Abstract
Purpose :
To investigate the effect of inducing hyperosmolarity using 5% w/v NaCl eye drops on the concentration of inflammatory markers in the human tear film.
Methods :
A single dose of 30µl 5%(w/v) NaCl or multiple doses of 30µl every 5mins for 25 mins (to simulate extended periods of hyperosmolarity) were applied to the ocular surface. Then a 1µL of tear sample was taken from the lower tear meniscus using a disposable, sterile, micro capillary tube. Each sample was analysed using a multiplex immunoassay (Milliplex, Merck Millipore, UK) to evaluate the presence and concentration of a panel of inflammatory biomarkers (IL1β, IL2, IL6, IL8, IFNγ and TNFα).
A pilot study was carried out to assess the dynamics of the inflammatory milieu (n=2, age 33 and 34 years 1F; 1M). Tear samples (1µl) were taken at a number of time points (baseline, 0, 2, 4, 6, 8, 10, 15, 30, 60, 180 minutes post instillation). This informed the main study (n=5, age range 33-53; mean 40±8 years, 2F; 3M) where tear samples were taken at 5 time points (prior it NaCl instillation, then 30, 60, 90 and 120 minutes post instillation).
Results :
From the pilot experiment it was clear that the early sample points were not required as induced reflex lacrimation was apparent. A change in the average concentration of all inflammatory markers following NaCl instillation was observed. However, these average changes did not reach statistically significance due to the high variation between individuals (Friedman test P>0.05).
In both methods (single or multiple application of NaCl), for individual subjects, the concentration of inflammatory markers (IL1β, IL2, IL6, IL8, IFNγ and TNFα) reduced during the first 30 mins post instillation. Interestingly, there was an increase in the concentration of these markers at 60 mins in both instillation methods.
Conclusions :
Based on these results, hyperosmolarity caused changes in inflammatory marker concentration. We hypothesize that the 5% NaCl induces reflex lacrimation, which caused an initial decrease in concentration of inflammatory markers during the first 30 min. It is apparent that tear hyperosmolarity took almost 60 min to increase the inflammatory markers in the tear film. This may explain why hyperosmolar inducing environmental condition such as air travel only becomes problematic if the exposure is lengthy (> 60 min).
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.