WASHINGTON — Corneal confocal microscopy can noninvasively reveal neuropathy early in diabetes and help in monitoring treatment response, speakers said at the annual scientific sessions of the American Diabetes Association.
By comparison, the clinical neurologic exam may be easier than corneal confocal microscopy but lacks sensitivity. Nerve conduction studies are time-consuming and only measure the function of large nerve fibers. Quantitative sensory testing also is easier to do, but relies on patient responses. Skin nerve biopsies can provide much information, but are “highly invasive,” said Mitra Tavakoli, a doctoral student at the University of Manchester (England).
Using a first-generation corneal confocal microscope, the ConfoScan P4 (Tomey Corp.), she and her colleagues obtain real-time micrographs of the cornea at up to 680 times magnification without directly contacting the eye. They studied 183 people including diabetics without neuropathy; diabetics with mild, moderate, or severe neuropathy; and controls without diabetes,
Diabetic neuropathy was associated with progressive, significant reductions in corneal sensitivity (as measured by noncontact corneal aesthesiometry), nerve fiber density, nerve branch density, and nerve fiber length. Nerve fiber tortuosity also became progressively worse as the severity of neuropathy worsened.
Measurements of corneal nerve morphology obtained with confocal microscopy correlated well with assessments of corneal sensitivity and neuropathy severity, using the Neuropathy Disability Score.
In a poster presented at the meeting, Ms. Tavakoli and her colleagues used corneal confocal microscopy to assess the effectiveness of pancreatic transplantation in improving neuropathy in 20 patients with type 1 diabetes (average age, 41 years).
Before transplantation, the diabetic patients had significantly reduced corneal sensitivity and significantly lower nerve fiber density, nerve branch density, and nerve fiber length on corneal confocal micrographs, compared with 18 individuals without neuropathy (average age, 55).
At 6 months after transplantation, repeat scans in 11 of the patients who had neuropathy showed that nerve fiber density and length had improved significantly.
In a related study, microscopy had sensitivity (71%) and specificity (77%) comparable with skin punch biopsy specimens (59% and 90%, respectively).
Confocal micrographs show nerves in a control patient without neuropathy.
By comparison, nerve density is lower in a diabetic patient with neuropathy. Photos courtesy Mitra Tavakoli