Corneal Dendritic Cell Dynamics Are Associated with Clinical Factors in Type 1 Diabetes.

Time-lapsed in vivo corneal confocal microscopy (IVCCM) has shown that corneal dendritic cells (DCs) migrate at approximately 1 µm/min in healthy humans. We have undertaken IVCCM of the whorl region to compare the density of rounded DCs, and DCs with (wDCs) and without (woDCs) dendrites and dynamics; trajectory (length travelled/time), displacement (distance from origin to endpoint/time) speeds and persistence ratio (displacement/trajectory) of woDCs in subjects with type 1 diabetes (T1D) (n = 20) and healthy controls (n = 10). Only the wDC density was higher (p = 0.02) in subjects with T1D compared to controls. There was no significant difference in cell dynamics between subjects with T1D and controls. woDC density correlated directly with HDL cholesterol (r = 0.59, p = 0.007) and inversely with triglycerides (r = −0.61, p = 0.005), whilst round-shaped cell density correlated inversely with HDL cholesterol (r = −0.54, p = 0.007). Displacement, trajectory, and persistency correlated significantly with eGFR (mL/min) (r = 0.74, p < 0.001; r = 0.48, p = 0.031; r = 0.58, p = 0.008, respectively). We show an increase in wDC density but no change in any other DC sub-type or alteration in cell dynamics in T1D. However, there were associations between DC density and lipid parameters and between DC dynamics and renal function. IVCCM provides evidence of a link between immune cell dynamics with lipid levels and renal function.

Eye health profile of affordable eye care service users.

CLINICAL RELEVANCE: Knowledge of the typical eye health profile of patients experiencing social or economic disadvantage is useful for health care modelling. BACKGROUND: The aim of this work is to profile the ocular health and sociodemographic characteristics of Australian College of Optometry service users of all ages and to explore the relationships between key sociodemographic characteristics and eye health. METHODS: For 3093 eye examinations, best-corrected distance visual acuity and mean spherical equivalent refractive error were tested non-parametrically by clinic category, remoteness area, number of co-morbidities, gender and indigenous status, also correlated against age and socioeconomic advantage/disadvantage. Covariates of interest were entered into linear mixed models of visual acuity and mean spherical equivalent refractive error, controlling for age. Risk estimates are reported for visual impairment (defined as ≤6/12 best-corrected distance visual acuity in one or both eyes) and ocular diagnoses. RESULTS: Visual impairment is more prevalent amongst service users examined in domiciliary settings. Increasing co-morbidities were associated with poorer best-corrected distance visual acuity. Aboriginal and Torres Strait Islander service users had lower visual impairment prevalence overall but proportionally fewer aged ≥50 years attended for eye care, compared to non-indigenous. CONCLUSIONS: Domiciliary eye examinations detect remediable visual impairment. Federal public health interventions delivered by the Australian College of Optometry for Aboriginal and Torres Strait Islander eye care appear effective but may not reach all aged ≥ 50 years; further research is required. Identification of multiple co-morbidities should prompt optometrists to tailor public health messages and signpost to low vision services earlier.

Corneal Confocal Microscopy Predicts the Development of Diabetic Neuropathy: A Longitudinal Diagnostic Multinational Consortium Study.

OBJECTIVE: Corneal nerve fiber length (CNFL) has been shown in research studies to identify diabetic peripheral neuropathy (DPN). In this longitudinal diagnostic study, we assessed the ability of CNFL to predict the development of DPN. RESEARCH DESIGN AND METHODS: From a multinational cohort of 998 participants with type 1 and type 2 diabetes, we studied the subset of 261 participants who were free of DPN at baseline and completed at least 4 years of follow-up for incident DPN. The predictive validity of CNFL for the development of DPN was determined using time-dependent receiver operating characteristic (ROC) curves. RESULTS: A total of 203 participants had type 1 and 58 had type 2 diabetes. Mean follow-up time was 5.8 years (interquartile range 4.2-7.0). New-onset DPN occurred in 60 participants (23%; 4.29 events per 100 person-years). Participants who developed DPN were older and had a higher prevalence of type 2 diabetes, higher BMI, and longer duration of diabetes. The baseline electrophysiology and corneal confocal microscopy parameters were in the normal range but were all significantly lower in participants who developed DPN. The time-dependent area under the ROC curve for CNFL ranged between 0.61 and 0.69 for years 1-5 and was 0.80 at year 6. The optimal diagnostic threshold for a baseline CNFL of 14.1 mm/mm2 was associated with 67% sensitivity, 71% specificity, and a hazard ratio of 2.95 (95% CI 1.70-5.11; P < 0.001) for new-onset DPN. CONCLUSIONS: CNFL showed good predictive validity for identifying patients at higher risk of developing DPN ∼6 years in the future.

