Variability of autonomic nerve activity in dry eye with decreased tear stability

Abstract

The autonomic nervous system plays a crucial role in the maintenance of homeostasis. Neurogenic inflammation due to decreased stability of tear film may induce changes in autonomic nerve activity, which could be associated with symptom expression.This study aimed to measure biological parameters that represent autonomic nerve activity in dry eye (DE)s caused by tear film dysfunction and investigate their relationship with symptom intensity. This prospective, cross-sectional, comparative study evaluated 34 eyes of 34 participants (mean age: 52.5 ± 13.4 years; range: 20–81 years) without keratoconjunctival damage. Nineteen eyes in the DE group showed DE symptoms and tear break-up time (TBUT) of ≤5 seconds (short TBUT DE); the 15 eyes in the non-DE group showed no DE symptoms. Autonomic nerve activity was measured for 10 minutes—starting and ending 5 minutes before and after instilling ophthalmic solution—and evaluated using the low-frequency component (LF) to the high-frequency component (HF) ratio of heart rate variability (autonomic balance). The pre-ophthalmic solution administration LF/HF ratio was not significantly different (P = 0.59) between the two groups, however, the standard deviation of the LF/HF ratio (LF/HF-SD) tended to be higher in the DE group than that in the non-DE group (P = 0.086). The DE symptom intensity was significantly related to LF/HF-SD (P = 0.005), which significantly decreased after ophthalmic solution administration in the DE group (P = 0.04). The large fluctuations in autonomic balance may be key for the understanding of the mechanism underlying DE symptoms.

Autonomic Nerve Activity Features According to Dry Eye Type

“…These results were similar to those of our previous study. 11 Of note, parasympathetic, but not sympathetic, activity plays an important role in the development of DE symptoms in sBUTDE. The autonomic nervous system plays a major role in the stress responses of the emotional pathways.…”

“…The sample size was determined based on a previous study. 11 Among the 24 patients with ADDEs, 14 had Sjögren's syndrome. The sBUTDE was diagnosed based on the presence of DE symptoms, tear BUT ≤5 seconds, and negative keratoconjunctival damage (keratoconjunctival vital staining <3 points).…”

“…We examined the autonomic nerve activity in sBUTDE and found that sBUTDE showed a large fluctuation in the autonomic nervous balance and that this fluctuation was related to the intensity of DE symptoms. 11 Therefore, we speculated that higher brain function sensitized by DE status is involved in the development of symptoms and destabilization of the autonomic nervous balance in sBUTDE. In this study, we reversed these results in patients with symptomatically refractory sBUTDE and compared them with those of patients with ADDE, focusing on sympathetic and/or parasympathetic nerve activities.…”