The Intriguing Role of Neuropeptides at the Ocular Surface

Infectious Keratitis in Patients Over 65: A Review on Treatment and Preserving Eyesight

Infectious keratitis (IK) represents a significant global health concern, ranking as the fifth leading cause of blindness worldwide despite being largely preventable and treatable. Elderly populations are particularly susceptible due to age-related changes in immune response and corneal structure. However, research on IK in this demographic remains scarce. Age-related alterations such as increased permeability and reduced endothelial cell density further compound susceptibility to infection and hinder healing mechanisms. Additionally, inflammaging, characterized by chronic inflammation that develops with advanced age, disrupts the ocular immune balance, potentially exacerbating IK and other age-related eye diseases. Understanding these mechanisms is paramount for enhancing IK management, especially in elderly patients. This review comprehensively assesses risk factors, clinical characteristics, and management strategies for bacterial, viral, fungal, and acanthamoeba keratitis in the elderly population, offering crucial insights for effective intervention.

Chronic Kidney Disease Has No Impact on Tear Film Substance P Concentration in Type 2 Diabetes

PURPOSE

The study aimed to ascertain the potential effects of chronic kidney disease (CKD) on substance P concentration in the tear film of people with type 2 diabetes.

METHODS

Participants were classified into two groups: type 2 diabetes with concurrent chronic kidney disease (T2DM-CKD (n = 25)) and type 2 diabetes without chronic kidney disease (T2DM-no CKD (n = 25)). Ocular surface discomfort assessment, flush tear collection, in-vivo corneal confocal microscopy, and peripheral neuropathy assessment were conducted. Enzyme-linked immunosorbent assays were utilized to ascertain the levels of tear film substance P in collected flush tears. Correlation analysis, hierarchical multiple linear regression analysis, and t-tests or Mann-Whitney U tests were used in the analysis of data for two-group comparisons.

RESULTS

There was no substantial difference between the T2DM-CKD and T2DM-no CKD groups for tear film substance P concentration (4.4 (0.2-50.4) and 5.9 (0.2-47.2) ng/mL, respectively; p = 0.54). No difference was observed in tear film substance P concentration between the low-severity peripheral neuropathy and high-severity peripheral neuropathy groups (4.4 (0.2-50.4) and 3.3 (0.3-40.7) ng/mL, respectively; p = 0.80). Corneal nerve fiber length (9.8 ± 4.6 and 12.4 ± 3.8 mm/mm2, respectively; p = 0.04) and corneal nerve fiber density (14.7 ± 8.5 and 21.1 ± 7.0 no/mm2, respectively; p < 0.01) were reduced significantly in the T2DM-CKD group compared to the T2DM-no CKD group. There were significant differences in corneal nerve fiber density (21.0 ± 8.1 and 15.8 ± 7.7 no/mm2, respectively; p = 0.04) and corneal nerve fiber length (12.9 ± 4.2 and 9.7 ± 3.8 mm/mm2, respectively; p = 0.03) between the low- and high-severity peripheral neuropathy groups.

CONCLUSION

In conclusion, no significant difference in tear film substance P concentration was observed between type 2 diabetes with and without CKD. Corneal nerve loss, however, was more significant in type 2 diabetes with chronic kidney disease compared to type 2 diabetes alone, indicating that corneal nerve morphological measures could serve greater utility as a tool to detect neuropathy and nephropathy-related corneal nerve changes.

Inflammatory profile of keratoconic corneal epithelium

BACKGROUND

Recent studies have presented inflammatory features on keratoconus (KC) and many inflammatory markers are described in the tears of patients with this disease. The KC pathogenesis is still unknown just like the correlation with inflammatory patterns. However, environmental and genetic issues may be part of the progress of KC. In addition, some systemic features, such as allergy and obesity, seem to be related to the progression of KC. Our purpose was to evaluate the neuropeptides vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), chemokines ligand 2 (CCL-2) and 5 (CCL-5), and interleukins 6 (IL-6) and 8 (IL-8) on corneal epithelial cells and blood of patients with KC and in healthy controls. In addition, the neutrophil-to-lymphocyte ratio (NLR) was evaluated to predict inflammation.

METHODS

This including prospective observational study included 32 KC patients who underwent corneal crosslinking (CXL) and 32 control patients who underwent photorefractive keratectomy (PRK). Patients' corneal epithelial cells were removed surgically, and blood (buffy coat) was analyzed. Samples in triplicate were evaluated on rt-PCR for neuropeptides (VIP e NPY), interleukins (IL-6 e IL-8), and chemokines (CCL-2 and CCL-5).

RESULTS

Our study showed statistically higher CCL-5 and IL-8 on corneal epithelial cells in patients with KC. Blood cells were statistically higher in VIP and NPY in the KC group. Interleukin-8 on blood cells was statistically significant in KC'S group; for CCL-2 and CCL-5 they were statistically lower in patients with KC compared with controls. NLR showed no difference between the groups.

CONCLUSIONS

Our data support the findings of other studies that suggested altering KC status, such as inflammatory corneal disease. The presence of IL-8 in the cornea and blood samples of KC's group suggested systemic disease with a possible local or repercussion action. Further studies are warranted to elucidate KC pathogenesis and its correlation to systemic disease.