Morphometric Changes to Corneal Dendritic Cells in Individuals With Mild Cognitive Impairment.

PURPOSE: There has been increasing interest in identifying non-invasive, imaging biomarkers for neurodegenerative disorders of the central nervous system (CNS). The aim of this proof-of-concept study was to investigate whether corneal sensory nerve and dendritic cell (DC) parameters, captured using in vivo confocal microscopy (IVCM), are altered in individuals with mild cognitive impairment (MCI) and Alzheimer's disease (AD). METHODS: Fifteen participants were recruited from the Australian Imaging Biomarkers and Lifestyle (AIBL) study in Melbourne, VIC, Australia. The cohort consisted of cognitively normal (CN) individuals (n = 5), and those with MCI (n = 5) and AD (n = 5). Participants underwent a slit lamp examination of the anterior segment, followed by corneal imaging using laser-scanning in vivo confocal microscopy (IVCM) of the central and inferior whorl regions. Corneal DC density, field area, perimeter, circularity index, aspect ratio, and roundness were quantified using Image J. Quantitative data were derived for corneal nerve parameters, including nerve fiber length (CNFL), fiber density (CNFD), branch density (CNBD), and diameter. RESULTS: Corneal DC field area and perimeter were greater in individuals with MCI, relative to CN controls, in both the central and inferior whorl regions (p < 0.05 for all comparisons). In addition, corneal DCs in the whorl region of MCI eyes had lower circularity and roundness indices and a higher aspect ratio relative to CNs (p < 0.05 for all comparisons). DC density was similar across participant groups in both corneal regions. There was a trend toward lower quantitative parameters for corneal nerve architecture in the AD and MCI groups compared with CN participants, however, the inter-group differences did not reach statistical significance. Central corneal nerve diameters were similar between groups. CONCLUSION: This study is the first to report morphological differences in corneal DCs in humans with MCI. These differences were evident in both the central and mid-peripheral cornea, and in the absence of significant nerve abnormalities or a difference in DC density. These findings justify future large-scale studies to assess the utility of corneal IVCM and DC analysis for identifying early stage pathology in neurodegenerative disorders of the CNS.

Rapid Corneal Nerve Fiber Loss: A Marker of Diabetic Neuropathy Onset and Progression.

OBJECTIVE: Corneal nerve fiber length (CNFL) represents a biomarker for diabetic distal symmetric polyneuropathy (DSP). We aimed to determine the reference distribution of annual CNFL change, the prevalence of abnormal change in diabetes, and its associated clinical variables. RESEARCH DESIGN AND METHODS: We examined 590 participants with diabetes (399 with type 1 diabetes [T1D] and 191 with type 2 diabetes [T2D]) and 204 control patients without diabetes with at least 1 year of follow-up and classified them according to rapid corneal nerve fiber loss (RCNFL) if CNFL change was below the 5th percentile of the control patients without diabetes. RESULTS: Control patients without diabetes were 37.9 ± 19.8 years old, had median follow-up of three visits over 3.0 years, and mean annual change in CNFL was -0.1% (90% CI -5.9% to 5.0%). RCNFL was defined by values exceeding the 5th percentile of 6% loss. Participants with T1D were 39.9 ± 18.7 years old, had median follow-up of three visits over 4.4 years, and mean annual change in CNFL was -0.8% (90% CI -14.0% to 9.9%). Participants with T2D were 60.4 ± 8.2 years old, had median follow-up of three visits over 5.3 years, and mean annual change in CNFL was -0.2% (90% CI -14.1% to 14.3%). RCNFL prevalence was 17% overall and was similar by diabetes type (64 T1D [16.0%], 37 T2D [19.4%], P = 0.31). RNCFL was more common in those with baseline DSP (47% vs. 30% in those without baseline DSP, P = 0.001), which was associated with lower peroneal conduction velocity but not with baseline HbA1c or its change over follow-up. CONCLUSIONS: An abnormally rapid loss of CNFL of 6% per year or more occurs in 17% of diabetes patients. RCNFL may identify patients at highest risk for the development and progression of DSP.

