Changes in rabbit corneal innervation induced by the topical application of benzalkonium chloride

Pediatric blepharokeratoconjunctivitis: A challenging ocular surface disease

Pediatric blepharokeratoconjunctivitis (PBKC) is a chronic and recurrent ocular surface inflammatory disorder affecting children in early life. It is frequently under- or late- diagnosed, representing a potential cause of severe visual morbidity worldwide. An expert panel consensus recently agreed on its definition and proposed diagnostic criteria for suspected and definitive PBKC to reduce confusion and avoid varied terminology previously used in the literature, improving early and precise diagnosis. Previous evidence has pointed to the role of the adaptive immune system in recognizing and handling antigenic eyelid bacterial products, particularly from the cell wall, and the direct toxic and inflammatory effects of their cytolytic exotoxins on the ocular surface. PBKC is a frequent referral in pediatric and cornea clinics characterized by a history of recurrent chalazia, blepharitis, meibomian gland dysfunction, conjunctival hyperemia, phlyctenules formation, and corneal infiltrates with vascularization and scarring. The latter is a major cause of significant visual loss and amblyopia. Current treatment strategies aim to control inflammation on the ocular surface, halt disease progression, and avoid corneal involvement. Further research on pathogenic mechanisms will shed light on novel potential therapeutic strategies. Awareness of PBKC should enhance early diagnosis, prompt adequate treatment, and improve outcomes. We compile current evidence on epidemiology, pathophysiology, clinical spectrum of disease, diagnostic criteria, and management strategies for PBKC.

Deep Corneal Nerve Plexus Selective Damage in Persistent Neurotrophic Corneal Epithelial Defects Detected by In Vivo Multiphoton Confocal Microscopy

Purpose

To investigate the corneal nerve damage in neurotrophic corneal persistent epithelial defects by an in vivo imaging system using in vivo multiphoton confocal microscopy (MCM) and calcitonin gene-related peptide (CGRP):GFP Tg mice.

Methods

Corneal epithelium was scraped, followed by administering a single dose of benzalkonium chloride (BAK) to develop a neurotrophic persistent epithelial defect. The defect was imaged with fluorescein staining for up to 24 hours, and wound closure percentage (%, WCP) was calculated. CGRP:GFP Tg mice were used in combination with in vivo MCM to acquire in vivo images of corneal nerve before and 24 hours after the creation of a corneal epithelial defect. GFP signals from CGRP-positive nerves were reconstructed into three-dimensional (3D) images, and nerve volume was analyzed. Additionally, corneal mechanosensation was evaluated using Cochet-Bonnet esthesiometry.

Results

BAK-treated eyes showed a significant delay in WCP at 24 hours. In CGRP:GFP Tg mice, CGRP-positive nerves were successfully captured by in vivo MCM and reconstructed into 3D images. BAK-treated eyes showed a significant decrease in both stromal nerve volume and corneal mechanosensation compared to no BAK eyes at 24 hours after corneal scraping, suggesting that BAK impaired the stromal nerves in both structural and functional asides.

Conclusions

Our in vivo corneal nerve imaging system using the combination of in vivo MCM and CGRP:GFP Tg mice demonstrated a longitudinal observation of murine corneal nerves. This system revealed that corneal stromal nerves were selectively damaged in persistent neurotrophic corneal epithelial defects and offered outstanding potential for various applications.

Implications of nanotechnology for the treatment of Dry Eye Disease: Recent advances

Managing Dry Eye Disease (DED), a prevalent condition affecting the ocular surface, remains challenging despite advancements in diagnostics and therapies. Current treatments primarily involve lubricating eye drops and anti-inflammatory medications, which often require prolonged use and generally provide only symptomatic relief. The current study focuses on improving DED treatments through nano-drug delivery technologies and advanced formulations. These systems aim to address the limitations of conventional therapies by providing extended, targeted, and sustained drug release. The development of innovative nanomaterials offers improved precision, control, and customization for DED management. By enabling controlled and sustained drug release, these nano-drug delivery systems could offer longer-lasting relief, addressing the chronic nature of DED more effectively than current symptomatic therapies. Future research should focus on integrating multiple therapeutic agents within these systems to simultaneously target inflammation and tear film instability. This review examines the potential of nano-based materials for DED treatment, with a particular emphasis on lipid-based, polymer-based and polysaccharide-based systems.

