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

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.