RGP EXTENDED WEAR
Revisiting RGP Extended Wear
By Brian Pall,
Although RGP extended wear is not
a new modality, new technology makes it worth a second look.
In the ongoing quest to provide our patients with the ideal answer to correcting their refractive errors, the practitioner is forced to weigh the advantages and disadvantages that accompany the available options.
The answer to this age-old dilemma must be an option that from both the patients' and doctors' perspectives is convenient, safe and affordable while at the same time providing excellent visual acuity. Though rigid gas permeable (RGP) extended wear is definitely not a new modality, new advances in technology and research makes it very deserving of another look.
Although RGP extended wear was initially reported by Garcia for aphakes in the mid-1970s, it wasn't until 1983 that Levy reported successful cosmetic RGP extended wear in his elderly myopic patients. During this same time period, hydrogel lenses received FDA approval for extended wear, and their resulting popularity among patients and practitioners was skyrocketing. However along with the overnight wear of soft contact lenses came the increase in reports of contact lens complications such as contact lens associated red eye (CLARE) and microbial keratitis. These reports somewhat tempered public demand for the extended wear modality. But research showed evidence that reducing hypoxic corneal stress may dramatically reduce the incidence of adverse events. Thus the focus among lens manufacturers shifted to developing contact lens materials of increasing oxygen permeability, or Dk values.
Rigid gas permeable lens manufacturers were able to easily achieve much higher Dk values as compared to their hydrogel counterparts. Therefore interest in RGP extended wear grew. In 1986, the FDA approved RGP extended wear in the United States.
Despite this long-standing approval, over 85 percent of contact lens wearers are currently wearing their contact lenses on a daily wear modality. Most of these patients claim that they would prefer extended wear, but they are afraid of potential adverse reactions. Fitting these patients into rigid gas permeable extended wear provides the convenience of full-time correction and superior optical clarity with a reduced risk of clinically significant complications.
The inherent characteristics of RGP lenses make them the most logical choice when fitting a patient in the extended wear modality. RGP lenses provide a smooth optical surface that often results in a sharper visual image to patients in need of both spherical and astigmatic corrections. RGP lenses tend to be easier to handle and are extremely durable. With the advent of fluorosilicone acrylate materials, the modern generation RGP lenses have combined superior oxygen permeability with effective deposit resistance and wettability. For patients who have adapted to them, RGP lenses are extremely comfortable, providing long-term wearing schedules with minimal symptoms of dryness. While strict compliance with replacement schedules is essential with hydrogel contact lenses, extended wear RGP lenses often do not require replacements for many months. With the decreased incidence of serious complications that are associated with RGP lenses, patients are less likely to jeopardize their ocular health if their compliance occasionally slips from their prescribed wearing schedule.
Microcycts, frequently seen with hydrogel extended wear,
are far less common with RGP extended wear.
In this very time-demanding world, the added convenience of not needing to clean the lenses on a nightly basis is often much appreciated. Patients whose occupations and lifestyles demand contact lens correction with minimal maintenance find RGP extended wear an ideal solution.
Patients are often surprised with how comfortable their eyes feel after their first of night of RGP extended wear. They often admit that they expected their eyes to feel irritated and dry in the morning but instead rarely have any lens awareness at all. Patients also fear lens decentration while they sleep but this too is an extremely rare occurrence.
While convenience is a paramount issue, patients are also very concerned with the health of their eyes. Most have been repeatedly warned about the detrimental effects that sleeping in their lenses will have on their eyes. Studies have shown that overnight corneal edema secondary to RGP wear resolves much quicker than swelling caused by hydrogel extended wear due to the
oxygen-rich tear layer and higher Dk/L values provided by most RGP lenses. Practitioners who are aware of the
potential risks associated with extended wear and are able to successfully manage, or even prevent, such complications can be confident in reassuring their patients that the risk of an adverse event with overnight RGP lens wear is minimal.
Vascularized limbal keratitis may prohibit RGP
RGP Extended Wear Candidates
The most ideal candidates for RGP extended wear are not always obvious. The clinician must be attuned to those characteristics that predispose a patient to RGP extended wear success.
Obviously, patients are more likely to accept the extended wear modality if they already have an interest or are highly motivated to sleep in their lenses. Often times, practitioners neglect to ask these questions in their case history and potential extended wear candidates are never identified. Inquiring about a patient's occupational and recreational demands is another good technique to screen for extended wear patients. However, this line of questioning often lacks the details needed to get a complete and accurate picture of the patient's true lifestyle. Therefore, developing a comprehensive pre-examination patient information sheet with appropriate questions can prove to be very beneficial in providing clues into the interests of your contact lens patients.
