Subbasal Nerve Research Articles

Long-Term Evaluation of Ocular Surface and Meibomian Gland Function after Laser Assisted in Situ Keratomileusis surgery.

Laser-assisted in Situ Keratomileusis (LASIK) is a common refractive surgery. But it may lead to temporary dry eye due to reversible damage to the corneal sub-basal nerve plexus. However, chronic ocular surface changes are unclear. This study reports the ocular surface changes, partial blinking rate, and meibomian gland status in eyes that underwent LASIK for at least 48 months. Cross-sectional, matched case-control comparison study, including 48 post-LASIK patients and 48 sex-, age-, smoking-, and axial length-matched healthy controls, recruited from a community eye screening program. Outcome measures include anterior segment clinical findings, keratographic and meibographic imagings. Totally 48 right eyes of 48 post-LASIK Chinese patients (39 females, 2 smokers) were analyzed with 48 right eyes of 48 matched healthy controls. The age on ocular surface examination was 50±11 years, and the axial length 26±1mm. Post-LASIK eyes had a lower quality of meibum (P=0.008) compared to healthy controls. Post-LASIK eyes were associated with a shorter Schimer test (P=0.03). The ocular surface disease index (OSDI) score was higher in post-LASIK patients (P=0.00001). Other anterior segment examination parameters, partial blinking rate, meibomian gland dropout, lipid layer thickness, non-invasive tear break-up time, and tear meniscus height were comparable between the 2 groups. Up to 75% of post-LASIK patients complained of chronic dry eye symptoms. Post-LASIK eyes were associated with a reduced aqueous tear production. Post-LASIK patients with chronic dry eye symptoms should have comprehensive ocular surface evaluation. Treatment should be commenced in patients with poor tear film stability.

Quantifying the Corneal Nerve Whorl Pattern.

The corneal nerves within the sub-basal nerve plexus (SBNP) display a distinctive whorl-like pattern, a highly dynamic structure that could be a marker of diseases. Previous studies have reported a decrease in whorl nerve density in patients with diabetes, indicating an avenue for noninvasive monitoring of diabetic neuropathy. However, conflicting results have since been reported, highlighting the need for improved quantitative analysis of the corneal whorl. We present an automated algorithm to characterize the whorl shape and test the hypothesis that the whorl organization is affected by diabetic neuropathy. The SBNP whorl was analyzed as a vector field, from which seven whorl metrics were calculated. The efficacy of these whorl metrics was demonstrated in synthetic images, ex vivo mouse corneas, and in a publicly available dataset of wide-field in vivo confocal microscopy (IVCM) images of diabetic and control subjects. Linear discriminant analysis and the Peacock test were used to test for statistical differences. Our analysis code is made freely available. Using our whorl metrics, we were able to quantify different whorl patterns in our patient population and statistically compare cohorts. We determined that whorl patterns tend to present bilaterally in patients (P < 0.001), but there were no significant differences between whorl patterns in patients with diabetes and control subjects, nor between patients with or without neuropathy symptoms. We present a generalizable framework to statistically compare corneal nerve patterns in cohorts of patients. SBNP whorl patterns could serve as a noninvasive marker for ocular diseases, whereas few quantitative IVCM endpoints have been identified to date.

Morphological aberration of corneal nerves in hyposecretory dry eye guinea pigs.

Dry eye, a common ocular surface disease associated with tear film instability and corneal impairment, is frequently accompanied by ocular discomfort and pain. Recent research has shown that corneal nerve dysfunction may play a role in certain pathologies of dry eye; however, the details remain unclear. To clarify the aberration in corneal nerves underlying sensory abnormalities, in addition to corneal impairment in dry eye, we examined the morphological alterations of nerve fibers in the corneas excised from guinea pigs with dry eye, where the lacrimal glands were surgically excised. Guinea pigs with dry eye exhibited reduced tear volume, increased spontaneous blink frequency, and corneal epithelial damage. Simultaneously, the subbasal nerve plexus in the cornea visualized using an anti-tubulin βIII antibody partially outgrew and became convoluted. The morphology of peptidergic nerves containing calcitonin gene-related peptide, which may function as a polymodal nociceptor, was also altered. These results indicate that guinea pigs with excised lacrimal glands can serve as useful tools for investigating the neuronal mechanisms underlying corneal pathology in dry eyes. Additionally, chronic tear deficiency may considerably alter nerve structure, including peptidergic nerves in the cornea, accompanied by epithelial damage and increased blink frequency.

