Abstract
This research assesses the brain activity and visual performance at baseline and after light therapy (LTH), of seventeen patients with strabismus and amblyopia (SA), and eleven healthy controls (HCs) from Querétaro, México. Quantitative electroencephalogram analysis (qEEG) was used to record the brain activity, and clinical metrics such as the visual acuity, angle of deviation, phoria state, stereopsis, and visual fields determined the visual performance. Results showed a constant higher alpha-wave frequency for HCs. Low voltages remained negative for HCs and positive for SA patients across stimulation. After LTH, high voltage increased in SA patients, and decreased in HCs. A second spectral peak, (theta-wave), was exclusively recorded in SA patients, at baseline and after LTH. Positive Spearman correlations for alpha-wave frequency, low and high voltages were only seen in SA patients. Synchronized brain activity was recorded in all SA patients stimulated with filters transmitting light in the blue but not in the red spectrum. Enhancement in the visual performance of SA patients was found, whereas deterioration of the phoria state and a decrease in the amount of stereopsis was seen in HCs. To conclude, only a suffering brain and a visual pathway which needs to be enabled can benefit from LTH.
Conclusions
qEEG analysis showed that the brain electrical response and visual performance of patients with SA differs from HCs after the administration of LTH. A higher alpha-wave frequency was recorded for HCs when compared to SA patients, both at baseline and after the LTH program, making the difference statistically significant for Groups (p < 0.001) and Time (p = 0.04). Negative low voltages were recorded for HCs at both conditions, whereas positive values were recorded for SA patients, making the difference statistically significant for Groups (p < 0.001). While high voltage values increased from Time 1 to Time 2 in SA patients, they decreased in HCs, showing a statistically significant difference for Time × Groups (p = 0.008). A second spectral peak, theta-wave was exclusively presented in SA patients, both, at baseline and after the LTH treatment, with no statistically significant changes in its frequency from Time 1 to Time 2 (p = 0.30). However, its distribution across brain regions became more homogenous, but still maintained a frontal lobe predominance. No theta-wave activity was recorded for HCs. SA patients showed positive Spearman correlations for alpha-wave frequency (p = 0.002); baseline and after LTH low and high voltages (p= 0.001 and < 0.001 resepctively). No correlations were found for HCs. After the LTH program, the interhemispheric synchronicity incremented from 23.5% to 76.5% and the alpha-wave distribution prompted towards the occipital regions from 41.2% to 70.6% in SA patients. No significant changes were recorded for HCs from Time 1 to Time 2. Significant enhancement in all evaluated visual abilities were recorded in SA patients, where (p < 0.001) for visual acuity, stereopsis, esotropia at far, and dynamic visual fields; (p = 0.001) for esotropia and exotropia at near, and (p = 0.008 and 0.005) for hypertropia at far and near respectively. Deterioration of the phoria state and a decrease in the amount of stereopsis (p = 0.001) were found in HCs. No changes were recorded for visual acuity, but larger visual fields were measured after the LTH program (p = 0.003). To summarize, LTH produced positive changes in the brain activity and visual performance of SA patients, whereas it deteriorated some of the visual abilities measured in HCs, without affecting the state of brain coherence. The permanent state of theta-waves in SA patients, makes strabismus and amblyopia attributable to an aberrant neurodevelopment process since early ages. LTH then, can only benefit a suffering brain and a visual pathway which needs to be enabled. Its use in healthy population can destabilize the visual system. Considering the importance of the visual system and the large cortical areas involved in processing visual information, LTH gives us the opportunity to modulate the brain activity of SA patients and enhance their visual performance.