Role of tear vasoactive intestinal peptide on dry eyes after laser keratorefractive surgery

BACKGROUND

To explore the changes in vasoactive intestinal peptide (VIP) concentration in tears post laser-assisted sub-epithelial keratomileusis (LASEK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgeries and related factors, possible association between postoperative dry eye symptoms and VIP concentration in tears, and factors influencing dry eye symptoms after different periods post LASEK and FS-LASIK surgeries.

METHODS

In this prospective, non-randomized, longitudinal cohort study, 23 and 22 subjects were recruited and underwent LASEK and FS-LASIK, respectively. After conducting an intact ophthalmic examination and collecting relevant surgical data, all subjects were examined for VIP concentration in their tears using ELISAs, tear-film breakup time, ocular staining and ocular surface disease index questionnaire before surgery and 1 day, 1 week, and 1 month post-surgery.

RESULTS

Tear VIP concentration increased significantly after both LASEK and FS-LASIK, with the highest concentration observed 1 week post-surgery (P ≤ 0.05). Tear VIP concentration correlated negatively with corneal ablation depth (AD). The extent of dry eyes was related to the operation method employed and postoperative recovery period. In FS-LASIK and LASEK subjects, dry eyes were mainly affected by the basic ocular surface status before surgery, and VIP concentration. Furthermore, in LASEK subjects, dry eyes were negatively correlated with AD.

CONCLUSION

VIP was stimulated and mobilized as an emergency protection post-refractive surgery and a trauma model affected by AD. It can indirectly indicate the inevitable relationship between postoperative dry eye and nerve injury. Elevated post-surgery tear VIP relieves dry eye symptoms, showing its neuroimmune role in regulating adverse injury stimulation. The present study provides a solution to the pathogenesis of postoperative dry eyes.

TRIAL REGISTRATION

The trial registration number: 2021JS22. Date of registration: 10 May 2021.

Variability of autonomic nerve activity in dry eye with decreased tear stability

The autonomic nervous system plays a crucial role in the maintenance of homeostasis. Neurogenic inflammation due to decreased stability of tear film may induce changes in autonomic nerve activity, which could be associated with symptom expression.This study aimed to measure biological parameters that represent autonomic nerve activity in dry eye (DE)s caused by tear film dysfunction and investigate their relationship with symptom intensity. This prospective, cross-sectional, comparative study evaluated 34 eyes of 34 participants (mean age: 52.5 ± 13.4 years; range: 20–81 years) without keratoconjunctival damage. Nineteen eyes in the DE group showed DE symptoms and tear break-up time (TBUT) of ≤5 seconds (short TBUT DE); the 15 eyes in the non-DE group showed no DE symptoms. Autonomic nerve activity was measured for 10 minutes—starting and ending 5 minutes before and after instilling ophthalmic solution—and evaluated using the low-frequency component (LF) to the high-frequency component (HF) ratio of heart rate variability (autonomic balance). The pre-ophthalmic solution administration LF/HF ratio was not significantly different (P = 0.59) between the two groups, however, the standard deviation of the LF/HF ratio (LF/HF-SD) tended to be higher in the DE group than that in the non-DE group (P = 0.086). The DE symptom intensity was significantly related to LF/HF-SD (P = 0.005), which significantly decreased after ophthalmic solution administration in the DE group (P = 0.04). The large fluctuations in autonomic balance may be key for the understanding of the mechanism underlying DE symptoms.

Characteristic of red eye related diseases of Han and Uygur population in Urumchi compared with Shanghai, China

AIM

To study the characteristics, relative distribution and to compare causes of red eye in ophthalmic clinics in Urumchi and Shanghai, China.

METHODS

Data on continuous cases of red-eye patients admitted to the Ophthalmology Center of Xinhua Hospital Affiliated to Shanghai Jiao Tong University and the First Affiliated Hospital of Xinjiang Medical University were collected between November 2018 and September 2019. Demographic data, the incidence of red eye and related disease distribution of all cases were obtained. The independent t-test method was used for age comparison, while the Chi-square test was used to compare classified data information.

RESULTS

The information on 335 and 415 patients with red eyes in Shanghai and Urumchi were collected, respectively. The main causes of red eye were conjunctival disease and dry eye. The age of female patients with red eyes was significantly higher than that of males, and the proportion of female patients with dry eyes was also higher. Red-eye-related diseases occurred more frequently in patients over 46 years old than in those under 18, and dry eye was more common with increasing age. The incidence of infectious conjunctivitis in Urumchi was significantly higher than that in Shanghai, and allergic conjunctivitis occurred more frequently in spring, summer, or autumn than in winter (all P<0.05).

CONCLUSION

Significant differences exist in the distribution of red-eye-related diseases in Urumchi and Shanghai regions of China, and distribution varies with age and season, the latter being an important feature of allergic conjunctivitis.

