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New Research on Virtual Reality for Exotropia
We are excited when new information about vision rehabilitation and virtual reality (VR) emerges. A research group in China recently evaluated a dichoptic VR-training platform with a group of 25 patients diagnosed with intermittent exotropia (IXT). Patients underwent a full evaluation and then six months of vision training. Each patient performed the VR training regimen for 20 minutes, twice daily. The results were incredibly favorable and found that with VR treatment, the degree of eye turn, as well as stereoacuity, improved.
Let’s Dive into the Specifics
This cohort of patients was comprised of 25 IXT patients age 5-39 years old. Patients underwent a full ophthalmic examination first, then started on a 6-month treatment program that used a push-pull treatment method in VR (personal communication with the author). The cohort of patients was then evaluated at 1, 3, and 6 months. Before any visual training, the average amount of eye turn was 21.44 prism diopters (± 13.25) -- this is actually quite a large eye turn. After 6 months of twice daily training, there was a significant reduction in the average amount of eye turn to 7.2 prism diopters (± 8.54). Of these 25 patients, 18 were able to achieve “satisfactory alignment” (defined as esophoria/tropia ≤ 5 prism diopters to exophoria/tropia ≤ 8 prism diopters). (Li) The success range used in this study is actually more strict that what most patients experience after strabismus (eye muscle) surgery for an eye turn, which is ~10 prism diopters in either direction. (Mills)
What is this Push-Pull Method?
Push-pull is a perceptual learning protocol used in amblyopia training. Patients are shown a sinusoidal grating at various orientations and contrast levels. The patient must determine the orientation of the grating during the training session. (Xu)
The goal of the push-pull method is to address sensory eye dominance. The best way to explain this is that each of us has a dominant eye, and usually this dominance is mild at best. Amblyopic patients, however, have extreme eye dominance—so much so that visual information from the non-dominant eye is suppressed by the visual system. While patching therapy helps the weak eye to “see better” (more focused on improving visual acuity) the push-pull method focus on exciting the weak eye’s neural channels while depressing the strong eye’s neural channels. In essence, these methods of treatment have an ultimate goal of rebalancing the excitatory-inhibitory interaction between the neural networks in the visual system. (Ooi)
Final Thoughts
We’re excited to see more evidence in the eye care world that uses VR for vision rehabilitation. We commend Dr. Xue Li and the rest of the individuals involved in this study and look forward to their next publication. Read the full article here: https://www.liebertpub.com/doi/pdf/10.1089/cyber.2018.0259.
References
Li X, Yang C, Zhang G, Zhang Y, Lan J, Chu H, Li J, Xie W, Wang S, Wiederhold BK, Wiederhold MD, Yan L, Zeng J. Intermittent Exotropia Treatment with Dichoptic Visual Training Using a Unique Virtual Reality Platform. Cyberpsychol Behav Soc Netw. 2019 Jan;22(1):22-30. doi: 10.1089/cyber.2018.0259. Epub 2018 Nov 17.
Mills MD, Coats DK, Donahue SP, Wheeler DT; American Academy of Ophthalmology. Strabismus surgery for adults: a report by the American Academy of Ophthalmology. Ophthalmology. 2004 Jun;111(6):1255-62.
Xu JP, He ZJ, Ooi TL. Push-pull training reduces foveal sensory eye dominance within the early visual channels. Vision Res. 2011;61:48-59.
Ooi TL, Su YR, Natale DM, He ZJ. A push-pull treatment for strengthening the 'lazy eye' in amblyopia. Curr Biol. 2013 Apr 22;23(8):R309-10. doi: 10.1016/j.cub.2013.03.004.
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