Tear osmolarity in keratoconus and allergic patients in Southern Brazil

Abstract

 

Purpose

 

Many studies showed ocular surface damage as well as the presence of pro-inflammatory cytokynes in allergic and keratoconus (KC) patients. Increased tear osmolarity is associated to ocular surface inflammation in dry eye disease.We tested the hypothesis that tear osmolarity and ocular surface disease index (OSDI) score were increased and correlated positively in keratoconus and allergic conjunctivitis (AC) when compared to control subjects (C).

 

Methods

 

This cross-sectional case control study enrolled ninety-eight patients (38 female,60 male) aged from 3 to 57 years (y):10 healthy C (median 21.5y[11;28]), 40 KC (median 11.5y [3;56]), 48 AC (median 31y [11;57]).The exclusion criteria were contact lens wearers, use of eye drops in the last seven days, glaucoma, pregnancy, breastfeeding and previous ocular surgery. Complete eye examination were done. Lab-on-chip tear osmolarity (TearLab Osmolarity System,San Diego,CA) measures were taken once in both eyes, during afternoon period in a controlled temperature and air humidity room. Placido-disk-based topography (EyeSys^C) were performed and power measures for K maximum (Kmax) were taken. Patients filled in an OSDI questionnaire. ANOVA, Bonferroni and Pearson’s tests were used to check the correlation between variables.

 

Results

 

The three groups were similar in gender (p=0,812), but statistical significant differences were observed in age and Kmax, which were higher (p<0,001;p<0,05) in keratoconus patients.No difference in average tear osmolarity values observed among the groups (p=0,058-0,064)).However, average tear osmolarity value was higher in all groups (right eyes 310.82 +/-11.37;left eyes 313.65 +/-14.52) when compared to previous data on osmolarity in healthy eyes (302 +/- 9.7 - 18.2 mOsm/L). No correlation was observed between OSDI score and tear osmolarity in the groups. C subjects had the lower OSDI score and a statistical significant difference in OSDI scores among the groups (p<0,05) was observed.

 

Conclusions

 

Our results could not find differences in average tear osmolarity values among healthy eyes, KC and AC eyes. Furthermore, there was no correlation between OSDI scores and tear osmolarity.However, OSDI was able to distinguish healthy subjects from AC and KC.Higher tear osmolarity values found in this study might be related to particular biogeographic features of the region where our patients live and more studies are necessary to elucidate these findings.