Corneal nerves and their role in dry eye pathophysiology

As the cornea is densely innervated, its nerves are integral not only to its structure but also to its pathophysiology. Corneal integrity depends on a protective tear film that is maintained by corneal sensation and the reflex arcs that control tearing and blinking. Furthermore, corneal nerves promote epithelial growth and local immunoregulation. Thus, corneal nerves constitute pillars of ocular surface homeostasis. Conversely, the abnormal tear film in dry eye favors corneal epithelial and nerve damage. The ensuing corneal nerve dysfunction contributes to dry eye progression, ocular pain and discomfort, and other neuropathic symptoms. Recent evidence from clinical studies and animal models highlight the significant but often overlooked neural dimension of dry eye pathophysiology. Herein, we review the anatomy and physiology of corneal nerves before exploring their role in the mechanisms of dry eye disease.

Elevated Neuropeptides in Dry Eye Disease and Their Clinical Correlations

PURPOSE

The goal of this study was to assess neuropeptide levels in patients with dry eye disease (DED) and investigate their correlations with clinical characteristics.

METHODS

This study included 38 eyes of 38 patients diagnosed with DED (DED group) and 38 eyes of 38 healthy volunteers without DED (control group). Ocular surface evaluation was performed. The severity of dry eye symptoms and signs in the DED group was graded. Neuropeptides [substance P (SP), alpha-melanocyte-stimulating hormone (α-MSH), β-endorphin, neurotensin, and oxytocin] and inflammatory cytokines levels were measured in basal tears. The link between neuropeptides and clinical parameters was investigated using Spearman rank correlation.

RESULTS

Overall, 76.3% of patients in the DED group showed dry eye symptoms and signs that were inconsistent in severity. Compared with the control group, the DED group showed higher levels of SP, α-MSH, and oxytocin in tears (P = 0.012, P = 0.030, and P = 0.006, respectively), but similar levels of β-endorphin and neurotensin (P = 0.269 and P = 0.052). The levels of SP, α-MSH, and oxytocin were elevated in DED patients with higher grading of symptoms than clinical signs (all P < 0.05). SP, α-MSH, and oxytocin levels in tears were positively correlated with Ocular Surface Disease Index scores, frequency of sensitivity to light, and frequency of blurred vision (all P < 0.05).

CONCLUSIONS

The increased tear levels of SP, α-MSH, and oxytocin may be linked to ocular discomfort in DED. Neuropeptides may play a key role in the development of DED, especially in DED patients with more severe symptoms than clinical signs.

Tear film and ocular surface neuropeptides: Characteristics, synthesis, signaling and implications for ocular surface and systemic diseases

Ocular surface neuropeptides are vital molecules primarily involved in maintaining ocular surface integrity and homeostasis. They also serve as communication channels between the nervous system and the immune system, maintaining the homeostasis of the ocular surface. Tear film and ocular surface neuropeptides have a role in disease often due to abnormalities in their synthesis (either high or low production), signaling through defective receptors, or both. This creates imbalances in otherwise normal physiological processes. They have been observed to be altered in many ocular surface and systemic diseases including dry eye disease, ocular allergy, keratoconus, LASIK-induced dry eye, pterygium, neurotrophic keratitis, corneal graft rejection, microbial keratitis, headaches and diabetes. This review examines the characteristics of neuropeptides, their synthesis and their signaling through G-protein coupled receptors. The review also explores the types of neuropeptides within the tears and ocular surface, and how they change in ocular and systemic diseases.

AS-OCT and Ocular Hygrometer as Innovative Tools in Dry Eye Disease Diagnosis

Dry eye disease (DED) is one of the conditions that most commonly leads patients to visit an ophthalmologist. Fast and accurate diagnosis relieves patient discomfort and spares them from long-term effects on the ocular surface. Many tests used in the diagnosis of DED may be considered subjective as they rely on an experienced observer for image interpretation, resulting in variations in diagnosis. On one hand, the non-contact nature of the anterior segment optical coherence tomography (AS-OCT) device and its rapid image acquisition enable the measurement of the tear meniscus parameter without reflex tearing. On the other hand, an ocular hygrometer allows a rapid, safe, but also efficient, analysis and is associated with low costs and the repeatability of the procedure.

Mass spectrometry analysis of human tear fluid biomarkers specific for ocular and systemic diseases in the context of 3P medicine

Over the last two decades, a large number of non-communicable/chronic disorders reached an epidemic level on a global scale such as diabetes mellitus type 2, cardio-vascular disease, several types of malignancies, neurological and eye pathologies-all exerted system's enormous socio-economic burden to primary, secondary, and tertiary healthcare. The paradigm change from reactive to predictive, preventive, and personalized medicine (3PM/PPPM) has been declared as an essential transformation of the overall healthcare approach to benefit the patient and society at large. To this end, specific biomarker panels are instrumental for a cost-effective predictive approach of individualized prevention and treatments tailored to the person. The source of biomarkers is crucial for specificity and reliability of diagnostic tests and treatment targets. Furthermore, any diagnostic approach preferentially should be noninvasive to increase availability of the biomaterial, and to decrease risks of potential complications as well as concomitant costs. These requirements are clearly fulfilled by tear fluid, which represents a precious source of biomarker panels. The well-justified principle of a "sick eye in a sick body" makes comprehensive tear fluid biomarker profiling highly relevant not only for diagnostics of eye pathologies but also for prediction, prognosis, and treatment monitoring of systemic diseases. One prominent example is the Sicca syndrome linked to a cascade of severe complications that include dry eye, neurologic, and oncologic diseases. In this review, protein profiles in tear fluid are highlighted and corresponding biomarkers are exemplified for several relevant pathologies, including dry eye disease, diabetic retinopathy, cancers, and neurological disorders. Corresponding analytical approaches such as sample pre-processing, differential proteomics, electrophoretic techniques, high-performance liquid chromatography (HPLC), enzyme-linked immuno-sorbent assay (ELISA), microarrays, and mass spectrometry (MS) methodology are detailed. Consequently, we proposed the overall strategies based on the tear fluid biomarkers application for 3P medicine practice. In the context of 3P medicine, tear fluid analytical pathways are considered to predict disease development, to target preventive measures, and to create treatment algorithms tailored to individual patient profiles.