Effect of Pupil Dilation with Tropicamide on Retinal Vascular Caliber.

Purpose: The retinal blood vessels reflect changes in the brain's micro-circulation and these changes have been shown to correlate with the incidence of diseases such as stroke, heart disease and Alzheimer's disease. Studies investigating the retinal vasculature routinely use pupil dilation with tropicamide to optimize image acquisition and quality. The aim of this study was to investigate the effects of tropicamide on retinal vascular parameters using retinal photography.Methods: The study was performed on 41 healthy young subjects of both sexes, using tropicamide to dilate only the right pupil, leaving the left as a control.Results: Pupil dilation with tropicamide resulted in reduced retinal vessel width measures based on standardized approaches, particularly reduced arteriolar caliber (p < .0005). However, closer investigation of the images revealed reduced fundus image magnification in the post-tropicamide images, based on reduced optic nerve head diameter (p < .0005) and longitudinal analysis with image registration and affine transformation (p < .0001). No change in vessel width parameters was observed after adjustment for image magnification.Conclusion: These results suggest that tropicamide does not change the width of the retinal vessels, however width parameters as measured by standard approaches may be reduced due to image magnification changes resulting from cycloplegia. In this study, improved optic nerve head segmentation for image scale conversion removed the magnification error. With this correction, the tropicamide intervention had no effect on vessel width parameters in young healthy people and could be utilized in future without affecting the results of retinal vascular analysis.

Corneal Nerve Migration Rate in a Healthy Control Population.

PURPOSE: The purpose of this study was to establish an age-dependent normative range and factors affecting the migration rate of the corneal subbasal nerve plexus in a healthy control population. METHODS: Corneal nerve migration rate was measured in 60 healthy participants grouped by age: A, aged 20 to 39 years (n = 20); B, 40 to 59 years (n = 20); and C, 60 to 79 years (n = 20). Laser-scanning corneal confocal microscopy was performed on the right eye of all participants at baseline and again after 3 weeks. Fully automated software was used to montage the frames. Distinctive nerve landmarks were manually reidentified between the two montages, and a software program was developed to measure the migration of these landmark points to determine corneal nerve migration rate in micrometers per week (µm/wk). RESULTS: The mean ± SD age of all participants in the study was 47.5 ± 15.5 years; 62% of participants were male. The average corneal nerve migration rates of groups A, B, and C were 42.0 ± 14.0, 42.3 ± 15.5, and 42.0 ± 10.8 µm/wk, respectively (P = .99). There was no difference in corneal nerve migration rate between male (41.1 ± 13.5 µm/wk) and female (43.7 ± 13.2 µm/wk) participants (P = .47). There was no significant correlation between age (P = .97), smoking (P = .46), alcohol use (P = .61), and body mass index (P = .49, respectively) with corneal nerve migration rate. However, exercise frequency correlated significantly (P = .04) with corneal nerve migration rate. CONCLUSIONS: Corneal nerve migration rate varies in healthy individuals and is not affected by age, sex, or body mass index but is related to physical activity.

Ocular Biomarkers of Alzheimer's Disease: The Role of Anterior Eye and Potential Future Directions.

Globally, Alzheimer's disease (AD) is a growing health and economic challenge that has no effective cure. Recent clinical trials indicate that preclinical treatment may be required but a routine screening tool for AD has been elusive. Hence, a simple, yet sensitive biomarker for preclinical AD, when the disease is most likely to be amenable to treatment, is lacking. Due to several features, the eye has been explored for this purpose and, among the ocular tissues, the retina has received the most attention. Currently, major works investigating the potential AD diagnosis by detecting amyloid-ß (Aß) signatures in the retinal tissue are underway, while the anterior eye is more accessible for in vivo imaging and examination. This report provides a concise review of current literature on the anterior eye components, including the crystalline lens, cornea, and aqueous humor, in AD. We also discuss the potential for assessment of the corneal nerve structure and regeneration as well as conjunctival tissue for AD-related alterations. The crystalline lens has received considerable attention, but further research is required to confirm whether Aß accumulates in the lens and whether it mirrors brain neuropathologic changes, particularly in preclinical AD. The rich corneal neural network and conjunctival vasculature also merit exploration in future studies to shed light on their potential association with AD pathologic changes.

