Can repetitive transcranial magnetic stimulation influence the visual cortex of adults with amblyopia? - systematic review.

Amblyopia is the most frequent cause of monocular vision loss. Transcranial Magnetic Stimulation (TMS) has been used to improve several vision parameters of the amblyopic eye in adulthood. This study is relevant in order to evaluate TMS effects and to raise awareness of the need for further research. Transcranial Magnetic Stimulation (TMS) is a neuromodulation technique capable of changing cortical excitability. In the last decade, it has been used to improve visual parameters in amblyopic patients. The main goal of this systematic review is to evaluate the influence of TMS in the amblyopic eye, in the visual parameters of amblyopic patients. Searches were done in PubMed and Embase databases, and a combined search strategy was performed using the following Mesh, EMBASE, and keywords: 'Amblyopia', 'Transcranial Magnetic Stimulation', and 'theta burst stimulation'. This review included randomised controlled studies, descriptive cases, and clinical case studies with adult amblyopes. All articles that had any of the following characteristics were excluded: children or animal studies, reviews, pathologies other than amblyopia, and other techniques rather than repetitive TMS (rTMS), or Theta Burst Stimulation (TBS). A total of 42 articles were found, of which only four studies (46 amblyopes) meet the criteria above. Three of the articles found significant improvement after one session of continuous TBS (cTBS) in visual parameters like visual acuity, contrast sensitivity, suppressive imbalance, and stereoacuity. One study found a significant visual improvement with 10 Hz rTMS. Only one stimulation-related dropout was reported. The few existing studies found in this review seem to show that through the usage of high-frequency rTMS and cTBS, it is possible to re-balance the eyes of an adult amblyope. However, despite the promising results, further research with larger randomised double-blind studies is needed for a better understanding of this process.

Pattern electroretinography response in amblyopic adults.

INTRODUCTION: Amblyopia is generally a unilateral disorder, defined by at least a difference of two lines of visual acuity between both eyes with the best-corrected visual acuity, a decrease in contrast sensitivity, and a decrease in stereopsis. Pattern electroretinogram (PERG) is a noninvasive technique that provides a retinal biopotential and is a highly sensitive indicator of changes in the macular area. Our aim was to evaluate if there are differences in the retinal response of an amblyopic eye compared with a normal eye (NE). METHODS: We evaluated twenty-four adult volunteers, twelve amblyopes (mean 43.42 ± 12.72 years old), and twelve subjects with NE (mean 35.58 ± 12.85 years old). None of the subjects in the two groups had comorbidities. A complete optometric examination was performed including parameters such as visual acuity (VA) by far and near with ETDRS chart, eye alignment with cover test, and evaluation of retinal cells response with PERG. RESULTS: The refractive error found in the NE group of subjects had a mean of - 0.95 ± 1.65D, while the amblyopic group showed a mean of - 2.03 ± 4.29D. The VA in amblyopic eyes had a mean of 0.38 ± 0.20 logMAR. Analyzing PERG data, we observed significant differences in the P50-N95 amplitudes of the amblyopic group compared with the NE group (p < 0.0001-amblyopic eye vs. NE; p = 0.039-fellow eye vs. NE). DISCUSSION: These findings suggest that amblyopic patients may also present other impairments beyond the visual cortex. PERGs seem to be an important complementary examination in the diagnosis of other impairments in amblyopia.

Longstanding effects of continuous theta burst stimulation in adult amblyopes.

CLINICAL RELEVANCE: Continuous theta burst stimulation may be an important tool in the therapeutic management of amblyopia, when trying to correct the established neuronal imbalance. It is important to understand whether two sessions of continuous theta burst stimulation produce greater and longstanding changes in visual acuity and suppressive imbalance than one session of continuous theta burst stimulation. BACKGROUND: We hypothesise that through the usage of continuous theta burst stimulation (cTBS) it is possible to change cortical excitability in a situation where visual impairment is present. METHODS: We selected 22 adult amblyopes, 18 females and 4 males, with an age range of 20-59 years. They were randomised into two groups: group A with 10 amblyopes was submitted to one session of cTBS and group B with 12 amblyopes submitted to two sessions of cTBS. Visual acuity (VA) and suppressive imbalance (SI) were evaluated immediately before and after stimulation in both groups A and B. A follow-up was done in both groups. RESULTS: For both group A and B, the VA improvements were significant after cTBS (p = 0.005 and p = 0.003, respectively). Regarding SI, both group A and B had significant improvements after cTBS (p = 0.03 and p = 0.005, respectively). Comparing groups, A and B no significant differences were found with regard to the results obtained both for VA (p = 0.72) and SI (p = 0.24). However, significant differences were found between group A and B with regard to the duration of stimulation effect for VA (p = 0.049) and SI (p = 0.03). CONCLUSION: We conclude that two sessions of cTBS do not produce better results than one session of stimulation. However, it seems that two sessions of cTBS produce longstanding effects in VA and SI.