In Vivo Femtosecond Laser Machined Transepithelial Nonlinear Optical Corneal Crosslinking Compared to Ultraviolet Corneal Crosslinking

Purpose

This study assessed the safety and efficacy of transepithelial crosslinking (CXL) using femtosecond (FS) laser-machined epithelial microchannels (MCs) followed by UVA CXL compared to FS laser (NLO CXL) in rabbits.

Methods

The epithelium of 36 rabbits was machined to create 2- by 25-µm MCs at 400 MCs/mm2. Eyes were treated with 1% riboflavin (Rf) solution for 30 minutes, rinsed, and then crosslinked using UVA or NLO CXL. Rabbits were monitored by epithelial staining, optical coherence tomography (OCT) imaging, and esthesiometry. After sacrifice at 2, 4, or 8 weeks, corneas were examined for collagen autofluorescence and immunohistochemistry.

Results

NLO CXL showed no epithelial damage compared to UVA CXL, which produced on average 23.89 ± 5.6 mm2 epithelial defects that healed by day 3. UVA CXL also produced loss of corneal sensitivity averaging 0.83 ± 0.24 cm force to elicit a blink response that persisted for 28 days and remained significantly lower than control or NLO CXL. OCT imaging detected the presence of a demarcation line only following UVA CXL but not NLO CXL.

Conclusions

Even with improved transepithelial Rf penetration, UVA CXL resulted in severe epithelial damage, loss of corneal sensitivity, and delayed wound healing persisting for a month. When MCs were paired with NLO CXL, however, these issues were mostly negated. This suggests that MC NLO CXL can achieve a faster visual recovery without postoperative pain or risk of infection.

Translational Relevance

UVA CXL is a successful procedure, but there is a need for a transepithelial protocol. The combination of MCs and NLO CXL is able to keep the benefits of UVA CXL without causing epithelial damage.

Aprepitant Restores Corneal Sensitivity and Reduces Pain in DED

Purpose

This study aims to assess the efficacy of two aprepitant formulations (X1 and X2), in a preclinical model of dry eye disease (DED) induced by benzalkonium chloride (BAK).

Methods

Two aprepitant formulations were tested on 7 to 8-week-old male mice for their efficacy. In vivo corneal fluorescein staining assessed epithelial damage as the primary end point on days 0, 3, 5, 7, 9, 12, and 14 using slit-lamp microscopy. The DED model was induced with 0.2% BAK twice daily for the first week and once daily for the next week. Mice were randomly assigned to 5 treatment groups: Aprepitant X1 (n = 10) and X2 (n = 10) formulation, 2 mg/mL dexamethasone (n = 10), control vehicle X (n = 10), 0.2% hyaluronic acid (n = 10), or no treatment (n = 10). Eye wiping, phenol red, and Cochet Bonnet tests assessed ocular pain, tear fluid secretion, and nerve function. After 7 days, the mice were euthanized to quantify leukocyte infiltration and corneal nerve density.

Results

Topical aprepitant X1 reduced BAK-induced corneal damage and pain compared to gel vehicle X (P = 0.007) and dexamethasone (P = 0.021). Aprepitant X1 and X2 improved corneal sensitivity versus gel vehicle X and dexamethasone (P < 0.001). Aprepitant X1 reduced leukocyte infiltration (P < 0.05) and enhanced corneal nerve density (P < 0.001). Tear fluid secretion remained statistically unchanged in both the X1 and X2 groups.

Conclusions

Aprepitant formulation X1 reduced pain, improved corneal sensitivity and nerve density, ameliorated epitheliopathy, and reduced leukocyte infiltration in male mouse corneas.