Subclinical corneal inflammation and subbasal nerve alterations in keratoconus detected by in vivo confocal microscopy: a cross-sectional study.

To investigate the intracorneal inflammation and subbasal nerve alterations in keratoconus. This prospective cross-sectional study recruited patients with keratoconus, who were diagnosed and graded the severity based on clinical examination and Schiempflug tomography. Laser in vivo confocal microscopy (IVCM) was performed on the corneal subbasal layer centrally to explore the inflammatory cells (ICs), subbasal nerve density (SND), and nerve tortuosity. Keratoconus severity and related factors including ocular allergy, systemic atopy, eye rubbing, floppy eyelids, and contact lens use were recorded. Association between the factors, IC density, SND and keratoconus severity were analyzed. Thirty-four keratoconus eyes were enrolled, and their IVCM findings were compared with those of 20 age-matched normal eyes. Keratoconus showed a significant increase in ICs (44.25 ± 7.01 vs. 13.06 ± 7.51 cells/mm2, p < 0.001) and a significant decrease in SND (16.54 ± 0.79 vs. 20.62 ± 0.72mm/mm2, p < 0.001) when compared to controls. The alterations were pronounced in severe keratoconus as the IC density was significantly higher (p < 0.001), whereas SND was lower (p = 0.001) in high-graded keratoconus than in low-graded keratoconus. However, there was no significant correlation between the number of IC and SND in keratoconus eyes (p = 0.835). Corneal sensitivity and nerve tortuosity were not different between keratoconus and the controls. No keratoconus-related factors were associated with IC density except the severity of keratoconus (p < 0.001, 95% CI [0.70, 0.95]). Keratoconus, a clinically noninflammatory corneal disease, demonstrates subclinical corneal inflammation and subbasal nerve decline as shown by IVCM. These alterations correlate considerably with the severity of keratoconus. What is known Traditionally, Keratoconus is a clinically noninflammatory corneal disease. What is new Our study suspected keratoconus may be subclinical corneal inflammatory disease. In our research, A Keratoconus patient was discovered to have corneal inflammation and a reduction in sub-basal nerve density through the use of In Vivo Confocal Microscopy. Increase in corneal inflammation is considerably correlated with the severity of keratoconus.

Chemotherapy Induced Corneal Changes Assessed by Corneal Confocal Microscopy: A Review.

The eye, and the cornea in particular, is a common site of chemotherapy induced toxicity, and ocular side effects of both traditional and novel agents have been reported. Corneal confocal microscopy (CCM) is an in vivo technique that allows for the study of all the corneal layers in an easy, non-invasive and reproducible way via the direct visualization of corneal cell morphologies as well as of sub-basal nerve plexus. Thus, it represents a useful way to identify and monitor chemotherapy induced corneal alterations. This work aims to review the use of CCM in identifying corneal toxicity secondary to chemotherapy treatment, as regards both corneal nerves alterations in the setting of chemotherapy induced peripheral neuropathy (CIPN) and other corneal structure changes, particularly involving the corneal epithelium.

Structural and functional changes of binocular corneal innervation and ocular surface function after unilateral SMILE and tPRK

AimsTo evaluate the bilateral changes in the sub-basal nerve plexus of the cornea and ocular surface function after unilateral small incision lenticule extraction (SMILE) and transepithelial photorefractive keratectomy (tPRK) procedures.Methods34...

Association of tear osmolarity and corneal nerves structure in dry eye disease: an in vivo study.

