Establishment of the mild, moderate and severe dry eye models using three methods in rabbits

Characterizing the Robustness of Distinct Clinical Assessments in Identifying Dry Eye Condition of Animal Models

PURPOSE

The study aims to characterize the robustness of distinct clinical assessments in identifying the underlying conditions of dry eye disease (DED), with a specific emphasis on the involvement of conjunctival goblet cells.

METHODS

Seven rabbits receiving surgical removal of the lacrimal and Harderian glands were divided into two groups, one with ablation of conjunctival goblet cells by topical soaking of trichloroacetic acid (TCA) to the bulbar conjunctiva (n = 3) and one without (n = 4), and the conditions of DED were assessed weekly using Schirmer test, tear breakup time (TBUT), tear osmolarity, and National Eye Institute (NEI) fluorescein staining grading. After 8 weeks, the rabbits were sacrificed, and the eyes were enucleated for histopathological examination.

RESULTS

Histopathological analysis revealed corneal epithelial thinning in both groups. While TCA soaking significantly decreased the density of conjunctival goblet cells, DED rabbits without TCA also showed a partial reduction in goblet cell density, potentially attributable to dacryoadenectomy. Both groups showed significant decreases in Schirmer test and TBUT, as well as an increase in tear osmolarity. In DED rabbits with TCA soaking, tear osmolarity increased markedly, suggesting that tear osmolarity is highly sensitive to loss and/or dysfunction of conjunctival goblet cells. Fluorescein staining was gradually and similarly increased in both groups, suggesting that fluorescein staining may not reveal an early disruption of the tear film until the prolonged progression of DED.

CONCLUSION

The Schirmer test, TBUT, tear osmolarity, and NEI fluorescein grading are distinct, yet complementary, clinical assessments for the evaluation of DED. By performing these assessments in definitive DED rabbit models, both with and without ablation of conjunctival goblet cells, the role of these cells in the homeostasis of tear osmolarity is highlighted. Characterizing the robustness of these assessments in identifying the underlying conditions of DED will guide a more appropriate management for patients with DED.

Animal Models in Eye Research: Focus on Corneal Pathologies

The eye is a complex sensory organ that enables visual perception of the world. The dysfunction of any of these tissues can impair vision. Conduction studies on laboratory animals are essential to ensure the safety of therapeutic products directly applied or injected into the eye to treat ocular diseases before eventually proceeding to clinical trials. Among these tissues, the cornea has unique homeostatic and regenerative mechanisms for maintaining transparency and refraction of external light, which are essential for vision. However, being the outermost tissue of the eye and directly exposed to the external environment, the cornea is particularly susceptible to injury and diseases. This review highlights the evidence for selecting appropriate animals to better understand and treat corneal diseases, which rank as the fifth leading cause of blindness worldwide. The development of reliable and human-relevant animal models is, therefore, a valuable research tool for understanding and translating fundamental mechanistic findings, as well as for assessing therapeutic potential in humans. First, this review emphasizes the unique characteristics of animal models used in ocular research. Subsequently, it discusses current animal models associated with human corneal pathologies, their utility in understanding ocular disease mechanisms, and their role as translational models for patients.

A Comprehensive Assessment of Tear-Film-Oriented Diagnosis (TFOD) in a Dacryoadenectomy Dry Eye Model

Tear film instability is a major cause of dry eye disease. In order to treat patients with short tear film breakup time (TBUT)-type dry eye, the development of tear film stabilizing agents is essential. However, the lack of an appropriate animal model of tear film instability has made drug development difficult. Although rabbit dry eye models have been reported in the past, there are only a few reports that focus on tear film instability. Herein, we assessed the tear film stability of a rabbit dry eye model induced by dacryoadenectomy. A clinical evaluation of the ocular surface, interferometry, and histological assessments of the cornea and conjunctiva were performed. Following the removal of the lacrimal glands, TBUT was shortened significantly, with dimple and random breakup patterns prominently observed. Furthermore, the blink rate in this model increased after dacryoadenectomy, suggesting that this model partially captured the phenotypes of human short TBUT-type dry eye and may be useful as an animal model for investigating potential drug candidates.

The Effects of Lycium chinense, Cuscuta chinensis, Senna tora, Ophiopogon japonicus, and Dendrobium nobile Decoction on a Dry Eye Mouse Model

Background and objective: Dry eye disease (DED) is a relatively common disorder associated with abnormal tear film and the ocular surface that causes ocular irritation, dryness, visual impairment, and damage to the cornea. DED is not a life-threatening disease but causes discomfort and multifactorial disorders in vision that affect daily life. It has been reported that all traditional medicinal plants exhibit anti-inflammatory effects on several diseases. We hypothesized that the decoction ameliorated ocular irritation and decreased cytokine expression in the cornea. This study aimed to investigate the molecular mechanisms of DED and discover a therapeutic strategy to reduce corneal inflammation. Material and Methods: We used a DED mouse model with extraorbital lacrimal gland (ELG) excision and treated the mice with a decoction of five traditional medicines: Lycium chinense, Cuscuta chinensis, Senna tora, Ophiopogon japonicus, and Dendrobium nobile for 3 months. The tear osmolarity and the ocular surface staining were evaluated as indicators of DED. Immunohistochemistry was used to detect the level of inflammation on the cornea. Results: After treatment with the decoction for three months, epithelial erosions and desquamation were reduced, the intact of corneal endothelium was maintained, and tear osmolarity was restored in the eyes. The IL-1β-associated inflammatory response was reduced in the cornea in the DED model. Conclusions: These data suggested that a mixture of traditional medicines might be a novel therapy to treat DED.

