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The Challenges and Emerging Vision Therapy for Management of Amblyopia in Adults (18 years or older)

by | Dec 1, 2022 | Manuscripts | 0 comments

Kartik Kumar Gupta, B. Optom

Intern Optom, BVDUMC, School of Optometry, Maharashtra, India

 

Background:

Amblyopia is clinically defined as a reduction of visual acuity [best corrected visual acuity (BCVA) for at least two lines of visual acuity charts] in one or both eyes, caused by abnormal binocular interaction during the critical period of visual development, that cannot be attributed to any ocular or visual system abnormality or to refractive error. (1,2) Based on aetiology, it can be classified as stimulus-deprivation amblyopia, strabismic, ametropic (anisometropia, myopia, hyperopia, meridional/astigmatic), idiopathic amblyopia and reverse amblyopia.(3) It causes a series of perceptual deficits in the vision of the amblyopic eye, including decreased visual acuity and stereo-acuity, position acuity, contrast sensitivity mostly at high spatial frequencies, range of visuo-motor deficits, and potential psychological sequelae as well as increased internal noise and prolonged manual and saccadic reaction times along with perceptual deficits in the strong eye, such as certain types of motion perception, reflecting altered neural responses and functional connectivity in visual cortex.(4)

Prevalence:

It was determined to be 1.44 % worldwide with the highest prevalence found in subjects over 20 years old (3.29%) and by 2040 it is estimated to be 221.9 million.(5)

Challenges:

Reduced vision in the amblyopic eye represented arrested sensory development and the traditional view suggests amblyopia treatment is effective during the critical period (7-8 years) when the neural system is plastic and improvement in quality of visual input becomes increasingly resistant to reversal with age due to decline in visual plasticity (4,6) because of  transient connections that go through a process of Hebbian competition in which stronger input signals are favoured and unused connections are pruned permanently. The functional magnetic resonance imaging has shown that visual dysfunctions in amblyopia occur both within and beyond primary visual cortex (V1) including extra striate and later specialised cortical areas (V4+/V8, lateral occipital complex) affecting both feedforward and feedback equally which agrees with the traditional view in which the visual system is assumed to be hard-wired long before adolescence.(7)

According to Brigitte Simonsz-Tóth et. al., compliance with occlusion therapy is more difficult in adults (17%) and the average increase in visual acuity after occlusion therapy was only 0.05 logMAR, compared to 0.25 logMAR following refractive correction.(8)

Emerging therapy:

Any treatment must be preceded by correction of the underlying ocular deficits. (9) Classically, the first step in treatment has been an optical correction, followed by patching and/or pharmacological treatment. (10) Unlike the traditional view, amblyopia is now considered a binocular disorder and many of these new therapeutic techniques are based on the idea that binocular approaches may be superior to monocular methods for treating amblyopia. Variable binocular approaches include- perceptual learning – AmbP iNet, Revital vision(11) (FDA approved for 9 years and older, figure 1), video game technique (Vivid Vision), dichoptic treatment (dichoptic video games, virtual reality based on the principle of monocular fixation in the binocular field, for example-interactive binocular treatment (I-BiT™). (4,10,12,13,14,15) Other options include- syntonic phototherapy utilising a red-orange filter (figure-2), and high-frequency transcranial random noise stimulation (hf-tRNS). (16,17,18)

Figure 1: Revital vision utilises Gabor patch for Amblyopia therapy, Image Courtesy- permission taken from Revital vision

 

Figure 2: Syntonic phototherapy (picture source- Caring Vision Therapy & Neuro-vision Rehabilitation Centre, Chennai, India)

Although no drugs have been approved specifically for amblyopia treatment, levodopa/carbidopa combination is frequently used to increase cortical plasticity in adults while Hermo Pharma Ltd has completed a phase II clinical trial of HER-801 for treatment of amblyopia in adults, the active component of which is fluoxetine. (19, 20)

The aforementioned therapy has shown improvement in stereo-acuity, contrast sensitivity, reduction in suppression, improved binocularity, and improvement of BCVA in the range of 0.1-0.3 logMAR in adults; however there is a lack of literature published on the stability of vision over a period in adults’ population.

Conclusion:

In adults, the management of amblyopia is difficult due to reduced cortical plasticity and poor compliance with traditional therapy. However, the adult population does have the potential to improve in binocularity and vision with the emerging vision therapy given actively as both home and office–based therapy.

Declaration of interest: The blog is written solely for educational purposes, and it does not have any financial support or conflict of interest.