To evaluate the structural changes in corneal sub-basal nerves of dry eye disease (DED) patients with tear hyperosmolarity versus normosmolar tears. A prospective evaluation of the tear film (keratograph 5M), tear osmolarity, and sub-basal corneal nerves (laser scanning in-vivo confocal microscopy) was performed in a cohort of 53 DED patients (106 eyes) diagnosed as per DEWS II criteria. Patients with tear hyperosmolarity (Group 1, n = 48 eyes) were compared with DED patients without tear hyperosmolarity (Group 2, n = 58 eyes). Of 53 patients (27 females), 28 had Sjogren's syndrome, and the rest had meibomian gland dysfunction. There were more SS patients (21 vs 7) and females in Group 1. The two groups were similar in age, TMH, NIBUT, meibomian gland loss, bulbar redness, and corneal staining, except for Schirmer I (p < 0.001), and tear osmolarity (p < 0.001; worse in group 1). The groups did not differ in dendritic cell density, whether immature (53.8 vs. 38) or mature (2.7 vs. 0). The significantly different corneal nerve parameters were nerve fiber length (p = 0.005), density (p = 0.01), and branching density (p = 0.04), with lower values observed in group 1. Only tear osmolarity had a weak negative correlation with corneal nerve fiber length (r, -0.38), density (r, -0.32), and branching (r, -0.28). SS patients with hyperosmolar tears had reduced nerve fiber length and branching compared to SS patients with normosmolar tears. Tear hyperosmolarity is associated with reduced nerve branching, fiber density, and fiber length despite similar levels of conjunctival congestion, tear film stability, and meibomian gland loss in DED patients. What is known • Corneal nerves are reduced in density and length in dry eye disease patients. • Laboratory studies have shown fragmentation of corneal nerves on exposure to hyperosmolar solutions. What is new • Tear hyperosmolarity is associated with reduced nerve branching, fiber density, and fiber length in dry eyes compared to normosmolar tears. • The effect is independent of dendritic cell density.

Concurrent Limbal Stem Cell Deficiency and Mild Neurotrophic Keratopathy in Graft-Vs-Host Disease

Purpose: The purpose of this study was to delineate the concurrence of limbal stem cell deficiency (LSCD) and neurotrophic keratopathy in patients with ocular graft-vs-host disease (oGVHD). Methods: Medical records of patients with oGVHD were reviewed. Parameters collected included corneal sensitivity measured by using a noncontact esthesiometer, corneal fluorescein staining score (National Eye Institute grading scale), tear volume (Schirmer I test), and subbasal nerve density and limbal structure assessed by in vivo confocal microscopy. Results: Twenty-eight patients (mean age: 60.8 ± 10.4 years) with oGVHD were included; 50% (n = 14) had partial LSCD (P-LSCD), and 32% (n = 9) had complete LSCD (C-LSCD). Patients with C-LSCD showed significantly reduced total nerve density and branch nerve density compared with those with P-LSCD (P &lt; 0.02, P &lt; 0.04) and no LSCD (P &lt; 0.01, P = 0.02). Dendritic cell density was significantly higher in the C-LSCD group compared with the no LSCD group (P &lt; 0.05). Corneal sensitivity was significantly reduced in patients with C-LSCD compared with those with P-LSCD (P = 0.01) and no LSCD (P &lt; 0.02). Patients with C-LCSD had higher corneal fluorescein staining scores than patients with P-LSCD (P &lt; 0.01) and no LSCD (P = 0.02). Conclusions: This study highlights a significant concurrence of LSCD and neurotrophic keratopathy in patients with oGVHD, underscoring the link between inflammation, neurodegeneration, and loss of stem cell function.

Use of in vivo confocal microscopy in suspected Acanthamoeba keratitis: a 12-year real-world data study at a Swedish regional referral center

