Corneal Sensitivity with the Non-contact Esthesiometer as Compared to the Cotton Wisp Test in Patients with Ocular...

Intact corneal sensation plays a vital role in maintaining ocular surface health. Various ocular surface pathologies can present with differing levels of decreased corneal sensation, while in some cases patients may instead experience heightened sensation. This study compared corneal sensitivity with the new quantitative non-contact esthesiometer (NCE, Brill, USA) and the conventional qualitative cotton wisp (CW) test in patients with ocular surface diseases (OSD).

A retrospective, cross-sectional study was conducted, including patients with OSDs, who had both CW and NCE test results available. Descriptive analysis of one eye per patient was performed to compare the distribution of patients according to NCE and CW responses.

Of 139 eyes (n = 139 patients), 129 (92.8%) were CW+ and 10 eyes were CW- (7.2%). Among these, 111 eyes responded to levels 1-3 when assessed with NCE, with 38 (34.2%) responding to level 1, 45 (40.5%) to level 2, and 28 (25.2%) to level 3. However, of CW+ eyes, 10 (7.8%) responded to level 4 and 6 (4.7%) responded to level 5 of NCE, while 2 (1.6%) had no response to any NCE stimulation (i.e., level 6), indicating varying degrees of hyposensitivity not detected by CW. Of the 10 eyes (7.2%) that did not respond to CW (CW-), 3 responded to level 4, and one to level 5 of NCE, while 4 eyes (40.0%) failed to respond to NCE (level 6). Notably, two CW- patients responded to level 1 NCE, suggesting potential hypersensitivity. Results showed high sensitivity (98.2%, 95% CI 93.8-99.8%) but low specificity (30.8%, 95% CI 14.3-51.8%) of the CW test in patients with OSD when level 4 of NCE (i.e., levels 4, 5, and 6) was used as the cutoff for defining corneal hyposensitivity.

Our results demonstrate that the low specificity of the qualitative CW test, combined with a broad confidence interval, indicates a high likelihood of false-positive results. This suggests that a positive CW test may not reliably rule out hyposensitivity, underscoring the need for further evaluation in the setting of a positive CW test result.