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G. Ferrari, F. Gemignani, F. Vitetta, C. Macaluso; In vivo Laser-Scanning Corneal Confocal Microscopy of Charcot Marie Tooth 1A Patients. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3712.
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To evaluate sub-basal corneal nerve plexus in patients affected by Charcot Marie Tooth 1A disease with no clinically evident eye disorder or topical medication.
8 patients and 5 controls of similar age underwent clinical ophthalmological evaluation to exclude any anterior segment eye disease. Patients affected by glaucoma, dry eye disease, diabetes or under topical eye medication were excluded. An informed consent was obtained. Oxybuprocaine chloridrate 0.4 % was administered prior to examination. Patients were examined with an in vivo laser confocal microscope (Heidelberg Retina Tomograph II with Rostock Cornea Module), and the sub-basal nerve plexum was imaged. At least 3 images of each eye were chosen based upon their clarity. We then used NIH IMAGEJ software to measure total nerve fiber length (NFL), intended as the total length of all nerve fibers and branches per square mm of corneal tissue, and nerve fiber density (NFD), intended as the total number of major nerves per square mm of corneal tissue. Finally, each image was graded for nerve tortuosity as suggested by Oliveira Sotos et al. (Cornea 20:374-384, 2001), with a scale ranging from 0 to 4 with 0 meaning straight nerves and 4 very tortuous nerves.
Qualitative observation of the corneal sub-basal nerve plexum showed obvious modifications in Charcot patients, with nerve rarefaction and increased tortuosity. Measured NFL was significantly reduced in the Charcot group as compared to normals (average NFL was 5.6±1.4mm/mm2 in patients, and 7.7±1.3mm/mm2 in controls, p=0.02), while no significant difference was found for NFD. Tortuosity grading was significantly higher in neuropathy patients (average tortuosity was 2.6±0.7 in patients and 1.2±0.4 in controls, p=0.0036).
In vivo corneal confocal microscopy is a non-invasive exam which allows direct visualization of peripheral nerves in living tissues,NFL has been shown to be a marker of diabetic peripheral neuropathy, while corneal nerve tortuosity has been described in dry eye disease. CMT disease is the most frequent genetic peripheral neuropathy, and its subtype CMT1A is characterized by prominent myelinic fiber damage and secondary axonal disruption of large nerve fibers. We show here preliminary evidence of involvement of small peripheral fibers in the cornea of Charcot peripheral neuropathy subjects in the form of a significant reduction in NFL and increased tortuosity. We suggest that this technique could represent a useful tool to non-invasively obtain information about nerve morphology in peripheral nerve diseases, and possibly an outcome measure in pharmacological trials.
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