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Edward Lum, Paul J Murphy; The effects of humidity on Cochet-Bonnet aesthesiometer measurements. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1015.
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© ARVO (1962-2015); The Authors (2016-present)
The Cochet-Bonnet (COBO) aesthesiometer is the current standard in corneal sensitivity assessment. This study investigates the influence of ambient room humidity levels on the stimulus force exerted by the instrument.
A COBO instrument (Luneau Opthalmologie, FR) with .08mm nominal nylon filament diameter was placed in an environment chamber (Electro-tech systems Inc., USA) at 25degsC and relative humidity (RH) level adjusted at either 20%, 40%, 60%, or 80%. After 12 hours in the chamber, the instrument was removed and exerted force measured by pressing the nylon filament onto the plate of an analytical microbalance (Mettler-Toledo AB265, SUI; precision ±0.00001g) from a perpendicular angle by a predetermine amount. Applied force onto the microbalance was recorded in grams for a specified filament length. Procedure was repeated for filament lengths 10 to 60mm, in 5mm steps. The instrument was returned to the chamber and procedure repeated at the next RH setting. Measurements at each filament lengths were compared using repeated-measures ANOVA and post hoc paired t-tests with Bonferroni correction. A p-value <0.05 denoted statistical significance.
Significant differences in exerted force were observed with alteration in RH levels for each filament length (all p<.001). Exerted force decreased significantly with increases in RH chamber setting for all filament lengths, with the %force decrease varying from 1% to 35% with each step rise in RH.
This study confirms previous suggestions that the rigidity of the COBO nylon filament is affected by ambient room humidity levels, with implications on the stimulus force exerted by the instrument. We provide a correction table when converting filament lengths to pressure for a range of relative humidity levels.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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