Does air gas aesthesiometry generate a true mechanical stimulus for corneal sensitivity measurement?

TitleDoes air gas aesthesiometry generate a true mechanical stimulus for corneal sensitivity measurement?
Publication TypeJournal Article
Year of Publication2018
AuthorsNosch, D., H. Pult, J. Albon, C. Purslow, and P. Murphy
JournalClinical and Experimental Optometry
Keywordsadult, air, air gas aesthesiometry, body temperature, clinical trial, Cornea, corneal sensitivity, devices, female, human, Humans, male, Mechanical, mechanical stimulus, mechanical stress, mechanoreceptor, Mechanoreceptors, optometry, perceptive threshold, physiology, Prospective Studies, prospective study, Sensory Thresholds, single blind procedure, Single-Blind Method, Stress, young adult

Background: Belmonte Ocular Pain Meter (OPM) air jet aesthesiometry overcomes some of the limitations of the Cochet-Bonnet aesthesiometer. However, for true mechanical corneal sensitivity measurement, the airflow stimulus temperature of the aesthesiometer must equal ocular surface temperature (OST), to avoid additional response from temperature-sensitive nerves. The aim of this study was to determine: (A) the stimulus temperature inducing no or least change in OST; and (B) to evaluate if OST remains unchanged with different stimulus durations and airflow rates. Methods: A total of 14 subjects (mean age 25.14 ± 2.18 years; seven women) participated in this clinical cohort study: (A) OST was recorded using an infrared camera (FLIR A310) during the presentation of airflow stimuli, at five temperatures, ambient temperature (AT) +5°C, +10°C, +15°C, +20°C and +30°C, using the OPM aesthesiometer (duration three seconds; over a four millimetre distance; airflow rate 60 ml/min); and (B) OST measurements were repeated with two stimulus temperatures (AT +10°C and +15°C) while varying stimulus durations (three seconds and five seconds) and airflow rates (30, 60, 80 and 100 ml/min). Inclusion criteria were age <40 years, no contact lens wear, absence of ocular disease including dry eye, and no use of artificial tears. Repeated measures (analysis of variance) and appropriate post-hoc t-tests were applied. Results: (A) Stimulus temperatures of AT +10°C and +15°C induced the least changes in OST (−0.20 ± 0.13°C and 0.08 ± 0.05°C). (B) OST changes were statistically significant with both stimulus temperatures and increased with increasing airflow rates (p < 0.001), and were more marked with stimulus temperature AT +10°C. Conclusion: A true mechanical threshold for corneal sensitivity cannot be established with the air stimulus of the Belmonte OPM because its air jet stimulus with mechanical setting is likely to have a thermal component. Appropriate stimulus selection for an air jet aesthesiometer must incorporate stimulus temperature control that can vary with stimulus duration and airflow rate. © 2017 Optometry Australia