Corneal confocal microscopy for identification of diabetic sensorimotor polyneuropathy: a pooled multinational consortium study.

AIMS/HYPOTHESIS: Small cohort studies raise the hypothesis that corneal nerve abnormalities (including corneal nerve fibre length [CNFL]) are valid non-invasive imaging endpoints for diabetic sensorimotor polyneuropathy (DSP). We aimed to establish concurrent validity and diagnostic thresholds in a large cohort of participants with and without DSP. METHODS: Nine hundred and ninety-eight participants from five centres (516 with type 1 diabetes and 482 with type 2 diabetes) underwent CNFL quantification and clinical and electrophysiological examination. AUC and diagnostic thresholds were derived and validated in randomly selected samples using receiver operating characteristic analysis. Sensitivity analyses included latent class models to address the issue of imperfect reference standard. RESULTS: Type 1 and type 2 diabetes subcohorts had mean age of 42 ± 19 and 62 ± 10 years, diabetes duration 21 ± 15 and 12 ± 9 years and DSP prevalence of 31% and 53%, respectively. Derivation AUC for CNFL was 0.77 in type 1 diabetes (p < 0.001) and 0.68 in type 2 diabetes (p < 0.001) and was approximately reproduced in validation sets. The optimal threshold for automated CNFL was 12.5 mm/mm2 in type 1 diabetes and 12.3 mm/mm2 in type 2 diabetes. In the total cohort, a lower threshold value below 8.6 mm/mm2 to rule in DSP and an upper value of 15.3 mm/mm2 to rule out DSP were associated with 88% specificity and 88% sensitivity. CONCLUSIONS/INTERPRETATION: We established the diagnostic validity and common diagnostic thresholds for CNFL in type 1 and type 2 diabetes. Further research must determine to what extent CNFL can be deployed in clinical practice and in clinical trials assessing the efficacy of disease-modifying therapies for DSP.

Ophthalmic and clinical factors that predict four-year development and worsening of diabetic retinopathy in type 1 diabetes.

AIMS: To investigate the role of ophthalmic imaging markers - namely retinal thickness measures and corneal nerve morphology - in predicting four-year development and worsening of diabetic retinopathy (DR) in type 1 diabetes (T1DM). METHODS: 126 eyes of 126 participants with T1DM were examined at baseline and after four years. Diabetic retinopathy (DR) was graded using the Early Treatment Diabetic Retinopathy Study scale. HbA1c, nephropathy, neuropathy, cardiovascular factors, and retinal thickness using optical coherence tomography (OCT) and corneal nerve fiber length (CNFL) using corneal confocal microscopy at baseline were assessed by univariate and step-wise multiple logistic regression, and their diagnostic capabilities for single and combined measures. RESULTS: Four-year development of DR was 19% (13 of 68 without DR at baseline). Worsening of DR was seen in 43% (25 of 58 with DR at baseline). When adjusted for potential confounders, a lower CNFL (AUC=0.637, p=0.040, 64% sensitivity and 64% specificity at 14.9mm/mm2 cut-off), higher triglycerides (AUC=0.669, p=0.012, 64% sensitivity, 62% specificity at 0.85mmol/L) and an elevated vibration threshold (AUC=0.708, p=0.002, 96% sensitivity, 40% specificity at 3.55Hz) were significant predictors for four-year worsening of DR. CONCLUSIONS: Reduced CNFL, elevated vibration perception threshold and higher triglycerides can predict future worsening of DR.

Corneal and Retinal Neuronal Degeneration in Early Stages of Diabetic Retinopathy.