PurposeTo report real-world data (RWD) on the use of in vivo confocal microscopy (IVCM) in handling cases of suspected Acanthamoeba keratitis (AK) cases at a regional referral center during a 12-year period.MethodsRetrospective study of patients with suspected AK presenting at a regional referral center for IVCM in Sweden from 2010 to 2022. Demographics, symptoms, outcomes, and clinical management were analyzed, and IVCM images were interpreted.ResultsOf 74 included patients with suspected AK, 18 (24%) were IVCM-positive, 33 (44%) were IVCM-negative, 15 had inconclusive IVCM results (20.2%), and 8 (11%) were referred for a second opinion based on IVCM, 4 of which were IVCM-positive (5.5%), yielding an overall IVCM-positive rate of 29.5%. Cultures were taken in 38 cases (51%) with only 2 cases (2.7%) culture-positive for AK. Of IVCM-negative cases, cultures were taken in 22 (67%) of cases and 100% of these were AK-negative. IVCM-positive cases had more clinic visits (median 30, P = 0.018) and longer follow-up time (median 890 days, P = 0.009) than IVCM-negative patients, while visual acuity improvement did not differ (P > 0.05). Of IVCM-positive cases, 10 (56%) underwent surgery despite prior anti-amoebic treatment, and 14 (78%) had 3 or more IVCM examinations during follow-up, with cysts (100%), dendritic cells (89%) and inflammatory infiltrate (67%) as the most prevalent features. Longitudinal IVCM indicated improvement in cysts, dendritic cells and subbasal nerves with treatment, while clinical resolution was not always consistent with complete absence of cysts.ConclusionsIn a real-world setting, IVCM has a high reliability in classifying AK-negative cases, while IVCM detects AK-positive cases more frequently than the gold-standard culture method, leading to its preferential use over the culture method where time or resources are limited. Despite this, a subset of cases are IVCM-inconclusive, the clinical course of referred patients is long requiring many hospital visits, and visual acuity in most cases does not improve with medical treatment alone. Information sharing across centers and standardization of referral and diagnostic routines is needed to exploit the full potential of IVCM in AK patient management.

Corneal Sensitivity and Neuropathy in Patients With Ocular Graft-Versus-Host Disease.

To assess corneal sensitivity changes in patients with ocular graft-versus-host disease using a non-contact and Cochet-Bonnet esthesiometer. In addition, we evaluate the association between corneal sensitivity and subbasal nerve changes and epitheliopathy in these patients. In this retrospective study, the clinical data and images were evaluated for 36 patients (19 female, 17 male) who fulfilled the inclusion criteria. The analyzed data included demographic and ocular surface parameters, including best-corrected visual acuity, corneal sensitivity with non-contact (mbar) and Cochet-Bonnet (cm) esthesiometer, corneal fluorescein staining (CFS) and symptoms scores, tear volume (Schirmer-I test, mm/5'), and subbasal nerve density (μm/mm2; assessed with in vivo confocal microscopy). The mean age of the study cohort was 59.9 ± 10.5 years. The mean corneal sensitivity assessed by Cochet-Bonnet and non-contact esthesiometer was 5.9 ± 0.3 cm and 7.3 ± 2.0 mbar, respectively. The ocular surface parameters included a corneal fluorescein staining (CFS) score, as per the National Eye Institute grading scheme, of 6.9 ± 3.5, and a Schirmer-I test result of 7.5 ± 6.2 mm/5 minutes.. Total corneal subbasal nerve density was inversely associated with CFS scores (r = -0.74; P < 0.001). Moreover, similar correlations between CFS scores and main trunk (r = -0.62; P < 0.001) and branch (r = -0.59; P < 0.001) nerve densities were observed. A significant correlation was found between reduced corneal sensitivity and higher CFS scores (r = 0.66; P < 0.001). Higher pressures were correlated with lower total (r = -0.83; P < 0.001), main trunk (r = -0.62; P < 0.001), and branch (r = -0.72; P < 0.001) nerve densities. The univariate analysis showed that corneal sensitivity loss (assessed with non-contact esthesiometer) was correlated with advanced age of the patients (P = 0.049) and inversely associated with total (P < 0.001), main trunk (P < 0.001), and branch (P < 0.001) nerve densities. In addition, sensitivity loss was inversely associated with punctal occlusion (cauterization (P = 0.001) or plug placement (P < 0.001). The multivariate analysis adjusted for age and punctal occlusion confirmed the associations in the univariate analysis. In this study, we observed that corneal sensitivity loss was associated with reduced main trunk, branch, and total nerve density in patients with ocular graft-versus-host disease. In addition, a significant correlation was observed between reduced corneal nerve density, corneal sensitivity, and severity of epitheliopathy.

