Aims: To determine the repeatability of measurement of the corneal sensation threshold using the Non-Contact Corneal Aesthesiometer (NCCA); to evaluate the effect of the air-jet diameter and stimulus duration on the threshold; and to compare the sensation thresholds found with the NCCA and with the Cochet-Bonnet Aesthesiometer (C-BA), on the same group of normal, human subjects.
Methods: For all experiments, only the central corneal sensation thresholds were measured. (1) NCCA Repeatability; 17 subjects tested at the same time on five separate days. (2) NCCA Air-Jet Diameter; 15 subjects tested using four different air-jets: 0.35, 0.5, 1 and 2 mm. (3) NCCA Stimulus Duration; 15 subjects tested using three stimulus durations: 0.5, 0.9 and 1.5 sec. (4) NCCA and C-BA; 43 subjects tested using each instrument in turn.
Results: (1) No significant differences in mean sensation threshold were detected across the five days of testing, or between individual days. (2) 0.5 and 1 mm air-jets produce least variability in mean sensation threshold. (3) No significant difference in mean sensation thresholds was found between the three test durations. (4) For each subject, there was no correlation between each instrument's mean sensation threshold.
Conclusions: (1) The NCCA was able to assess the corneal sensation threshold in an accurate and repeatable manner. (2) The optimum test parameters were found using the 0.5 mm air-jet, over a stimulus duration of 0.9 sec. (3) The C-BA has serious deficiencies in its design which limit its ability to accurately measure corneal sensitivity at low stimulus thresholds.