Purpose: To study whether there is a correlation between the macular and optic nerve morphological condition and the retinal ganglion cells (RGCs) and visual pathways' function, and to investigate whether visual acuity (VA) changes might be related to the morpho-functional findings in chronic non-arteritic ischemic optic neuropathy (NAION).
Methods: In this retrospective study, 22 patients (mean age 62.12 ± 6.87) with chronic unilateral NAION providing 22 affected and 22 fellow eyes without NAION (NAION-FE), and 20 (mean age 61.20 ± 7.32) healthy control subjects were studied by spectral domain optical coherence tomography (Sd-OCT) for investigating macular thickness (MT) and volume (MV) of the whole (WR), inner (IR) and outer retina (OR), and the peripapillary retinal nerve fiber layer thickness (RNFL-T) measured overall and for all quadrants. Also, simultaneous 60' and 15' pattern electroretinogram (PERG) and visual evoked potentials (VEP) and VA were assessed. Differences of MT and MV of WR, IR, OR, and RNFL-T overall and for all quadrants, PERG amplitude (A), VEP implicit time (IT), and A and VA values between NAION eyes and controls were assessed by one-way analysis of variance. Pearson's test was used for regression analysis. A p value < 0.01 was considered as significant.
Results: In NAION eyes as compared to NAION-FE eyes and controls, significant (p < 0.01) changes of MT, MV of WR and IR, RNFL-T, 60' and 15' PERG A, VEP IT and A, and VA were found. No significant (p > 0.01) OR changes were observed between groups. In NAION eyes, significant (p < 0.01) correlations between MV of WR and IR and 15' PERG A were found. Overall, RNFL-T values were significantly correlated (p < 0.01) with those of 60' PERG A and VEP IT and A; temporal RNFL-T values were correlated (p < 0.01) with 15' PERG A and VEP IT and A ones. Temporal RNFL-T, MV-IR, and 15' PERG A as well as VEP IT were significantly (p < 0.01) correlated with VA. Significant (p < 0.01) linear correlations between 60' and 15' PERG A findings and the corresponding values of 60' and 15' VEP A were also found.
Conclusion: Our findings suggest that in chronic NAION, there is a morpho-functional impairment of the IR, with OR structural sparing. VA changes are related to the impaired morphology and function of IR, to the temporal RNFL-T reduction and to the dysfunction of both large and small axons forming the visual pathway.
Keywords: Ischemic optic neuropathy; PERG; Sd-OCT; VEP.