Abstract
Purpose:
To measure corneal temperature in mild-moderate dry eye (DE) patients and to correlate values with the onset and intensity of subjective discomfort symptoms.
Methods:
40 eyes of DE patients (n=20, DEWS severity grade 2-3) were included in the study along with 30 eyes of age-matched normal control subjects (n=15). Subjective symptoms of discomfort were scored with OSDI questionnaire and a 100 mm horizontal VAS (Visual Analogue Scale) technique served for measuring symptom intensity. Dynamic infrared non-contact thermal imaging (Tomey TG 1000, Nagoya, Japan) was used to measure Central Cornea Temperature (CCT, 4 mm circular area). After training, subjects were asked to force the eye to remain open and signal the moment of discomfort onset while forcedly still not blinking. Temperature was measured at eye opening (T0) and every second during 10 seconds of sustained eye opening (T1). Time of the first occurrence of discomfort sensation (Discomfort Onset Time, DOT) was measured by a chronometer and the corresponding CCT recorded. Schirmer I test, Break Up Time (BUT), Oxford grade score were performed in all subjects. Recorded temperature values were correlated (r or ρ coefficient) with the clinical tests, OSDI, VAS and DOT, and data were statistically evaluated (significance p<0.05).
Results:
Corneal temperature immediately after eye opening was significantly lower in DE patients as compared to controls, in correlation to subject age, VAS and BUT (r= -0.46, -0.48 and 0.43 respectively,p<0,0001). VAS was also correlated to OSDI score, BUT, Schirmer I test (respectively r=0.818, -0.785, p<0,0001 and r=-0.410, p<001) but not to Oxford score ( ρ=0.12, p=0.7). DOT was significantly lower in DE patients vs controls (7.51±1.52 vs 16.3±2.81, p<0.0001) and in correlation to corresponding CCT recorded and BUT in DE patients (r=0.56, p=0.006 and r=0.91, p<0.0001 respectively). DOT was delayed after BUT with a significantly shorter interval in DE patients vs controls (0.9±1.4 vs 4.2±1.2 seconds, p<0.0001).
Conclusions:
Subjective sensation of discomfort at eye opening was not found to be related to corneal damage and it occurred earlier in DE patients, in correlation to lower corneal temperature and enhanced tear evaporation.