Deep-learning based analysis of in-vivo confocal microscopy images of the subbasal corneal nerve plexus’ inferior whorl in patients with neuropathic corneal pain and dry eye disease

PurposeTo evaluate and compare subbasal corneal nerve parameters of the inferior whorl in patients with dry eye disease (DED), neuropathic corneal pain (NCP), and controls using a novel deep-learning-based algorithm to analyze in-vivo confocal microscopy (IVCM) images. MethodsSubbasal nerve plexus (SNP) images of the inferior whorl of patients with DED (n = 49, 77 eyes), NCP (n = 14, 24 eyes), and controls (n = 41, 59 eyes) were taken with IVCM and further analyzed using an open-source artificial intelligence (AI)-based algorithm previously developed by our group. This algorithm automatically segments nerves, immune cells, and neuromas in the SNP. The following parameters were compared between groups: nerve area density, average nerve thickness, average nerve segment tortuosity, junction point density, neuroma density, and immune cell density. Results160 eyes of 104 patients (63 % females), aged 56.8 ± 15.4 years, were included. The mean nerve area density was significantly lower in the DED (P = 0.012) and NCP (P < 0.001) groups compared to the control group. The junction point density was lower in the NCP group compared with control (P = 0.001) and DED (P = 0.004) groups. The immune cell density was higher in the DED group compared with controls (P < 0.001). ConclusionsDeep-learning-based analysis of IVCM images of the corneal SNP inferior whorl distinguished a decreased mean nerve area density in patients with DED and NCP compared with controls and an increased immune cell density in patients with oGVHD- and SS-associated DED. These findings suggest that the inferior whorl could be used as landmark to distinguish between patients with DED and NCP.

Multimodal Approach in Dry Eye Disease Combining In Vivo Confocal Microscopy and HLA-DR Expression.

The purpose of this study was to determine the association between corneal images provided by in vivo confocal microscopy (IVCM) with clinical parameters and conjunctival expression of HLA-DR antigen in patients with dry eye disease (DED). Two hundred fourteen eyes of 214 patients with DED were analyzed, consisting of 2 groups of patients - 63 with autoimmune dry eye disease (AIDED) and 151 with non-autoimmune dry eye disease (NAIDED). Patients underwent a full clinical examination, including symptom screening, using the Ocular Surface Disease Index (OSDI) questionnaire, and objective analysis of DED signs by Schirmer's testing, tear break-up time (TBUT), Oxford's test, and IVCM corneal imaging. The IVCM scoring criteria were based on corneal sub-basal nerve density (ND), nerve morphology (NM), and inflammatory cell (IC) density. Quantification of conjunctival HLA-DR antigen was performed by flow cytometry. The total IVCM score (T-IVCM) as well as the IVCM-IC subscore (sc) were positively correlated with HLA-DR levels with r = 0.3, P < 0.001 and r = 0.3, P < 0.01, respectively in the total population of patients with DED. The IVCM-NDsc was negatively correlated with TBUT in patients with AIDED (r = -0.2, P < 0.05) and with the Schirmer's test in patients with NAIDED (r = -0.24, P < 0.05). However, the IVCM-NMsc was positively correlated with the Oxford score only in patients with AIDED (r = 0.3, P < 0.05). The proposed IVCM scoring system showed significant correlations with clinical parameters along with conjunctival HLA-DR quantification in patients with DED. The IVCM grading score represents an interesting point of commonality among clinical parameters, imaging, and molecular investigation of the ocular surface.

Confocal Microscopy of the Cornea in Aqueous-Deficient Dry Eye Disease-A Literature Review.

In vivo confocal microscopy (IVCM) is a vital tool in studying dry eye disease (DED), providing insights into morphological changes at ocular surface unit levels. This review presents the main differences in corneal structure between aqueous-deficient dry eye disease (AD-DED) and normal eyes. A comprehensive search of PubMed, Web of Science, Embase, and MEDLINE databases from January 2000 to December 2023 was conducted. The study selection process, as well as data selection and examination, were independently performed by two members of the review team. The review reveals a consistent decrease in corneal surface epithelial cell density in AD-DED cases compared to a control group, but conflicting data on basal epithelial cell density. Notably, the abnormal hyperreflectivity of keratocytes in patients with Sjogren's syndrome was recorded, and there was a significant keratocyte density in AD-DED subjects compared to evaporative DED and control groups. Studies also found a decrease in sub-basal nerve density, increased tortuosity, and the fragmentation of nerve fibers. Dendritic cell density and dendritic cell dendrites increase in AD-DED patients compared to healthy subjects. IVCM is a powerful tool for enhancing our understanding of the pathophysiological mechanisms underlying DED. However, the review underscores the urgent need to standardize the terminology, analysis, and units used for accurate interpretation, a crucial step in advancing our knowledge of DED.