Benzalkonium Chloride for Experimental Dry Eye Induction in a Rabbit Model

Purpose: This study compared the clinical parameters and histological findings according to the benzalkonium chloride concentration (BAC; 0.05%, 0.1%, and 0.2%) for inducing experimental dry eye (EDE) in a rabbit model.Methods: Rabbits were divided into four groups according to the BAC concentration: untreated group, 0.05%, 0.1%, and 0.2% BAC. BAC was instilled topically in both eyes of the rabbits twice daily until they were euthanized after 14 days. Tear volume, tear break-up time (TBUT), and corneal fluorescein staining score (CFS) were measured 0, 3, 5, 7, and 14 days after treatment. After excising tissues on day 14, the conjunctival goblet cell density and corneal epithelial apoptosis were quantified.Results: The tear volume and TBUT were lower and the CFS was higher than baseline values after 14, 10, and 5 days in the 0.05, 0.1, and 0.2% BAC groups, respectively (all p < 0.05). At 14 days, the 0.2% BAC group showed more significant aggravation of all clinical parameters, and the 0.1% BAC group had a lower CFS (all p < 0.05) than the 0.05% BAC group. In all BAC groups, the conjunctival goblet cell density was lower and corneal epithelial apoptosis was significantly higher than in the untreated group (all p < 0.01). The conjunctival goblet cell density was lower in the 0.2% BAC group than in the 0.05% BAC group. Between-group differences in corneal epithelial apoptosis were observed in all experimental groups (all p < 0.01).Conclusions: Instilling BAC for 14 days induced EDE in the 0.05, 0.1, and 0.2% BAC groups. Although 0.2% BAC cannot be used for a severe EDE model, it is useful for inducing EDE in a rabbit model in a short time.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Corneal lesions related to an anesthetic mixture of medetomidine, midazolam, and butorphanol treatment in rats

An anesthetic mixture of medetomidine, midazolam and butorphanol (MMB) has been recently used in laboratory animals. We observed corneal opacity in nephrectomized rats that had undergone two operations under MMB anesthesia at 4 and 5 weeks of age. To evaluate the features of this corneal opacity, ophthalmic examinations were conducted in 83 nephrectomized rats, and 8 representative animals with corneal opacity were evaluated histopathologically 4 weeks after operation. The ophthalmic examinations revealed that 66/83 animals had corneal opacity, which was characterized histopathologically by mineralization with or without inflammation in the corneal stroma. In addition, to examine the possible causes of this corneal opacity, we investigated whether similar corneal changes were induced by the MMB anesthetic treatment in normal rats. The MMB anesthetic was administered twice to 4- and 5-week-old normal SD rats (5 animals/age) in the same manner as for the nephrectomized rats. Ophthalmic examinations were conducted in all the animals once a week, and the animals were necropsied 4 weeks after the first administration. In normal rats, similar corneal opacity was observed after the first administration, and increases in the severity and size of the corneal opacity were noted after the second administration. In conclusion, this study revealed the features of corneal opacity in rats undergoing nephrectomy under MMB anesthesia and the occurrence of similar corneal opacity in normal rats treated with MMB anesthetic. To the best of our knowledge, this is the first report of corneal opacity related to MMB anesthetic treatment in rats.

Formulation and development of tacrolimus-gellan gum nanoformulation for treatment of dry eye disease

The present study aimed at the development and evaluation of tacrolimus gellan gum nanoparticles (TGNPs) for the effective management of dry eye disease (DED) following topical application. TGNPs were developed by ionotropic gelation between gellan gum and aluminum chloride. Developed TGNPs were nanosized (274.46 ± 8.90 nm) with high % encapsulation efficiency (74.2 ± 2.4%) and loading capacity (36.14 ± 1.7%). The nanosize and spherical morphology of TGNPs was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FTIR) revealed no interaction between drug and GG. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) confirms the conversion of crystalline tacrolimus to amorphous post encapsulation in the nanoparticle. TGNPs showed prolonged drug release throughout 12 h and higher pre-corneal retention compared to tacrolimus solution. HET-CAM studies, histopathological evaluation, and Draize test confirmed the safety of the formulation for ocular use. Further, the pharmacodynamic studies using experimental DED in rabbits showed that TGNPs are effective in treating symptoms of DED. In conclusion, topical delivery of TGNPs could hold potential for efficient management of DED.

