Relative Role of ON/OFF Pathways in Resolving and Adapting to Blur in Myopes and Emmetropes.

Purpose: To investigate the contribution of ON/OFF pathways to resolution in the presence of blur and adaptation of the human eye to blur. Methods: Twenty-three healthy young adults (24 ± 4 years) participated, including 11 myopes and 12 emmetropes exhibiting mean spherical equivalent refractive errors of -1.5 ± 0.7 diopters (D) and -0.02 ± 0.2 D, respectively. Visual acuity (VA) was examined over 30 minutes of exposure to +1.00 D myopic blur while overstimulating the ON pathway by viewing a chart displaying brighter letters than background, or the OFF pathway by viewing a luminance- and contrast-matched chart displaying darker letters than background. Linear mixed models examined the blur-induced VA loss and the subsequent relative changes in logMAR VA over time (i.e., blur adaptation), associated with ON/OFF pathways and refractive group. Results: The blur-induced VA loss was significantly less when overstimulating the ON pathway (0.33 ± 0.03 logMAR) compared to the OFF pathway (0.43 ± 0.03 logMAR; P < 0.001), with no significant difference between refractive groups (P = 0.79). Significant blur adaptation was also observed (P < 0.001), which was greater during ON-pathway overstimulation (-14% ± 2%) compared to OFF-pathway overstimulation (-9% ± 2%). Blur adaptation was significantly greater in emmetropes (-18% ± 3%) than myopes (-4% ± 3%; P = 0.004), particularly during ON-pathway overstimulation (interaction effect P = 0.008). Conclusions: Short-term overstimulation of the ON pathway was associated with a smaller blur-induced worsening in VA than overstimulation of the OFF pathway but yielded a greater blur adaptation response, which was more pronounced in emmetropes. Future studies are necessary to examine whether deficient blur adaptation in the ON pathway could serve as a psychophysical biomarker of myopic eye growth.