The Psychophysics Of ON- Versus OFF- Pattern Recognition And Myopia - Info and Reading Options

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the prevalence of myopia was around 10%, but today nearly 90% of young adults are afflicted [1]. In the United States and Europe, the prevalence has doubled over the last half-century with half of young adults now having myopia[1]. The consequence of myopia extends beyond the inconvenience of using optical correction. Myopia is associated with increased incidence of diseases such as retinal damage, cataract, and glaucoma [1]. Increased levels of near-work have commonly been associated with the onset of myopia [2]. It is therefore important to gain a better understanding of what is happening from a functional and anatomical standpoint when subjects complete near-work tasks. There are two different types of text, texts that have positive contrast (white text on a darker background) and texts that have negative contrast (black text on a lighter background). Aleman et. al (2018) found that negative contrast texts produced a thinning effect on the choroid (-16.13土4.54 μm), and positive contrast produced a thickening effect on the choroid(9.96土 6.51μm) [3]. Aleman et. al interpreted these results in the context of ON and OFF pathways in the visual system [4]. They suggested negative contrast texts stimulate the OFF pathway, while positive contrast texts stimulate the ON pathway. Choroidal thickening and thinning in both chicks and marmosets has been observed to be a precursor to a decrease or an increase in axial growth respectively [5, 6, 7]. The latter leading to the development of myopia. Trolio et. al documented 20 μm of choroidal thinning in myopia induced marmoset eyes and 12 μm of thickening in eyes induced with hyperopia [5]. It is hypothesized that the choroid either acts as a mechanical buffer or a diffusion barrier for the sclera [5]. Qualitatively, Aleman et al’s data showed the thinning effect was more pronounced in myopic individuals as compared to their emmetropic counterparts [3], but their sample size was insufficient to draw quantitative conclusions. The plasticity of the human choroid is an important link to animal models. For example, Read et. al found that among a group of 39 myopic individuals subfoveal choroidal thickness was 50 μm thinner than nonmyopic age-matched children [8]. Retinal Ganglion Cells are organized in an ON center OFF surround arrangement or vice versa [2]. ON cells become depolarized to an increment in light, while OFF depolarize in response to decrements in light. OFF retinal ganglion cells are twice as numerous and half the size of ON rental ganglion cells in the fovea. Several studies such as Mazade et. al, Lu et. al, and Tyler et. al corroborated the different spatial tuning and cortical connectivity of the ON and OFF pathway [9, 10, 11]. Mazade et al showed maximal cortical responses for small fast stimuli in the OFF pathway and maximal cortical responses for slow slow global stimuli in the ON pathway [10]. Zhong-Lin et. al found negative stimuli (or decrements in light) to be 25% more effective than equal magnitude positive stimuli (or increments in light) across eleven different types of stimuli [11]. Taken together, these studies support a distinct roles for the ON and OFF pathways in the visual system. The goal of our study is threefold. We aim to replicate the changes in choroidal thickness in response to negative and positive contrast with a larger subject group. We aim to measure the sensitivity to positive and negative contrast tasks and compare the ratio of contrast sensitivity to these two contrast types among refractive error/axial length. Finally, we will monitor the changes in sensitivity to positive and negative contrast as the session proceeds as to understand the functional implications choroidal thickness changes may have.

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