Greater corneal nerve loss at the inferior whorl in obesity

Background: Diabetic neuropathy is a dying-back neuropathy with evidence of greater distal corneal nerve loss at the inferior whorl. Individuals with obesity exhibit neuropathy and central corneal nerve loss. We have assessed whether there was evidence of greater corneal nerve loss at the inferior whorl indicative of a dying back neuropathy in subjects with obesity with and without diabetes. Methods: Fifty-seven individuals with obesity, with diabetes (OBDM+), without diabetes (OBDM−) (n = 30 and n = 27 respectively) and age and sex-matched normal weight controls (n = 21) underwent venous blood sampling and assessment of the neuropathy symptom profile (NSP), neuropathy disability score (NDS), vibration, cold and warm threshold testing, cardiac autonomic function and corneal confocal microscopy (CCM). Results: The Neuropathy Symptom Profile and Neuropathy Disability Score were significantly higher in OBDM− (NSP: p < 0.0001; NDS p < 0.01) and OBDM+ (NSP p < 0.0001; NDS p < 0.001) subjects compared to controls. Vibration perception threshold was significantly higher (p = 0.001) and deep breathing heart rate variability was significantly lower (p = 0.01) in OBDM+ compared to controls. Corneal nerve fibre density (CNFD) [26.8 ± 6.22 vs 26.8 ± 6.01 vs 35.3 ± 7.41, p < 0.0001], branch density [55.4 ± 28.2 vs 58.4 ± 28.5 vs 88.2 ± 31.1, p < 0.001], fibre length (CNFL) [17.6 ± 4.43 vs 19.9 ± 5.43 vs 26.7 ± 5.31, p < 0.0001], inferior whorl length (IWL) [17.9 ± 6.10 vs 18.6 ± 7.42 vs 35.3 ± 9.70, p < 0.0001] and total nerve fibre length (TNFL) [35.5 ± 9.58 vs 38.5 ± 11.0 vs 62.0 ± 12.3, p < 0.0001] were significantly lower in OBDM+ and OBDM− compared to control but comparable between the two groups of individuals with obesity. The inferior whorl showed a disproportionately greater loss of nerve fibres compared to the central cornea in OBDM+ and OBDM− patients. The mean % difference (between patients and controls) for IWL was 65.4 % and 62.8 % for OBDM− and OBDM+ respectively. This difference was numerically greater than the mean % difference (between patients and controls) for CNFL which was 41.1 % and 29.2 % for OBDM− and OBDM+ respectively. Conclusion: We provide evidence of a distal dying back small fibre damage by demonstrating greater corneal nerve loss at inferior whorl in obesity regardless of diabetes status.