Laughter is ‘best’ medicine for dry eye disease

A recent study has found that laughing can be as effective as artificial tears (ie, 0.1% sodium hyaluronic acid eye drop) in relieving ocular surface discomfort in patients with dry eye disease (DED) with limited corneal staining.

"[L]aughter exercise, four times a day, was noninferior to 0.1% sodium hyaluronic acid, four times a day, in improving DED symptoms and clinical signs,” the researchers said. “As a safe, environmentally friendly, and low-cost intervention, laughter exercise could serve as a first-line, home-based treatment for people with symptomatic DED and limited corneal staining.”

This randomized controlled trial recruited individuals with symptomatic DED aged 18−45 years with ocular surface disease index score ranging from 18−80 and tear film break-up time of ≤8 seconds from clinics and community. The study was conducted at Zhongshan Ophthalmic Center in China between 18 June 2020 and 8 January 2021.

Overall, 299 participants (mean age 28.9 years, 74 percent female) were randomly assigned to receive either laughter exercise (n=149) or artificial tears (n=140, control) four times daily for 8 weeks. The laughter exercise group watched an instructional video and vocalized the phrases “Hee hee hee, hah hah hah, cheese cheese cheese, cheek cheek cheek, hah hah hah” 30 times per 5-minute session.

The researchers who assessed the study outcomes were masked to the group assignment, but the participants were unmasked for practical purposes.

Noninferior

Of the participants, 283 (95 percent) completed the trial. At 8 weeks, the mean change in ocular surface disease index score was −10.5 points (95 percent confidence interval [CI], −13.1 to −7.82) with laughter exercise and −8.83 (95 percent CI, −11.7 to −6.02) with 0.1% sodium hyaluronic acid eye drop. [BMJ 2024;386:e080474]

The upper boundary of the CI for difference in change between the laughter exercise and control groups was lower than the noninferiority margin (mean difference −1.45 points, 95 percent CI, −5.08 to 2.19; p=0.43), indicating noninferiority.

For the other outcomes, the laughter exercise was more effective than artificial tears in improving noninvasive tear break-up time (mean difference, 2.30 seconds, 95 percent CI, 1.30−3.30; p<0.001), but there was no significant between-group difference in the proportion of patients with a decrease from baseline in ocular surface disease index score of at least 10 points.

In terms of safety, both the laughter exercise and the control groups reported no adverse events.

“Our results showed that laughter exercise was noninferior to 0.1% sodium hyaluronic acid in alleviating DED symptoms,” the researchers said. “Additionally, we found that laughter exercise appeared to improve tear film stability and the meibomian gland function.”

Mechanism

The biological explanations for the beneficial effect of laughing on DED remains unclear. However, studies have shown that the lacrimal gland, which secretes aqueous tears, and the meibomian gland, which secretes lipid, are both “innervated” by parasympathetic nerves. [Prog Retin Eye Res 2009;28:155-177]

Additionally, laughing, particularly abdominal breathing, causes the respiratory muscles to contract, thus stimulating the autonomic nervous system, including the activation of sympathetic and parasympathetic nervous system. As a result, laughter exercise induces tear secretion via the autonomic nervous system activation. [Emotion 2008;8:714-719; Ocul Surf 2017;15:404-437]

Previous studies have also shown that positive emotions in animals stimulate tear secretion through the release of oxytocin, which could be triggered by laughter. [Curr Biol 2022;32:R869-70; Biol Psychol 2022;172:108377]

"In our study, we hypothesized that positive emotions may also prompt tear secretion through deep breathing, relaxation, and laughter during the laughter exercise,” the researchers said. “The biological mechanisms underlying this effect warrant further study.”