Noninvasive assessment of corneal sensitivity in young and elderly diabetic and nondiabetic subjects

PURPOSE. To investigate the effect of age and diabetes on corneal sensitivity using the noncontact corneal aesthesiometer (NCCA). METHODS. One hundred sixteen nondiabetic subjects and III diabetic subjects (33 type I and 78 type II) were recruited and divided into three age groups: Young (less than or equal to29 years), Middle (30-59 years) and Older (greater than or equal to60 years). The exclusion criteria included patients with severe retinopathy requiring treatment, a history of invasive ocular surgery, or a history of conditions known to affect corneal sensitivity. The corneal cooling sensation threshold, for the right eye of each subject, was assessed with a double-staircase method-of-limits technique with the NCCA. This instrument uses a controlled pulse of air to produce a small, localized reduction in the surface temperature of the eye, which is detected by the nerves in the corneal epithelium. RESULTS. Analysis of the scatterplot of each subject's central cooling sensation threshold revealed a gradual loss of sensitivity with increasing age (nondiabetic, r(2) = 0.349; diabetic, r(2) = 0.131). Within the nondiabetic group, inter-age-group comparisons found significant differences between the central corneal cooling sensation thresholds for the three age groups (t-test, P < 0.01). Within the diabetic group, a significant difference was found between the Middle and Older categories only (t-test, P < 0.05). In summary, the Young group was more sensitive than the Middle group, which was more sensitive than the Older group. Within both type I and type II diabetic subjects, there was neither a significant relationship between duration of the disease and corneal sensitivity (t-test, P > 0.05) nor a gender-based difference (t-test, P > 0.05). CONCLUSIONS. There is a gradual reduction in corneal sensitivity with increasing age in both nondiabetic subjects and diabetic subjects, along with an increasing variation in the measured threshold. There is no relationship between corneal sensitivity and the time since diagnosis of diabetes for a thermally cooling stimulus, suggesting that the Apartial derivative and C fibers of the corneal innervation are affected differently by abnormal glucose metabolism in the diabetic cornea.