Can pattern electroretinography be a relevant diagnostic aid in amblyopia? - A systematic review.

INTRODUCTION: Pattern Electroretinography (PERG) is a highly sensitive electrophysiological technique used as an indicator of changes in retinal macular area. Amblyopia seems to result from a cortical visual imbalance but changes at the retinal level may also be present. The purpose of this systematic review was to evaluate if there are any consistent changes described in the scientific literature in PERG responses of amblyopic eyes. MATERIALS AND METHODS: Searches were conducted in PubMed and Embase databases, using the keywords "Electroretinography" and "Amblyopia", combined with MeSH or Emtree terms "Pattern Electroretinography", "amblyopia", "PERG" and "amblyopia". PERG P50-N95 amplitude and P50 latency were analysed as well as the methodology used. RESULTS: A total of 234 articles were found and 6 articles were included for review. One of the articles reported results in adults and five of them in children. One of the articles in children reported no changes in either P50-N95 amplitude or P50 latency. All articles that described differences between the amblyopic eye and the normal eye found a decrease in P50-N95 amplitude and/or a delay in P50 latency. CONCLUSIONS: This review shows promising findings for the use of PERG in amblyopia as an aid in the diagnostic protocol, since this technique may be able to detect an apparent functional impairment of the amblyopic eye.

Theta burst stimulation in adults with symmetric and asymmetric visual acuity.

PURPOSE: Theta Burst Stimulation can influence adult neuro-visual response in imbalanced visual pathways, possibly by influencing cortical excitability. Our objective was to compare suppressive imbalance (SI) and visual acuity (VA) after applying repetitive Transcranial Magnetic Stimulation between groups of subjects with normal binocular vision, visual asymmetry, and amblyopia. METHODS: Thirty-five volunteers between 19 and 51 years of age were split into three groups: 6 volunteers with asymmetric VA (group A); 19 amblyopes (group B); and 10 subjects with normal binocular vision (group C). VA and SI of all groups were evaluated before and after a single session of continuous Theta Burst Stimulation (cTBS) or placebo stimulation over the right occipital cortex. RESULTS: In both groups A and B, we found a significant VA improvement in the non-dominant eye after cTBS (p = 0.04 and p = 0.01, respectively). In SI evaluation, group A and group B also revealed a significant improvement after the cTBS session (p = 0.03 and p = 0.01, respectively). Finally, in the group of volunteers with normal binocular vision and for placebo groups A and B, there were no significant differences in VA and SI after cTBS. CONCLUSIONS: Amblyopic and visually asymmetric individuals improved VA and SI of the non-dominant eye after cTBS when compared to baseline and to placebo stimulation. These enhancements were not found in the group of volunteers with normal binocular vision. We can therefore reasonably assume that cTBS may interfere with the visual system of subjects that present some kind of asymmetry, possibly by improving neuronal imbalances.

Transcranial Magnetic Stimulation in Adults With Amblyopia.

BACKGROUND: Through transcranial magnetic stimulation (TMS) it is possible to change cortical excitability of the visual cortex, and to influence binocular balance. The main goal of our study is to assess the effect of transcranial magnetic stimulation, specifically theta burst stimulation (TBS), in a group of amblyopic volunteers measuring several visual parameters: visual acuity, suppressive imbalance, and stereoacuity. METHODS: Thirteen volunteers aged 19 to 24 years, randomly split in 2 groups, underwent 1 session of continuous TBS, stimulating the right occipital lobe. The first group with 8 volunteers was exposed to active stimulation with cTBS, and the other group with 5 volunteers was exposed to placebo stimulation. RESULTS: Significant improvements in visual acuity, suppressive imbalance, and stereoacuity were found in the amblyopic eye after cTBS. The average value of amblyopia in visual acuity before stimulation was 0.32 ± 0.20 logMar and after cTBS was 0.19 ± 0.17 logMar. The mean value for the control group before placebo stimulation was 0.28 ± 0.17 and after placebo stimulation was 0.28 ± 0.16. The suppressive imbalance in the group of amblyope subjects stimulated before cTBS was 0.26 ± 0.18 and after was 0.12 ± 0.12; the suppressive imbalance of the control group before the placebo stimulation was 0.34 ± 0.37 and after was 0.32 ± 0.40. CONCLUSIONS: Visual acuity, suppressive imbalance, and stereoacuity had significant enhancements compared with baseline after cTBS over the right occipital lobe in an ambliopic population.