We previously reported results from our primary cohort (n = 28) enrolled in a randomized clinical trial of contrast-rebalanced binocular amblyopia treatment with the Dig Rush game on an iPad versus patching (NCT02365090).1 The Dig Rush game was dichoptic and had reduced contrast for components of the game display seen by the fellow eye (contrast rebalancing) to allow the child to overcome interocular suppression and experience binocular vision while playing the game. Dig Rush was effective in treating childhood amblyopia, and the visual acuity improvement achieved with Dig Rush was significantly greater than with patching.1 Completion of enrollment into our pre-planned secondary cohort combined with the primary cohort (n = 48) has provided a sufficient opportunity to identify baseline and clinical factors that may be predictive of response to binocular and patching treatment.
The research protocol observed the tenets of the Declaration of Helsinki, was approved by the institutional review board of the University of Texas Southwestern Medical Center, and conformed to the requirements of the U.S. Health Insurance Portability and Privacy Act. Informed consent was obtained from a parent or legal guardian before testing and after explanation of the nature and possible consequences of the study. Assent was obtained from participants 10 years or older.
From February 20, 2015, to July 2, 2018, eligible children 4 to 10 years of age diagnosed with amblyopia due to strabismus, anisometropia, or both were referred to the Retina Foundation of the Southwest by pediatric ophthalmologists in the Dallas–Fort Worth area. Eligible children had amblyopic eye best-corrected visual acuity of 0.3 to 0.8 logMAR (20/40 to 20/125) and fellow eye amblyopic eye best-corrected visual acuity of 0.1 logMAR (20/25) or better (0.2 logMAR or better for 4-year-olds) and an interocular difference of ≥0.3 logMAR (three lines or more). In addition, eligible children were required to have been wearing their glasses for at least 8 weeks to be eligible for enrollment. Strabismic children were initially diagnosed with esotropia, but were aligned with surgery and/or spectacle correction to within 4 prism diopters of orthotropia at distance and near. None of the children were born at less than 32 weeks' post-menstrual age or had coexisting ocular or systemic disease, congenital infections/malformations, or developmental delay. Medical records were obtained from referring ophthalmologists to extract diagnosis, current alignment, cycloplegic refraction, and prior treatment.
This study was a randomized clinical trial (NCT02365090) with the goal of enrolling two pre-planned cohorts1: (1) primary cohort: 28 children to determine the effectiveness of the binocular game as amblyopia treatment and whether it is more effective than patching and (2) an additional 20 children to be combined with the primary cohort to allow for evaluation of factors that may affect treatment outcomes including baseline factors (age, amblyopic eye best-corrected visual acuity, stereoacuity, and suppression) and clinical factors (etiology, age at initial diagnosis, prior amblyopia treatment, and current alignment). Data from the primary cohort of 28 children have been reported previously.1 Here, we report results from analysis of baseline and clinical factors based on the combined cohorts (n = 48). The trial protocol and statistical analysis plan are available on ClinicalTrials.gov (NCT02365090).
Randomization was performed by a statistician who provided individual sealed sequentially numbered envelopes. Two randomization schedules were created: one for children with prior amblyopia treatment (patching, atropine) and one for children with no prior treatment. Randomization (1:1) was prepared in permuted blocks of four or six. After confirming eligibility and obtaining informed consent, an investigator opened the envelope, enrolled the child, and assigned the child to the appropriate treatment.
Children randomized to binocular game treatment were loaned an iPad with Dig Rush, a contrast-rebalanced dichoptic game.1 Children were asked to play the game at home for 1 hour a day, 5 days a week for 2 weeks (10 hours of total binocular treatment). During game play, children wore red-green anaglyphic glasses that separate game images seen by each eye, so that reduced contrast components of the game screen were seen by the fellow eye, whereas high-contrast components of the game screen were seen by the amblyopic eye. Background images were high contrast and seen by both eyes. Both eyes must see their respective game components for successful game play. Amblyopic eye contrast remained at 100% contrast, whereas fellow eye contrast started at 20% but increased gradually with game success. The patching protocol was the current standard of care for amblyopia treatment.2 Children were provided with Ortopad eye patches (OrtopadUSA, Tuscon, AZ) and asked to patch their fellow eye 2 hours a day, 7 days a week for 2 weeks (28 hours of total patching treatment). Children randomized to the patching group were offered the opportunity to play the binocular game after they completed the 2-week primary outcome visit.
For both groups, vision assessments were conducted at baseline and at 2 weeks and included (1) crowded monocular amblyopic eye best-corrected visual acuity using the e-ETDRS protocol3 for children 7 years or older at the baseline visit or the Amblyopia Treatment Study HOTV protocol for children younger than 7 years at the baseline visit4; (2) stereoacuity using the Randot Preschool Stereoacuity and Stereo Butterfly Tests (Stereo Optical Co., Inc., Chicago, IL); and (3) extent of suppression scotoma using the Worth four-dot test at seven different distances.5
Parents or legal guardians were provided a personalized calendar to record the number of minutes per day their child played the game or patched the fellow eye. A log file was also obtained from the iPad that contained the number of minutes played and the fellow eye contrast for each play session.