Translational Relevance

Aprepitant emerges as a safe, promising therapeutic prospect for the amelioration of DED's associated symptoms.

Ocular topical application of alpha-glucosyl hesperidin as an active pharmaceutical excipient: in vitro and in vivo experimental evaluation

Alpha-glucosyl hesperidin (GH) is an aqueous soluble, amphipathic hesperidin derivative with several pharmacological effects, and it is postulated in this manuscript that GH could potentially be utilized as an active pharmaceutical excipient in eyedrops. The ocular safety of GH was evaluated according to in vitro cytotoxicity and in vivo ocular tolerance. The in vivo corneal permeation of coumarin-6 (Cou-6) with or without GH was characterized, and the in vivo inducing corneal wound healing using bisdemethoxycurcumin (BDMC) with or without GH was also evaluated to determine whether GH is an active pharmaceutical excipient in eyedrops. The results demonstrated that as high as 30 mg/ml of GH exhibits high-level in vitro and in vivo safety profiles according to four in vitro and in vivo evaluations. GH improved the corneal permeation of Cou-6 in mice, as well as demonstrated in vitro antioxidant activity. Concerning in vivo activity, a BDMC-GH suspension was shown to be synergistic in promoting corneal wound healing in mice, as well as restoring corneal sensitivity, promoting corneal epithelial wound healing, and restoring the corneal tissue structure without inflammatory cell infiltration. Overall, GH could be a novel and promising active excipient in eyedrops.

The molecular aspect of anti-glaucomatous eye drops - are we harming our patients?

Glaucoma is one of the leading causes of irreversible blindness. Progression is halted with a reduction in intraocular pressure (IOP), which is most often achieved with eye drops. A major challenge in the topical treatment of glaucoma patients is the many side effects and the resulting reduced adherence. Side effects may of course be due to the molecular properties of the active pharmaceutical ingredients (APIs). There are currently six different APIs available: prostaglandin analogues, β-adrenergic inhibitors, α-adrenergic agonists, carbonic anhydrase inhibitors, rho-kinase inhibitors and muscarinic 3 agonists. But the additives used in eye drops are also known to cause damage to the ocular surface and to some extent also to the deeper tissues. Said additives are considered inactive molecular components and are added to secure for instance viscosity and pH value, and to prevent contamination. There has been an increasing focus on the harmful effects of preservatives, with the most commonly used preservative benzalkonium chloride (BAK) being particularly controversial. BAK has long been recognized as a toxin that increases the risk of ocular discomfort. This can affect the adherence and ultimately result in lack of disease control. Other issues include the addition of certain buffers, such as phosphates, and varying pH values. This review will address the different molecular components of the IOP-lowering eye drops and what to be aware of when prescribing topical glaucoma treatment.

A review of the epithelial and stromal effects of corneal collagen crosslinking

Induced corneal collagen crosslinking and mechanical stiffening via ultraviolet-A photoactivation of riboflavin (UVA CXL) is now a common treatment for corneal ectasia and Keratoconus. Some effects of the procedure such as induced mechanical stiffening, corneal flattening, and cellular toxicity are well-known, but others remain more controversial. Authors report a variety of contradictory effects, and provide evidence based on individual results and observations. A full understanding of the effects of and mechanisms behind this procedure are essential to predicting its outcome. A growing interest in modifications to the standard UVA CXL protocol, such as transepithelial or accelerated UVA CXL, makes analyzing the literature as a whole more urgent. This review presents an analysis of both the agreed-upon and contradictory results reported and the various methods used to obtain them.

