Objective: Nystagmus consists of involuntary to and fro movements of the eyes. Although studies have shown that memantine and gabapentin can reduce acquired nystagmus, no drug treatment has been systematically investigated in congenital nystagmus.
Methods: We performed a randomized, double-masked, placebo-controlled study investigating the effects of memantine and gabapentin on congenital nystagmus over a period of 56 days. The primary outcome measure was logarithmic minimum angle of resolution (logMAR) visual acuity; the secondary outcome measures were nystagmus intensity and foveation, subjective questionnaires about visual function (VF-14) and social function. Analyses were by intention to treat.
Results: Forty-eight patients were included in the study. One patient in the placebo group dropped out. Patients were randomized into either a memantine group (n=16), gabapentin group (n=16), or placebo group (n=15). Mean visual acuity improvements showed a significant effect between treatment groups (F=6.2; p=0.004, analysis of variance) with improvement in both memantine and gabapentin groups. Participants with afferent visual defects showed poorer improvements in visual acuity to medication than those with apparently normal visual systems. However, eye movement recordings showed that both nystagmus forms improved in nystagmus intensity (F=7.7; p=0.001) and foveation (F=8.7; p=0.0007). Participants subjectively reported an improvement in vision after memantine and gabapentin treatment more often than in the placebo group (p=0.03). However, there were no significant differences between the treatment groups with visual function (VF-14) or social function questionnaires because all groups reported improvements.
Interpretation: Our findings show that pharmacological agents such as memantine and gabapentin can improve visual acuity, reduce nystagmus intensity, and improve foveation in congenital nystagmus.