Regional Differences in the Relationship Between Retinal Structure and ON-OFF Pathway Function in Myopic Patients

Abstract

Purpose: The purpose of this study was to measure the effect of myopia on ON and OFF pathway asymmetries displayed between 5˚ to 30˚ of eccentricity and examine the structure-function relationship between retinal thickness and visibility of light and dark stimuli in eccentric quadrants of myopic eyes. Methods: Eighteen eyes were randomly selected from human subjects and all myopic subjects underwent testing with habitual soft contact lens correction. Subjects underwent ON-OFF perimetric testing in the test eye. The complete procedure is referenced and discussed in the body of the manuscript. Stimuli were presented at various contrasts across 30-degrees of the visual field and stimuli increased in size as a function of eccentricity. Structural and functional testing, including ultra-wide field macular optical coherence tomography (OCT), 30-2 static automated perimetry (SAP) mean sensitivity, peripheral autorefractive (AR) measurements, and axial length (AL), were also measured. All testing, except axial length measurements, were taken with subjects fully corrected in soft contact lenses. Results: There was a statistically significant positive correlation between AL and combined light and dark errors across the entire testing area of 5-30° (p=0.0019) as well as each eccentric range (5-10° p=0.0389; 11-20° p=0.0015; 21-30° p =0.0008). There was a statistically significant positive correlation between errors to light stimuli as a function of AL across the entire testing area of 5-30° (p=0.0251), 11-20° (p=0.0207) and 21-30° (p =0.0178). There was a statistically significant positive correlation between AL and dark stimuli errors across the entire testing area of 5-30° (p=0.0461), 11-20° (p=0.0424) and 21-30° (p =0.024). There was no statistically significant correlation when analyzing errors to light and dark stimuli separately at the 5-10° eccentricity. There was a statistically significant negative correlation between RE and combined light and dark errors across the entire testing area of 5-30° (p=0.0444) and a statistically significant negative correlation at the most peripheral eccentric range of 21-30° (p=0.0128). Subjects displayed higher errors to light stimuli over the entire testing area 5-30° (p=0.0166) and 21-30° (p=0.0007), but not at 5-10° or 11-20° (5-10° p=0.7043; 11-20° p=0.2572). The quadrant with the greatest average retinal thickness (IT) was associated with the lowest %errors (6.45 ± 6.56) and highest visual field mean sensitivity (VFMS, 30.9 ± 1.08 dB), whereas the quadrant with the least average retinal thickness (SN) was associated with the highest % errors (22.77 ± 15.93, p=8.91 x 10-9 for IT vs SN comparison) and among the lowest MS (29.43 ± 1.34, p=0.0020 for IT vs SN comparison). Conclusion: Higher levels of myopia are associated with greater response errors during ON-OFF perimetric testing, with higher error rates in response to light targets compared to dark targets. Both findings are most pronounced at the 21–30-degree eccentricity and have a stronger correlation with axial length compared to refractive error. Higher rates of error on ON-OFF perimetry correspond to thinner retinal thickness in the corresponding retinal quadrant. The highest average percent errors on ON-OFF perimetric testing were present in the superonasal visual field, which coincides with the thinnest total retinal thickness in the corresponding region of the retina (interotemporal). Better understanding of the structural and correspond to thinner retinal thickness in the corresponding retinal quadrant. The highest average percent errors on ON-OFF perimetric testing were present in the superonasal visual field, which coincides with the thinnest total retinal thickness in the corresponding region of the retina (interotemporal). Better understanding of the structural and corresponding functioning relationship between ON-OFF perimetric testing and retinal thickness may enhance our understanding of myopic refractive development.