Overnight corneal reshaping (OCR) or corneal refractive therapy (CRT) is a nonsurgical method of improving vision and decreasing dependence on glasses or traditional contact lenses. To compare patients’ experiences and preferences between OCR lenses and 2-week disposable soft lenses, currently the most commonly used mode of contact lens correction, we conducted a crossover study in which each subject wore each type of lens for 8 weeks.
DISCUSSION
Soft disposable lenses provide clear, comfortable vision correction for millions of wearers (approximately 33 million in the United States—nearly 12% of the U.S. population—representing approximately 50% of those who need vision correction between the ages of 18 and 34). Even so, many SCL wearers are not comfortable wearing lenses all day or for all activities. At the end of 2004, it was estimated that there were 50,000 OCR wearers in the United States. Previous studies have documented the corneal responses to OCR lenses and to soft disposable lenses. Soft disposable lenses have been used since the late 1980s, whereas Paragon’s CRT lens was granted U.S. Food and Drug Administration approval in June of 2002. Given the chance to experience these 2 modes of lens wear, two thirds of our study subjects preferred OCR lenses. This study population was mildly to moderately myopic. As such, these results must be considered relevant for such patients only.
The outcomes in this study show some definite differences between OCR and SCL wear. First, logMAR acuity with SCL was better than acuity with OCR. Even so, subjects’ rating of their vision was not significantly different between the 2 modes. Second, subjects felt less activity-restricted, had fewer symptoms of discomfort, and felt less dependent on correction while in the OCR mode but were more affected by glare while wearing the OCR lenses. It is apparent that subjects separate vision from comfort. As described in the “Results,” subjects who chose OCR rated their symptoms 20 points better (less symptoms) with OCR than with SCL.
On the other hand, subjects choosing SCL rated their clarity of vision 23 points higher with SCL and glare 40 points better with SCL. Wavefront testing that is becoming standard in LASIK evaluations may explain some of the reasons for the glare/visual distortions. A recent study of higher-order aberrations in clinically successful OCR cases showed significant increases in third-order (coma-like) and fourth-order (spherical-like) aberrations. Their study concluded that the increases in higher-order aberrations correlated with the amount of the myopic correction. It would be very helpful to be able to predict which patients will be bothered by glare/aberrations before treatment, but this study’s data could not be used to make that distinction.
Comparing mean OCR results on the RQL-42 with the normative data shows close similarities on all attributes except “glare” (lower with OCR, 58.3 vs. 76.4 in the normative data or more bothersome with OCR), “symptoms” (better with OCR, 90.3 vs. 79.2 in the normative data), and “dependence on correction” (better with OCR, 94.6 vs. 42.3 in the normative study or less dependent with OCR). The SCL mean results showed very close correlation to normative data on all attributes.
Although SCL are easy to wear, both the SCL preference group and the OCR preference group rated their symptoms as better with the OCR lenses. Subjective choice in this study showed a majority (67.7%) choosing to continue with OCR lenses.
In comparing alternative modes of vision correction, one study compared RQL-42 scores for a group of patients with OCR (CRT) versus a group of patients undergoing LASIK. That study showed no significant vision-related quality-of-life differences between the 2 groups at 3 months after treatment. These data suggest that OCR may compete with or complement LASIK as a result of similar candidate profiles. Another study compared RQL-42 of OCR with silicone/hydrogel lenses worn for 30 days continuously showing a significant difference in the “dependence on correction” attribute (possibly because of the nature of the instrument questions). The other attributes did not show statistically significant differences.
Safety in various modes of contact lens wear is a serious consideration. In this study, there were no adverse events with OCR or SCL. However, the 8-week follow up in this study was not long enough to establish relative safety or frequency of adverse events with either mode of lens wear. Previous studies have evaluated risk of adverse events while wearing soft disposable contact lenses on a daily-wear basis. Estimates are between one in 1500 and one in 15,000 soft lens wearers per year having events of microbial keratitis. There have been no studies as to the incidence of microbial keratitis with OCR, although there are published case reports of these events that total 41 cases worldwide (7 in the United States and 34 in other countries).
The strengths of this study were:
1) It was a randomized crossover study in which each subject wore both modes, they were their own control.
2) The RQL-42 is a validated instrument and there are normative data for refractive quality-of-life attributes.
3) The study outcomes were subjective and patient-focused.4) Investigator bias was minimized because most of the outcomes were based on the patient’s self-report, not on investigator evaluations.
Also, there was equal sponsorship by the manufacturer of each mode of lens wear. One weakness of the study is that most patients attracted to the study stated they were interested in these “new” type lenses. Subjects may have been somewhat biased toward the OCR lens mode because of their interest in OCR or because of problems with their current lenses (a large majority previously wore SCL). Also, there was no cost to subjects for lenses in the study. Cost factors could influence patient preferences in a clinical practice setting. The study only dealt with subjects who had lower levels of myopia and therefore does not provide information on OCR versus SCL use in subjects with moderate to high myopia.
Visual acuity was good with both modes of lens wear but slightly better with SCL. However, this difference alone was not enough to determine overall preference. Our data show that of those subjects who experienced both modes of lens wear, 67.7% preferred OCR with a decreasing OCR preference as myopic refractive error increased. Lens preference is likely influenced by factors in addition to visual acuity. As the RQL-42 findings show, attributes like dependence on correction, glare, symptoms, and activity limitations differ between lens types and play a role in the patient’s overall assessment of their lens preference.
Conclusion.
In subjects with mild myopia who experienced both SCL and OCR, better visual acuity and less glare resulted from SCL wear, whereas activity limitations, symptoms, and dependence on refractive correction were less troublesome with OCR wear. When the study was completed, 67.7% chose OCR lenses worn only while sleeping, whereas 32.3% preferred 2-week disposable soft lenses worn during the day as their preferred correction.
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