Experimental Models, Induction Protocols, and Measured Parameters in Dry Eye Disease: Focusing on Practical Implications for Experimental Research

Dry eye disease (DED) is one of the major ophthalmological healthcare challenges worldwide. DED is a multifactorial disease characterized by a loss of homeostasis of the tear film, and its main pathogenesis is chronic ocular surface inflammation related with various cellular and molecular signaling cascades. The animal model is a reliable and effective tool for understanding the various pathological mechanisms and molecular cascades in DED. Considerable experimental research has focused on developing new strategies for the prevention and treatment of DED. Several experimental models of DED have been developed, and different animal species such as rats, mice, rabbits, dogs, and primates have been used for these models. Although the basic mechanisms of DED in animals are nearly identical to those in humans, proper knowledge about the induction of animal models is necessary to obtain better and more reliable results. Various experimental models (in vitro and in vivo DED models) were briefly discussed in this review, along with pathologic features, analytical approaches, and common measurements, which will help investigators to use the appropriate cell lines, animal, methods, and evaluation parameters depending on their study design.

Optogenetic Inhibition of Nav1.8 Expressing Corneal Afferents Reduces Persistent Dry Eye Pain

Purpose

The aim of the present study was to investigate the contribution of Nav1.8 expressing corneal afferent neurons to the presence of ongoing pain in lacrimal gland excision (LGE)-induced dry eye.

Methods

The proton pump archaerhodopsin-3/eGFP (ArchT/eGFP) was conditionally expressed in corneal afferents using Nav1.8-cre mice. Dry eye was produced by unilateral LGE. Real time place preference was assessed using a three-chamber apparatus. A neutral, unlit center chamber was flanked by one illuminated with a control light and one illuminated with an ArchT activating light. For real-time preference, animals were placed in the neutral chamber and tracked over five 10-minute sessions, with the lights turned on during the second and fourth sessions. In other studies, movement was tracked over three 10-minute sessions (the lights turned on only during the second session), with animals tested once per day over the course of 4 days. A local anesthetic was used to examine the role of ongoing corneal afferent activity in producing place preference.

Results

The corneal afferent nerves and trigeminal ganglion cell bodies showed a robust eGFP signal in Nav1.8-cre;ArchT/eGFP mice. After LGE, Nav1.8-cre;ArchT/eGFP mice demonstrated a preference for the ArchT activating light paired chamber. Preference was prevented with pre-application to the cornea of a local anesthetic. Nav1.8-cre;ArchT/eGFP mice with sham surgery and LGE wild-type control mice did not develop preference.

Conclusions

Results indicate LGE-induced persistent, ongoing pain, driven by Nav1.8 expressing corneal afferents. Inhibition of these neurons represents a potential strategy for treating ongoing dry eye-induced pain.

Animal models of dry eye disease: Useful, varied and evolving (Review)

Dry eye disease (DED), which is a prevalent disease that still lacks successful treatment options, remains a major challenge in ophthalmology. Multiple animal models of DED have been used to decipher its pathophysiology and to develop novel treatments. These models use mice, rats, rabbits, cats, dogs and non-human primates. Each model assesses aspects of DED by focusing on elements of the lacrimal functional unit, which controls the homeostasis of the tear film. The present review outlines representative DED animal models and assesses their contribution to the study of DED. Murine models are the most extensively used, followed by rabbit models; the latter offer the advantage of larger eyes, a favorable biochemical profile for drug studies, experimental ease and relatively low cost, contrasting with non-human primates, which, although closer to humans, are not as accessible and are expensive. No comprehensive ‘ideal’ animal model encompassing all aspects of human DED exists nor is it feasible. Investigators often choose an animal model based on their experimental needs and the following four features of a given model: The size of the eye, its biochemical composition, the available research reagents and cost. As research efforts in DED expand, more refined animal models are needed to supplement the enormous contribution made to date by existing models.

Animal models of dry eye: Their strengths and limitations for studying human dry eye disease

Dry eye disease (DED), also called the keratoconjunctivitis sicca, is one of the most common diseases in the ophthalmology clinics. While DED is not a life-threatening disease, life quality may be substantially affected by the discomfort and the complications of poor vision. As such, a large number of studies have made contributions to the investigation of the DED pathogenesis and novel treatments. DED is a multifactorial disease featured with various phenotypic consequences; therefore, animal models are valuable tools suitable for the related studies. Accordingly, selection of the animal model to recapitulate the clinical presentation of interest is important for appropriately addressing the research objective. To this end, we systemically reviewed different murine and rabbit models of DED, which are categorized into the quantitative (aqueous-deficient) type and the qualitative (evaporative) type, based on the schemes to establish. The clinical manifestations of dry eye on animal models can be induced by mechanical or surgical approaches, iatrogenic immune response, topical eye drops, blockage of neural pathway, or others. Although these models have shown promising results, each has its own limitation and cannot fully reproduce the pathophysiological mechanisms that occur in patients. Nonetheless, the animal models remain the best approximation of human DED and represent the valuable tool for the DED studies.