Autoimmune Epithelitis and Chronic Inflammation in Sjögren's Syndrome-Related Dry Eye Disease

Autoimmune epithelitis and chronic inflammation are one of the characteristic features of the immune pathogenesis of Sjögren’s syndrome (SS)-related dry eye disease. Autoimmune epithelitis can cause the dysfunction of the excretion of tear fluid and mucin from the lacrimal glands and conjunctival epithelia and meibum from the meibomian glands. The lacrimal gland and conjunctival epithelia express major histocompatibility complex class II or human leukocyte antigen-DR and costimulatory molecules, acting as nonprofessional antigen-presenting cells for T cell and B cell activation in SS. Ocular surface epithelium dysfunction can lead to dry eye disease in SS. Considering the mechanisms underlying SS-related dry eye disease, this review highlights autoimmune epithelitis of the ocular surface, chronic inflammation, and several other molecules in the tear film, cornea, conjunctiva, lacrimal glands, and meibomian glands that represent potential targets in the treatment of SS-related dry eye disease.

Corneal Lymphangiogenesis: Current Pathophysiological Understandings and Its Functional Role in Ocular Surface Disease

The cornea is a transparent and avascular tissue that plays a central role in light refraction and provides a physical barrier to the external environment. Corneal avascularity is a unique histological feature that distinguishes it from the other parts of the body. Functionally, corneal immune privilege critically relies on corneal avascularity. Corneal lymphangiogenesis is now recognized as a general pathological feature in many pathologies, including dry eye disease (DED), corneal allograft rejection, ocular allergy, bacterial and viral keratitis, and transient corneal edema. Currently, sizable data from clinical and basic research have accumulated on the pathogenesis and functional role of ocular lymphangiogenesis. However, because of the invisibility of lymphatic vessels, ocular lymphangiogenesis has not been studied as much as hemangiogenesis. We reviewed the basic mechanisms of lymphangiogenesis and summarized recent advances in the pathogenesis of ocular lymphangiogenesis, focusing on corneal allograft rejection and DED. In addition, we discuss future directions for lymphangiogenesis research.

The Role of Neuropeptides in Pathogenesis of Dry Dye

Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.

Corneal lymphangiogenesis in dry eye disease is regulated by substance P/neurokinin-1 receptor system through controlling expression of vascular endothelial growth factor receptor 3

PURPOSE

To evaluate the role of substance P (SP)/neurokinin-1 receptor (NK1R) system in the regulation of pathologic corneal lymphangiogenesis in dry eye disease (DED).

METHODS

Immunocytochemistry, angiogenesis assay, and Western blot analysis of human dermal lymphatic endothelial cells (HDLECs) were conducted to assess the involvement of SP/NK1R system in lymphangiogenesis. DED was induced in wild-type C57BL/6 J mice using controlled-environment chamber without scopolamine. Immunohistochemistry, corneal fluorescein staining, and phenol red thread test were used to evaluate the effect of SP signaling blockade in the corneal lymphangiogenesis. The expression of lymphangiogenic factors in the corneal and conjunctival tissues of DED mouse model was quantified by real-time polymerase chain reaction.

RESULTS

NK1R expression and pro-lymphangiogenic property of SP/NK1R system in HDLECs were confirmed by Western blot analysis and angiogenesis assay. Blockade of SP signaling with L733,060, an antagonist of NK1R, or NK1R-targeted siRNA significantly inhibited lymphangiogenesis and expression of vascular endothelial growth factor (VEGF) receptor 3 stimulated by SP in HDLECs. NK1R antagonist also suppressed pathological corneal lymphangiogenesis and ameliorated the clinical signs of dry eye in vivo. Furthermore, NK1R antagonist effectively suppressed the lymphangiogenic factors, including VEGF-C, VEGF-D, and VEGF receptor 3 in the corneal and conjunctival tissues of DED.

CONCLUSIONS

SP/NK1R system promotes lymphangiogenesis in vitro and NK1R antagonism suppresses pathologic corneal lymphangiogenesis in DED in vivo.

