Improvement of uncorrected visual acuity and contrast sensitivity with perceptual learning and transcranial random noise stimulation in individuals with mild myopia

Abstract

Perceptual learning has been shown to produce an improvement of visual acuity (VA) and contrast sensitivity (CS) both in subjects with amblyopia and refractive defects such as myopia or presbyopia. Transcranial random noise stimulation (tRNS) has proven to be efficacious in accelerating neural plasticity and boosting perceptual learning in healthy participants. In this study, we investigated whether a short behavioral training regime using a contrast detection task combined with online tRNS was as effective in improving visual functions in participants with mild myopia compared to a 2-month behavioral training regime without tRNS (Camilleri et al., 2014). After 2 weeks of perceptual training in combination with tRNS, participants showed an improvement of 0.15 LogMAR in uncorrected VA (UCVA) that was comparable with that obtained after 8 weeks of training with no tRNS, and an improvement in uncorrected CS (UCCS) at various spatial frequencies (whereas no UCCS improvement was seen after 8 weeks of training with no tRNS). On the other hand, a control group that trained for 2 weeks without stimulation did not show any significant UCVA or UCCS improvement. These results suggest that the combination of behavioral and neuromodulatory techniques can be fast and efficacious in improving sight in individuals with mild myopia.

The application of online transcranial random noise stimulation and perceptual learning in the improvement of visual functions in mild myopia

“…Naturally, in the case of refractive defects, sensory training does not modify the structure of the eye; nonetheless improvements on uncorrected (that is: in absence of any optical correction) VA and contrast sensitivity (CS) using perceptual learning paradigms have been found; the proposed underlying mechanism in the case of non-cortical visual defects is an increase of signal-to-noise ratio of the de-focused retinal image (Durrie & McMinn, 2007;Tan & Fong, 2008). PL with the use of single Gabor stimuli, has been shown to be able to increase VA and CS in a clinical population of patients with amblyopia (Zhou, et al, 2006), and in recent studies conducted by Camilleri, Pavan, Ghin, Battaglini, et al (2014) and Casco et al (2014) it was found that PL using a simple contrast detection task is able to improve uncorrected VA in participants with mild myopia.…”

“…So far, PL has been shown to be effective in improving, among other dysfunctions, visual abilities in amblyopia (Campana, Camilleri, Pavan, Veronese, & Lo Giudice, 2014;Hussain, Webb, Astle, & McGraw, 2012;Levi & Li, 2009;Li, Young, Hoenig, & Levi, 2005;Polat, 2009;Polat, Ma-Naim, Belkin, & Sagi, 2004;Zhou, et al, 2006), mild refractive defects like myopia (Camilleri, Pavan, Ghin, Battaglini, et al, 2014;Tan & Fong, 2008) and presbyopia (Polat, et al, 2012), and central or peripheral vision loss and cortical blindness (Chung, 2011;Das, Tadin, & Huxlin, 2014;Huxlin, et al, 2009;Kasten, et al, 1998;Plank, et al, 2014;Rosengarth, et al, 2013;Sabel, Kenkel, & Kasten, 2005). In myopia, visual input is limited by an optical de-focus, despite normal neuronal connectivity and image processing.…”

“…In the past decade, PL has started to be considered a useful tool for improving visual functions in clinical populations due to its generalizable effects. In fact, under specific conditions, PL is able to transfer to other stimuli, tasks and circumstances (Camilleri, Pavan, Ghin, Battaglini, et al, 2014;Jeter, Dosher, Petrov, & Lu, 2009;Liu & Weinshall, 2000;Maniglia, et al, 2011;McGovern, Webb, & Peirce, 2012;Webb, Roach, & McGraw, 2007;Xiao, et al, 2008;Zhou, et al, 2006), making it a practical tool that may yield potential benefits for various types of visual impairments. In general, most studies point to a localized increase in processing efficiency in V1 following practice on a visual perceptual task.…”

“…This notion of visual network plasticity is paramount not only in helping us achieve a better understanding of the human visual system and of visual plasticity mechanisms, but also in identifying noninvasive treatment tools and protocols to provide visual rehabilitation following injury, such as hemianopia following stroke (Huxlin, et al, 2009;Kasten, Wust, Behrens-Baumann, & Sabel, 1998), amblyopia, and even when the visual deficit is at the non-cortical level such as in cases of myopia and presbyopia. In the latter case especially, being able to manipulate neuroplasticity might help us achieve visual recovery through compensatory strategies (Camilleri, Pavan, Ghin, Battaglini, & Campana, 2014;Casco, et al, 2014;Durrie & McMinn, 2007;Tan & Fong, 2008).…”

“…Despite its proven effectiveness, PL techniques require lengthy protocols in order to yield effective outcomes (usually a minimum of two months training of up to three to four times weekly) (Camilleri, Pavan, Ghin, Battaglini, et al, 2014;Polat, et al, 2004;Tan & Fong, 2008). Random noise stimulation could optimize the effects of a behavioral training with measurable changes in the brain by modulating neuronal excitability that are involved in long-term potentiation (Fritsch, et al, 2010;Stagg, et al, 2009) which may ultimately lead to neuroplasticity.…”