Eye Examination for Early Detection of Diabetic Neuropathy-Role of Corneal Confocal Microscopy

Abstract

Diabetes mellitus registers an alarming increase globally, taking epidemic proportions. Diabetic neuropathies are considered the most prevalent chronic complications of diabetes, affecting up to 50% of subjects with diabetes during lifetime. Distal symmetric polyneuropathy (DSPN), a length-dependent injury of peripheral nerves is the most frequent type among diabetic patients. Small nerve fibers are the first affected in the natural progression of the disease and their early damage can be assessed using corneal confocal microscopy (CCM). We applied CCM to the study group of 90 patients with type 2 diabetes, to identify early signs of diabetic neuropathy, to stratify patients into classes of severity of diabetic neuropathy and to find potential correlation between clinical, metabolic parameters and diabetic neuropathy severity. In our study, 88.89% of the patients were diagnosed as having DSPN, 37.77% of them with mild form, 38.88% with moderate neuropathy and 12.22% with severe neuropathy. Patients with diabetic neuropathy had a significantly higher BMI (p = 0.04) and abdominal circumference, higher HbA1c (p = 0.36) and a higher total cholesterol (p = 0.43) compared with patients without DSPN. Also, the Toronto Clinical Neuropathy Score was significantly higher in patients with pathological changes of the sub-basal corneal plexus (p = 0.04). Patients with DSPN had a significantly longer duration of diabetes (p = 0.04) and a worse glycemic control, compared with patients without DSPN. The result of our study proved that CCM can be used as a reliable diagnosis tool for early detection of small nerve fiber damage, considering that corneal sub-basal plexus changes precede clinically detected peripheral nerve changes.