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

Preclinical animal studies provide valuable opportunities to better understand human diseases and contribute to major advances in medicine. This review provides a comprehensive overview of ocular parameters in humans and selected animals, with a focus on the ocular surface, detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition. We describe major pitfalls that tremendously limit the translational potential of traditional laboratory animals (i.e., rabbits, mice, and rats) in ophthalmic research, and highlight the benefits of integrating companion dogs with clinical analogues to human diseases into preclinical pharmacology studies. This One Health approach can help accelerate and improve the framework in which ophthalmic research is translated to the human clinic. Studies can be conducted in canine subjects with naturally occurring or noninvasively induced ocular surface disorders (e.g., dry eye disease, conjunctivitis), reviewed herein, and tear fluid can be easily retrieved from canine eyes for various bioanalytical purposes. In this review, we discuss common tear collection methods, including capillary tubes and Schirmer tear strips, and provide guidelines for tear sampling and extraction to improve the reliability of analyte quantification (drugs, proteins, others).

A Novel Eyes Topical Drug Delivery System: CsA-LNC for the Treatment of DED

PURPOSE

The objective of the present work was to prepare safe and effective Ciclosporin A Lipid nanocapsule (CsA-LNC) eye-drops for the treatment of DED.

METHODS

The phase-inversion method was used to prepared different sizes CsA-LNC. CsA biodistribution in ocular after topical administration in rabbits was analyzed by a validated UPLC-MS/MS method. The efficacy of CsA-LNCs (25 nm, 50 nm, 85 nm) was evaluated using the tear breakup time, fluorescein staining, tear production, inflammatory cytokines and histopathology tests. The safety of CsA-LNCs was study by the score of ocular irritation and histological examination study.

RESULTS

CsA-LNCs(20-100 nm) were successfully prepared, An in vivo PK study showed significant improvement of the bioavailability (4.20-fold (25 nm), 2.15-fold (50 nm) and 2.33-fold (85 nm)) in bulbar conjunctiva, and great permeability was observed in the cornea for CsA-LNCs compared with CsA emulsion. An in vivo PD study showed that CsA-LNCs have great efficacy for DED, and the effect was improved over CsA emulsion. CsA-LNCs were safe and not cause significant irritation to the eyes surface of rabbits.

CONCLUSION

This work has demonstrated CsA-LNCs, in particular small sizes CsA-LNC, are safe and effective with promising potential to treat DED. Grapical abstract.

A New Rabbit Model of Chronic Dry Eye Disease Induced by Complete Surgical Dacryoadenectomy

Purpose/Aim: Dry eye disease (DED), common and suboptimally treated, is in need of novel animal models to understand its pathophysiology and assess the efficacy and other parameters of new pharmacological agents for its treatment. The more than 10 rabbit models of DED described to date have significant limitations including induction of mild disease, lack of consistency, and off-target effects when chemical agents are used for disease induction. Our aim was to develop a new model of chronic DED in rabbits that overcomes the limitations of existing models.

MATERIALS AND METHODS

We performed a complete surgical resection of all orbital lacrimal glands (LGs; dacryoadenectomy) in normal adult New Zealand White rabbits. One week after removal of the nictitating membrane, we surgically removed the orbital superior LG, followed by removal of the palpebral superior LG, and finally removal of the inferior LG. Surgery was performed under anesthesia, required about 1 h/eye, and was well-tolerated.

RESULTS

Dacryoadenectomy induced severe DED, evidenced by >90% reduction in the tear break up time test, 50% reduction in the Schirmer tear test, 10% increase in tear osmolarity, and a marked increase in the rose bengal staining score. DED was sustained and essentially unchanged for the eight weeks of observation. Sham-operated rabbits showed no such changes, with the exception of a non-significant and transient reduction in the tear break up time test, a response to ocular surgery.

CONCLUSIONS

This model of stable, chronic, predominantly aqueous-deficient DED recapitulates key clinical and histological features of human DED and is suitable for the study of ocular surface homeostasis, of the pathophysiology of DED, and of the efficacy of candidate drugs for DED treatment.

Corneal regeneration by conditioned medium of human uterine cervical stem cells is mediated by TIMP-1 and TIMP-2

The aim of the present study was to evaluate the effect and the mechanism of action of the conditioned medium from human uterine cervical stem cells (CM-hUCESC) on corneal wound healing in a rabbit dry eye model. To do this, dry eye and corneal epithelial injuries were induced in rabbits by topical administration of atropine sulfate and NaOH. Hematoxylin-Eosin (H&E) and Ki-67 immunostaining were carried out to evaluate corneal damage and cell proliferation, and real-time PCR was used to evaluate proinflammatory cytokines in the cornea. In addition, in order to investigate possible factors involved in corneal regeneration, primary cultures of rat corneal epithelial cells (rCECs) were used to evaluate cell migration, proliferation, and apoptosis before and after immunoprecipitation of specific factors from the CM-hUCESC. Results showed that CM-hUCESC treatment significantly improved epithelial regeneration in rabbits with dry eye induced by atropine and reduced corneal pro-inflammatory TNF-α, MCP-1, MIP-1α and IL-6 cytokines. In addition, metalloproteinase inhibitors TIMP-1 and TIMP-2, which are present at high levels in CM-hUCESC, mediated corneal regenerative effects by both inducing corneal epithelial cell proliferation and inhibiting apoptosis. In summary, CM-hUCESC induces faster corneal regeneration in a rabbit model of dry eye induced by atropine than conventional treatments, being TIMP-1 and TIMP-2 mediators in this process. The results indicate that an alternative CM-based treatment for some corneal conditions is achievable, although future studies would be necessary to investigate other factors involved in the multiple observed effects of CM-hUCESC.