Purpose: To examine the neuronal structural integrity of cornea and retina as markers for neuronal degeneration in nonproliferative diabetic retinopathy (NPDR). Methods: Participants were recruited from the broader Brisbane community, Queensland, Australia. Two hundred forty-one participants (187 with diabetes and 54 nondiabetic controls) were examined. Diabetic retinopathy (DR) was graded according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. Corneal nerve fiber length (CNFL), corneal nerve branch density (CNBD), corneal nerve fiber tortuosity (CNFT), full retinal thickness, retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), focal (FLV) and global loss volumes (GLV), hemoglobin A1c (HbA1c), nephropathy, neuropathy, and cardiovascular measures were examined. Results: The central zone (P = 0.174), parafoveal thickness (P = 0.090), perifovea (P = 0.592), RNFL (P = 0.866), GCC (P = 0.798), and GCC GLV (P = 0.338) did not differ significantly between the groups. In comparison to the control group, those with very mild NPDR and those with mild NPDR had significantly higher focal loss in GCC volume (P = 0.036). CNFL was significantly lower in those with mild NPDR (P = 0.004) in comparison to the control group and those with no DR. The CNBD (P = 0.094) and CNFT (P = 0.458) did not differ between the groups. Conclusions: Both corneal and retinal neuronal degeneration may occur in early stages of diabetic retinopathy. Further studies are required to examine these potential markers for neuronal degeneration in the absence of clinical signs of DR.

Presence of Peripheral Neuropathy Is Associated With Progressive Thinning of Retinal Nerve Fiber Layer in Type 1 Diabetes.

Purpose: Reduced retinal nerve fiber layer (RNFL) thickness has been demonstrated in patients with diabetic peripheral neuropathy (DPN) in cross-sectional studies. This prospective study defines longitudinal alterations to the RNFL thickness in individuals with type 1 diabetes without (DPN-ve) and with (DPN+ve) DPN and in relation to risk factors for nerve damage. Methods: A cohort of 105 individuals with type 1 diabetes (20% DPN+ve) with predominantly mild or no retinopathy and no previous retinal photocoagulation underwent spectral-domain optical coherence tomography (SD-OCT) at baseline, 2 years, and 4 years. SD-OCT scans were acquired at 3.45-mm diameter around the optic nerve head and the overall RNFL and RNFL in the nasal, superior, temporal, and inferior quadrants were quantified. By including serial quantified RNFL parameters, linear mixed models were applied to assess the change in RNFL thickness over time and to explore the associations with other clinical variables. Results: There was a significant decline in the overall RNFL thickness (-0.7 µm/y, P = 0.02) and RNFL in the superior quadrant (-1.9 µm/y, P < 0.01) in the DPN+ve group compared with DPN-ve group. The overall RNFL thickness and RNFL in the superior and nasal quadrants were inversely associated with age (ß = -0.29, -0.41, and -0.29, respectively; P ≤ 0.02). Sex, retinopathy, diabetes duration, hemoglobin A1c, lipid profile, blood pressure, cigarette use, alcohol consumption, and body mass index did not show any significant effects (P > 0.05). Conclusions: Individuals with DPN showed a progressive RNFL thinning overall and in the superior quadrant, which was more pronounced in older individuals. There may be common pathways for retinal and peripheral neurodegeneration that are independent of conventional DPN risk factors.

Optical coherence tomography predicts 4-year incident diabetic neuropathy.

PURPOSE: To examine the capability of optical coherence tomography-derived retinal thickness measures in detecting 4-year incident diabetic peripheral neuropathy (DPN). METHODS: 145 eyes of 145 participants with diabetes but no DPN at baseline were examined for incident DPN. HbA1c levels, nephropathy, neuropathy (DPN), cardiovascular measures, and various retinal thickness measures were examined at baseline and after 4 years. Incidence of DPN was defined as newly developed DPN at follow-up. Baseline factors were assessed by univariate and a step-wise multiple logistic regression, and the predictors were examined for diagnostic capabilities. RESULTS: Of the 145 participants without DPN at baseline, 51 had developed DPN when examined after 4 years (35% incidence). Of the ophthalmic variables, the mean (S.D.) of the overall thickness in the parafovea at baseline was 315 (18) µm in the no DPN group and 306 (18) µm in the 'incidence' group, and the differences were significant, p = 0.005. The superior hemisphere parafovea (mean (S.D.): 318 (17) µm vs 310 (20) µm, p = 0.02) and inferior hemisphere parafovea (313 (19) µm vs 302 (18) µm, p = 0.002) were different in the incident DPN group compared with the no DPN group. When adjusted for age, retinal thickness in the parafovea (AUC = 0.65, p = 0.003, 86% sensitivity and 44% specificity at 321 µm criterion), and body mass index or BMI (AUC = 0.65, p = 0.003, 49% sensitivity and 83% specificity at 29.3 kg m-2 criterion) at baseline were significant predictors for 4-year incident DPN. CONCLUSIONS: A lower retinal thickness at the parafovea and a higher BMI can predict 4-year incident neuropathy in patients with diabetes, with acceptable diagnostic accuracies. This OCT-derived measure may serve as a potential ophthalmic marker in the screening of patients at risk of developing DPN.