Try not to rule out the extended wear modality to patients solely because of their age. Both college students with their unorthodox schedules and some senior citizens with reduced fine motor skills have found their extended wear RGP lenses to be extremely liberating.
Patients who inquire about refractive surgery are also potential candidates. RGP extended wear should be introduced to them as another viable option. Often they are grateful for being made aware of a non-surgical method that will provide full-time correction with superior optical clarity.
While modern-generation RGP extended wear lenses are among the safest available, there are still some potential risks that clinicians must be aware of in order to ensure maximum comfort and safety to their patients.
Oxygen transmissibility of a contact lens is a major factor in influencing the potential risks associated with RGP extended wear. The landmark study by Holden and Mertz established that a lens needs to have a minimum Dk/L value of 34 for an eye to recover within a few hours from overnight lens-induced edema. Ideally, values should be above 87 Dk/L units to achieve the goal of no excess overnight lens-induced swelling. Even though the Dk/L values of many RGP lenses far exceed those measured in hydrogel lenses, few actually measure up to the ideal value. RGP extended wear patients are not immune from hypoxia-induced corneal side effects that include corneal edema, epithelial microcysts and endothelial morphological changes.
Compared to the obvious central cornea clouding induced by PMMA wear, corneal edema secondary to modern RGP materials is quite subtle. Any overnight swelling that does occur will resolve rapidly upon awakening and may likely be undetectable within an hour. If these chronic hypoxic conditions are allowed to continue, the long-term health of the cornea may be ultimately compromised.
Microcysts are tiny refractile lesions that are often described as bundles of cellular debris. They originate from the deep epithelial layers and eventually migrate to the corneal surface. Microcysts are generally an indicator of chronic corneal hypoxia or other metabolic disorders and are usually detected after several weeks or months of extended wear. Clinical trials have reported microcystic changes ranging from seven to 35 percent in enrolled subjects. This seems to support the need for frequent follow-up visits to detect which patients have higher corneal oxygen demands.
It has been widely accepted that hypoxia will result in altering the size and shape of corneal endothelial cells. While the role that RGP extended wear plays on polymegathism and pleomorphism is not fully understood, some research suggests that higher Dk/L lenses can result in fewer morphological changes. The controversy that still remains is if these cellular changes result in any clinically significant complications.
Staining from posterior surface deposits.
Inferior edge liftoff and staining.
Other potential risks with RGP extended wear involve the fitting characteristics of the lens. One of the more serious complications is lens adherence, characterized by a non-mobile lens upon awakening. Although the incidence of clinically significant lens adherence ranges between 10 to 22 percent, the consequences can sometimes lead to corneal distortion or even ulceration. Like corneal edema, actual lens adherence is often undetected by clinicians unless examinations are performed soon after awakening. However, lens adherence may cause a characteristic inferior arcuate staining pattern, and the astute clinician will discover this subtle finding with careful slit lamp examinations.
Peripheral corneal desiccation (3 o'clock and 9 o'clock staining) is another risk that is generally associated with an inappropriate RGP lens design or fit. If the localized drying is left unchecked, vascularized limbal keratitis or corneal thinning may occur.
Corneal molding has also been widely reported in the literature with the trend showing an increased flattening of the steeper corneal meridians after RGP extended wear. The resultant effect is an overall reduction in the corneal toricity. With mild corneal molding there appears to be no detectable structural changes or reduction in visual acuity.
Another benign but notable consequence of RGP extended wear is the development of an upper lid ptosis by several subjects as reported by Fonn and Holden (1988). Though the observed ptosis resolved after discontinuing lens wear, it might be a cosmetically unacceptable side effect for some patients.
Minimal edge lift.
Although the potential for adverse events to occur exists within the RGP extended wear modality, the chances of having these side effects become clinically significant are actually quite rare. This can be mostly attributed to the advent of higher Dk lens materials, better fitting techniques and frequent follow-up visits.
Clinical trials of increasingly higher Dk RGP lenses have shown that the incidence of serious complications have become almost negligible. Ichijima (1992) reported that as RGP oxygen transmissibility was increased, the swelling and desquamation of superficial epithelial cells was no longer observed. Practitioners should always consider a high oxygen permeable lens material when fitting an RGP extended wear modality.
Contact lens fitting experience has had a dramatic impact on increasing the number of successful RGP extended wear patients. The most relevant pointers involve reducing lens adherence and peripheral corneal desiccation. Swarbuck and Holden (1996) reported a higher frequency of lens adherence in those patients with thinner corneas, greater eyelid tension and low amounts of corneal astigmatism. Additionally, Schnider (1988) showed that those patients with increased baseline conjunctival hyperemia, viscous tear films, and poor lens centration and movement may be more prone to significant 3 o'clock and 9 o'clock staining. Identifying these patient characteristics prior to fitting contact lenses allows the practitioner to customize the care needed for extended wear success.
