The LSM differences in axial elongation from baseline between the two cohorts are shown in Table 9. Consistent with results from the GLMM, the difference in axial elongation between the control and test cohorts was not statistically significant at any of the three follow-up visits.
The GLMM model (Table 8) indicated that baseline refraction was not a significant factor and is therefore removed from the final model and not included in the table, whereas baseline AL was a significant factor (p = 0.005) and was included in the statistical model for adjustment. Based on the coefficient estimate, the longer the AL was at the second baseline, the greater the myopia progression. Meanwhile, neither lens type nor lens-by-time interaction was a significant factor in predicting change in refraction.
Least-squares mean analysis of SECAR changes during the withdrawal phase indicated that, at the 6-month visit, there was a small, but statistically significant, difference (test – control) between the two cohorts, favoring the test cohort by 0.124D (Table 9). A slightly smaller difference (0.121D) was identified at the 18-month visit. At 12 months, the difference was even smaller (0.113D) and not significantly different (Table 9). These results suggested that the change in refraction across time was not significantly different between the two study cohorts during the withdrawal phase.
In the withdrawal phase, after cessation of investigational lens wear, there were no significant differences in either axial elongation or SECAR change between the prior control and the prior test cohorts. Although the change in refraction appeared to be smaller in the test cohort during the withdrawal phase, the difference was not more than 0.25D, the prespecified boundary of clinical significance across the 18-month follow-up period of the withdrawal phase.
Because of early termination of the treatment phase, interpretation of data at each follow-up visit in the withdrawal phase is somewhat challenging because the baseline of the withdrawal phase of the study was derived from subjects treated for a variable interval during the treatment phase of the double-masked study. Nonetheless, all eligible subjects wore the test article for at least 12 months before entry into the withdrawal phase, and the average length of wear and the frequency distributions of treatment durations between cohorts were similar (Pearson χ2 test of independence, p = 0.169). To address this limitation, treatment duration was first included in the GLMM efficacy analysis. It was found that lens type–by–treatment duration interaction was not a significant factor for predicting change in AL (p = 0.231) or SECAR (p = 0.054). In addition, statistical analysis was repeated on the 82 subjects who participated in both phases of the study to investigate their rate of myopia progression (defined as the slope of the linear fit of axial elongation and SECAR change) during the treatment and withdrawal phases. The results (Fig. 4) showed that the rate of axial elongation was statistically different between the two cohorts during the treatment phase, whereas it was not statistically different during the withdrawal phase. This is evidenced by a statistically significant lens type–by–time interaction term during the treatment phase (coefficient estimate, −0.001; 95% CI, −0.002 to −0.001; p = 0.001) and a nonstatistically significant lens type–by–time interaction term during the withdrawal phase (coefficient estimate, 0.000; 95% CI, −0.001 to +0.001; p = 0.646). Meanwhile, the difference in the rate of SECAR change was not statistically significant in the 82 subjects during either the treatment phase (p = 0.072) or the withdrawal phase (p = 0.074). The coefficient estimates of the lens type–by–time interaction term were 0.002 (95% CI, −0.000 to 0.004) and 0.002 (95% CI, −0.000 to 0.003) during the treatment and withdrawal phases, respectively.
Among the 127 randomized subjects, there were a total of four ocular adverse events (AEs) involving two subjects (1.6%) that were reported during the course of the treatment phase. Of these, two were from two eyes of one subject in the control cohort (contact dermatitis) and two were from two eyes of one subject in the test cohort (allergic conjunctivitis). All AEs were classified as nonsignificant and were deemed unlikely to be related to wearing the study contact lenses. All AEs were followed to resolution, and both subjects completed the study per protocol. There were no unanticipated adverse device effects and no loss of best corrected visual acuity reported.
Grade 3 and higher slitlamp findings using the FDA slitlamp classification system were considered clinically significant; there were no grade 3 slitlamp findings throughout the conduct of the study.
One incident of grade 2 corneal neovascularization was observed in one eye in the control cohort at a single (6-month) follow-up visit.