Remission of corneal and peripheral neuropathy after bariatric surgery in people with diabetes

PurposeDiabetic peripheral neuropathy can be detected using non-invasive in vivo confocal microscopy of the cornea (IVCM) and such abnormalities may precede the development of clinical neuropathy. The current study aimed to assess any progression or remission of corneal and peripheral neuropathy in patients with type 2 diabetes undergoing bariatric surgery. MethodsPeople with known type 2 diabetes for at least five years and listed for bariatric surgery were recruited. Participants were assessed before, and 12, 26, and 52 weeks following bariatric surgery. IVCM and corneal sensitivity measurements were performed. A modified total neuropathy score (mTNS) was obtained from neuropathy questionnaire, clinical assessment and biothesiometry. ResultsTwenty-nine participants (M:F, 11:18) with mean BMI of 44.7 ± 6.4 kg/m2, and 11 ± 7.6 years duration of diabetes, were assessed. Corneal sub-basal nerve fibre length (CNFL), displayed an increase from a baseline mean of 12.20 ± 1.00 to 17.48 ± 0.92 mm/mm2 at 52 weeks (p < 0.0001). Corneal sensitivity threshold displayed a decrease over time, thus corneal sensitivity improved, falling from a mean of 1.11 ±0 .15 to 0.62 ± 0.11 (mBAR) (p < 0.0001). Clinical neuropathy scores demonstrated significant improvements from baseline, displaying a decrease in average mTNS score from 3.29 ± 0.68 to 0.76 ± 0.30 (p < 0.0001). A significant inverse relationship was shown between CNFL and sensitivity (β coefficient = −0.047, p < 0.001), and CNFL and mTNS (β coefficient = −0.178, p < 0.001). ConclusionBariatric surgery led to an improvement in metabolic control of diabetes and weight loss, along with improvement in corneal nerve microstructure, corneal sensitivity, and neuropathic symptoms, suggesting a reversal of both small and large fibre neuropathy.

Corneal nerve fiber morphology following COVID-19 infection in vaccinated and non-vaccinated population

To examine corneal subbasal nerve changes in patients who received vaccination against SARS-CoV-2 virus and underwent COVID-19 infection compared to infected non-vaccinated patients and healthy controls. Twenty-nine eyes of 29 vaccinated patients (mean age: 36.66 ± 12.25 years) within six months after PCR or Ag test proven COVID-19 infection and twenty-eight eyes of 28 age-matched infected, non-vaccinated patients (mean age: 42.14 ± 14.17 years) were enrolled. Twenty-five age-matched healthy individuals (mean age: 47.52 ± 18.45 years) served as controls. In vivo confocal microscopy (Heidelberg Retina Tomograph II Rostock Cornea Module, Germany) was performed in each group. Corneal subbasal nerve plexus morphology and corneal dendritic cells (DC) were evaluated. Significantly higher corneal nerve fiber density (P < 0.001), nerve branch density (P < 0.001), nerve fiber length (P < 0.001), total branch density (P = 0.007), nerve fiber area (P = 0.001) and fractal dimension (P < 0.001) values were observed in vaccinated patients after COVID-19 infection compared to the non-vaccinated group. Significantly higher DC density was observed in the non-vaccinated group compared to the control group (P = 0.05). There was a statistically significant difference in the size of mature DCs (P < 0.0001) but the size of immature DCs did not differ significantly among the 3 groups (P = 0.132). Our results suggest that SARS-CoV-2 vaccination may have a protective effect against the complications of COVID-19 disease on the corneal subbasal nerve fibers.

Tear Fluid Progranulin as a Noninvasive Biomarker for the Monitoring of Corneal Innervation Changes in Patients With Type 2 Diabetes Mellitus.