Sex Hormones Related Ocular Dryness in Breast Cancer Women

Background: Dry eye syndrome (DES) is strictly connected to systemic and topical sex hormones. Breast cancer treatment, the subsequent hormonal therapy, the subsequent hyperandrogenism and the early sudden menopause, may be responsible for ocular surface system failure and its clinical manifestation as dry eye disease. This local dryness is part of the breast cancer iatrogenic dryness, which affects overall mucosal tissue in the fragile population of those with breast cancer. Methods: A literature review regarding the role of sex hormone changes and systemic hormonal replacement treatments (SHRT) in DES available on PubMed and Web of Science was made without any restriction of language. Results: Androgens exert their role on the ocular surface supporting meibomian gland function and exerting a pro-sebaceous effect. Estrogen seems to show a pro/inflammatory role on the ocular surface, while SHRT effects on dry eye are still not well defined, determining apparently contradictory consequences on the ocular surface homeostasis. The role of sex hormones on dry eye pathogenesis is most likely the result of a strict crosstalk between the protective androgens effects and the androgen-modulating effects of estrogens on the meibomian glands. Conclusions: Patients with a pathological or iatrogenic hormonal imbalance, such as in the case of breast cancer, should be assessed for dry eye disease, as well as systemic dryness, in order to restore their social and personal quality of life.

Ocular redness - II: Progress in development of therapeutics for the management of conjunctival hyperemia

Conjunctival hyperemia is one of the most common causes for visits to primary care physicians, optometrists, ophthalmologists, and emergency rooms. Despite its high incidence, the treatment options for patients with conjunctival hyperemia are restricted to over-the-counter drugs that provide symptomatic relief due to short duration of action, tachyphylaxis and rebound redness. As our understanding of the immunopathological pathways causing conjunctival hyperemia expands, newer therapeutic targets are being discovered. These insights have also contributed to the development of animal models for mimicking the pathogenic changes in microvasculature causing hyperemia. Furthermore, this progress has catalyzed the development of novel therapeutics that provide efficacious, long-term relief from conjunctival hyperemia with minimal adverse effects.

Naso-ocular neuropeptide interactions in allergic rhinoconjunctivitis, rhinitis, and conjunctivitis

Background

Ocular as well as nasal symptoms contribute to allergic response but remain poorly characterized. The aim of this study was to analyze the levels of substance P (SP), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP) in tears and nasal secretions of patients with allergic rhinoconjunctivitis (ARC), allergic rhinitis, and allergic conjunctivitis, while exploring possible mechanisms of naso-ocular interactions.

Methods

A total of 21 patients with ARC, 17 with allergic rhinitis, 13 with allergic conjunctivitis, and 15 healthy controls were enrolled in the study. Nasal secretions and tears were collected. Patient demographics and clinical characteristics were recorded and levels of substance P, VIP, and CGRP were measured.

Results

SP levels in nasal secretions and tears were significantly higher in the ARC, AR, and AC groups. Similar results were obtained for VIP levels. CGRP levels in tears were also significantly higher in the 3 patient groups. The level of SP was significantly higher in the nasal secretions than in the tears of the ARC, AR, and AC patient groups. The level of VIP was significantly higher in the nasal secretions than in the tears in the ARC and AR groups. The level of CGRP was significantly higher in the nasal secretions than in the tears in the ARC and AC groups. Finally, both of the nasal and tear levels of SP and VIP but not CGRP were positively correlated with the visual analog scale (VAS) score in the patients with ARC.

Conclusion

The results of this study suggested that SP, VIP, and CGRP play important roles in the mechanism of ARC and that nasal neurotransmitters and neuropeptides might have more important roles than those of ocular origin.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

Corneal angiogenic privilege and its failure

The cornea actively maintains its own avascular status to preserve its ultimate optical function. This corneal avascular state is also defined as "corneal angiogenic privilege", which results from a critical and sensitive balance between anti-angiogenic and pro-angiogenic mechanisms. In our review, we aim to explore the complex equilibrium among multiple mediators which prevents neovascularization in the resting cornea, as well as to unveil the evolutive process which leads to corneal angiogenesis in response to different injuries.

The cornea IV immunology, infection, neovascularization, and surgery chapter 1: Corneal immunology

PURPOSE

of Review: This review offers an informed and up-to-date insight on the immune profile of the cornea and the factors that govern the regulation of such a unique immune environment.

SUMMARY

The cornea is a unique tissue that performs the specialized task of allowing light to penetrate for visual interpretation. To accomplish this, the ocular surface requires a distinct immune environment that is achieved through unique structural, cellular and molecular factors. Not only must the cornea be able to fend off invasive infectious agents but also control the inflammatory response as to avoid collateral, and potentially blinding damage; particularly of post-mitotic cells such as the corneal endothelium. To combat infections, both innate and adaptive arms of the inflammatory immune response are at play in the cornea. Dendritic cells play a critical role in coordinating both these responses in order to fend off infections. On the other side of the spectrum, the ocular surface is also endowed with a variety of anatomic and physiologic components that aid in regulating the immune response to prevent excessive, potentially damaging, inflammation. This attenuation of the immune response is termed immune privilege. The balance between pro and anti-inflammatory reactions is key for preservation of the functional integrity of the cornea.

RECENT FINDINGS

The understanding of the molecular and cellular factors governing corneal immunology and its response to antigens is a growing field. Dendritic cells in the normal cornea play a crucial role in combating infections and coordinating the inflammatory arms of the immune response, particularly through coordination with T-helper cells. The role of neuropeptides is recently becoming more highlighted with different factors working on both sides of the inflammatory balance.

Ocular surface diabetic disease: A neurogenic condition?