 

References:

  1. Zagui, R. M. B. (2019). Amblyopia: Types, diagnosis, treatment, and new perspectives. American Academy of Ophthalmology, 25, 2-4.
  2. Sharbatoghli, L., Hashemi, H., Mohamadi, A., Jafarzadehpur, E., Yekta, A., Mirzajani, A., & Khabazkhoob, M. (2020). Visual acuity improvement in adult anisometropic amblyopes after active vision therapy. Clinical Optometry, 12, 183.
  3. Ansons, A. M., & Davis, H. (2008). Diagnosis and management of ocular motility disorders. John Wiley & Sons.
  4. Levi, D. M. (2020). Rethinking amblyopia 2020. Vision research, 176, 118-129.
  5. Fu, Z., Hong, H., Su, Z., Lou, B., Pan, C. W., & Liu, H. (2020). Global prevalence of amblyopia and disease burden projections through 2040: a systematic review and meta-analysis. British Journal of Ophthalmology, 104(8), 1164-1170.
  6. Hensch, T. K., & Quinlan, E. M. (2018). Critical periods in amblyopia. Visual neuroscience, 35.
  7. Rosa, A. M., Silva, M. F., Ferreira, S., Murta, J., & Castelo-Branco, M. (2013). Plasticity in the human visual cortex: an ophthalmology-based perspective. BioMed research international, 2013.
  8. Simonsz-Tóth, B., Joosse, M. V., & Besch, D. (2019). Refractive adaptation and efficacy of occlusion therapy in untreated amblyopic patients aged 12 to 40 years. Graefe’s Archive for Clinical and Experimental Ophthalmology, 257(2), 379-389.
  9. Boniquet-Sanchez, S., & Sabater-Cruz, N. (2021). Current management of amblyopia with new technologies for binocular treatment. Vision, 5(2), 31.
  10. Žiak, P., Holm, A., Halička, J., Mojžiš, P., & Piñero, D. P. (2017). Amblyopia treatment of adults with dichoptic training using the virtual reality oculus rift head mounted display: preliminary results. BMC ophthalmology, 17(1), 1-8.
  11. https://doctors.revitalvision.com/about/vision-improvement-technology/ [last Accessed: 18Nov2022, 20:00Hrs AEDT]
  12. Papageorgiou, E., Asproudis, I., Maconachie, G., Tsironi, E. E., & Gottlob, I. (2019). The treatment of amblyopia: current practice and emerging trends. Graefe’s Archive for Clinical and Experimental Ophthalmology, 257(6), 1061-1078.
  13. Gao, T. Y., Guo, C. X., Babu, R. J., Black, J. M., Bobier, W. R., Chakraborty, A., … & BRAVO Study Team. (2018). Effectiveness of a binocular video game vs placebo video game for improving visual functions in older children, teenagers, and adults with amblyopia: a randomised clinical trial. JAMA ophthalmology, 136(2), 172-181.
  14. McCulloch, D. L. (2007). Visual evoked potentials in infants. Infant EEG and event-related potentials, 39-63.
  15. Simon, M. A., Origlieri, C. A., Dinallo, A. M., Forbes, B. J., Wagner, R. S., & Guo, S. (2015). New management strategies for ectopia lentis. Journal of Pediatric Ophthalmology & Strabismus, 52(5), 269-281.
  16. Joly, O., & Frankó, E. (2014). Neuroimaging of amblyopia and binocular vision: a review. Frontiers in integrative neuroscience, 8, 62.
  17. Campana, G., Camilleri, R., Pavan, A., Veronese, A., & Lo Giudice, G. (2014). Improving visual functions in adult amblyopia with combined perceptual training and transcranial random noise stimulation (tRNS): a pilot study. Frontiers in psychology, 5, 1402.
  18. Rodán, A., Marroquín, E. C., & García, L. C. J. (2022). An updated review about perceptual learning as a treatment for amblyopia. Journal of Optometry, 15(1), 3-34.
  19. Erdinest, N., London, N., Lavy, I., Levinger, N., Pras, E., & Morad, Y. (2022). utilising low-dose atropine as an isolated therapy or in combination with other optical measures: A retrospective cohort study.
  20. Suttle, C. M. (2010). Active treatments for amblyopia: a review of the methods and evidence base. Clinical and Experimental Optometry, 93(5), 287-299.

Extra sources of information:

  1. Falcone, M. M., Hunter, D. G., & Gaier, E. D. (2021, May). Emerging therapies for amblyopia. In Seminars in Ophthalmology (Vol. 36, No. 4, pp. 282-288). Taylor & Francis.
  2. Ara, J. (2020). Early Chronic Monocular Visual Deprivation Compromises the Retinal Function of the Deprived Eye (Doctoral dissertation, University of Maryland, College Park).

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