Visual acuity in the context of retinal neuroaxonal loss in people with epilepsy

Abstract

Objective: Recent studies reported a significant retinal neuroaxonal loss in people with epilepsy (PWE). However, the impact of these structural alterations on visual function, i.e., visual acuity is yet unknown.

Methods: In this prospective cohort study, 70 PWE and 76 healthy controls (HC), all aged 18-55 years, underwent an assessment of visual acuity with 100 % high contrast (HCVA) and 2.5 % low contrast (LCVA) Sloan letter charts. Thickness of the global peripapillary retinal nerve fiber layer (G-pRNFL) and volume of the ganglion cell inner plexiform layer (GCIP) were assessed with spectral-domain optical coherence tomography (OCT). For the statistical analyses, the epilepsy group was subdivided into PWE with sodium channel blocking (SCB)-drug intake (n = 52) and PWE without SCB-drug intake (n = 18), since an effect of SCB-drugs on visual perception has been reported previously.

Results: The overall PWE cohort presented significantly lower structural retinal measures, i.e., G-pRNFL thickness (97.57 ± 9.06 µm) and GCIP volume (1.99 ± 0.13 mm³) than HC (101.31 ± 8.28 µm, p = .01; 2.10 ± 0.15 mm³, p < .001). Subgroup analyses revealed that PWE who were treated with SCB-drugs had a significantly reduced G-pRNFL thickness (96.61 ± 9.70 µm, p = .01) and GCIP volume (1.98 ± 0.14mm³, p < .001) compared to HC, while PWE without SCB-drugs (100.36 ± 6.32 µm, 2.01 ± 0.13 mm³) did not differ from HC or PWE with SCB-drugs. In visual acuity tests (HCVA and LCVA), the overall PWE cohort (52.28 ± 8.56; 31.71 ± 8.49) scored significantly lower than HC (56.57 ± 4.74, p = .001; 35.13 ± 5.50, p = .04). In subgroup analyses only PWE with SCB-drugs presented significantly lower HCVA (51.25 ± 9.35, p = .003) and LCVA (30.04 ± 8.93, p = .03) scores compared to HC, while visual acuity scores did not differ between PWE without SCB-drugs (55.25 ± 4.75, 36.53 ± 4.50) and HC. PWE with SCB-drugs had significantly lower LCVA scores than PWE without SCB-drugs (p = .03). Importantly, no association was found between visual acuity scores and structural parameters, neither in the overall sample, nor in any of the subgroups.

Significance: Retinal neuroaxonal loss in PWE was not associated with reduced visual acuity under high and low contrast. Instead, our findings reinforce SCB-drug intake as an important factor for reduced visual acuity under high and low contrast.

Keywords: Optical coherence tomography; Sloan letter charts; Sodium-channel blocking drugs; Visual acuity.