Uncorrected Myopia Affects the Visual Resolution of OFF Pathways More Than ON Pathways

Abstract

"Introduction: The balance between ON- and OFF-pathway responses is believed to play a significant role in the progression of myopia in children [1, 2]. In a recent study, we found that uncorrected myopic children exhibited poorer visual acuity—approximately 1.5 logMAR lines—when identifying dark optotype stimuli (primarily processed by the OFF-pathway) compared to light stimuli (processed by the ON-pathway). In this study, we examine whether this asymmetry between light and dark stimuli is associated with the severity of myopia. Methods: Cycloplegic refractive error was used to calculate the spherical equivalent (SEQ). Based on SEQ, children aged 8 to 12 years were divided into two groups: a myopic group (−0.75D to −6.00D, N=11) and a non-myopic control group (−0.38D to +1.25D, N=15). Corrected and uncorrected right eye visual acuity (VA) was assessed using E-ETDRS charts with either light or dark optotypes presented at full contrast (on dark or light backgrounds, respectively) in randomized order, repeated twice with a 30-minute interval. Light-dark asymmetry was quantified using the ON-OFF VA ratio. Results: The myopic group demonstrated significantly greater light-dark asymmetry compared to the control group (1.15 ± 0.08 vs. 1.00 ± 0.02, p < 0.001), indicating that uncorrected myopic eyes experience increased difficulty in resolving dark optotypes relative to light ones. Furthermore, a modest yet statistically significant correlation was observed between spherical equivalent (SEQ) and the ON-OFF visual acuity ratio (r = 0.38; t = −2.4, p = 0.02), suggesting that this asymmetry becomes more pronounced with increasing severity of myopia. Conclusions: These findings suggest that uncorrected myopic eyes have more difficulty perceiving dark compared to light stimuli, and that this ON-OFF pathway imbalance is associated with the degree of myopia. Further research is warranted to explore the potential of light-dark asymmetry as a biomarker for monitoring myopia progression in children."