Changes in tear glucose and insulin concentrations following an oral glucose tolerance test

ABSTRACT

Clinical relevance

Tear glucose and insulin are responsible for the health of the ocular surface; thus, it is important for clinicians to detect the tear glucose and insulin using point-of-care methods.

Aim

To determine if changes in blood glucose and insulin levels following an oral glucose tolerance test are reflected in the tears and to test the association between gene expression and tear insulin and glucose.

Methods

Twenty healthy young adults were enrolled. Basal tears and peripheral blood samples were collected to assess glucose and insulin using a point-of-care glucometer and ELISA assays in fasted subjects, and 1.5 and 3 h after an oral glucose challenge. Conjunctival impression cytology was collected to determine gene expression of insulin receptor (INSR) and glucose transporters (GLUT1 and GLUT4). Changes were examined using non-parametric one-way ANOVA. Spearman tests were conducted to examine associations between variables.

Results

Glucose and insulin levels increased 1.5 h after oral glucose in both blood (P < 0.001) and tears (P < 0.049) and returned to near baseline values after 3 h. There was a positive correlation between glucose levels in the blood and tears (rho = 0.57, P < 0.001), but not between blood and tear insulin levels (P = 0.18). Glucose and insulin levels in tears were correlated (rho = 0.32, P = 0.048). Tear glucose concentration at 1.5 h after oral glucose was associated with INSR expression (rho = 0.49, P = 0.03), and there was a trend with GLUT1 (P = 0.06) but not GLUT4.

Conclusion

Tear glucose reflected blood glucose levels but this correspondence was not observed for insulin. Further studies are required to determine the role of glucose and insulin on the ocular surface in both health and diabetes.

KEYWORDS:

• Conjunctival glucose transporter
• conjunctival insulin receptor
• ocular surface
• oral glucose tolerance test
• tear glucose
• tear insulin

Acknowledgements

We would like to thank Prof. Young Bin Choy (Seoul National University, College of Medicine) and Mr. Alexander Schill (UHCO, NIH-NEI P30 EY007551) for helping with the construction of the tear glucometer. Also, we would like to acknowledge Prof. Alan Burns for helpful comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).