Article Date: 1/1/2002

SILICONE HYDROGEL

A Clinical Look at a Silicone Hydrogel Extended Wear Lens

John McNally, OD, FAAO, and Curtis McKenney, OD
January 2002

Compare a high Dk silicone hydrogel lens worn for 30 days to a low Dk conventional hydrogel lens worn for six nights.

Have you ever heard a colleague say, "I'm not an extended wear practitioner?" This position reflects a troublesome history of extended wear with low Dk lenses that caused significant corneal hypoxia. However, with new alternatives available, it's time to rethink our approach to extended wear.

With the FDA approval of CIBA Vision's Focus Night & Day (lotrafilcon A), the first approval of a silicone hydrogel lens for up to 30 nights of continuous wear, we now are able to offer our patients a choice for the convenience and freedom of round-the-clock vision correction that many desire. This desire for round-the-clock vision correction should not be underestimated. A recent study comparing extended wear and daily disposable lenses found that, after wearing each lens type for a month, two out of three patients preferred the convenience of extended wear lenses. Patients who were considering refractive surgery at the beginning of the study were over three times as likely to prefer extended wear lenses at the end of the study. The percentage of patients who report sleeping in their lenses is always higher when patients are asked by a third party, as compared to what they report to their practitioners. Even normally compliant daily wear patients occasionally sleep in their lenses overnight. Therefore, it can be beneficial to prescribe lenses that can offer the convenience and freedom sought by lens wearers but also provide the largest margin of safety against hypoxia regardless of wearing schedule.

Because new high Dk lenses were designed specifically to reduce the hypoxic effects on the cornea, they have shown a level of biocompatibility not yet seen with contact lenses. Focus Night & Day lenses have oxygen permeability of 140 (x 10-11 cm2 /sec) which translates to a central oxygen transmissibility (Dk/t) of 175 barrers for minus lenses. This is six times higher than many hydrogels and well above the threshold for corneal anoxia cited by Harvitt and Bonnano (125 barrers), for limbal hyperemia determined by Papas (125 barrers) and for corneal edema established by Holden and Mertz (also 125 barrers, recently updated from 87 barrers).

Since its introduction into the global marketplace in 1999, scientists and clinical researchers have shown that lotrafilcon A lenses have virtually eliminated contact lens-induced overnight corneal swelling. Results have shown a reduction in the corneal acidosis (pH shift) and an increase in epithelial permeability associated with low oxygen transmission lenses. Researchers also found a reduction or elimination of hypoxic corneal changes such as endothelial polymegathism, epithelial cell size increase and microcysts. They have reported a reduction in limbal redness and elimination of the increases in myopia observed with extended wear of low Dk hydrogels. New findings have been reported showing that bacterial binding to the cornea is not increased with these high Dk lenses as it is with lower Dk lenses.

Scientific studies have shown that high oxygen transmissibility indeed can offer an improvement in the physiological performance of contact lenses. How have the lenses performed in clinical trials when worn for up to 30 nights of continuous wear? This paper summarizes the results of a year-long study of patients using Focus Night & Day lenses for up to 30 consecutive days and nights compared to a conventional hydrogel lower Dk lenses (Vistakon Acuvue UV, etafilcon A) worn for up to six consecutive days and nights.

Methods

Participants in the year-study were recruited from 59 practices around the United States. A total of 1,395 patients were randomized to either the Focus Night & Day lens (a 24-percent water, Group I, non-ionic lens) or the control lens (a 58-percent water, Group IV, ionic lens) bilaterally for the duration of the trial. Approximately half of the participants in each group were previously successful daily wear patients, just over one-third were previously successful extended wear patients, and the remainder were new to contact lenses. All patients were free of ocular disease. The patients ranged from 18 to 70 years, and the gender distribution was 70 percent female and 30 percent male. The power range of lenses worn was from +6.00D to ­6.50D. In the study, 658 patients were dispensed Focus Night & Day lenses, and 681 patients were dispensed the control lenses. All patients gave informed consent to participate, were examined before they began the study, then were fitted with the randomized lens type. After dispensing new lenses, patients were examined at one day, one week, one month, three months and then every three months for the rest of the year.

Results

Lens Fitting and Wearing Time During this study, Focus Night & Day lenses were available only in an 8.6mm base curve geometry. Of the participants that were dispensed lenses, approximately 12 percent discontinued early in the study due to inadequate fit and/or discomfort at follow-up visits, the majority of these in the first week. An important factor in the evaluation of fit with silicone hydrogel lenses is subjective comfort. While the lenses may appear to have good centration and movement, patients may comment on discomfort often noted at the lower lid. Because the modulus of these lenses is somewhat higher than standard hydrogels, edge lift may occur with an inadequate fit. Figure 1 shows an obvious case of edge lift, but in subtle cases, the patient's evaluation of comfort may be the telltale sign. In these cases, a steeper base curve should be evaluated. Focus Night & Day lenses are now available in an 8.4mm base curve as well. A recent study at the University of Waterloo found a base curve usage of 75 percent in the 8.6 mm base curve and 25 percent in the 8.4mm base curve to achieve optimal fits.

Figure 1. Edge lift with Focus Night & Day 30-day extended wear lens.

Even though only one base curve for Focus Night & Day lenses was used in this study, 75 percent of the wearers were able to successfully complete the year with the wearing schedule of up to 30 continuous nights and days. These "30-night wearers" did not always use the lens for 30 consecutive days and nights. During the year, 88 percent of the continuous wearing periods were greater than seven days and nights, with the vast majority reported between 22 and 31 consecutive days and nights. The average reported wearing time for Focus Night & Day lenses was 26 to 27 continuous days. As with all contact lenses, removal is recommended if irritation or redness is noted. It is particularly important with extended wear to caution wearers not to sleep in lenses if their eyes feel irritated. Lenses should be removed during times of sickness, and caution should be taken when involved in water-related activities as these can be sources of infection-causing bacteria.