PURPOSE

To investigate clinical and inflammatory changes in the ocular surface of insulin-dependent type I diabetic patients.

METHODS

Two hundred and nine eyes of 106 patients with diagnosis of type I diabetes were recruited in a prospective observational study. Ocular surface clinical assessment, corneal sensitivity and tear film stability tests were performed to evaluate ocular surface system function. Ocular Surface Disease Index (OSDI) questionnaire was administered to all enrolled subjects. Conjunctival impression cytology specimens were also collected to detect neuromediators and inflammatory molecules. Duration of disease, HbA1c levels and diabetic retinopathy stage were recorded.

RESULTS

Corneal sensitivity assessed by Cochet-Bonnet esthesiometer was reduced in patients with more chronic disease, higher HbA1c levels and proliferative diabetic retinopathy. Tear break-up time (TBUT) was reduced in subjects with long-standing diabetes or with more severe retinopathy. OSDI questionnaire scores showed direct correlation with increased HbA1c values. Significant increase of NPY, STAT-5 and ICAM-1 was found in diabetic patients compared to healthy controls. A direct correlation between NPY concentration and ICAM-1 values in patients with type I diabetes was demonstrated.

CONCLUSIONS

Patients with long-standing type I diabetes showed chronic inflammation of the ocular surface, due to neurogenic dysregulation of para-inflammatory homeostatic mechanisms. These patients with ocular surface system failure complained of ocular discomfort but had modest reduction of corneal sensitivity and no signs of neurotrophic keratopathy. Disease duration, increased HbA1c levels and severe diabetic retinopathy appear the most critical factors.

Longitudinal Corneal Endothelial Cell Changes in Patients Undergoing Hematopoietic Stem Cell Transplantation

PURPOSE

To evaluate longitudinally corneal endothelial cell changes in patients undergoing hematopoietic stem cell transplantation (HSCT) and to further investigate possible correlations with hematological and ocular characteristics.

METHODS

Prospective observational study conducted at a single center. All patients underwent a comprehensive ophthalmological examination, before and after HSCT, including slitlamp examination, Schirmer test, tear breakup time, ocular surface staining, specular microscopy of corneal endothelium, and Ocular Surface Disease Index questionnaire.

RESULTS

Twenty-five patients undergoing HSCT and 25 age- and sex-matched controls were included. At baseline, hematological patients showed significantly lower values of endothelial cell density (ECD) compared with those of controls (2514.5 ± 390.2 vs. 2723.7 ± 298.0 cells/mm, P = 0.038). After HSCT, ocular surface disease index score significantly increased (P = 0.020) and tear breakup time significantly decreased (P = 0.036). Conversely, no significant changes were found in Schirmer test and corneal fluorescein staining (always P > 0.05). Eight patients (32%) developed ocular graft-versus-host disease (GVHD). ECD values significantly decreased after HSCT (from 2514.5 ± 390.2 to 2409.5 ± 330.9 cells/mm, P = 0.009). The decrease in ECD values after HSCT was more pronounced in patients with ocular GVHD compared with those without (231.1 ± 188.8 vs. 45.6 ± 156.5, P = 0.016). No significant correlations between the changes in ECD and hematological and ocular characteristics were found (always P > 0.05).

CONCLUSIONS

Hematological patients showed a lower endothelial cell count already before HSCT, compared with controls. After HSCT, the endothelial cell count further significantly decreased, particularly in patients who developed ocular GVHD.

Mast Cells Populate the Corneoscleral Limbus: New Insights for Our Understanding of Limbal Microenvironment

Purpose

Although stem cell activity represents a crucial feature in corneal and ocular surface homeostasis, other cells populating this region and the neighboring zones might participate and influence local microenvironment. Mast cells, the long-lived and tissue-sited immune cells, have been previously reported in corneoscleral specimens. Herein, mast cells were investigated in corneoscleral tissues and related to microenvironment protein expression.

Methods

Twenty-six (14 male/12 female; older than 60 years) human corneoscleral specimens were sectioned for light and fluorescent immunostaining (CD45, p63, Ck-3/7/12/19, tryptase/AA1, and chymase/CC1). Corneal, limbal, and conjunctival squares were produced for molecular and biochemical analysis. Statistical comparisons were carried out by ANOVA.

Results

Toluidine blue staining identified metachromatic intact or degranulated mast cells in the area below the palisades' Vogt (Ck-3/12-positive epithelium and underneath p63 immunoreactivity). Tryptase immunoreactivity was observed close to palisades' Vogt, whereas no specific signal was detected for chymase. Tryptase/AA1 transcripts were quantified in limbal and conjunctival RNA extracts, whereas no specific amplification was detected in corneal ones. Few mediators were overexpressed in limbal extracts with respect to corneal (Neural cell adhesion molecule (NCAM), Intercellular adhesion molecule 3 (ICAM3), Brain-derived Neurotrophic factor (BDNF), and neurotrophin 3 (NT3); P < 0.00083) and conjunctival (NCAM, ICAM3, and NT3; P < 0.05) protein extracts. A trend to an increase was observed for Nerve Growth Factor (NGF) in limbal extracts (P > 0.05).

