1. https://nei.nih.gov/health/diabetic/retinopathy
2. https://www.sciencedirect.com/science/article/pii/S0042698917300470#b0240
3. https://www.ncbi.nlm.nih.gov/pubmed/28099212
4. https://www.ncbi.nlm.nih.gov/pubmed/16227818
5. https://www.reviewofophthalmology.com/article/mucins-foundation-of-a-good-tear-film