Neurosensory abnormalities and stability of a mouse model of dry eye disease

This study aimed to use a mouse model of dry eye disease (DED) induced by topical administration of benzalkonium chloride (BAK) and assess its stability and the presence of neurosensory abnormalities, including ocular pain. Eight-week-old C57BL6/6 N male mice were used in this study. Mice were treated with 10 μL of 0.2% BAK dissolved in artificial tears (AT), administered twice daily for 7 days. After one week, animals were randomized into two groups: one was administered with 0.2% BAK in AT once per day for 7 days, while the other was not further treated. Corneal epitheliopathy was quantified at days 0, 3, 7, 12, and 14. Moreover, tear secretions, corneal nociception, and corneal nerve integrity were measured after BAK treatment. After sacrifice, corneas were dissected to assess nerve density and leukocyte infiltration by immunofluorescence. Topical BAK instillation for 14 days significantly increased corneal fluorescein staining (p < 0.0001) compared to day 0. On the other hand, interruption of BAK instillation was associated with improvement of corneal epitheliopathy (day 12, p < 0.0001; day 14, p < 0.001). BAK treatment increased ocular pain (p < 0.0001) and resulted in a significant increase in leukocyte infiltration in the cornea (p < 0.01). Moreover, corneal sensitivity was reduced (p < 0.0001), together with corneal nerve density (p < 0.0001) and tear secretion (p < 0.0001). One week twice a day, followed by one additional week once a day, of 0.2% BAK topical administration induces stable clinical and histological signs of DED, which is associated with neurosensory abnormalities, including pain.

Topical Decorin Reduces Corneal Inflammation and Imparts Neuroprotection in a Mouse Model of Benzalkonium Chloride-induced Corneal Neuropathy

Purpose

We evaluated the neuroprotective and immunomodulatory effects of topical decorin in a murine model of benzalkonium chloride (BAK)-induced corneal neuropathy.

Methods

Topical BAK (0.1%) was administered daily to both eyes of female C57BL/6J mice (n = 14) for 7 days. One group of mice received topical decorin (1.07 mg/mL) eye drops to one eye and saline (0.9%) to the contralateral eye; the other group received saline eye drops to both eyes. All eye drops were given three times daily over the experimental period. A control group (n = 8) received daily topical saline only, instead of BAK. Optical coherence tomography imaging was performed before (at day 0) and after (day 7) treatment to evaluate the central corneal thickness. Whole-mount immunofluorescence staining was performed to evaluate the density of corneal intraepithelial nerves and immune cells.

Results

BAK-exposed eyes showed corneal epithelial thinning, infiltration of inflammatory macrophages and neutrophils, and a lower density of intraepithelial nerves. No change to the corneal stromal thickness or dendritic cell density was observed. After BAK exposure, decorin-treated eyes had a lower density of macrophages and less neutrophil infiltration and a higher nerve density than the saline-treated group. Contralateral eyes from the decorin-treated animals showed fewer macrophages and neutrophils relative to saline-treated animals. A negative correlation was found between corneal nerve density and macrophage or neutrophil density.

Conclusions

Topical decorin provides neuroprotective and anti-inflammatory effects in a chemical model of BAK-induced corneal neuropathy. The attenuation of corneal inflammation by decorin may contribute to decreasing corneal nerve degeneration induced by BAK.

A Critical Appraisal of the Physicochemical Properties and Biological Effects of Artificial Tear Ingredients and Formulations

Dry eye disease is among the most prevalent diseases affecting the ocular surface. Artificial tears remain the cornerstone therapy for its management. There are currently a wide variety of marketed artificial tears available to choose from. These artificial tears differ significantly in their composition and formulation. This article reviews the physicochemical and biological properties of artificial tear components and how these characteristics determine their use and efficacy in the management of dry eye. Furthermore, this article also discusses the various formulations of artificial tears such as macro and nanoemulsion and the type of preservatives present in them.

Glaucoma and Ocular Surface Disease: More than Meets the Eye

Understanding the association between ocular surface disease and glaucoma is important for improving adherence to treatment and introducing practical solutions. While topical antihypertensive medications for glaucoma are well tolerated according to short-term studies, there is little evidence on their long-term effects. Since they are often required for many years, the effects of these drops on the ocular surface become important in regard to quality of life and adherence. In this nonsystematic review performed in April 2022, we summarize what is known about the relationship between glaucoma and ocular surface disease. Specifically, we examine how each class of topical glaucoma drops affects the ocular surface. We then review the treatment of ocular surface disease for patients on topical glaucoma therapy. Finally, we discuss treatments that may reduce or eliminate the burden of topical medications.