No Increase in Adverse Events Although there was a greater than four times increase in the average consecutive days of continuous wear compared to the control lenses, no statistical increase in ocular complications was reported with Focus Night & Day lenses. Approximately 5 percent of the wearers experienced corneal infiltrates during the year, with less than 1 percent of these associated with peripheral non-infectious infiltrates, sometimes also referred to as contact lens peripheral ulcers (CLPU).

No cases of infectious ulcerative keratitis were reported during the year of study. Although this was the largest pre-market clinical study conducted for a contact lens, the incidence of extremely rare conditions such as infectious keratitis cannot be determined with adequate statistical confidence. In post-market analysis in 40 countries where the product has been used for the last two years, the findings are encouraging, as the rate appears very low. CIBA Vision has initiated a year-long, post-market evaluation of 5,000 wearers to provide increased confidence for both practitioners and wearers.

Papillary conjunctivitis was reported at a higher rate with Focus Night & Day compared to the control, although the rate, at just under 4 percent, is not atypical for contact lenses. The majority of the cases reported were patients with a previous history of papillary conjunctivitis. The incidence may have been related to mechanical irritation from loose-fitting lenses, as all cases occurred in the first three months. Nonetheless, exercise caution in prescribing the lenses for patients with a history of the problem.

This study also showed that wearers of both lens types who had a previous corneal infiltrative episode were more likely to have a repeat occurrence during the year than patients without a history. Therefore, patients with a previous history of corneal inflammation should be advised and monitored more closely.

Figure 2. Focus Night & Day lenses exhibited a lower protein deposition than the Acuvue UV control lenses.

Subjective Comfort and Dryness on Waking Fewer Focus Night & Day lens wearers reported symptoms of lens dryness compared to the control lens group. This included fewer overall complaints of dryness (p=0.001), less dryness upon awakening (p=0.001) and fewer unscheduled removals because of dryness (p=0.02). Although the rate differences are small, these reports have been borne out in anecdotal comments from the international marketplace. This difference could be due to the low protein deposition found with the lenses (Figure 2), the lower water content of lotrafilcon A, or it may be related to the reduction in hypoxia. The latter may be important since the biggest difference in comfort is experienced in the morning upon awakening.

Stabilization of Refractive Error Another problem seen in extended wear of low Dk hydrogels is a gradual increase in myopia ("myopic creep"). In this study, 1.5 percent of the control lens subjects had an increase in myopia greater than 1.00D during the e year. In contrast, no Focus Night & Day lens wearers showed this increase in myopia, even though the continuous wearing time was longer. Three moderate to high myopic patients (0.5 percent) actually showed a decrease in myopia of greater than 1.00D, perhaps in recovery from their previous lenses.

This is important to consider when advising patients transferring from low Dk extended wear. Myopic patients may experience and appreciate a slight reduction in myopia. Although not observed in this study, hyperopic patients who have had a myopic shift with previous lenses may experience reversal to their previous refractive error, a situation that may require counseling the patient that the long-term health benefits of the lens make this more hyperopic refractive error change worthwhile. Although the mechanism of myopic creep is not fully understood, prevention of this change is a good reason for recommending a high Dk hydrogel lens for an adult patient who is otherwise slowly increasing his myopia.

Visual Acuity Excellent vision is taken for granted with contact lenses, but it's important to mention these benefits to our patients. As mentioned above, many patients are interested in hassle-free, around-the-clock vision correction. The interest in refractive surgery has been evidence of this. Now that patients have the option of contact lenses for up to 30 nights of continuous wear, a comparison with refractive surgery is warranted. In this trial, 83 percent of wearers reported 20/20 or better visual acuity at all visits in the trial. This compares with a recent FDA laser approval for LASIK with 65.2 percent of the subjects reporting visual acuity of 20/20 or better. At visual acuity of 20/25 or better, the comparison still looks advantageous with 94.6 percent of Focus Night & Day wearers at this level compared to 80.4 percent in the above-mentioned laser study. No patients lost two lines of best-corrected acuity with the contact lenses as compared to 1.2 percent in the laser trial. There is also the ongoing flexibility to easily adapt the prescription as required, for example in younger patients, emerging presbyopes or during pregnancy. Most importantly, patients may try these lenses for a month without the concern of irreversibility.

Conclusions

Focus Night & Day is the first lens of its kind to receive FDA approval for the indication of up to 30 nights and days of continuous wear. In market research, 40 percent of wearers have expressed interest in a product providing the freedom of round-the-clock vision. If there is a lens wearer in your family, you have probably heard the expression when you're getting ready to go: "Just a minute while I put my eyes in." Or just the opposite when they're dead tired: "Just a minute while I take my eyes out." You can understand why 12 million wearers in the United States alone would like to simplify their lens care procedures. Many have stayed away from lenses for this very reason and now are potential new wearers.

With its extremely high oxygen transmissibility, Focus Night & Day offers many reasons to choose it, even if you don't consider yourself an "extended wear fitter." Its increased oxygen transmissibility offers many advantages in addition to the freedom of round-the-clock vision correction: excellent visual acuity compared to LASIK, decreased hypoxic problems, no myopic creep and fewer reports of lens dryness, particularly morning dryness with extended wear.

 

Dr. McNally graduated from the School of Optometry at the University of California Berkeley. He is head of Continuous Wear Research and Development Projects at Ciba Vision.

 

Dr. McKenney graduated from Ferris State University, School of Optometry. He is Senior Clinical Project Manager and leads the clinical testing programs for silicone hydrogels and continuous wear lenses.

 


Contact Lens Spectrum, Issue: January 2002