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Applications for 30-Day Continuous Wear SH Lenses

How today's continuous wear contact lenses can play a role in your practice.

HEIDI WAGNER, O.D., M.P.H., FORT LAUDERDALE, FLA.

The initial zenith of 30-day contact lens wear arrived in the 1980s. Although eyecare practitioners initially embraced continuous wear, anecdotal reports and epidemiological evidence emerged warning that patients who wore their lenses for up to 30 consecutive days were at greater risk for ocular complications than were those who wore lenses with traditional wear schedules.

A 1989 New England Journal of Medicine report estimated the incidence of ulcerative keratitis among those in extended-wear soft lenses to be 20.9 per 10,000; while that figure was 4.1 per 10,000 among those in daily-wear soft lenses.¹

Also, researchers found that patients who wore extended-wear lenses overnight had a 10-fold to 15-fold greater risk of ulcerative keratitis compared with patients in daily wear lenses.²

In 1989, the Food and Drug Administration (FDA) reduced contact lens wearing time to a maximum of one week, citing the relative risk of keratitis when patients wore lenses overnight.

Although hypoxia took the blame for these corneal ulceration problems, researchers recognized that this was a case of "guilt by association," as limited evidence indicated hypoxia's involvement.³ Higher Dk lens materials became the Holy Grail in the quest for continuous wear lenses. High Dk silicone hydrogel lenses (SH) emerged worldwide in 1999. The FDA approved the first SH lens for 30-day continuous wear in 2001. To date, two SH lenses have received FDA-approval for 30-day wear: Night & Day (lotrafilcon A, CIBA Vision) and PureVision (balafilcon A, Bausch & Lomb). A third lens, Menicon Z (tisilfocon A, Menicon Co. Ltd), is currently the only hyper-Dk rigid gas-permeable (GP) lens material approved for 30-day wear.

This Strategic Skill Builders Continuing Education article is made possible by a grant from CIBA Vision. The content is independently produced by Optometric Management. Please submit your answer card by May 15, 2009.

Lens materials

Adding silicone to hydrogel lenses increases its oxygen permeability, or Dk. In low-Dk soft lenses made from hydrogel polymers, the oxygen permeability increases in proportion to the water content. In SH lenses, this relationship is less predictable because low water content SH lenses generally exhibit a high Dk.

The water content of a lens varies indirectly with its modulus. In the context of lens materials, modulus describes the lens material's elasticity or its resistance to deformation. Thus, high modulus materials typically result in stiff contact lenses. In addition, lens thickness also influences stiffness — that is, thick lens materials are typically stiffer than thin materials. A high modulus lens material is easier to handle and less easily inverted than a low modulus lens; however, it's less likely to conform to the shape of the cornea.

Silicone is inherently hydrophobic and associated with poor surface wettability — a property that may translate into lens-associated discomfort for some patients. Contact lens manufacturers have made technological advancements to enhance wettability, including plasma oxidation, surface treatments and internal wetting agents.

In GP materials, it's worth noting that increasing the proportion of silicone is associated with material instability and poor surface wetting. Consequently, other manufacturing methods have emerged for GP lenses, including the use of purified silicone, among the development of other high Dk monomers.

Fitting tips

Precursors for successful 30-day continuous wear typically include good systemic health, normal biomicroscopic examination and a history of patient compliance. Smoking is a relative contraindication to continuous wear. Young patients, particularly males, appear to be at greatest risk for adverse events associated with continuous contact lens wear.^4,5

Fitting SH lenses is similar to traditional low-Dk lens materials, except that you must accommodate for the higher modulus of the new lenses approved for continuous wear. These materials exhibit more movement than the prior generation of low-Dk lenses prescribed for overnight wear. Lens fluting or edge stand off is associated with edge awareness and ocular surface damage. You may observe these if the lens-to-cornea fitting relationship is flat. A change in base curve radius or lens type easily remedies lens fluting. PureVision and Night & Day have a higher modulus relative to older generations of SH lenses.

Patient education is a precursor to good compliance. Carefully review with the patient lens storage and care, including the use of appropriate rewetting agents. Strictly reinforce wearing and replacement schedules. Overnight wear is contraindicated with illness. Discourage swimming in lenses. Reinforce that patients self-assess vision, ocular comfort and appearance on a daily basis. Patients should demonstrate proficiency in lens insertion and removal before they leave your office. Ensure patients have back-up spectacles. Examine all patients for signs of hypoxia the morning after the first night of lens wear, regardless of previous wearing history, with additional follow-up appointments scheduled as needed. Strongly recommend to patients annual comprehensive examinations with six-month follow-up schedules.

Other applications

In 2007, more than half of new soft lens fits in the United States were with SH lenses.⁶ Practitioners have embraced SH lenses for a broad spectrum of wearing schedules. I've found that the most likely reason SH lenses may not be appropriate for a particular patient is that parameter availability is limited.