The primary outcome was change in amblyopic eye best-corrected visual acuity at the 2-week visit. In an intent-to-treat analysis, an independent t test was conducted to determine whether improvement in visual acuity differed between the binocular game and patching groups at the 2-week visit. For analyses of predictive factors, baseline and clinical variables were dichotomized, based on criteria commonly used in clinical treatment trials for amblyopia6–12: age at enrollment (4.0 to 6.9 vs. 7.0 to 10.9 years), amblyopic eye best-corrected visual acuity (moderate amblyopia, 0.3 to 0.6 logMAR, vs. severe amblyopia, 0.7 to 0.8 logMAR), stereoacuity (40 to 800 arcsec vs. nil), suppression (foveal/macular fusion vs. peripheral/nil fusion), etiology (anisometropic vs. strabismic/combined), age at initial diagnosis (<4 vs. 4 to 8 years), prior amblyopia treatment (none vs. patching/atropine), and current alignment (ortho vs. tropic). Independent t tests were conducted to evaluate whether each was associated with visual acuity improvement. Because eight baseline variables and four clinical variables were evaluated, only P ≤ .006 was considered statistically significant (Bonferroni correction for multiple comparisons). A Pearson correlation was conducted to examine the relationship between hours of binocular game play and the amount of visual acuity improvement observed at the 2-week visit. All analyses were conducted with an intent-to-treat approach.
Between February 2015 and July 2018, 48 patients were enrolled in the study; 24 were randomized to binocular game treatment and 24 to patching treatment. The 2-week outcome visit was completed by 47 of 48 children (Appendix Fig. A1, available at http://links.lww.com/OPX/A447); one child was unable to complete the 2-week visit because of illness. Baseline characteristics are provided in Appendix Table 1, available at http://links.lww.com/OPX/A448. Twenty-seven children (56%) were diagnosed with anisometropic amblyopia and 21 (44%) with strabismic or combined mechanism amblyopia. The mean ± standard deviation age was 6.8 ± 1.8 years (range, 4.3 to 10.8 years). Mean amblyopic eye best-corrected visual acuity ± standard deviation at enrollment was 0.49 ± 0.16 logMAR (~20/63 ± 1.6 lines; range, 0.3 to 0.8 logMAR; 20/40 to 20/125). Visual acuity values were 0.3 to 0.6 logMAR (20/40 to 20/80) in 38 children (79%) and 0.7 to 0.8 logMAR (20/100 to 20/125) in 10 children (21%). Twenty-eight children (58%) received prior amblyopia treatment with patching, atropine, or both.
Adherence to Protocol
Compliance using the personalized calendar was similar to the iPad log, but the parents overestimated the time spent playing the game by 13% (1.3 ± 3.0 hours). In all reported analyses, the iPad log was used. Compliance for patching was tabulated using the personalized calendar. Children assigned to the binocular game completed 10.3 ± 3.0 hours (103% prescribed treatment time). Fellow eye contrast for children assigned to the binocular game was 50 ± 19% at the 2-week visit. Children assigned to patching reported that they completed 27.7 ± 2.6 hours (99% prescribed treatment time).
At the 2-week primary outcome visit, a larger improvement in amblyopic eye best-corrected visual acuity was found with binocular game compared with patching (0.15 vs. 0.07 logMAR; 95% confidence interval for the difference, 0.03 to 0.13; t45 = 3.05, P = .004; Fig. 1). For the binocular game group, improvement ranged from 0.0 to 0.4 logMAR; 21 children (87.5%, 95% confidence interval, 69 to 96%) improved by 0.1 logMAR or more (2 improved by 0.3 to 0.4 logMAR, 10 improved by 0.2 logMAR, 9 improved by 0.1 logMAR), and 3 children did not improve (12.5%; 95% confidence interval, 4 to 31%). For the patching group, improvement ranged from −0.1 to 0.2 logMAR; 12 children (50%, 95% confidence interval, 31 to 69%) improved by 0.1 logMAR or more (5 improved by 0.2 logMAR, 7 improved by 0.1 logMAR), and 11 children (46%; 95% confidence interval, 28 to 65%) did not improve, and 1 child (4%, 95% confidence interval, 1 to 20%) decreased by −0.1 logMAR.
At the 2-week visit, 35% (95% confidence interval, 19 to 55%) of children playing the binocular game had recovered normal visual acuity for age (≤0.2 logMAR; 20/32 or better). Only 8% (95% confidence interval, 2 to 26%) of the children in the patching group had recovered normal visual acuity for age at the 2-week visit.
Baseline factors included age at enrollment, baseline amblyopic eye best-corrected visual acuity, baseline fusion, and baseline stereoacuity. In the binocular game group (Fig. 2), only baseline visual acuity was associated with response to amblyopia treatment. Children with moderate amblyopia had more improvement than did children with severe amblyopia (0.15 vs. 0.07 logMAR; 95% confidence interval for the difference, 0.06 to 0.08; t22 = 15.40, P < .001). In the patching group (Fig. 3), we were unable to confidently identify any association between baseline factors and response to amblyopia treatment (P values ranged from .12 to .50 for the four factors evaluated).
