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B. Golebiowski, E. B. Papas, F. Stapleton; Clinical Comparison of the CRCERT-Belmonte and Cochet-Bonnet Aesthesiometers. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2560.
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The Cochet-Bonnet (CoBo) is the most widely used aesthesiometer in clinical studies examining ocular surface sensitivity. However, its critical limitations have resulted in the development of newer instruments, most recently the CRCERT-Belmonte aesthesiometer (CBA). This study compares corneal sensitivity results obtained with the CBA to those of the CoBo, in order to examine the relationship between measurements made with these two instruments.
Corneal sensation threshold was measured in 18 subjects with normal corneas (8M:10F, 34.4±8.0yrs) using the CBA and the CoBo aesthesiometers. Measurements were carried out on the corneal apex of the right eye only and the order in which the instruments were used was randomised. The CoBo was used with both the 0.08 and 0.12mm diameter filaments (CoBo 0.08 and CoBo 0.12). Threshold to stimulation was determined using the ascending method of limits. Pearson’s correlation and Spearman’s rho were used to examine the relationship between threshold results with the CBA and the CoBo. All results were converted to force and pressure and degree of agreement between measurements made with the CBA and the Co-Bo was determined using the statistical approach of Bland and Altman and the Wilcoxon Signed rank test. A 95% confidence level was used.
Mean group corneal thresholds to stimulation (raw values) were: 64.4±29.4 ml/min with CBA; 4.5±1.2 cm with CoBo 0.08; 5.5±0.8 cm with CoBo 0.12. Threshold results for 10 of 18 subjects were outside the stimulus range of the CoBo 0.12 and 2 were outside the range of either filament; all measurements were within the range of the CBA. There was no significant correlation between threshold measured with the CBA and that measured using the CoBo 0.08 or 0.12. In terms of force exerted by the stimulus, corneal threshold was measured to be higher with the CoBo than with the CBA by 0.01mN (Co-Bo 0.08) and 0.05mN (Co-Bo 0.12) (p<0.02). Likewise with respect to pressure, threshold was measured to be higher with the CoBo than with the CBA.
Corneal sensitivity measurements made with the CBA and the CoBo are not comparable, probably due to dissimilarities in the composition of their stimuli and thus mode of stimulation. The underestimation of corneal sensitivity by the Cochet-Bonnet aesthesiometer and its inability to measure sensitivity on a proportion of subjects are important considerations in the measurement of sensitivity loss, as this instrument is unlikely to detect subtle changes, particularly at high sensitivity levels.
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