Corneal confocal microscopy best identifies the development and progression of neuropathy in patients with type 1 diabetes.

A sub-set of 38 individuals with type 1 diabetes that fulfilled a strict criterion of "normal" classification for all 7 measures of neuropathy at baseline, were identified and followed. Corneal nerve morphology, as captured with corneal confocal microscopy demonstrated the greatest, and most sustained degeneration over a 4 year period.

Abnormal Anterior Corneal Morphology in Diabetes Observed Using In Vivo Laser-scanning Confocal Microscopy.

PURPOSE: To assess if diabetes alters corneal epithelial, anterior stromal and subbasal nerve plexus morphology and to determine the associations between these and other clinical variables. METHODS: A cohort of 78 participants with diabetes (39 with Type 1 and 39 with Type 2 diabetes) and 29 age-matched healthy controls underwent laser-scanning confocal microscopy of the central cornea. Intermediate cell density (ICD), basal cell density (BCD), anterior stromal cell density (ASCD), corneal nerve fiber density (CNFD) and nerve fiber length (CNFL) were quantified. RESULTS: Compared with controls, participants with diabetes showed reduced ICD (6097 ± 669 vs. 5548 ± 669 no/mm2, P<.01), BCD (8925 ± 1196 vs. 7842 ± 1040 cell/mm2, P<.01), CNFD (23.4 ± 9.1 vs. 17.5 ± 9.7 no/mm2, P<.01) and CNFL (21.0 ± 4.0 vs. 17.4 ± 4.9 mm/mm2, P<.01), with no difference in ASCD (785 ± 262 vs. 733 ± 278 cell/mm2, respectively, P=.40). None of these structural parameters were associated with type of diabetes (P>.06). Multiple regression analysis showed that ICD and BCD were inversely associated with the diabetes duration and diastolic blood pressure (P<.05) and positively associated with CNFD (P<.01). CNFD and CNFL were inversely associated with HbA1c (P<.01), while ASCD was inversely associated with age (P<.01). CONCLUSIONS: Corneal epithelial cells and subbasal nerve fibers are reduced in patients with diabetes; however, anterior stromal cells show no difference. Furthermore, abnormalities in corneal epithelial cells and nerves are interrelated and correlated with modifiable risk factors.

A rapid decline in corneal small fibers and occurrence of foot ulceration and Charcot foot.

We present clinical, neuropathy and corneal nerve morphology data in a participant with type 2 diabetes who developed diabetic foot ulceration, partial amputation and Charcot during a longitudinal observational study. While conventional measures of neuropathy did not deteriorate significantly, corneal nerve parameters showed a rapid reduction prior to the development of foot complications.

Repeatability of Measuring Corneal Nerve Migration Rate in Individuals With and Without Diabetes.