Among the 82 enrolled subjects, there were a total of two ocular AEs involving allergic conjunctivitis in both eyes of one subject (1.2%). In addition, there was one nonocular AE, a bone fracture, reported during the course of the study. All three AEs were found in subjects who were in the test cohort during the double-masked study. Both ocular AEs were classified as nonsignificant, and the relationship to the study contact lens was “remote (unlikely).” There were no unanticipated adverse device effects reported in this study.
There were no slitlamp findings of grade 3 or higher throughout the course of this phase of the study.
The intent of the novel soft contact lens design used in this study was to correct retinal hyperopic blur caused by negative SA during accommodation. To examine the success of this goal, lens-on-eye wavefront aberrations or, more specifically, lens-on-eye SAs with and without accommodation were monitored throughout the course of the study. The results (to be published in a subsequent article) indicated that lens-on-eye SA with the test lens closely matched the expected result when adding together the SA of the eye and lens. Optical modeling shows that the introduced +SA also has the net effect of reducing relative peripheral hyperopia. We, therefore, measured off-axis refraction at ±25° along the horizontal meridian of the retina and made comparisons between the two cohorts. The results (to be published in a subsequent article) showed that the test lens introduced a myopic shift in relative off-axis refraction at the temporal 25° field of the subjects' retina, which was significantly more negative than with the control lens. The relative off-axis refraction at the nasal 25° field remained hyperopic and was not significantly different from that of the control lens. We hypothesize that the asymmetric impact on off-axis refraction of the test lens may be caused by lens decentration on the eye. Overall, these findings were consistent with the intended design of the test lens for the control of myopia progression. Further investigation of the data will focus on establishing associations between such lens-on-eye optical performance and myopia control effect.
Another consideration of a soft contact lens with a relatively large amount of +SA is its impact on visual performance. Therefore, logMAR visual acuity (measured at 4 m with the Early Treatment Diabetic Retinopathy Study charts by Precision Vision) was monitored throughout the study. The results indicated that, during initial lens fitting and dispensing, monocular distance visual acuity with the test lens was 0.06 ± 0.062 logMAR (mean ± SD), which was about one-half a line worse than that of the control lens (0.00 ± 0.076). However, during subsequent follow-up visits, there was no significant difference in visual acuity between the two cohorts. It appeared that visual acuity deteriorated in both study cohorts presumably because of undercorrection as a result of myopia progression, and the difference in visual acuity between the two cohorts diminished across time throughout each of the 6-month dispensing interval until the lens prescription was updated. Meanwhile, the study was designed to evaluate each subject's acceptance of vision before lens dispensing so that subjects who deemed their study lenses to be unacceptable were not dispensed with study lenses. During the entire course of the study, no subject discontinued because of unacceptable vision. It appeared that, although visual acuity with the test lens was not optimal compared with conventional single-vision lenses, monocular vision of the subjects on average was about 20/25, which would not be expected to affect activities of daily living. We also hypothesize that, since myopia usually progresses in 8- to 13-year-old children with conventional correction, these children may constantly experience some degree of blurry vision because of undercorrection until the prescription is updated, which was shown in the current study. This may explain why an average of 20/25 monocular vision was “acceptable” to the study subjects and no subject discontinued from the study because of unacceptable vision.
Despite the significant slowing in axial elongation induced by the test lens (e.g., a 65.3% and 38.6% slowing of axial elongation after 6 and 12 months of treatment, respectively), this slowing of axial elongation was not manifest as a clinically significant reduction in progression of myopic error, that is, the change in myopic error was less than 0.25D within the first year of treatment. The difference between the change in axial elongation and the change in refractive error could be attributable to the fact that the overall treatment effect was relatively small within the first year, that is, a 0.14-mm difference in axial elongation after 1 year of treatment. Another possibility is that the signal generated by the IOLMaster was more robust, with a repeatability of 30 to 40 μm compared with the WAM-5500 with reported repeatability of 0.11 to 0.21D under cycloplegic conditions.51,52 Finally, there might be a true “mismatch” of reduction in SECAR change compared with AL change because of some kind of “compensatory” mechanisms from other optical components of the eye. Although, in this study, we measured corneal radius of curvature (K values from the auto-refractor) and corneal topography, there were no significant differences in corneal curvature between the two study cohorts. Future studies may consider including measures of other optical metrics of the eye, including anterior chamber depth and lens curvature and thickness, to investigate the apparent discrepancy in myopia control efficacy between AL and SECAR further.