Clinical factors included etiology, age at diagnosis, prior treatment, and ocular alignment. In the binocular game group (Fig. 2), only ocular alignment was associated with response to amblyopia treatment. Orthotropic children had significantly more visual acuity improvement than did children with esotropia <5 prism diopters (0.17 vs. 0.09 logMAR; 95% confidence interval for the difference, 0.06 to 0.10; t22 = 7.96, P < .001). In the patching group (Fig. 3), we were unable to confidently identify any association between clinical factors and response to amblyopia treatment (P values ranged from .09 to .57 for the four factors evaluated).
In the binocular game group (Fig. 4, top), there was a moderate linear relationship between hours of binocular game play with fellow eye contrast <100% and the amount of visual acuity improvement observed (r = 0.545; 95% confidence interval, 0.17 to 0.78). Based on the linear best fit, children who played for 5 hours (50% adherence) improved approximately 0.1 logMAR (one line), those who played 10 hours (100% adherence) improved approximately 0.18 logMAR (1.8 lines), and those who played 15 hours (150% adherence) improved approximately 0.26 logMAR (2.6 lines).
In the patching group (Fig. 4, bottom), we were unable to confidently identify a relationship between hours of patching and the amount of visual acuity improvement observed.
Stability of Visual Acuity Gains
In the binocular game group, most children returned to patching treatment after completion of the study. However, eight children had no treatment other than glasses for 3 to 6 months after study participation. In this subset of participants, there had been a mean improvement in visual acuity of 0.19 logMAR.
The contrast-rebalanced Dig Rush game was effective in treating amblyopia in children aged 4 to 10 years, improving visual acuity by 1.5 lines with 10 hours of game play for 2 weeks. With baseline visual acuity of 0.3 to 0.8 logMAR, 35% of children in the binocular game group achieved visual acuity of 0.2 or better at 2 weeks compared with only 8% in the patching group. Baseline visual acuity, ocular alignment, and adherence to the treatment protocol were associated with binocular amblyopia treatment success. The 1.5 lines improvement in visual acuity observed at 2 weeks (10 hours of game play) compares favorably with recent studies of 16 weeks (224 hours) of 2 hours per day of patching treatment of amblyopia. Specifically, in recent studies that required spectacle wear for a sufficient period to establish stable visual acuity before enrollment, 16 weeks of patching has resulted in 1.3 to 2.3 lines of visual acuity improvement.13–16
There remains substantial controversy about whether binocular amblyopia treatment is effective. Table 1 highlights some differences among the randomized clinical trials that have been reported in the literature. First, note the decreasing amount of visual acuity improvement among the various studies as a function of the average age of those enrolled. Participants in this study (shown in the first row) were younger than those enrolled in other studies. Our focus was on enrolling young children, not children who had abandoned treatment and were judged to have intractable residual amblyopia. Our cohort included only four children who had prior patching but had stopped patching because of lack of visual acuity improvement before enrolling in our study. The remaining children had either no prior patching or took a break from patching to participate in this randomized clinical trial. Compare that to the older participants in other randomized clinical trials in the table, where most participants had abandoned patching, had intractable residual amblyopia, and sought an experimental treatment because all other options (spectacles, patching, atropine) had failed.
In our cohort, even small angle deviations up to 4 prism diopters seemed to limit the benefit of binocular treatment. The 4-prism-diopter limit was chosen for inclusion based on research showing that strabismus of 4 prism diopters or less was compatible with stereoacuity.20 Nonetheless, we found that even small angles of ocular misalignment of 1 to 4 prism diopters were associated with less benefit of binocular amblyopia treatment compared with orthotropia. Perhaps this is a consequence of the antisuppression approach; children with small angle tropia may suppress the amblyopic eye when not engaged in contrast-rebalanced game play to avoid diplopia. Orthotropic children may maintain the release from suppression experienced during game play, so that it persists beyond the game. Overall, only 21% of children in the present study had tropia of 1 to 4 prism diopters, whereas other randomized clinical trials had 26 to 55% with strabismus, including some with tropia >4 prism diopters.
There are several limitations to our study. This was a single-site, small-cohort randomized clinical trial. The inclusion/exclusion criteria may limit generalization to other groups of amblyopic children. Visual acuity testing was not masked, but we did use a computer visual acuity test system designed to minimize the role of the tester. Although the sample size was sufficient to examine baseline and clinical variables in a dichotomous manner, we are not able to look at the relationship between these variables and visual acuity outcome in finer detail. In addition, our results may be dependent on the criteria chosen to dichotomize each variable. The brief duration of the study may have limited the amount of visual acuity improvement observed. Although the iPad did provide an objective log of the number of minutes of game play per day, it is possible that children did not wear their red-green glasses for all periods of game play. We were not able to monitor the number of hours of patching objectively and relied on a calendar log completed by the parents.
Binocular amblyopia treatment was effective in treating childhood amblyopia, especially among orthotropic children with moderate amblyopia who had more game play time.
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