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James Alesana Slater, Stuti Misra, Geoffrey D Braatvedt, Charles N McGhee; Corneal Confocal Microscopy in Type 1 Diabetes Mellitus: a Six-Year Longitudinal Study. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1809.
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Nerve biopsy or skin punch biopsy allows direct examination of peripheral nerve damage in diabetes mellitus (DM). However, both are invasive procedures and may be associated with persistent pain and other side-effects. The sub-basal nerves of the cornea may be damaged by hyperglycaemia and can be assessed non-invasively. The current study investigates the role of corneal in vivo confocal microscopy (IVCM) in predicting the effect of time and diabetic control on sub-basal corneal nerve density over a six year period.
Thirty participants with type 1 DM (56.8±12.8 yrs at follow-up), and 16 control participants (54±13.9 yrs) were assessed in 2011 and 2017. All underwent corneal IVCM in the eye previously examined. Exclusion criteria included bilateral cataract surgery or the development of DM in controls. Central corneal sensitivity was evaluated by a non-contact aesthesiometer. A modified total neuropathy score was obtained from a combination of neuropathy questionnaire, clinical assessment and biothesiometry. Statistical analysis was performed using SPSS v24.0.
The median duration of diabetes mellitus was 36 ±13.2 years. The sub-basal nerve density was low, but minimally increased in Type 1 DM subjects (10.58±3.98mm/mm2 to 11.28±4.69mm/mm2, p = 0.395) and decreased in control participants (21.89±3.63mm/mm2 to 18.77±3.46mm/mm2, p = 0.001). The corneal sensitivity in DM subjects also improved marginally (1.43±1.14mBAR to 1.27±0.88mBAR, p = 0.001) and declined in the control group (0.16±0.26mBAR to 0.78±0.39mBAR, p =0.002). There was no significant change in HbA1c in the DM subjects (59.9±13.3mmol/mol to 58.3±12.9mmol/mol); nor in their modified total neuropathy scores (2.1±2.54 to 2.97±3.71, p = 0.19).
The study shows there was no clinically significant change in corneal nerve density in DM over a six year period of follow up. However, the nerve density values were highly significantly lower than controls at both time points consistent with a peripheral neuropathy. An unexpected, paradoxical, minimal, improvement in both corneal nerve density and corneal aesthesiometry measurements was not reflected in DM subjects modified total neuropathy scores.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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