To the extent that the current design slowed axial elongation of the eye, our results confirm the findings of similar studies that have found that soft contact lens technologies can slow the progression of myopia. Table 10 summarizes the efficacy findings of these studies for both AL and refractive error. Various methodologies have been used in these studies, and they may be of importance in interpreting the findings.
Anstice and Phillips45 used a contralateral-eye design in which test and control lenses were worn simultaneously in each subject. Although sympathetic eye effects are generally considered to be minor in terms of refractive development, even a small level of interdependence between eyes could have a significant impact on the apparent treatment effect. Sankaridurg et al.47 used a control group from a separate study with participants who wore spectacle lenses. Although this separate study was also prospective and randomized, it is unclear how the separation of the studies in which test and control devices were worn may impact the outcome. In their 2013 article, Walline et al.48 used a historical control group of contact lens–wearing subjects and matched these to their treatment group by age and sex. It is unclear how the lack of randomization of the subjects and the execution of the study under separate protocols might have impacted the results. The study design most similar to the one we have used was conducted by Lam et al.,46 in that it was randomized, controlled, and double masked and of 2 years' duration.
Data shown in Table 10 also indicate that there appeared to be a reduction in the treatment effect across time. It is not immediately apparent from the data if the trend toward a reduced effect across time is real, a factor of the study designs, or inherent random variation. In the study of Lam et al.,46 there was little evidence of a reduced effect across time, although the general magnitude of the effect is relatively modest compared with the other studies. In the current study, the apparent extent of myopia control varied considerably depending on the parameter considered and the time point. At 6 months, the reduction in axial elongation and refractive progression was at the higher end (65.3 and 54.0%, respectively) compared with results from all studies of soft lens technologies (Table 10). Although the apparent impact on axial elongation remained at what might be considered a clinically important level (38.6%) at the 12-month time point, the reduction in refractive error progression of 20.2% was not statistically significant and is unlikely to be considered clinically significant. This substantial change occurred despite the sample size remaining robust for this time point (N = 57 and N = 52 for the control and test cohorts, respectively). Case analysis showed that this finding could not be attributed to outliers.
Although no statistical analyses were performed during the second year of the treatment phase, because of a significant reduction in sample sizes, based on the unadjusted means of change in AL and SECAR at the 18-month follow-up visit, myopia progression was 34.7% less (change in AL) and 34.3% less (change in SECAR) in the test cohort compared with the control cohort. The lack of effect shown at 24 months does need to be considered against the background of the small sample size at this time point. The apparent swings in effect on refractive progression do not appear to be caused by seasonal effects because subjects were enrolled fairly evenly during a 12-month period.
Another interesting feature observable in Table 10 is that the reduction of axial elongation brought about by the test lenses is of greater magnitude than the reduction in refractive progression for all time points in all studies except Walline et al.48 The size of this effect is 22% on average including the Walline data or 30% excluding the Walline data during 1 year of treatment. Again, it is unclear whether this effect is real, but it is certainly worth tracking in future studies, particularly where myopia control with soft lenses is compared against orthokeratology, where AL is the only viable parameter for tracking refractive development.
Furthermore, the choice of control lens remains a matter of debate. Of the five studies on controlling myopia progression with soft contact lenses, four, including the current study, used conventional soft contact lens as the control, whereas only one used the spectacle lens. A spectacle lens control has the advantage of being the standard of care for correcting myopia in most children in the targeted age range. Reporting of results from a spectacle-wearing control group raises issues as to whether factors other than the optical component of soft lenses for myopia control may impact refractive development.
