Decreased corneal sensitivity to chemical and thermal stimuli in keratoconus patients

Abstract

Purpose: To investigate corneal sensitivity to selective mechanical, chemical, and thermal (heat and cold) stimulation in patients with keratoconus.

Methods: Corneal sensitivity to different modalities of stimulus was determined in one randomized eye in 17 patients with mild or moderate keratoconus (KC) and in 15 healthy subjects (control). Mechanical, chemical, and thermal (hot and cold) thresholds were determined at the center of the cornea using a Belmonte's gas esthesiometer. Patients with a history of contact lens wear were excluded from the study. All patients completed a questionnaire to assess dry-eye disease symptoms (ocular surface disease index - OSDI).

Results: There was no significant difference in age, gender and OSDI between the KC and the control group. Mean corneal threshold sensitivity values to chemical stimulation (KC: 33.22 ± 0.77 % CO2 vs. control: 30.82 ± 0.21 % CO2; p<0.001), heat (KC: 0.73 ± 0.38 °C vs. control: 0.39 ± 0.18 °C; p=0.003) and cold (KC: -0.88 ± 0.52 °C vs. control: -0.31 ± 0.15 °C; p<0.001) were significantly increased in patients with keratoconus, whereas threshold responses to mechanical stimulation did not vary significantly in the two study groups (KC: 108.78 ± 29.7 mL/min vs. control: 107.39 ± 13.67 mL/min; p>0.05). Strong correlation was found between sensitivity thresholds to chemical and heat stimulation (r= 0.66, p= 0.005). There was no correlation between OSDI score and threshold sensitivity values to any stimulation in either group.

Conclusions: Corneal sensitivity to chemical and thermal stimulation is decreased in keratoconus patients. The significantly impaired sensitivity suggesting that axonal damage and/or altered expression of membrane ion channels involved in transduction and membrane excitability affects primarily the cold and polymodal nociceptor terminals. Corneal mechanoreceptors remain largely unaffected in keratoconus.

Keywords: 574 keratoconus