Friday, April 26, 2013

Dichoptic training enables the adult amblyopic brain to learn


....Adults with amblyopia, a common visual cortex disorder caused primarily by binocular disruption during an early critical period, do not respond to conventional therapy involving occlusion of one eye. But it is now clear that the adult human visual cortex has a significant degree of plasticity, .... One possibility is an inhibitory signal from the contralateral eye that suppresses cortical inputs from the amblyopic eye. .... Here we provide direct evidence that alleviating suppression of the amblyopic eye through dichoptic stimulus presentation induces greater levels of plasticity than forced use of the amblyopic eye alone. This indicates that suppression is a key gating mechanism that prevents the amblyopic brain from learning to see.....

Comments: The research continues to show that adults with amblyopia have a treatable condition AND that amblyopia is not just related to decreased visual acuity in one eye. Amblyopia is a two-eyed-brain problem! When are my colleagues going to realize that you should not treat amblyopia by patching alone?

 The current research tends to support the sequence of therapeutic approaches for amblyopia as noted below:

The [...] indicate my opinion, methodologies, and approaches to care not necessarily support by research at this time. I have no financial interest in any of the products, computer programs or services mentioned unless otherwise noted.
1.) Rx the most appropriate pair of glasses. The patient should wear these full time for 1-3 months.
2. Return for follow-up 1-3 months after Rx wear. Continue to wear the Rx as acuity improves.
3.) Change the Rx as needed.

[Since amblyopes often have poor accommodative systems (focusing), I will frequently prescribe a multifocal lens (bifocal) to improve accommodative function. Hyperopic amblyopes frequently cannot accept the full amount of correction initially. I will cut the distance to an amount I believe the patient can accept, and then add this power to the multifocal/bifocal.]

4.) When improvement in visual acuity reaches a plateau, start to patch the better seeing eye. You usually DO NOT have to patch all day. The research supports from 2-6 hours of patching the better eye per day depending upon the beginning acuity level. 

5.) Once the improvement in visual acuity has once again reached a plateau, start hand-eye activities at home. 

[I will add several different hand-eye activities. Neuroplasticity works best when attention, arousal, and novelty is used as part of the therapy program. Change the therapy fairly often. I typically use the Amblyopia iNet computer program at this stage. Other computer programs I use include Perceptual Visual Tracking Program, ADR iNet (Dynamic Reader), Track and Read, and any number of similar programs. I usually suggest one hour of patching with active therapy and one hour doing normal activities, 5-6 days/week minimum.] 

6.) Continue with the at home activities until visual acuity improvement stops. 

7.) Start in office optometric vision therapy that emphasizes the development of binocular vision (heavy on the anti-suppression). 

[There are 4 phases of optometric vision therapy. These are monocular, biocular, binocular, and integration/stabilization. Individual doctors may start at the monocular phase and then work all the way thru each of the other phases. Other doctors may start at other phases of therapy. I often begin monocularly. The biocular phase is where much of the anti-suppression therapy occurs. The binocular phase is where vergence abilities are improved significantly. The integration/stabilization phase makes the patient use all binocular vision skills (oculomotor, hand-eye, accommodation, vergence) simultaneously. Each phase may work on hand-eye, oculomotor, focusing, vergence, stereopsis and more. Each phase may emphasize one area over another area; for instance, once the monocular phase is completed, hand-eye and oculomotor skills are often greatly improved. The integration/stabilization phase (as well as other phases) may also include cognitive processing, use of distractors, auditory support, various aspects of rhythm/timing, visual-perceptual tasks and other activities to improve habituation of the visual skill.] 

8.) Continue until all visual skills normalize (not only visual acuity, but also hand-eye, accommodation (focusing), binocularity, stereopsis (3D). 

9.) Continue therapy through the integration and stabilization phase. (Integrate all visual skills simultaneously and make sure these skills have been stabilized). 

10.) Discontinue in-office therapy when all skills have been normalized. 

11.) Put the patient on an at home maintenance therapy program. 

[I often continue to use the computer programs noted above for this at home phase of the program.] 

12.) Follow-up in 3 months. 

13.) If visual acuity and all other binocular skills are normal, follow at 6 months and/or annually. 

Research also notes that if you abruptly stop therapy, the visual acuity tends to regress. An at home maintenance program ensures little to no regression. We do not yet know how long the therapy effects last, but research and clinical experience suggests that it lasts for some time. 

There is some research to support the use of specifically designed lenses to improve the treatment of amblyopia. (Bobier W., Shaw P.J. A consideration of binocular parameters in the spectacle correction of anisometropic amblyopia: A Case Report. Optom Vis Dev 2012;43(2):67-71). Please note that I do not currently have a financial interest in this lens. I may have such an interest at some point in the future. 

The take home from this blog discussion of amblyopia is that treatment has only begun once visual acuity improves. In order to keep the visual acuity at an appropriate level and to have that last for some time, binocular vision therapy is needed along with maintenance therapy and appropriate follow-up. Please note that your doctor's approach to treating amblyopia may differ from what is written here. This does not necessarily mean that his/her approach is wrong. The therapeutic approach noted here however, tends to use the latest evidence based science to support the therapy recommended. See a few references below.  DM 

Li J, et al. The role of suppression in amblyopia. Invest. Ophthalmol. Vis. Sci. 2011;52:4169–4176. [PubMed]

To L, et al. A game platform for treatment of amblyopia. IEEE Trans. Neural Syst. Rehabil. Eng. 2011;19:280–289. [PubMed] 

Agrawal R, Conner IP, Odom JV, Schwartz TL, Mendola JD. Relating binocular and monocular vision in strabismic and anisometropic amblyopia. Arch. Ophthalmol. 2006;124:844–850. [PubMed] 

Hess RF, Mansouri B, Thompson B. A new binocular approach to the treatment of amblyopia in adults well beyond the critical period of visual development. Restor. Neurol. Neurosci. 2010;28:793–802. [PubMed] 

Hess RF, Mansouri B, Thompson B. A binocular approach to treating amblyopia: antisuppression therapy. Optom. Vis. Sci. 2010;87:697–704. [PubMed] 

Webber AL, Wood J. Amblyopia: prevalence, natural history, functional effects and treatment. Clin. Exp. Optom. 2005;88:365–375. [PubMed] 

Levi  D. Perceptual learning in adults with amblyopia: A reevaluation of criticalperiods in human vision. Developmental Psychobiology. Special Issue: Critical Periods Re-examined: Evidence from Human Sensory Development. 2005;46(3):222–232 (full pdf) 



1 comment:

  1. everybody talks about dichoptic tetris, but nobody offers a download link


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