Basal Tear Secretory Capacity Measured With Novel CO2 Emitting Device

Measuring basal tear secretory capacity using CO2 stimulation may be useful in the early diagnosis and management of dry eye disease.

A novel CO2-emitting corneal stimulation device creates maximal reflex tearing, which in turn stimulates basal tearing to its maximum secretory capacity in the contralateral eye, according to a study published in Ocular Surface. Measuring this maximum secretory capacity may aid clinicians in diagnosing dry eye disease (DED), according to the report.  

Researchers included 88 volunteers in a clinical trial consisting of 2 control groups and 2 cohorts of patients with DED. Control group A included 17 students aged 20 to 30 years and control group 2 included 29 individuals obtained via convenience sampling. The DED cohort consisted of individuals who exhibited DED signs upon examination, but were asymptomatic (n=12; mean age, 56 years; 67% women) and patients with Sjögren syndrome (n=30; mean age, 51 years; 90% women). 

All participants underwent sensory corneal nerve stimulation following delivery of CO2 gas to 1 eye with the device. The research team measured tear volume using Schirmer strips over 3 minutes in the eye receiving treatment before stimulation (stimulated tear volume) and basal tear volume in the contralateral eye.

The tear volume (basal: 14.6 mm; stimulated: 19.0 mm) increased significantly in 78% of control group participants, which reflected a mean tear reserve volume (stimulated volume – basal tear volume) of 4.4 mm. No differences were noted in the incidence of positive responses or in the mean basal or stimulated tear volume between the 2 control groups, according to the report. 

This procedure may be useful for the diagnosis and follow-up of DED patients.

Patients with DED who were asymptomatic displayed weaker responses to stimulation, evidenced by lower stimulated tear volumes. Both the basal and stimulated tear volumes of patients with Sjögren syndrome were significantly lower compared with control individuals.

Researchers highlight the utility of using the CO2 emitting device in detecting DED. “This procedure may be useful for the diagnosis and follow-up of DED patients,” according to the study authors. “Moreover, it may help evaluate and prevent the appearance of eye dryness in patients with a critically low [tear reserve volume] before they are exposed to therapeutic procedures that may potentially reduce the corneal sensory nerve input that maintains reflex tear secretion.”

Study limitations include the use of convenience sampling, a small sample size, and the use of shortened Schirmer testing. 

Disclosure: Multiple study authors declared affiliations with biotech, pharmaceutical, and/or clinical research organizations. Please see the original reference for a full list of authors’ disclosures. 


Merino ML, Belmonte J, Rosas J, Acosta MC, Gallar J, Belmonte C. Maximal tear secretion evoked by controlled stimulation of corneal sensory nerves in healthy individuals and dry eye subjects. Ocul Surf. Published online November 14, 2022. doi:10.1016/j.jtos.2022.11.005