Conclusions

The specific observation of tryptase phenotype and the interesting protein signature of microenvironment (adhesion molecules, growth factors, and neurotrophins), known to partake mast cell behavior, at least in other areas, would provide additional information to better understand this crucial zone in the framework of ocular surface healthiness.

Neuropeptides in gut-brain axis and their influence on host immunity and stress

In recent decades, neuropeptides have been found to play a major role in communication along the gut-brain axis. Various neuropeptides are expressed in the central and peripheral nervous systems, where they facilitate the crosstalk between the nervous systems and other major body systems. In addition to being critical to communication from the brain in the nervous systems, neuropeptides actively regulate immune functions in the gut in both direct and indirect ways, allowing for communication between the immune and nervous systems. In this mini review, we discuss the role of several neuropeptides, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), corticotropin-releasing hormone (CRH) and phoenixin (PNX), in the gut-brain axis and summarize their functions in immunity and stress. We choose these neuropeptides to highlight the diversity of peptide communication in the gut-brain axis.

Neurokinin-1 Receptor Antagonism Ameliorates Dry Eye Disease by Inhibiting Antigen-Presenting Cell Maturation and T Helper 17 Cell Activation

Neuroinflammation plays an important role in the pathogenesis of ocular surface disease, including dry eye disease (DED), but little is known about the contribution of substance P (SP) to DED. In this study, we investigated the expression of SP at the ocular surface and evaluated its effect on maturation of antigen-presenting cells (APCs), the key cell component involved in the induction of type 17 helper T-cell (Th17) response in DED. The effect of topical blockade of SP signaling was further investigated using neurokinin-1 receptor (NK1R) inhibitors on APC maturation, Th17 cell activation, and disease severity in a mouse model of DED. The results demonstrate that SP is constitutively expressed at the ocular surface, and trigeminal ganglion neurons are the major source of SP in DED. SP derived from trigeminal ganglion enhanced the expression of major histocompatibility complex class II maturation marker by bone marrow-derived dendritic cells, an effect that is abrogated by blockade of SP signaling using NK1R antagonist spantide. Finally, using a well-established murine model of DED, topical treatment of DED mice with NK1R antagonists CP-99,994 and L-733,060 suppressed APC acquisition of major histocompatibility complex class II, reduced Th17 cell activity, and ameliorated DED severity. These findings are of translational value, as they suggest that antagonizing NK1R-mediated SP signaling may be an effective strategy in suppressing Th17-mediated ocular surface disease.

A Pyrrhic Victory: The PMN Response to Ocular Bacterial Infections

Some tissues of the eye are susceptible to damage due to their exposure to the outside environment and inability to regenerate. Immune privilege, although beneficial to the eye in terms of homeostasis and protection, can be harmful when breached or when an aberrant response occurs in the face of challenge. In this review, we highlight the role of the PMN (polymorphonuclear leukocyte) in different bacterial ocular infections that invade the immune privileged eye at the anterior and posterior segments: keratitis, conjunctivitis, uveitis, and endophthalmitis. Interestingly, the PMN response from the host seems to be necessary for pathogen clearance in ocular disease, but the inflammatory response can also be detrimental to vision retention. This "Pyrrhic Victory" scenario is explored in each type of ocular infection, with details on PMN recruitment and response at the site of ocular infection. In addition, we emphasize the differences in PMN responses between each ocular disease and its most common corresponding bacterial pathogen. The in vitro and animal models used to identify PMN responses, such as recruitment, phagocytosis, degranulation, and NETosis, are also outlined in each ocular infection. This detailed study of the ocular acute immune response to infection could provide novel therapeutic strategies for blinding diseases, provide more general information on ocular PMN responses, and reveal areas of bacterial ocular infection research that lack PMN response studies.

Mapping the entire nerve architecture of the cat cornea

OBJECTIVE

To provide a complete nerve architecture and neuropeptide distribution in the cat cornea.

ANIMALS STUDIED

Two adult domestic cats.

PROCEDURE

The cat corneas were stained with protein gene product (PGP) 9.5 antibody-a pan marker for nerve fibers-and then divided into four quarters and double labeled with calcitonin gene-related peptide (CGRP) or substance P (SP) antibodies. Relative corneal nerve fiber densities and nerve terminals were evaluated in whole mount images by computer-assisted analysis.

RESULTS

An average of 21.5 ± 2.1 thick stromal nerves enters the cornea around the limbus where they split into many branches going up to the anterior stroma. Some branches link to each other, but most of them penetrate the basement membrane in the periphery to give origin to subbasal bundles, which run centripetally and merge to form a whirl-like structure (vortex) at the center. These nerve bundles send out many fine terminals that innervate the epithelial cells. Subbasal nerve density and nerve terminals were greater in the center than in the periphery of the cornea. Additionally, CGRP-positive central epithelial nerve fibers and terminals were more abundant than SP-positive nerves and terminals.

CONCLUSION

The architecture of cat corneal nerves shows similarities to human and mouse cornea innervation. This study provides useful data for researchers who use the cat model to assess corneal nerve pathological alterations, as well as in the veterinary field where corneal opacities, ulcerations, and infections damage the nerves and decrease sensitivity.

