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Maria Markoulli, Edward Lum, Jingjing You, Carmen Duong, Jonathan Tolentino, Juno Kim; CORNEAL NERVE MORPHOLOGY AND TEAR FILM SUBSTANCE P IN DIABETES. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6153.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo corneal confocal microscopy has been used to detect peripheral neuropathy by identifying morphological alterations to the sub-basal nerve plexus (SBNP). This work aims to characterise the relationship between changes in the tear film neuropeptide Substance P and the SBNP in diabetes.
Seventeen healthy control participants and twelve participants with diabetes were recruited in this cross-sectional study. Total protein content (TPC) and substance P (SP) concentrations were determined in the flush tears of participants. Corneal nerve morphology was assessed by capturing the SBNP using the Heidelberg Retinal Tomograph II with Rostock Corneal Module in the central cornea. Corneal nerve fiber density (CNFD) was measured using ACCMetrics on captured images. Hb1Ac levels and duration of diabetes were obtained through a questionnaire. Comparisons between groups were made using independent samples t-tests. Correlations between parameters were analysed using Pearson’s correlations.
SP concentrations were significantly lower in the tears of participants with diabetes compared to the normal group (4223.80 ± 2677.67 vs 994.16 ± 1130.56 pg/mL respectively, p=0.04). There was a significant difference in total protein content between the groups (3.70 ± 2.21 vs 2.24 ± 1.87 mg/mL in healthy normals and participants with diabetes, respectively, p=0.04). CNFD was significantly lower in the participants with diabetes compared to the control group (21.46 ± 7.02 vs 16.09 ± 5.70 mm/mm2: p=0.05). There was a moderate correlation between SP and CNFD (r=0.62, p=0.02). There were no correlations between SP and Hb1Ac, SP and duration of diabetes, corneal NFD and Hb1Ac and CNFD and duration of diabetes.
Substance P is expressed at a significantly lower level in the tears of people with diabetes compared with healthy normals. The positive correlation between Substance P and corneal nerve density indicates that Substance P may be a potential biomarker for corneal nerve health.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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