The novel model: Experimental optical coherence tomography-guided anterior segment imaging chick embryo model

Purpose

The aim of this study was to present an experimental optical coherence tomography (OCT)-guided anterior segment (AS) imaging chick embryo model. Through this model, we aimed to reveal similarities and differences between human cornea, AS tissues, and chick embryo tissues by quantitative image analysis.

Methods

Ex vivo, the chick embryos' globes were determined by detailed AS camera of spectral-domain (SD)-OCT in 10 fertilized specific pathogen-free eggs on the 20^th day. Quantitative image analysis of anterior chamber tissues was performed with SD-OCT in detail. After imaging, cross sections of the chick embryo globes containing cornea with anterior chamber were histologically examined and compared with human tissues. The similarities of our model with data in the human cornea and AS studies in the literature were compared.

Results

SD-OCT imaging was able to successfully delineate the AS tissues of chick embryos such as the cornea, iris, lens, pupil, conjunctiva, ciliary body, anterior chamber, and lens. Quantitative semi-automated measurements showed the following: mean central corneal thickness: 213.4 ± 7.05 μm (197-223 μm), mean anterior chamber depth: 878.9 ± 41.74 (804-919 μm), mean anterior chamber area: 2.43 ± 0.16 mm² (2.17-2.73 mm²), mean corneoscleral junction (limbal) thickness: 322.8 ± 20.05 μm (289-360 μm), and mean iris thickness: 230.4 ± 13.27 μm (203-245 μm). In addition, detailed histological comparisons of the AS tissues with human tissues were evaluated to be very similar.

Conclusion

In conclusion, this chick embryo model mimics human tissues and it can be considered as a platform for the study of teratogen-induced malformations and AS dysgenesis during gestation of AS tissues. In addition, this study demonstrates the feasibility of SD-OCT in the quantitative assessment of AS structures in chick embryo model.

Gelatin-epigallocatechin gallate nanoparticles with hyaluronic acid decoration as eye drops can treat rabbit dry-eye syndrome effectively via inflammatory relief

Introduction

Dry-eye syndrome (DES) is a general eye disease. Eye drops are the common ophthalmological medication. However, the ocular barrier makes it difficult to attain high drug bioavailability. Nanomedicine is a promising alternative treatment for ocular diseases and may increase drug content in the affected eye.

Methods

To explore this potential, we constructed nanoparticles (NPs) containing an anti-inflammatory agent for DES treatment. The NPs were made of gelatin-epigallocatechin gallate (EGCG) with surface decoration by hyaluronic acid (HA) and designated "GEH". The particle size, surface charge, and morphology were evaluated. The in vitro biocompatibility and anti-inflammation effect of nanoparticles were assayed via culturing with human corneal epithelium cells (HCECs) and in vivo therapeutic effect was examined in a DES rabbit's model.

Results

The synthesized GEH NPs had a diameter of approximately 250 nm and were positively charged. A coculture experiment revealed that 20 µg/mL GEH was not cytotoxic to HCECs and that an EGCG concentration of 0.2 µg/mL downregulated the gene expression of IL1B and IL6 in inflamed HCECs. Large amounts of GEH NPs accumulated in the cytoplasm of HCECs and the ocular surfaces of rats and rabbits, indicating the advantage of GEH NPs for ocular delivery of medication. Twice-daily topical treatment with GEH NPs was performed in a rabbit model of DES. The ocular surface of GEH-treated rabbits displayed normal corneal architecture with no notable changes in inflammatory cytokine levels in the cornea lysate. The treatment improved associated clinical signs, such as tear secretion, and fluorescein staining recovered.

Conclusion

We successfully produced GEH NPs with high affinity for HCECs and animal eyes. The treatment can be delivered as eye drops, which retain the drug on the ocular surface for a longer time. Ocular inflammation was effectively inhibited in DES rabbits. Therefore, GEH NPs are potentially valuable as a new therapeutic agent delivered in eye drops for treating DES.

Subconjunctival dendrimer-drug therapy for the treatment of dry eye in a rabbit model of induced autoimmune dacryoadenitis

PURPOSE

To investigate the efficacy of a single subconjunctival injection of dendrimer-dexamethasone conjugate in a rabbit model of induced autoimmune dacryoadenitis (AID).

METHODS

Dendrimer biodistribution after subconjunctival injection in AID animals was evaluated using Cy5-labelled dendrimer (D-Cy5) and confocal microscopy. Diseased animals were treated with free dexamethasone (Free-Dex), dendrimer-dexamethasone (D-Dex), or saline via a single subconjunctival injection. The efficacy was evaluated using various clinical evaluations, such as Schirmer's test, tear breakup time (TBUT), and fluorescein and rose Bengal staining. Histopathology was evaluated by H&E staining and immunostaining. Levels of inflammatory cytokines and aquaporin proteins in the LGs were determined by real-time PCR.

