Quantification of tear glucose levels and their correlation with blood glucose levels in dogs

Abstract

Background No previous studies have quantified tear glucose (TG) levels in dogs or compared changes in TG and blood glucose (BG) concentrations. Objective To quantify TG concentration and evaluate its correlation with BG level in dogs. Methods Twenty repetitive tests were performed in alternate eyes of four dogs, with a minimum washout period of 1 week. Tears and blood were collected at 30‐min intervals with successive glucose injections (1 g/kg) every 30 min. Cross‐correlations of BG and TG levels were assessed. The delay and association between TG and corresponding BG levels were analysed for each dog; samples were collected at 5‐min intervals. The tears were collected using microcapillary tubes. Collected tears and blood were analysed for glucose concentration using a colorimetric assay and commercially available glucometer, respectively. Results The average baseline BG and TG levels were 4.76 ± 0.58 and 0.39 ± 0.04 mmol/L, respectively. Even with highly fluctuating BG levels, a significant cross‐correlation coefficient (r = 0.86, p < 0.05) was observed between changes of BG and TG levels. The delay time between BG and TG levels was 10 min. On average, BG levels were 16.34 times higher than TG levels. There was strong correlation between BG and TG levels (rs = 0.80, p < 0.01). Significant differences in TG concentrations between normoglycaemia, mild hyperglycaemia, and severe hyperglycaemia were found (p < 0.05). Conclusions Canine TG concentrations have not been quantified previously. Our findings suggest preliminary data for future research on TG levels in dogs and show TG measurement could be used to screen for diabetes mellitus in dogs.

In-depth correlation analysis between tear glucose and blood glucose using a wireless smart contact lens

“…4e-(i) shows the representative TG and BG data for a normal beagle subject 1. The BG levels increased rapidly from a baseline of 3.94 mM, which was within the reported normal range for beagles 32 , then reached a maximum value of 16.72 mM at 5 min after the glucose injection. Subsequently, it gradually decreased to 5.67 mM approaching the normal range.…”

“…Subsequently, it gradually decreased to 5.67 mM approaching the normal range. In the case of TG, it was at a fasting level of 0.24 mM showing a similar value with the reported normal beagle's TG range 32 . TG further increased to 0.91 mM after the IV glucose injection and then decreased to 0.279 mM after 105 min due to the action of insulin.…”

“…In addition, these conventional methods usually allow single measurement of TG, limiting continuous tracking of TG changes, and further failing to demonstrate their relationship with dynamic BG behaviors along with lag time. Lag time is the time for BG to diffuse into tears, and it is an important factor determining the degree of correlation between TG and BG 32 . The accurate estimation of the lag time can be obtained by the continuous and frequent measurement of the dynamic changes of TG and BG.…”

“…Since the feasibility of diagnosing diabetes through tears has been demonstrated, there has been extensive interest in the development of wearable devices that can monitor TG levels [22][23][24][25] . Revealing the relationship between TG and BG is crucial to evidence the usefulness of TG as a noninvasive alternative of BG, and significant efforts have been made, as summarized in Supplementary Table 1; however, the correlation between these two still remains controversial 12,[18][19][20][22][23][24][26][27][28][29][30][31][32][33][34][35][36][37][38][39] . A strong candidate for the cause of this controversy is the variation in the composition of tears depending on the tear collection method.…”

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

“…In addition, lipids (cholesterol, cholesteryl ester, phospholipids), small molecules (uric acid, ascorbic acid, lactate, glucose), electrolytes (sodium, potassium, calcium, magnesium) are contained in tears. − Among these substances, several constituents have been found to correlate with blood levels and can serve as biomarkers for metabolic diseases. For instance, the correlation between blood and tear glucose levels has been studied, with tear glucose levels reflecting blood glucose levels with a time delay of around 10 min. − Furthermore, Song et al conducted tests on rabbits that had been fed a cholesterol-rich chow diet, and the results of the tests revealed that cholesterol levels had increased for several weeks in both tears and blood, indicating that cholesterol in tears can be used as a biomarker to reflect blood cholesterol levels . These findings suggest that tears have the potential to serve as a noninvasive tool for personalized medicine and healthcare in the context of metabolic diseases.…”