A Narrative Review of Ocular Surface Disease Related to Anti-Glaucomatous Medications

Topical anti-glaucomatous medications are still the most important measure to lower intraocular pressure. Large number of studies have confirmed that long-term use of anti-glaucomatous eye drops, especially containing benzalkonium chloride, a preservative, can cause or aggravate ocular surface injury. Ocular surface diseases damage the ocular microenvironmental health status, reduce the patients’ compliance with the treatment, and finally affect the treatment result. Therefore, the ocular surface management of patients with glaucoma is very important. This includes the selection of drugs that are better tolerated according to individual conditions, preservative-free formulations, drugs that protect against ocular surface disease, or selecting surgery and laser treatment, to prevent the damage to the ocular surface by topical anti-glaucomatous drugs.

Effect of the Preservative Benzalkonium Chloride in Prostaglandin Analogues on Corneal Sensitivity

Purpose: To investigate the effect of a prostaglandin (PG) analogue with or without preservative benzalkonium chloride (BAK) on corneal sensitivity.Methods: Central corneal sensitivity was measured prospectively with a Cochet–Bonnet esthesiometer in patients with normal tension glaucoma (NTG) or primary open angle glaucoma (POAG) before and 1 and 3 months after treatment. All patients began treatment with PG monotherapy with or without BAK preservative.Results: The study enrolled 84 patients: 52 NTG and 32 POAG. The treatment was PG with BAK preservative in 45 eyes and without BAK preservative in 39 eyes. Without BAK, the mean corneal sensitivity was 58.22 ± 3.56, 57.77 ± 4.59, and 56.33 ± 5.47 mm before and after 1 and 3 months, respectively; with BAK the mean corneal sensitivity was 58.20 ± 4.51, 56.31 ± 6.22, and 55.52 ± 6.23 mm. Corneal sensitivity was reduced significantly in patients using PG with the preservative BAK after 3 months (p = 0.033). Co-administration of artificial tears did not affect this reduction in corneal sensitivity.Conclusions: PG with the preservative BAK reduced corneal sensitivity and artificial tears did not improve this reduction. Reduced corneal sensitivity and accompanying side effects should be considered in the long-term use of PG with the preservative BAK.

Categorization of Marketed Artificial Tear Formulations Based on Their Ingredients: A Rational Approach for Their Use

Dry eye disease is a common ocular condition affecting millions of people worldwide. Artificial tears are the first line therapy for the management of dry eye disease. Artificial tear formulations contain a variety of active ingredients, biologically active excipients, and preservatives. Many of these formulations are also available as preservative-free. This study was conducted to inspect artificial tear formulations currently marketed in the United States for their active ingredients, biologically relevant excipients, and preservatives. The marketed artificial tears were examined at various US retail pharmacy chains and using the manufacturers’ website to compile information about active ingredients, inactive ingredients, and preservatives. The currently marketed artificial tears can be grouped into four categories based on their active ingredients. The artificial tears also contain biologically active chemicals listed as inactive ingredients, which have osmoprotectant, humectant, and tear film lipid layer or mucous layer mimicking properties. Most artificial tears contain vanishing type preservatives such as purite or sodium perborate and safer quaternary compound polyquaternium-1. The majority of these artificial tear formulations are also available as preservative-free single dose unit. The study provides a formulary of artificial tears based on active ingredients, biologically active excipients, and the preservative-free option. The formulary should assist healthcare providers in making a stepwise and rational selection of appropriate artificial tears for patients suffering from dry eye disease.

Optimization of a Rabbit Dry Eye Model Induced by Topical Instillation of Benzalkonium Chloride

Purpose

To optimize a rabbit dry eye model induced by topical instillation of benzalkonium chloride (BAC), reduce the days of instillation of the original model by increasing the concentration of BAC from 0.1% to 0.2%.