RESULTS

Subconjunctivally administered dendrimers selectively localized in the inflamed LGs, and were taken up by the infiltrating cells. At two weeks post single dose-treatment, the D-Dex group showed improved clinical evaluations. No significant changes were observed in other groups. H&E staining demonstrated less inflammatory cell infiltration and fewer atrophic acini in D-Dex group, compared to those treated with saline or Free-Dex. Immunohistochemistry demonstrated that the intensity of CD-18 (+) and RTLA (+) was weaker in LGs in the D-Dex group than in other treatment groups. Pro-inflammatory gene expression levels of MMP9, IL6, IL8, and TNFα were significantly decreased in the D-Dex group compared to the Free-Dex and saline group.

CONCLUSIONS

The dendrimer exhibits pathology-dependent biodistribution in the inflamed LGs. Subconjunctivally administered D-Dex suppressed LG inflammation, leading to partial recovery of LG function with clinical improvement in induced AID. Sjögren's patients may benefit from this targeted nanomedicine approach.

A new dry eye mouse model produced by exorbital and intraorbital lacrimal gland excision

Chronic dry eye is an increasingly prevalent condition worldwide, with resulting loss of visual function and quality of life. Relevant, repeatable, and stable animal models of dry eye are still needed. We have developed an improved surgical mouse model for dry eye based on severe aqueous fluid deficiency, by excising both the exorbital and intraorbital lacrimal glands (ELG and ILG, respectively) of mice. After ELG plus ILG excision, dry eye symptoms were evaluated using fluorescein infiltration observation, tear production measurement, and histological evaluation of ocular surface. Tear production in the model mice was significantly decreased compared with the controls. The corneal fluorescein infiltration score of the model mice was also significantly increased compared with the controls. Histological examination revealed significant severe inflammatory changes in the cornea, conjunctiva or meibomian glands of the model mice after surgery. In the observation of LysM-eGFP^(+/−) mice tissues, postsurgical infiltration of green fluorescent neutrophils was observed in the ocular surface tissues. We theorize that the inflammatory changes on the ocular surface of this model were induced secondarily by persistent severe tear reduction. The mouse model will be useful for investigations of both pathophysiology as well as new therapies for tear-volume-reduction type dry eye.

Pilot Study of a "Large-Eye," Surgically Induced Dry Eye Rabbit Model by Selective Removal of the Harderian, Lacrimal, and Meibomian Glands

Background/Aims

Establish a reliable rabbit dry eye (DE) model.

Methods

An interventional cohort study surgically removing glands contributing to the tear film. Eight rabbits were studied after removal of left lacrimal, Harderian, or both glands. Additional rabbits had Meibomian glands in the left eye thermally obstructed. All were followed for 10 weeks with phenol red thread (PRT) and slit-lamp examination with 2% fluorescein. We assessed corneal sensitivity using a Cochet-Bonnet esthesiometer. Outcome measures were severity/duration of reduced PRT, punctate epithelial erosions (PEE), and histologic evidence of corneal pannus.

Results

Fluorescein staining demonstrated signs of dryness including PEE in all of the interventional eyes. The subjective measurement of epithelial erosions correlated with decreased tear production. PRT measurements in the control eyes averaged 31.54 mm (±1.83) and 22.71 mm (±1.60) in the eight left eyes, without loss of corneal sensitivity.

Conclusions

Surgical removal of either the Harderian or lacrimal gland results in statistically significant decreases in tear volume and the development of severe DE. Removal of both glands results in the occurrence of a DE of comparable severity/duration to removal of either the lacrimal or Harderian gland alone. Meibomian gland obstruction contributes less to the DE model.

Herbal Supplement in a Buffer for Dry Eye Syndrome Treatment

Dry eye syndrome (DES) is one of the most common types of ocular diseases. There is a major need to treat DES in a simple yet efficient way. Artificial tears (AT) are the most commonly used agents for treating DES, but are not very effective. Herbal extractions of ferulic acid (FA), an anti-oxidant agent, and kaempferol (KM), an anti-inflammatory reagent, were added to buffer solution (BS) to replace ATs for DES treatment. The cytotoxicity and anti-inflammatory effects were examined in vitro by co-culture with human corneal epithelial cells (HCECs) to obtain the optimal concentration of KM and FA for treating HCECs. Physical properties of BS, such as pH value, osmolality, and refractive index were also examined. Then, rabbits with DES were used for therapeutic evaluation. Tear production, corneal damage, and ocular irritation in rabbits’ eyes were examined. The non-toxic concentrations of KM and FA for HCEC cultivation over 3 days were 1 µM and 100 µM, respectively. Live/dead stain results also show non-toxicity of KM and FA for treating HCECs. Lipopolysaccharide-stimulated HCECs in inflammatory conditions treated with 100 µM FA and 1 µM KM (FA100/KM1) showed lower IL-1B, IL-6, IL-8, and TNFα expression when examined by real-time PCR. The BS with FA100/KM1 had neutral pH, and a similar osmolality and refractive index to human tears. Topical delivery of BS + FA100/KM1 showed no irritation to rabbit eyes. The corneal thickness in the BS + FA100/KM1 treated group was comparable to normal eyes. Results of DES rabbits treated with BS + FA100/KM1 showed less corneal epithelial damage and higher tear volume than the normal group. In conclusion, we showed that the combination of FA (100 µM) and KM (1 µM) towards treating inflamed HCECs had an anti-inflammatory effect, and it is effective in treating DES rabbits when BS is added in combination with these two herbal supplements and used as a topical eye drop.

