Resting in darkness improves downbeat nystagmus: evidence from an observational study

Abstract

Resting in an upright position during daytime decreases downbeat nystagmus (DBN). When measured in brightness only, that is, without intermitting exposure to darkness, it does not make a significant difference whether patients have previously rested in brightness or in darkness. In real-world scenarios, people are often exposed to brightness and darkness intermittently. The aim of this study was to analyze whether resting in brightness or resting in darkness was associated with a lower post-resting DBN after intermitting exposures to brightness and darkness. Eight patients were recorded with three-dimensional video-oculography in brightness and darkness conditions, each following two 2-h resting intervals under either brightness or darkness resting conditions. The dependent variable was DBN intensity, measured in mean slow phase velocity. A repeated measures ANOVA with the factors measurement condition (brightness vs. darkness), resting condition (brightness vs. darkness), and time (after first vs. second resting interval) showed a significant effect for the factor resting condition, where previous resting in darkness was associated with a significantly lower DBN relative to previous resting in brightness (P < 0.01). The clinical relevance is to advise patients with DBN to rest in darkness.

Downbeat nystagmus: a clinical review of diagnosis and management

“…Resting in upright position is thought to enable otolithic input to stabilize the already disinhibited SVN, causing upward drifting [18]. The same research group also showed resting in the dark decreased SPV by nearly two times the reduction when resting in bright conditions [119]. DBN also improves throughout the day and is at its worse in the morning when arising from sleep, usually in a supine position [7].…”

Downbeat nystagmus: a clinical and pathophysiological review

“…Other influences can be considered, such as the role of extraocular proprioception (102), efference copy (103,104), sleep inertia, which is a transient state of reduced arousal that occurs immediately after awakening from sleep (105-107) and has a negative influence on Purkinje cell function. Finally, the effect of resting for 2 h in darkness was also considered, which significantly lowered the post-rest DBN, in contrast to the effect of resting in light (108).…”

Nystagmus

“…A broad range of drugs has been investigated regarding their effect on different forms of nystagmus [69 & ]. For channelopathies as familial hemiplegic migraine, acetazolamide is effective for treating ] and resting in darkness for 2 h (compared with remaining in bright light), resulting in a relative reduction of vertical slow-phase eye velocity by about one-third [73]. Advanced therapeutic interventions in acquired nystagmus include the attachment of a T-plate to the lateral orbital rim and the inferior rectus muscle tendon [74], the implantation of an oculomotor prosthesis [75] and retrobulbar botulinum-toxin A injections [76], resulting in reduced nystagmus amplitude and oscillopsia in all cases.…”