Identification of presumed corneal neuromas and microneuromas using laser-scanning in vivo confocal microscopy: a systematic review.

BACKGROUND/AIMS: This systematic review critically evaluated peer-reviewed publications describing morphological features consistent with, or using terms related to, a 'neuroma' or 'microneuroma' in the human cornea using laser-scanning in vivo confocal microscopy (IVCM). METHODS: The review was prospectively registered on PROSPERO (CRD42020160038). Comprehensive literature searches were performed in Ovid MEDLINE, Ovid Embase and the Cochrane Library in November 2019. The review included primary research studies and reviews that described laser-scanning IVCM for examining human corneal nerves. Papers had to include at least one of a pre-specified set of keyword stems, broadly related to neuromas and microneuromas, to describe a corneal nerve feature. RESULTS: Twenty-five papers (20 original studies; 5 reviews) were eligible. Three original studies evaluated corneal nerve features in healthy eyes. Most papers assessed corneal nerves in ocular and systemic conditions; seven studies did not include a control/comparator group. There was overlap in terminology used to describe nerve features in healthy and diseased corneas (eg, bulb-like/bulbous, penetration, end/s/ing). Inspection of IVCM images within the papers revealed that features termed 'neuromas' and 'microneuromas' could potentially be physiological corneal stromal-epithelial nerve penetration sites. We identified inconsistent definitions for terms, and limitations in IVCM image acquisition, sampling and/or reporting that may introduce bias and lead to inaccurate representation of physiological nerve characteristics as pathological. CONCLUSION: These findings identify a need for consistent nomenclature and definitions, and rigorous IVCM scanning and analysis protocols to clarify the prevalence of physiological, as opposed to pathological, corneal nerve features.

Laser scanning in vivo confocal microscopy (IVCM) for evaluating human corneal sub-basal nerve plexus parameters: protocol for a systematic review.

INTRODUCTION: Laser scanning in vivo confocal microscopy (IVCM) enables non-invasive, high-resolution imaging of the cornea. In recent years, there has been a vast increase in researchers using laser scanning IVCM to image and quantify corneal nerve parameters. However, a range of methodological approaches have been adopted. The primary aim of this systematic review is to critically appraise the reported method(s) of primary research studies that have used laser scanning IVCM to quantify corneal sub-basal nerve plexus (SBNP) parameters in humans, and to examine corneal nerve parameters in healthy individuals. METHODS AND ANALYSIS: A systematic review of primary studies that have used laser scanning IVCM to quantify SBNP parameters in humans will be conducted. Comprehensive electronic searches will be performed in Ovid MedLine, Embase and the Cochrane Library. Two reviewers will independently assess titles and abstracts, and exclude studies not meeting the inclusion criteria. For studies judged eligible or potentially eligible, full texts will be independently assessed by two reviewers to determine eligibility. A third reviewer will resolve any discrepancies in judgement. Risk of bias will be assessed using a custom tool, covering five methodological domains: participant selection, method of image capture, method of image analysis, data reporting and other sources of bias. A systematic narrative synthesis of findings will be provided. A multilevel random-effects meta-analysis will be performed for corneal nerve parameters derived from healthy participants. This review will be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. ETHICS AND DISSEMINATION: As this review considers published data, ethical approval is not required. We foresee that this synthesis will serve as a reference for future studies, and can be used to inform best practice standards for using IVCM in clinical research. A manuscript reporting the results of the review will be published and may also be presented at scientific conferences.

Optical Coherence Tomography Reveals Changes to Corneal Reflectivity and Thickness in Individuals with Tear Hyperosmolarity.

PURPOSE: To investigate whether tear hyperosmolarity, a feature of dry eye disease (DED), affects central corneal thickness (CCT), corneal light reflectivity, and/or tear film reflectivity. METHODS: This prospective, cross-sectional study involved 48 participants (38 with hyperosmolar tears and 10 controls with normo-osmolar tears). Symptoms and signs of DED (tear osmolarity, sodium fluorescein tear break-up time, ocular surface staining, Schirmer test) were assessed. CCT, and the reflectivity of the cornea and the tear-epithelial interface were quantified relative to background noise using Fourier-domain optical coherence tomography (FD-OCT). RESULTS: CCT of eyes with severe tear hyperosmolarity, defined as eyes in the upper quartile of the hyperosmolar group, was less than control eyes (539.1 ± 7.4 vs. 583.1 ± 15.0 µm, P = 0.02) and eyes with less severe tear hyperosmolarity, defined as hyperosmolar eyes in the lower quartile (622.7 ± 5.8 µm, P < 0.0001). CCT showed a negative linear relationship with tear osmolarity for values above 316 mOsmol/L (R2 = 0.17, P = 0.01). Central corneal reflectivity was lower in hyperosmolar eyes than normo-osmolar eyes (45.1 ± 0.3 vs. 48.1 ± 0.6 pixels, P = 0.02); the greatest relative difference was in the anterior stroma, where corneal reflectivity was 4.7 ± 1.9% less in hyperosmolar eyes (P < 0.01). Peak reflectivity of the tear-epithelial interface was 4.8% ± 3.5% higher in the hyperosmolar group than the normo-osmolar tear group (P = 0.04). CONCLUSION: Individuals with significant tear hyperosmolarity and clinical signs of symptoms of DED show reduced CCT and altered corneal reflectivity. TRANSLATIONAL RELEVANCE: Anterior segment FD-OCT provides novel insight into corneal microstructural differences in individuals with DED.

Monitoring of strain-dependent responsiveness to TLR activation in the mouse anterior segment using SD-OCT.

PURPOSE: To determine whether spectral-domain optical coherence tomography (SD-OCT) can be used to longitudinally monitor inflammation in the mouse anterior segment and to identify any strain-dependent differences in responsiveness to distinct toll-like receptor (TLR) ligands. METHODS: Corneal inflammation was induced in BALB/c and C57BL/6 mice following central corneal abrasions and topical application of saline, TLR-4 ligand, lipopolysaccharide (LPS), or TLR-9 ligand, CpG-oligodeoxynucleotide (CpG-ODN; CpG). Anterior-segment images were captured using SD-OCT at baseline, 24 hours, and 1 week post treatment. Corneal thickness, stromal haze, and the number of keratic precipitates (KP) and anterior chamber (AC) cells were longitudinally compared to determine differences between mouse strains, time points, and TLR activation. RESULTS: In both mouse strains, treatment with CpG, but not saline or LPS, resulted in a similar number of KPs and AC cells. In C57BL/6 mice, central corneal thickness (CCT) increased in CpG- and LPS-treated eyes at 24 hours, which normalized by 1 week. In BALB/c mice, a significant increase in CCT occurred in eyes treated with CpG at 1 week. Stromal haze peaked in C57BL/6 eyes treated with LPS- or CPG-treatment at 24 hours; however, BALB/c eyes showed persistent and marked increases in corneal haze compared with baseline at 1 week post treatment. CONCLUSIONS: Spectral-domain OCT enables high-resolution, longitudinal, in vivo imaging of anterior segment inflammation in mice and revealed novel strain- and time-dependent differences in response to distinct TLR activation in the cornea.