Indicated for use in children aged 4 to 9 years of age who have less than 5 prism diopters (D) of strabismus with the diagnosis of amblyopia, dichoptic therapy provides a robust alternative that can improve compliance in pediatric patients.
What is dichoptic therapy?
In dichoptic viewing, a separate, independent image is presented to each eye. In order to explain dichoptic therapy, it is first necessary to understand amblyopia.
Amblyopia is a disorder of visual development that results in limited best-corrected visual acuity (VA) because of a weak brain-eye connection. It is a cortical problem more so than an ocular problem.
Overview of amblyopia
There are several causes of amblyopia:
- Refractive Error: An optical blur of images that can usually be corrected with spectacle-wear.
- Strabismus: A misalignment of the eyes that causes the brain to favor one eye.
- Visual Deprivation: Conditions such as cataract (a cloudy lens), ptosis (droopy eyelid), corneal scars, etc., that block vision in the eye.
In amblyopia, optical correction alone may not be sufficient to improve vision. The standard of treatment involves correcting refractive error, strabismus, and any obstruction of the line of sight. Dichoptic therapy is most useful when there is minimal strabismus or visual obstruction, and there is an interocular difference in acuity—meaning one eye sees better than the other, despite wearing glasses consistently.
Dichoptic therapy is a treatment modality that involves presenting a different visual stimulus to each eye independently—altering it in a way to encourage the use of an amblyopic eye with simultaneous binocular function. This is typically done by reducing contrast of the better-seeing eye to a point that overcomes suppression of the amblyopic eye.
Recent research on dichoptic therapy for amblyopia
Birch et al. studied the effects of binocular versus sham games in children ages 3 to 7 years, with improvement in the binocular group’s VA but with no significant effect on stereoacuity (true sense of depth perception).
Some patients of each study group also patched, but in those who were compliant (i.e., completed at least 50% of intended treatment time), similar improvement was observed regardless of whether the patient patched or not.1,2
Due to these impressive preliminary results, the Pediatric Eye Disease Investigator Group (PEDIG) network studied binocular iPad-based dichoptic treatment. When comparing the “falling-blocks” game (similar to Tetris) to patching and glasses, both younger (ages 5 to 12) and older (ages 13 to 18) cohorts of children had greater improvement with part-time patching than with iPad therapy.3
The study authors felt it is most likely the nature of the game that resulted in its limited benefit. Children did not find the game fun, thus compliance with iPad therapy was a major issue. Less than 20% of kids finished the prescribed treatment.4
Dichoptic therapy games and clinical outcomes
Dig Rush
Initial results were discouraging with the falling blocks game, so investigators tried to address the issue of compliance with a more engaging game—Dig Rush. This iPad-based dichoptic therapy used anaglyph (red-blue) glasses to present a significantly reduced-contrast image to the sound eye. The study question was altered to whether dichoptic iPad therapy could be better than spectacle treatment alone.
While the younger cohort of kids showed an initial 4-week outpacing of the glasses alone group, everything was similar by 8 weeks out, and the study concluded there was no difference between groups in vision or stereoacuity.5,6,7
Compliance was better than in the falling blocks studies, but barely half of the children completed 75% of the prescribed time. As for our practices, we feel that the dichoptic stimulus games in their current iterations lack strong support for effectiveness or patient engagement.
In recent years, two digital therapeutics presenting streaming content in a dichoptic fashion have received US Food and Drug Administration (FDA) approval for their use in the treatment of amblyopia—Luminopia and CureSight.
Luminopia
Luminopia is a virtual reality (VR) headset that presents dichoptic images projected at optical infinity. The device is paired with a smartphone to stream content licensed from shows on PBS, Nickelodeon, Sesame Street, and Dreamworks, among others.
The system treats amblyopia in a twofold fashion, reducing the contrast in the better to 15%, along with complementary masking in each eye such that binocularity is necessary to see the full video. Specifically, the center of the amblyopic eye was kept clear.
David G. Hunter, MD, and his team at Boston Children’s studied the device.8,9 Children aged 4 to 7 had a 1.5-line improvement in VA after 12 weeks versus 1.2 lines after patching in an age-matched cohort, with significant gains in stereopsis. Even older children (8 to 12 years) and kids with 1 year of prior treatment had improvement.
It must be noted there was significantly better compliance with Luminopia compared to patching and similar dichoptic treatments.4,7 The contrast was also kept at 15% while other dichoptic studies gradually increased contrast over time.10,11
CureSight
NovaSight received FDA approval for their device, CureSight, about 1 year after Luminopia. We have yet to prescribe this to patients, but there may be some advantages over other dichoptic therapies. Similar to the iPad-based dichoptic play, CureSight uses anaglyph glasses to create the dichoptic environment, rather than a VR headset.
CureSight modifies its approach by incorporating eye-tracking software that allows the device to selectively blur and reduce contrast to only the fovea of the sound eye. This means that as the child glances around the digital device, the eye-tracking continuously alters the area of blur.
The magnitude and diameter of the blurred area are fit according to the visual acuity of both the amblyopic and the dominant eye. The lower the visual acuity and the larger the interocular difference, the greater the blur amplitude and diameter. Peripheral fields are not blurred to encourage binocularity.
The strongest evidence supporting the use of CureSight comes from a randomized, noninferiority trial of 103 children between 4 to 9 years of age. It was a 16-week study randomizing children in a 1:1 fashion to 90min/day, 6 days a week of CureSight, versus 2hr/day of patching 7 days a week.
This device may offer a wider appeal to older children since the digital platform allows for streaming of any site with parental controls able to be placed. Of note, Netflix, Prime Video, Disney Plus, YouTube, and Hulu are all accessible on CureSight.
For the older children who have reported growing tired of the digital media library of Luminopia, or feeling the content skews towards a younger audience, this solves that issue. Compliance in the study demonstrated its popularity, with 91% of children completing prescribed treatment.12
Recommendations for parents on amblyopia therapy
We would like to emphasize that optical correction and patching are still the gold standard of amblyopia therapy and should be attempted before moving on to other modalities like dichoptic therapy. Once dichoptic therapy has been prescribed, the device will be mailed, and a cell phone will be needed to stream visual media to the platform.
These devices are typically calibrated to optical infinity and are meant to be worn over glasses. Luminopia is not suitable for children with a pupillary distance of less than 52mm. This, on the other hand, is not a limit with CureSight’s spectacle system.
Takeaways on dichoptic therapy
- Correcting any refractive error is the first step in treating amblyopia.
- Patching is still the gold standard and most studied form of treatment—usually, the next step in treating amblyopia if improvement with glasses alone is not sufficient or not indicated.
- Dichoptic therapy is still very new in its conception but has demonstrated similar efficacy to patching with less time involved.
- Current dichoptic therapy is studied and indicated for children aged 4 to 9 years.
- CureSight studies show significant promise with even more impressive results than patching. The authors will likely use this over the next couple of years.
Final thoughts
We’re at an exciting crossroads in the treatment of amblyopia. Digital therapeutics offer the potential to attract children to amblyopia therapy without some of the stigma and discomfort that comes with patching or atropine penalization.
However, the American Academy of Pediatrics continues to recommend that children ages 2 to 5 watch no more than 1 hour of digital media per day. Balancing therapeutics with digital media, especially for those children who may require more hours of treatment, is an important consideration.