Daily and/or flexible wear may be the best option for patients who have a history of hypoxic events. Typically, you can eliminate limbal injection by refitting patients from low-Dk to high-Dk lens material. SH lenses provide the ideal carrier for piggyback lens systems prescribed for keratoconus and for post-surgical lens fitting. Currently three brands are FDA-approved for such uses. They are: Acuvue Oasys with Hydraclear Plus (senofilcon a, Vistakon), PureVision (balaficlon A, Bausch & Lomb) and Night & Day.

A recent literature review suggests that dry eye symptoms have an inflammatory origin and, as a result, symptomatic patients may benefit from being refit into high-Dk lens materials.⁷

Ocular anomalies

As anticipated, the introduction of high-Dk lens materials has reduced adverse events associated with hypoxia.⁸ The frequent replacement schedules that have emerged since the first generation of extended wear lenses have lessened events associated with lens spoilage. While solution interaction with continuous wear is now reduced, interactions can still occur. Furthermore, certain ocular anomalies are associated with SH lenses and are consequently associated with 30-day continuous wear.

You should understand the potential for mechanical and inflammatory events and their possible recurrence and review their underlying etiology and management.⁹

Epithelial microcysts have long been associated with continuous wear with low-Dk contact lenses. Recently, researchers recognized that subjects who are refit from low-Dk to high-Dk lenses may exhibit an initial increase in the number of microcysts after one week. However, microcyst levels return to normal through a one- to three-month period.¹⁰ While microcysts are traditionally associated with hypoxia, this phenomenon appears to be associated with altered ocular metabolism. Myopic creep appears to be largely eliminated by high-Dk lens materials. Patients whom you refit from low-Dk to high-Dk lens materials may experience a hyperopic shift.¹¹

Other entities traditionally associated with hypoxia, such as corneal neovascularization, limbal and bulbar hyperemia, epithelial erosions and corneal thinning, have been minimized with the introduction of high-Dk lens materials.

Giant papillary conjunctivitis (GPC) — an adverse event associated with the early days of extended wear lenses — is still present, despite more frequent lens replacement. However, today's GPC is more focal in presentation when compared with GPC in low-Dk hydrogel lenses, presumably as the result of a mechanical etiology.

Superior epithelial arcuate lesions (SEALS), which are thought to be of mechanical origin, are rarely associated with the low-Dk lenses often prescribed during the previous decade; thus, SEALS have reemerged with SH lenses, particularly with high modulus materials.^12,13 Manage SEALS by temporarily discontinuing lens wear and refitting the patient in a different material.

Researchers hypothesized that mucin balls are produced by the mechanical shearing of the tear's mucin layer into round balls that become trapped between the contact lens and corneal epithelium. Mucin balls are generally not of any physiological or visual consequence.

While solution incompatibility for patients who strictly adhere to a 30-day continuous wear is of modest concern, you should recognize the potential for interaction between care products and SH lens materials, as this interaction has been reported in conjunction with corneal staining.

Increased lipid deposits are associated with SH lenses. Patients can minimize these deposits by replacing lenses at the prescribed frequency. However, certain patients may need to experiment with different lens materials and/or care regimens before finding the right combination.

Contact lens acute red eye (CLARE) is an acute inflammatory response to gram-negative bacteria, such as Pseudomonas aeruginosa. It is associated with subepithelial infiltrates and conjunctival hyperemia. It generally is self-limiting and resolves upon lens removal.

Contact Lens Peripheral Ulcer (CLPU) is an inflammatory response to gram-positive bacteria (Staphylococcus aureus). CLPU is often self-limiting with temporary discontinuation of lens wear. Therapeutic regimens for CLPU range from artificial tears to a combination antibiotic/steroid, if you choose to implement them.

Recently, investigators have reported that corneal staining and limbal redness may predict the subsequent development of an infiltrative event among continuous wear lens patients.¹⁴ A recent literature review suggested that SH lenses prescribed for 30-day continuous wear demonstrate about a two-fold greater risk for corneal inflammatory events when compared with low-Dk lenses prescribed for seven days.¹⁵ Despite this observation, the same authors promoted SH lenses for both continuous and daily wear based upon the benefits described previously.

Other investigators countered that practitioners exhibit a predilection for fitting "high-risk" patients into SH lenses, thus increasing patient risk factors at baseline in at least some of the SH lens studies analyzed.¹⁶

Further study will likely better define the relationship between SH lenses and inflammatory events.

Looking back and ahead

A post-market surveillance study mandated by the FDA followed the experiences of more than 6,000 people who were prescribed Night & Day for up to 30 nights of consecutive wear, for one year. The overall annual rate of presumed microbial keratitis was 18 per 10,000. Two of the participants developed presumed microbial keratitis with loss of visual acuity, for an annual rate of 3.6 per 10,000, and there were an additional eight cases without loss of visual acuity at an annual rate of 14.4 per 10,000. You can conclude that the incidence of loss of visual acuity due to microbial keratitis among users of the SH lenses is low but that the overall rate of presumed microbial keratitis with 30-day SH continuous wear lenses is similar to previous estimates of risk with overnight lens wear.¹⁷

You should compare these risks with the risks associated with refractive surgery for that group of patients who ultimately choose either extended wear lenses or refractive surgery to correct their vision. Continuous wear lenses provide an alternative for patients who are concerned about a large initial financial investment and/or are unwilling to confront the risk of surgery. With continuous lens wear, vision expectations are predictable, and visual symptoms, such as night-time glare, are unlikely. Because lens correction is reversible, it provides additional alternatives through time — particularly for patients whose vision needs may change through time.