Review of Biomarkers in Ocular Matrices: Challenges and Opportunities

Biomarkers provide a powerful and dynamic approach to improve our understanding of the mechanisms underlying ocular diseases with applications in diagnosis, disease modulation or for predicting and monitoring of clinical response to treatment. Defined as measurable indicator of normal or pathological processes, biomarker evaluation has been used extensively in drug development within clinical settings to better comprehend effectiveness of treatment in ocular diseases. Biomarkers in the eye have the advantage of access to multiple ocular matrices via minimally invasive methods. Repeat sampling for biomarker assessment has enabled reproducible objective measures of disease process or biological responses to a drug treatment. This review describes the usage of biomarkers with respect to four commonly sampled ocular matrices in clinic: tears, conjunctiva, aqueous humor and vitreous. Issues that affect the evaluation of biomarkers are discussed along with opportunities to leverage biomarkers such that ultimately, they can be used for customized targeted therapy.

Vasoactive Intestinal Peptide Promotes Corneal Allograft Survival

Corneal transplantation is the most prevalent form of tissue transplantation. The success of corneal transplantation mainly relies on the integrity of corneal endothelial cells (CEnCs), which maintain graft transparency. CEnC density decreases significantly after corneal transplantation even in the absence of graft rejection. To date, different strategies have been used to enhance CEnC survival. The neuropeptide vasoactive intestinal peptide (VIP) improves CEnC integrity during donor cornea tissue storage and protects CEnCs against oxidative stress-induced apoptosis. However, little is known about the effect of exogenous administration of VIP on corneal transplant outcomes. We found that VIP significantly accelerates endothelial wound closure and suppresses interferon-γ- and tumor necrosis factor-α-induced CEnC apoptosis in vitro in a dose-dependent manner. In addition, we found that intracameral administration of VIP to mice undergoing syngeneic corneal transplantation with endothelial injury increases CEnC density and decreases graft opacity scores. Finally, using a mouse model of allogeneic corneal transplantation, we found for the first time that treatment with VIP significantly suppresses posttransplantation CEnC loss and improves corneal allograft survival.

When Clarity Is Crucial: Regulating Ocular Surface Immunity

The ocular surface is a unique mucosal immune compartment in which anatomical, physiological, and immunological features act in concert to foster a particularly tolerant microenvironment. These mechanisms are vital to the functional competence of the eye, a fact underscored by the devastating toll of excessive inflammation at the cornea - blindness. Recent data have elucidated the contributions of specific anatomical components, immune cells, and soluble immunoregulatory factors in promoting homeostasis at the ocular surface. We highlight research trends at this distinctive mucosal barrier and identify crucial gaps in our current knowledge.

Role of Corneal Stromal Cells on Epithelial Cell Function during Wound Healing

Following injury, corneal stromal keratocytes transform into repair-phenotype of activated stromal fibroblasts (SFs) and participate in wound repair. Simultaneously, ongoing bi-directional communications between corneal stromal-epithelial cells also play a vital role in mediating the process of wound healing. Factors produced by stromal cells are known to induce proliferation, differentiation, and motility of corneal epithelial cells, which are also subsequently the main processes that occur during wound healing. In this context, the present study aims to investigate the effect of SFs conditioned medium (SFCM) on corneal epithelial cell function along with substance P (SP). Antibody microarrays were employed to profile differentially expressed cell surface markers and cytokines in the presence of SFCM and SP. Antibody microarray data revealed enhanced expression of the ITGB1 in corneal epithelial cells following stimulation with SP whereas SFCM induced abundant expression of IL-8, ITGB1, PD1L1, PECA1, IL-15, BDNF, ICAM1, CD8A, CD44 and NTF4. All these proteins have either direct or indirect roles in epithelial cell growth, movement and adhesion related signaling cascades during tissue regeneration. We also observed activation of MAPK signaling pathway along with increased expression of focal adhesion kinase (FAK), paxillin, vimentin, β-catenin and vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Additionally, epithelial-to-mesenchymal transition (EMT) regulating transcription factors Slug and ZEB1 expression were enhanced in the presence of SFCM. SP enriched the expression of integrin subunits α4, α5, αV, β1 and β3 whereas SFCM increased α4, α5, αV, β1 and β5 integrin subunits. We also observed increased expression of Serpin E1 following SP and SFCM treatment. Wound healing scratch assay revealed enhanced migration of epithelial cells following the addition of SFCM. Taken together, we conclude that SFCM-mediated sustained activation of ZEB1, Slug in combination with upregulated migration-associated integrins and ERK (Extracellular signal-regulated kinase)-FAK-paxillin axis, may lead to induce type 2 EMT-like changes during corneal epithelial wound healing.

Ocular Emergencies: Red Eye

"Red eye" is used as a general term to describe irritated or bloodshot eyes. It is a recognizable sign of an acute/chronic, localized/systemic underlying inflammatory condition. Conjunctival injection is most commonly caused by dryness, allergy, visual fatigue, contact lens overwear, and local infections. In some instances, red eye can represent a true ocular emergency that should be treated by an ophthalmologist. A comprehensive assessment of red eye conditions is required to preserve the patients visual function. Severe ocular pain, significant photophobia, decreased vision, and history of ocular trauma are warning signs demanding immediate ophthalmological consultation.