TFOS DEWS II Tear Film Report

The members of the Tear Film Subcommittee reviewed the role of the tear film in dry eye disease (DED). The Subcommittee reviewed biophysical and biochemical aspects of tears and how these change in DED. Clinically, DED is characterized by loss of tear volume, more rapid breakup of the tear film and increased evaporation of tears from the ocular surface. The tear film is composed of many substances including lipids, proteins, mucins and electrolytes. All of these contribute to the integrity of the tear film but exactly how they interact is still an area of active research. Tear film osmolarity increases in DED. Changes to other components such as proteins and mucins can be used as biomarkers for DED. The Subcommittee recommended areas for future research to advance our understanding of the tear film and how this changes with DED. The final report was written after review by all Subcommittee members and the entire TFOS DEWS II membership.

The Effect of Dry Eye Disease on Scar Formation in Rabbit Glaucoma Filtration Surgery

The success rate of glaucoma filtration surgery is closely related to conjunctival inflammation, and the main mechanism of dry eye disease (DED) is inflammation. The aim of this study was to evaluate the effect of DED on bleb scar formation after rabbit glaucoma filtration surgery. Sixteen New Zealand white rabbits were randomly divided into control and DED groups. A DED model was induced by twice-daily topical administration of 0.1% benzalkonium chloride (BAC) drops for three weeks. Ocular examinations were performed to verify the DED model. Surgical effects were assessed, and histologic assessments were performed on the 28th postoperative day. Higher fluorescein staining scores, lower basal tear secretion levels and goblet cell counts, and increased interleukin 1β (IL-1β) levels were observed in the DED group. The DED eyes displayed significantly higher intraocular pressure (IOP)% on the 14th postoperative day; a smaller bleb area on days 14, 21 and 28; and a shorter bleb survival time. Moreover, proliferating cell nuclear antigen (PCNA) and alpha-smooth muscle actin (α-SMA) levels were significantly increased in the DED group. These results demonstrate that DED promotes filtering bleb scar formation and shortens bleb survival time; these effects may be mediated via IL-1β.

Conjunctival Goblet Cell Function: Effect of Contact Lens Wear and Cytokines

This review focuses on conjunctival goblet cells and their essential function in the maintenance of eye health. The main function of goblet cells is to produce and secrete mucins that lubricate the ocular surface. An excess or a defect in those mucins leads to several alterations that makes goblet cells central players in maintaining the proper mucin balance and ensuring the correct function of ocular surface tissues. A typical pathology that occurs with mucous deficiency is dry eye disease, whereas the classical example of mucous hyperproduction is allergic conjunctivitis. In this review, we analyze how goblet cell number and function can be altered in these diseases and in contact lens (CL) wearers. We found that most published studies focused exclusively on the goblet cell number. However, recent advances have demonstrated that, along with mucin secretion, goblet cells are also able to secrete cytokines and respond to them. We describe the effect of different cytokines on goblet cell proliferation and secretion. We conclude that it is important to further explore the effect of CL wear and cytokines on conjunctival goblet cell function.

Synergistic Effect of Artificial Tears Containing Epigallocatechin Gallate and Hyaluronic Acid for the Treatment of Rabbits with Dry Eye Syndrome

Dry eye syndrome (DES) is a common eye disease. Artificial tears (AT) are used to treat DES, but they are not effective. In this study, we assessed the anti-inflammatory effect of AT containing epigallocatechin gallate (EGCG) and hyaluronic acid (HA) on DES. Human corneal epithelial cells (HCECs) were used in the WST-8 assay to determine the safe dose of EGCG. Lipopolysaccharide-stimulated HCECs showing inflammation were treated with EGCG/HA. The expression of IL-1ß, IL-6, IL-8, and TNF-α was assessed by real-time PCR and AT physical properties such as the viscosity, osmolarity, and pH were examined. AT containing EGCG and HA were topically administered in a rabbit DES model established by treatment with 0.1% benzalkonium chloride (BAC). Tear secretion was assessed and fluorescein, H&E, and TUNEL staining were performed. Inflammatory cytokine levels in the corneas were also examined. The non-toxic optimal concentration of EGCG used for the treatment of HCECs in vitro was 10 μg/mL. The expression of several inflammatory genes, including IL-1ß, IL-6, IL-8, and TNF-α, was significantly inhibited in inflamed HCECs treated with 10 μg/mL EGCG and 0.1% (w/v) HA (E10/HA) compared to that in inflamed HCECs treated with either EGCG or HA alone. AT containing E10/HA mimic human tears, with similar osmolarity and viscosity and a neutral pH. Fluorescence examination of the ocular surface of mouse eyes showed that HA increased drug retention on the ocular surface. Topical treatment of DES rabbits with AT plus E10/HA increased tear secretion, reduced corneal epithelial damage, and maintained the epithelial layers and stromal structure. Moreover, the corneas of the E10/HA-treated rabbits showed fewer apoptotic cells, lower inflammation, and decreased IL-6, IL-8, and TNF-α levels. In conclusion, we showed that AT plus E10/HA had anti-inflammatory and mucoadhesive properties when used as topical eye drops and were effective for treating DES in rabbits.