This study aimed to investigate the expression levels of progranulin (PGRN) in the tears of patients with diabetic retinopathy (DR) versus healthy controls. Additionally, we sought to explore the correlation between PGRN levels and the severity of ocular surface complications in patients with diabetes. In this prospective, single-visit, cross-sectional study, patients with DR (n = 48) and age-matched healthy controls (n = 22) were included and underwent dry eye examinations. Tear fluid was collected, and its components were analyzed using the Luminex assay. The subbasal nerve plexus of all participants was evaluated by in vivo confocal microscopy. Patients with DR exhibited more severe dry eye symptoms, along with a reduction in nerve fiber density, length, and branch density within the subbasal nerve plexus, accompanied by an increase in the number of dendritic cells. Tear PGRN levels were also significantly lower in patients with diabetes than in normal controls, and the levels of some inflammatory factors (TNF-α, IL-6, and MMP-9) were higher in patients with DR. Remarkably, the PGRN level significantly correlated with nerve fiber density (R = 0.48, P < 0.001), nerve fiber length (R = 0.65, P < 0.001), and nerve branch density (R = 0.69, P < 0.001). Tear PGRN levels might reflect morphological changes in the corneal nerve plexus under diabetic conditions, suggesting that PGRN itself is a reliable indicator for predicting the advancement of neurotrophic keratopathy in patients with diabetes. PGRN insufficiency on the ocular surface under diabetic conditions was found to be closely associated with nerve impairment, providing a novel perspective to discover the pathogenesis of diabetic complications, which could help in developing innovative therapeutic strategies.

Co-existence of Neurotrophic Keratopathy in Eyes With Limbal Stem Cell Deficiency

PurposeTo investigate whether neurotrophic keratopathy is present in limbal stem cell deficiency (LSCD) by measuring corneal sensation and characterizing corneal subbasal nerve plexus. DesignProspective, cross-sectional “case-control” comparative study. MethodsForty-six eyes with LSCD and 14 normal eyes were recruited from 2019 to 2022. Corneal sensation was measured using a Cochet-Bonnet esthesiometer and subbasal nerve plexus was imaged using in vivo confocal microscopy (IVCM) at the central cornea and 4 limbal regions. Subbasal nerve density (SND, number of nerve/mm2), subbasal nerve length (SNL, total length of nerve/mm2) and subbasal nerve branch density (SNBD, number of branch/mm2) were quantified. LSCD was graded to stage 1, 2 and 3 using a previously established staging method` consisting of clinical scores, basal cell density, central corneal epithelial thickness and SNL. ResultsThe mean (±SD) cornea sensation in the central cornea and limbus were 29.2 ± 21.5 and 33.6 ± 15.1 mm in the LSCD group and 57.6 ± 5.8 and 54.3 ± 4.7 mm in the control group, respectively (all P < 0.001). In sectoral LSCD, the sensation in the affected regions (29.1 ± 17.6 mm) decreased significantly compared to the unaffected regions (41.4 ± 18.2 mm, P < 0.001). Central corneal SND, SNL and SNBD were reduced by 84.6%, 82.6%, and 89.2%, respectively in LSCD compared to the control (all P < 0.05). The central corneal sensation negatively correlated with the severity of LSCD (rho = -0.64, P < 0.0001) and positively correlated with SND, SNL, and SNBD (rho=0.63, 0.66, and 0.56, respectively; all P < 0.001). ConclusionsCorneal sensation was reduced in eyes with LSCD. The degree of corneal sensation reduction positively correlated with the severity of LSCD. This finding demonstrated the co-existence of neurotropic keratopathy in LSCD.

Three-Dimensional Reconstruction of Subbasal Nerve Density in Eyes With Limbal Stem Cell Deficiency: A Pilot Study.

Corneal subbasal nerve parameters have been previously reported using 2-dimensional scans of in vivo laser scanning confocal microscopy (IVCM) in eyes with limbal stem cell deficiency (LSCD). This study aims to develop and validate a method to better quantify corneal subbasal nerve parameters and changes from reconstructed 3-dimensional (3D) images. IVCM volume scans from 73 eyes with various degrees of LSCD (mild/moderate/severe) confirmed by multimodal anterior segment imaging including IVCM and 20 control subjects were included. Using ImageJ, the scans were manually aligned and compiled to generate a 3D reconstruction. Using filament-tracing semiautomated software (Imaris), subbasal nerve density (SND), corneal nerve fiber length, long nerves (>200 μm), and branch points were quantified and correlated with other biomarkers of LSCD. 3D SND decreased in eyes with LSCD when compared with control subjects. The decrease was significant for moderate and severe LSCD ( P < 0.01). 3D SND was reduced by 3.7% in mild LSCD, 32.4% in moderate LSCD, and 96.5% in severe LSCD. The number of long nerves and points of branching correlated with the severity of LSCD ( P < 0.0001) and with declining SND (R 2 = 0.66 and 0.67, respectively). When compared with 2-dimensional scans, 3D reconstructions yielded significant increases of SND and branch points in all conditions except severe LSCD. 3D analysis showed a 46% increase in long nerves only in mild LSCD ( P < 0.01). This proof-of-concept study validates the use of 3D reconstruction to better characterize the corneal subbasal nerve in eyes with LSCD. In the future, this concept could be used with machine learning to automate the measurements.

