to return to daily wear or occasional flexwear.

Severe complications such as corneal infiltration (Fig. 3) and corneal ulceration (Fig. 4) require aggressive treatment due to the potential consequences on visual function.

FIG. 3: CORNEAL INFILTRATES ARE A COMPLICATION OF CONTACT LENS EXTENDED WEAR.

FIG. 4: CORNEAL ULCERS RESULTING FROM CONTACT LENS EXTENDED WEAR REQUIRE AGGRESSIVE TREATMENT.

A corneal ulcer is defined by the presence of corneal infiltrates with an overlying epithelial defect. Ulceration may indicate active microbial infection.

Immune reaction -- Immune reactions present with relatively small (less than 2.0mm), sterile (culture negative) lesions that typically inhabit the peripheral cornea, leaving an area of clear cornea between the lesion and the limbus. You can usually expect minimal to no patient symptoms, minimal to no anterior chamber reaction and mild staining over the lesion. The antigens typically responsible for triggering the immune response are exotoxins produced from staphylococcal organisms. This normal bacterial flora may be present in high concentration secondary to active lid disease, adherence to the contact lens or stagnation of the tear film behind the contact lens.

Therefore, management may include discontinuation of contact lens wear, as well as antibiotic therapy to decrease microbial concentration and prevent infection at the sight of the epithelial defect. Common therapies include Polytrim or a topical fluoroquinolone solution every four hours while awake and an antibiotic ointment (Polysporin or erythromycin) applied to the lid margin t.i.d. The decrease in bacteria and subsequent exotoxin production will arrest the hypersensitivity reaction.

Some practitioners manage the inflammatory response directly with a topical steroid or antibiotic/steroid combination. However, the best guard against infection in the cornea's compromised state is a stand-alone antibiotic used initially, adding a steroid if the immune response persists. Educate patients on the nature of the problem and instruct them to regularly perform hot compresses and lid scrubs to improve hygiene and limit staphylococcal overgrowth.

Infectious corneal ulcer -- An infectious corneal ulcer is characterized by a number of significant signs and symptoms. Patients complain of profuse tearing, marked redness, pain, intense photophobia and sometimes a decrease in vision. A moderate to severe anterior chamber reaction can present with 2 to 4+ cells and/or flare with possible hypopyon formation. The infiltrative lesion is characterized by a well excavated epithelial defect that will stain intensely.

Due to the rapid and sometimes unpredictable nature of the condition, refer any patient with a lesion that impinges on the visual axis to a corneal specialist. These lesions, as well as those within the central six millimeters of the cornea, should be cultured and undergo sensitivity testing to determine the appropriate antimicrobial therapy. Some practitioners choose to treat lesions outside the central six millimeters with broad-spectrum antibiotics and pursue culturing only if no response to treatment occurs. It's best to assume that central or midperipheral corneal infiltrates without an overlying epithelial defect are infectious until proven otherwise. This presentation is likely a pre-ulcer stage where the epithelium has not yet become necrotic.

Studies have shown that a 0.3% fluoroquinolone (Ciloxan or Ocuflox) as a stand-alone medication is equally effective as the hallmark regimen of a combination of fortified antibiotics (cefazolin and gentamicin or tobramycin). Advantages to prescribing a fluoroquinolone versus fortified antibiotics include availability and possible improved patient compliance due to less bottle confusion and less burning and stinging upon instillation. Reports of fluoroquinolone resistance and the possibility of fungal or protozoan infection highlight the value of culture and sensitivity testing at the initial presentation or upon a 24-hour follow-up visit that shows progression of the condition.

In addition to antibiotic therapy, topical cycloplegics and oral analgesics are helpful in managing patient discomfort. Pressure patching when treating any condition in a contact lens patient is contraindicated due to the proliferative environment it affords opportunistic microbes. CLS

ADDITIONAL TIPS FOR REDUCING THE RISK OF COMPLICATIONS

Limiting the nights of continuous wear can help diminish ocular complications. Even though the FDA has approved six nights of continuous wear, recommend overnight wear only when needed, such as over a camping weekend or during the nights a physician is on-call. Instilling rewetting drops throughout the day, and especially at bedtime and upon awakening, aids tear exchange and can help prevent lens adherence. Instruct conventional wear patients to digitally clean and disinfect their lenses at each nighttime removal; instruct disposable lens wearers to replace their lenses at each removal. Advise patients to purchase lens products in the smallest size available to avoid solution contamination. Instruct them to replace their lens cases frequently, and to always clean them with hot water and allow them to air dry in between uses. Dr. Nixon is a clinical instructor at The Ohio State University College of Optometry, Columbus.