One studio recently evaluated the differences in endothelial cell density (EDC) and central corneal thickness (CCT) in patients with both type 1 and type 2 diabetes mellitus, to better understand the effects of diabetes mellitus on the corneal endothelium and offer a more comprehensive evaluation of diabetic patients.
Diabetes mellitus and corneal complications
The diabetes mellitus (DM) is a major global problem as it is a rapidly growing serious disease and the International Diabetes Federation has estimated that 578 million people will have diabetes by 2030, worldwide. Type 1 DM (DMT1) is less frequent and is caused by an autoimmune reaction against cells β pancreatic glands that, as a result, do not produce insulin or produce it in small amounts. This disease is more prevalent in children and young people; it is referred to as juvenile diabetes. Type 2 DM (DMT2) is the most common form and affects approximately 90% of diabetics worldwide. In these patients, hyperglycaemia results from the inability of somatic cells to respond appropriately to insulin signalling, so-called 'insulin resistance'. This induces an increase in insulin production, which manages to maintain normal blood glucose for many years, but over time leads to cell failure. β of the pancreas.
Diabetic retinopathy is the most frequent ocular complication in diabetic patients. However, it is not the only retinal complication associated with this disease, as macular oedema can occur in some cases, and corneal abnormalities have also been described, and some studies have identified metabolic dysfunction of corneal endothelial cells in diabetic patients. However, damage to the corneal endothelium has been less studied than damage affecting the retina.
The corneal endothelial cells cover the inner side of the cornea and maintain the correct dehydration of the stroma, through an electro-osmotic gradient and the action of the cell junctions, which allow fluid loss in the anterior chamber. Endothelial cell density (EDC) at birth reaches 7500 cells/mm2 and progressively decreases during life. The cornea of healthy subjects in adulthood has approximately 3200-3500 cells/mm2organised like a mosaic. When the CED drops to 1200 cells/mm2the integrity of the monolayer is compromised with the endothelial pumping function and, finally, if the cell density falls below 500-700 cells/mm2an irreversible hydration imbalance is caused that swells the stroma and produces permanent opacity of the cornea. When this happens, the only available treatment option is transplantation.
In this context, it was hypothesised that increased central corneal thickness (CCT) could be an early marker of corneal endothelial dysfunction. Furthermore, studies suggest that patients with diabetes have increased CCT due to impaired Na+/K+ pump as a consequence of hyperglycaemia, reduced insulin levels and impaired corneal endothelial cells.
What the new study tells us
The recent review with meta-analysis involved a systematic literature search to find articles combining the study of DMT1 and/or DMT2 and corneal endothelium, conducted in recent years. The meta-analysis assessed the role of each type of DM on corneal endothelial cell density and pachymetry. Age was included in the statistical calculation to discriminate between normal corneal changes due to ageing and the effect of the disease. 17 studies, of the 752 initially analysed, were included in the meta-analysis.
The results showed that patients with DMT1 had, on average, 193 cells/mm2 less than control patients. In contrast, patients with DMT2 had 151 cells/mm2 less than healthy controls. Both DMT1 and DMT2 patients showed an increase in pachymetry compared to control patients and, in both groups, the increase was associated with disease duration.
Conclusions
This new study showed that both types of DM reduced CED and increased corneal pachymetry values. These differences were higher in patients with type 1 diabetes mellitus compared to control patients and also compared to patients with type 2 diabetes mellitus. In DMT1, the reduction in CED was not correlated with time since diagnosis and, in both groups, patients had a reduction in CED due to ageing, similar to what was observed in control patients.
Basically, the results obtained make it possible to confirm that each type of diabetes contributes differently to the impairment of the corneal endothelium, and this requires special attention on the part of clinicians.
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