Finally, the most important way to prevent adverse events from RGP extended wear is to schedule frequent contact lens check-ups for your patients. Quite literally, corneal complications that are attributed to the RGP extended wear modality don't just happen overnight. Rather, the changes occur over the long-term. Therefore quarterly office visits will allow for mild corneal changes to be detected earlier and the appropriate changes in lens material or fitting characteristics to be made.
- Minimize Peripheral Corneal Desiccation
- Make sure the lens has a heavy blend
- Widen or flatten the peripheral curve system
- Taper the anterior edge if edge thickness is excessive
- Reorder lens with decreased edge lift if lift is
Minimize Lens Adhesion
- Reduce lens diameter
- Fit with minimal apical clearance (0.25 to 0.50 steeper
than fit K)
- Ensure moderate blending of the transition zones
- Design the lens with wide and flat peripheral curves
- Avoid lens care solutions and medications that
decrease aqueous volume
- Use of rewetting drops prior to sleep
I recommend that patients be successfully fit in daily wear RGP lenses for at least four weeks before considering them for extended wear. Successful daily wear should constitute a minimum of 10 hours per day asymptomatic wearing time with no signs of corneal compromise. Consider appropriate extended wear lens designs when fitting a patient into RGP lenses for the first time so that there is an easy transition to extended wear with no additional orders.
Fitting RGP extended wear contact lenses requires only the most basic in contact lens fitting knowledge. Selecting a material that is FDA-approved for extended wear is of utmost importance (Table 1). With the introduction of modern fluorosilicone acrylate and fluro-siloxanyl styrene lenses, high Dk values are possible without sacrificing the wettability or deposit resistance of the lenses. Try to achieve a lid attachment fit with lens centration and minimal apical alignment. The peripheral curve system and lens positioning should demonstrate a good tear pump without lens adherence or excessive movement.
After the first night of extended wear, practitioners should attempt to examine the patient early the next morning to assess any corneal swelling or other hypoxic effects. Subsequent follow-up visits should be performed one week, one month and three months after the first night of wear. Contact lens check-ups should then be scheduled every three months after extended wear has been deemed successful. Perform careful corneal slit lamp examinations with fluorescein dye at every follow-up visit to evaluate corneal health.
Keratometry readings will show if significant corneal molding is taking place and an inconsistent manifest refraction will reveal if any visual distortion has occurred secondary to lens wear. If at any point significant signs of corneal hypoxia or mechanical trauma are noted, extended wear should be immediately discontinued.
Currently, the maximum wearing schedule approved by the FDA for RGP extended wear is seven days and six nights. Lenses must then be removed for the seventh night and left out of the eye for at least eight hours. Upon lens removal, patients should perform a digital cleaning with an appropriate RGP-approved disinfection system and soak the lenses overnight. I also highly recommend a monthly enzymatic treatment to help keep the surfaces of the lenses deposit-free. Rewetting drops often prove to be beneficial to some patients especially first thing in the morning in order to lubricate the lens and promote morning comfort. Using rewetting drops immediately before bed also seems to help with preventing lens adherence while asleep.
The Future of RGP Extended Wear
Although the Menicon Z lens was recently approved for six nights of extended wear, a multi-center clinical trial is presently underway to investigate its safety in a 30-day extended wear modality. If successful, the Menicon Z lens could become the only currently available contact lens material to be granted approval and made available for 30-days of continuous extended wear.
Other manufacturers are designing higher Dk RGP lens materials to be worn on a frequent replacement schedule. Researchers have found that the incidence of lens adherence, corneal staining and mucus coating was significantly less on those patients who replaced their RGP extended wear lenses every three months.
RGP extended wear is a wearing modality that has much to offer to both patient and practitioner. As technological advances continue within the contact lens manufacturing community, the popularity and interest in RGP extended wear will undoubtedly rise. The result of combining full-time contact lens wear with the superior qualities of RGP lenses may be the elusive answer to the age-old dilemma we have been looking for. CLS
References are available upon request to the editors of Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #65. (Be sure to have a fax number ready.
Dr. Pall is a 1999 graduate of The Ohio State University College of Optometry. He is a second-year Cornea and Contact Lens Advanced Resident/Advanced Practice Fellow at The Ohio State University College of Optometry.
TABLE 1Approved Rigid Gas Permeable Extended Wear Materials
|Paragon Vision Science
Contact Lens Spectrum, Issue: November 2000