Abstract
Purpose: :
Corneal sensation is reduced in diabetic patients due to a loss of corneal nerve fibers, which could lead to recurrent corneal erosions and neurotrophic ulcerations. In vivo confocal microscopy studies have shown nerve alterations in diabetic corneas, but the detailed pathological changes remain unclear. We developed a new method of immunofluorescence staining and imaging that allows us to construct, for the first time, the entire human corneal nerve architecture (ARVO-2009). Here, we used this method to examine the nerve structure in diabetic corneas and compared epithelial nerve density with normal corneas.
Methods: :
Eight fresh human eyes from 4 diabetic donors (aged 33-61 years old, with insulin-dependent diabetes mellitus for 5 -10 years), and 10 eyes from 5 normal donors (aged from 40 - 63 years old) were obtained from NDRI. After fixation, corneas were stained with mouse monoclonal anti-tublin III antibody and images were acquired to build a whole view of the corneal nerve architecture of both epithelia and stroma To obtain the transected view of corneal nerves, the same corneas were embedded in OCT and serially sectioned, and then images were taken. Corneal nerve density was calculated based on the whole view of the corneal nerves. Differences between diabetic and normal corneas in corneal epithelial nerve densities and main stromal nerve numbers were compared by analysis of variance (ANOVA).
Results: :
In the diabetic corneas, neuropathies around the peripheral cornea were often found in areas where the epithelial nerve bundles emerged. These neuropathies appeared as irregular lesions of nerve fibers present in the superficial stroma beneath the basement membrane. A striking pathological change was the presence of abundant nerve fiber loops in the anterior stroma. These loops seemed to form due to the resistance present in the basement membrane; this prevents penetration of stromal nerve branches into the epithelia. Quantitative analysis of corneal nerve distribution based on the whole mount images showed that there was no difference in the numbers of main stromal nerve trunks between corneas from diabetic and normal donors, but there was a significant decrease in central epithelial nerve density in the diabetic cornea.
Conclusions: :
This is the first study to show a complete view of the nerve structure in human diabetic corneas. The decreased epithelial nerve density, due to corneal peripheral neuropathy and reduced numbers of stromal nerves penetrating the epithelium, can explain the poor healing and persistent epithelial defects seen in diabetic patients.
Keywords: diabetes • cornea: basic science • immunohistochemistry