Age-related Defects in Ocular and Nasal Mucosal Immune System and the Immunopathology of Dry Eye Disease

Dry eye disease (DED) is a prevalent public health concern that affects up to 30% of adults and is particularly chronic and severe in the elderly. Two interconnected mechanisms cause DED: (1) an age-related dysfunction of lacrimal and meibomian glands, which leads to decreased tear production and/or an increase in tear evaporation; and (2) an age-related uncontrolled inflammation of the surface of the eye triggered by yet-to-be-determined internal immunopathological mechanisms, independent of tear deficiency and evaporation. In this review we summarize current knowledge on animal models that mimic both the severity and chronicity of inflammatory DED and that have been reliably used to provide insights into the immunopathological mechanisms of DED, and we provide an overview of the opportunities and limitations of the rabbit model in investigating the role of both ocular and nasal mucosal immune systems in the immunopathology of inflammatory DED and in testing novel immunotherapies aimed at delaying or reversing the uncontrolled age-related inflammatory DED.

Evaluating the Functionality of Conjunctiva Using a Rabbit Dry Eye Model

Purpose. To assess the conjunctival functionality in a rabbit dry eye (DE) model. Methods. Nictitating membrane, lacrimal and Harderian glands were surgically excised from male New Zealand white rabbits using minimally invasive surgery. Fluorescein/rose Bengal staining of ocular surface (OS) and Schirmer test were done before (BE) and after excision (AE). The expression of interleukin- (IL-) 1β, tumor necrosis factor- (TNF-) α, and MUC5AC proteins were estimated by immunoblotting from conjunctival impression cytology specimens. MUC5AC mRNA was quantified as well. The effect of epithelial sodium channel (ENaC) blockers on tear production and potential differences (PD) of OS were assessed under anesthesia in rabbits with and without surgery. Results. Increase in corneal and conjunctival staining was observed 1 month AE compared to BE. Schirmer tests failed to show decrease in tear production. Elevated IL-1β, and TNF-α, 1 month AE indicated inflammation. MUC5AC expression was elevated 1 month AE. ENaC blockers did not improve tear production in rabbit eyes AE but characteristic changes in PD were observed in rabbits with surgery. Conclusions. DE biomarkers are important tools for OS assessment and MUC5AC expression is elevated in rabbit DE. PD measurement revealed significant electrophysiological changes in rabbits with surgery.

Is the main lacrimal gland indispensable? Contributions of the corneal and conjunctival epithelia

The ocular surface system is responsible for ensuring that the precorneal tear film is sufficient in both quality and quantity to preserve optimal vision. Tear secretion is a complex, multifactorial process, and dysfunction of any component of the ocular surface system can result in tear film instability and hyperosmolarity with resultant dry eye disease. The tear film is primarily composed of lipids, aqueous, and mucins, with aqueous accounting for most of its thickness. The aqueous is produced by the main lacrimal gland, accessory lacrimal glands, and corneal and conjunctival epithelia. Although the main lacrimal gland has long been considered an indispensable source of the aqueous component of tears, there is evidence that adequate tear secretion can exist in the absence of the main lacrimal gland. We review and discuss the basics of tear secretion, the tear secretory capacity of the ocular surface, and emerging treatments for dry eye disease.

A systematic assessment of goblet cell sampling of the bulbar conjunctiva by impression cytology

The purpose of this study was to assess the apparent goblet cell density (GCD) from conjunctival impression cytology (CIC) samples in relation to the number of conjunctival cells collected onto the filters. CIC specimens were collected from the superior-temporal bulbar conjunctiva of 16 pigmented rabbits onto Biopore (Millicell-CM) membranes, fixed with buffered glutaraldehyde and stained with Giemsa. Different numbers of microscope fields of view in each of the specimens were imaged by light microscopy using a 20× magnification objective lens (200× final magnification), and the goblet cells marked and counted. The GCD values/sq. mm were calculated. The same conjunctival region of 3 other rabbits was also prepared for transmission electron microscopy (TEM) by fixation, in situ, with the same buffered glutaraldehyde. Mean values for GCD estimates were found to vary from 399 to 1576 cells/sq. mm, depending on the image sampling and analysis strategy chosen, with the lowest inter-sample variance of around 10% being found if a maximum goblet cell count was taken on substantially multilayered regions of the CIC specimens. Counts of the number of goblet cells per 1000 visible conjunctival epithelial cells yielded a value of close to 90 (range 36-151), with modest inter-sample variability of around 30%. A three or ten 200× microscope field and random sampling strategy yielded mean GCD values between 542 and 670 cells/sq. mm, but with very high intra- and inter-sample variance of at least 60% and sometimes higher than 100%. TEM confirmed the multilayered organization of the conjunctiva and the deeper lying goblet cells. The general use of a goblet cell count as an objective marker for conjunctival normality or health is likely to be highly variable unless a more specific strategy is adopted. Beyond providing details of exactly the counting strategy used, it would be very useful to provide full details of the actual microscope field size used as well as information on the intra-sample variability in goblet cell counts.