Although there have been reports that have not found statistically significant differences in progression of myopia between spectacle- and contact lens–wearing groups, such studies have not tested for equivalence per se. Small differences such as those observed by Walline et al.53 may have considerable impact when assessing the relatively small differences between treatment and control cohorts in myopia studies.
In this study, we did not find evidence indicating that there was a rebound effect after subjects ceased wearing the novel soft contact lens for myopia control. Rebound has been observed with studies using atropine for myopia control.54,55 There has been no conclusive evidence in the literature indicating that withdrawal of optical treatments in humans results in accelerated myopia progression; however, the magnitude of effect and the sensitivity of study designs to measure an effect should be kept in mind. Consistent with the finding of this study, Berntsen et al.56 reported no rebound effect after subjects were treated with progressive addition lenses. Most recently, Swarbrick et al.57 reported more rapid growth in eyes after ceasing orthokeratology treatment in a contralateral crossover study (N = 24), although, with a similar study design, no obvious acceleration of eye growth or refraction change were found in eyes treated with “dual-focus” soft contact lenses.45 Possible differences observed between optical and pharmacological might be explained by different modes of action in controlling myopia progression. Continued research is warranted to further the understanding of mechanisms of myopia control through different treatment methods.
There are a number of limitations to this study. Although the control lens used was made of the same material and the same manufacturing process, and with the same diameter and base curve as the investigational lens, because of the +SA in the design of the lens, the visual performance of the test lens was not optimal compared with the control lens, which had the conventional spherical design. Therefore, visual acuity measurement during experimental sessions may have given some clue to the investigator as to the identity of lenses being worn. This was mitigated by using a different masked examiner to measure the primary endpoints and performing a lens prescription update.
In addition, the control contact lens had a conventional spherical optical design. Inherent in spherical soft contact lens optics is a small amount of negative SA, which varies in magnitude with the power of the lens. This negative SA could have introduced a small confounding effect; a lens with zero SA would be the ideal control against which to test the technology used here.
Another limitation of the study is that not all of the patients randomized into the two cohorts at baseline of the treatment phase were followed through to their 24-month completion date per protocol. As stated, the study was terminated early, although not because of any safety-related concerns. This means that the sample size of the two cohorts was largest at the month 6 visit and progressively decreased visit by visit; the sample size of each cohort at month 24 of the treatment phase was about 80% smaller than on the month 6 visit. As a result of the progressively decreasing sample size, statistical analyses were not performed at months 18 and 24. Therefore, data during the second year of the treatment phase presented in this article should only be treated as exploratory and be interpreted as inconclusive.
In this study, we found that soft contact lenses with +SA slowed axial elongation of the eye, thereby showing potential in controlling myopia progression. After cessation of test lens wear, subjects showed no signs of a rebound effect. Despite control of axial elongation with the current lens design, the magnitude of this effect did not translate into a sustained statistically significant reduction in refraction change, which we consider requisite for the lens to be clinically viable. Future designs should focus on methods to allow achieving a larger treatment effect, which may include increasing the magnitude of +SA in the lens design while minimizing its visual impact.
Johnson and Johnson Vision Care Inc.
7500 Centurion Parkway Ste 100/W-2A
Jacksonville, FL 32256
Trial Registration: CR-1561 AD-NCT01829191; CR-1561AF-NCT01829230.
Presented at the 14th International Myopia Conference in 2013 at Asilomar, California.
Xu Cheng, Jing Xu, Khaled Chehab, and Noel Brennan are all paid employees of Johnson and Johnson Vision Care, Inc. Joan Exford of Korb & Associates is a contract principal investigator paid by Johnson and Johnson Vision Care, Inc.
We thank Dr. Jichang He of New England College of Optometry and Dr. Victor Finnemore of Korb & Associates for collecting data for the study and Dr. Myles Jaffe of Innova Medical Communications, LLC, who is a contract medical writer paid by Johnson and Johnson Vision Care, Inc. for preparing this manuscript.
Received April 1, 2015; accepted September 24, 2015.
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Keywords:© 2016 American Academy of Optometry
axial length; myopia control; myopia progression; positive spherical aberration; soft contact lens