PURPOSE: To assess the repeatability of measuring the corneal nerve migration rate in individuals with and without neuropathy. METHODS: Wide-field montages of the subbasal corneal nerve plexus were generated at baseline and after 3 weeks for 14 participants. Montages were manually examined side by side to identify a referent landmark in the inferior whorl region (origin) and throughout each montage. A software program was developed to measure nerve migration of all identified points relative to the origin. Repeatability was determined by measurement of nerve migration for within observer (one researcher on 2 occasions, 5 days apart) and between observers (2 observers) within 4 different zones based on the distance from the origin and in the vertical section of the wide-field montage. The impact of images being montaged with fully automated software on repeatability was also investigated. RESULTS: The mean difference between observations 1 and 2 for observer 1 was 0.02 ± 1.3 µm/wk (P = 0.94), with an intraclass correlation coefficient (ICC) of 0.99 [95% confidence interval (CI) = 0.99-1.00], and the mean difference between observer 1 and 2 was 0.3 ± 1.2 µm/wk (P = 0.41), with an ICC of 0.99 (95% CI = 0.99-1.00). The mean difference between observations 1 (images montaged by semiautomated software) and 2 (images montaged by fully automated software) was 1.2 ± 4.9 µm/wk (P = 0.41), with an ICC of 0.96 (95% CI = 0.87-1.00). CONCLUSIONS: Measuring corneal nerve migration rate is highly repeatable for within and between observers and when using different methods of image montaging.

Development of a Novel Technique to Measure Corneal Nerve Migration Rate.

PURPOSE: We have developed a novel technique to measure in vivo corneal nerve migration. METHODS: Wide-field montages of the subbasal corneal nerve plexus were generated at baseline and after 3 weeks. The 2 montages were manually examined side by side to identify a referent landmark in the inferior whorl region and 20 additional nerve landmarks throughout each montage. A software program was developed to measure nerve migration by quantifying the movement of the nerve landmarks relative to the inferior whorl landmark over the 3-week period. To illustrate the utility of this technique, nerve migration was measured in 2 individuals with diabetes (one with and the other without neuropathy) and a healthy control participant. RESULTS: The average nerve migration rate was calculated to be 18.4, 49.9, and 41.5 µm/wk for the diabetic individuals with and without neuropathy and the control participant, respectively. The number of landmarks for tracking nerve migration in the participants was 26, 21, and 20, and they were at an average distance of 1500, 1940, and 1461 µm, from the whorl, respectively. The rate of migration depended on the distance from the whorl; hence, linear equations were generated for each subject for comparison. CONCLUSIONS: This novel imaging technique allows rapid measurement of in vivo corneal nerve migration. The results indicate that diabetic neuropathy may be associated with reduced nerve migration; however, because of the high level of manual input required in this technique and the apparent complex characteristics of corneal nerve migration, repeatability and characterization studies are needed.

Risk Factors Associated With Corneal Nerve Alteration in Type 1 Diabetes in the Absence of Neuropathy: A Longitudinal In Vivo Corneal Confocal Microscopy Study.

PURPOSE: The aim of this study was to determine alterations to the corneal subbasal nerve plexus (SNP) over 4 years using in vivo corneal confocal microscopy in participants with type 1 diabetes and to identify significant risk factors associated with these alterations. METHODS: A cohort of 108 individuals with type 1 diabetes and no evidence of peripheral neuropathy at enrollment underwent laser-scanning in vivo corneal confocal microscopy, ocular screening, and health and metabolic assessment at baseline, and the examinations continued for 4 subsequent annual visits. At each annual visit, 8 central corneal images of the SNP were selected and analyzed to quantify corneal nerve fiber density, corneal nerve branch density and corneal nerve fiber length. Linear mixed model approaches were fitted to examine the relationship between risk factors and corneal nerve parameters. RESULTS: A total of 96 participants completed the final visit and 91 participants completed all visits. No significant relationships were found between corneal nerve parameters and time, sex, duration of diabetes, smoking, alcohol consumption, blood pressure, or body mass index. However, corneal nerve fiber density was negatively associated with glycated hemoglobin (ß = -0.76, P < 0.01) and age (ß = -0.13, P < 0.01) and positively related to high-density lipids (ß = 2.01, P = 0.03). Higher glycated hemoglobin (ß = -1.58, P = 0.04) and age (ß = -0.23, P < 0.01) also negatively impacted corneal nerve branch density. Corneal nerve fiber length was only affected by higher age (ß = -0.06, P < 0.01). CONCLUSIONS: Glycemic control, high-density lipid, and age have significant effects on SNP structure. These findings highlight the importance of diabetic management to prevent corneal nerve damage and the capability of in vivo corneal confocal microscopy for monitoring subclinical alterations in the corneal SNP in diabetes.