Corneal innervation changes ın Alzheimer's: implications for sensory dysfunction.

To compare, between Alzheimer's disease (AD) patients and healthy individuals, corneal subbasal nerve plexus (CSNP) parameters and corneal sensitivities. Twenty-two patients who were followed up with Alzheimer's disease (Alzheimer's group) and 18 age- and gender-matched healthy individuals (control group) were included in this cross-sectional study. CSNP parameters, including nerve fiber length (NFL), nerve fiber density (NFD), and nerve branch density (NBD), were evaluated using in vivo confocal microscopy. Corneal sensitivity was evaluated using a Cochet-Bonnet esthesiometer. The results were compared between the two groups. In the Alzheimer's group, NFL was 12.2 (2.4) mm/mm2, NFD was 12.5 [3.1] fibers/mm2, and NBD was 29.7 [9.37] branches/mm2. In the control group, NFL was 16.5 (2.0) mm/mm2, NFD was 25.0 [3.13] fibers/mm2, and NBD was 37.5 [10.9] branches/mm2. All three parameters were significantly lower in the Alzheimer's group compared to the control group (p < 0.001, p < 0.001, and p = 0.001, respectively). Similarly, corneal sensitivity was significantly lower in the Alzheimer's group (55.0 [5.0] mm) compared to the control group (60.0 [5.0] mm) (p < 0.001). We determined that, in AD, corneal sensitivity decreases significantly, in parallel with the decrease in corneal nerves. Changes in the corneal nerve plexus and a decrease in corneal sensitivity may be used in the early diagnosis and follow-up of AD. In addition, ocular surface problems secondary to these changes should also be kept in mind.

Tear film hTERT and corneal nerve characteristics in dry eye disease

ABSTRACT Clinical relevance The behaviour of human telomerase reverse transcriptase (hTERT) in tears reflects its role in maintaining the ocular surface homoeostasis, as it is increased after the initial fitting of contact lenses and post-overnight lid closure. Background hTERT has been shown to respond to cellular stress in neurodegenerative diseases and to enhance axonal regeneration after peripheral axotomy in an animal model. This work investigated whether the behaviour of hTERT in the tear film reflects ocular surface inflammation and neuronal changes in the presence of dry eye disease. Methods Flush tears were collected from 18 participants with dry eye disease (14 females, 4 males, mean age 34.7 ± 5.2 years) and from 18 healthy participants without dry eye disease (8 females, 10 males, mean age 31.9 ± 5.8 years). Dry eye disease status was defined using the TFOS DEWS II diagnostic criteria. hTERT levels in tears were measured using enzyme-linked immunosorbent assays. Confocal images were taken at the level of the subbasal nerve plexus at the central cornea and at the inferior whorl, and the densities of corneal immune cells were evaluated as well as corneal nerve morphology metrics using a fully automated technique (University of Manchester, United Kingdom). Results In participants with dry eye disease, hTERT levels were significantly higher compared to controls (median [interquartile range]: 434 [320–600] ng/ml, and 184 [42–390] ng/ml, respectively, p = 0.01). Increased nerve fibre width at the inferior whorl, was seen in those with dry eyes (0.0219 [0.0214–0.0236] mm/mm compared to controls 0.0217 [0.0207 0.0222] p < 0.001), but no significant differences were found in the density of corneal immune cells. Conclusions hTERT levels were elevated in participants with dry eye disease, and this was accompanied by increased nerve thickness in the inferior cornea. The hTERT response may reflect the stress induced to the ocular surface and corneal nerves due to having dry eye disease.