The evidence supports continued growth of SH lenses and other high-Dk lens materials. Manufacturers will continue to introduce technological advancements to enhance wettability and comfort. Lens materials that minimize microbial adhesion and further diminish adverse events, such as microbial keratitis, are on the horizon. Expanded parameters should increase the potential candidates for SH lens wear for both daily and 30-day continuous wear.

Contact lenses provide convenience, reversibility and a reasonable margin of safety for daily and continuous wear. You can prescribe lens materials for 30-day continuous wear to promote a lifetime of healthy contact lens wear. OM

1. Poggio EC, Glynn RJ, Schein OD, , et al. The incidence of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. N Engl J Med. 1989 Sep 21;321:779-83.

2. Schein OD, Glynn RJ, Poggio EC, et al. Microbial Keratitis Study Group. The relative risk of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. A Case-Control Study. N Engl J Med. 1989 Sep 21;321:773-8.

3. Efron N. Will increased oxygen really decrease extended wear infections? Optom Vis Sci. 1999 Jul;76(7):435-6.

4. Chalmers RL, McNally JJ, Schein OD, et al. Risk factors for corneal infiltrates with continuous wear of contact lenses. Optom Vis Sci. 2007 Jul;84(7):573-9.

5. Morgan PB, Efron N, Brennan NA, et al. Risk factors for the development of corneal infiltrative events associated with contact lens wear. Invest Ophthalmol Vis Sci. 2005 Sep;46(9):3136-43.

6. Contact Lens Spectrum. Morgan PB, Woods CA, Knajian R, et al. International contact lens prescribing in 2007. www.clspectrum.com/article.aspx?article=10 1241. Accessed July 11, 2008.

7. Dillehay SM. Does the level of available oxygen impact comfort in contact lens wear?: A review of the literature. Eye Contact Lens. 2007 May;33(3):148-55.

8. Donshik PC. Extended wear contact lenses. Ophthalmol Clin North Am. 2003 Sep;16(3):305-9.

9. Donshik P, Long B, Dillehay SM, et al. Inflammatory and mechanical complications associated with 3 years of up to 30 nights of continuous wear of lotra-filcon A silicone hydrogel lenses. Eye Contact Lens. 2007 Jul;33(4):191-5.

10. Keay L, Jalbert I, Sweeney DF, Holden BA. Microcysts: clinical significance and differential diagnosis. Optometry. 2001 Jul;72(7):452-60.

11. Dumbleton KA, Chalmers RL, Richter DB, Fonn D. Changes in myopic refractive error with nine months' extended wear of hydrogel lenses with high and low oxygen permeability. Optom Vis Sci. 1999 Dec;76(12): 845-9.

12. Dumbleton K. Noninflammatory silicone hydrogel contact lens complications. Eye Contact Lens. 2003 Jan;29 (1 Suppl): S186-S9; discussion S190-1, S192-4.

13. O'Hare N, Stapleton F, Naduvilath T, et al. Interaction between the contact lens and the ocular surface in the etiology of superior epithelial arcuate lesions. Adv Exp Med Biol. 2002;506(Pt B):973-80.

14. Szczotka-Flynn L, Debanne SM, Cheruvu VK, et al. Predictive factors for corneal infiltrates with continuous wear of silicone hydrogel contact lenses. Arch Ophthalmol. 2007 Apr;125(4):488-92.

15. Szczotka-Flynn L, Diaz M. Risk of corneal inflammatory events with silicone hydrogel and low dk hydrogel extended contact lens wear: a meta-analysis. Optom Vis Sci. 2007 Apr;84(4):247-56.

16. Dillehay SM, Bergenske P, Long B. To the editor: risk of corneal inflammatory events with silicone hydrogel and low Dk hydrogel extended contact lens wear: a meta-analysis.[comment]. Optom Vis Sci. 2007 Sep;84(9):924-5; author reply 5-6.

17. Schein OD, McNally JJ, Katz J, et al. The incidence of microbial keratitis among wearers of a 30-day silicone hydrogel extended-wear contact lens. Ophthalmology. 2005 Dec;112(12):2172-9.

Dr. Wagner is associate professor and chair, Department of Clinics, at Nova Southeastern University College of Optometry in Fort Lauderdale, Fla. She is a member of the Speakers Alliance for Alcon Laboratories. Through the past five years, she has received additional sponsorship from CIBA Vision. Dr. Wagner has no direct financial interest in any of the products mentioned in this article. e-mail her at wagner@nova.edu.