Materials and Methods

An experimental, prospective, and randomized study was performed on 10 male New Zealand white rabbits, divided into two groups, considering both eyes: 5 rabbits as control (n = 10) and 5 rabbits with 0.2% BAC treatment (n = 10). Saline solution (control) and 0.2% BAC were instilled for 5 consecutive days, twice daily. Tear secretion with and without anesthesia, tear breakup time, tear osmolarity, corneal staining, conjunctival hyperemia, density of goblet cells, height of mucin cloud, and transcript levels of IL-6 were measured before and after the treatment.

Results

After the instillation of 0.2% BAC for 5 consecutive days, there was a significant increase in tear secretion without anesthesia (P < 0.001), corneal staining (P < 0.001), conjunctival hyperemia (P < 0.001), and levels of IL-6 mRNA (P=0.005) compared to the control group. Conversely, there was a decrease in tear secretion with anesthesia (P < 0.001), tear breakup time (P=0.007), tear osmolarity (P < 0.001), density of goblet cells (P < 0.001), and height of mucin cloud (P < 0.001).

Conclusions

The topical instillation of 0.2% BAC for 5 consecutive days, twice daily, was a proper procedure to induce a rabbit dry eye model, reducing the number of days of instillation compared to the original model (14 days).

Enhanced Transepithelial Riboflavin Delivery Using Femtosecond Laser-Machined Epithelial Microchannels

Purpose

This study describes a femtosecond laser (FS) approach to machine corneal epithelial microchannels for enhancing riboflavin (Rf) penetration into the cornea prior to corneal crosslinking (CXL).

Methods

Using a 1030-nm FS laser with 5- to 10-µJ pulse energy, the corneal epithelium of slaughterhouse rabbit eyes was machined to create 2-µm-diameter by 25-µm-long microchannels at a density of 100 or 400 channels/mm². Rf penetration through the microchannels was then determined by applying 1% Rf in phosphate-buffered saline for 30 minutes followed by removal of the cornea and extraction from the central stromal button. Stromal Rf concentrations were then compared to those obtained using standard epithelial debridement or 0.01% benzalkonium chloride (BAK) to disrupt the epithelial barrier.

Results

Microchannels formed using a 5-µJ/pulse at a density of 400 channels/mm² achieved a stromal Rf concentration that was 50% of that achieved by removal of the corneal epithelium and imbibing with 1% Rf. Stromal Rf levels were also equal to that of debrided corneas soaked with 0.5% Rf, threefold higher than those soaked with 0.1% Rf, and twofold higher than corneas soaked in BAK without epithelial debridement. Organ culture of treated corneas showed a normal corneal epithelium following FS machining while BAK-treated corneas showed extensive epithelial and stromal damage at 24 hours posttreatment.

Conclusions

FS corneal epithelial machining can be used to enhance penetration of Rf into the stroma for corneal CXL.

Translational Relevance

The creation of epithelial microchannels allows for stromal Rf concentrations high enough to perform true transepithelial crosslinking.

Effects of topical autologous serum on the ocular surface in patients with toxic corneal epitheliopathy induced by anti-glaucoma drugs

PURPOSE

To investigate the effects of topical autologous serum application on the ocular surface in patients with toxic corneal epitheliopathy induced by anti-glaucoma drugs.

METHODS

The patients who had corneal epitheliopathy because of preservative-containing anti-glaucoma eye drops were prospectively enrolled. The epitheliopathy was refractory to preservative-free artificial tear treatment. The patients topically applied 20% autologous serum to the eye eight times per day for 1 month. Baseline and one-month change in symptoms and signs were assessed by the Ocular Surface Disease Index (OSDI) questionnaire, tear film break-up time (TFBUT), Schirmer I values, corneoconjunctival staining scores, corneal sensitivity, InflammaDry^® tear immunoassay, and tear cytokine profiles using a bead-based multiplex assay.

RESULTS

A total of ten consecutive patients were enrolled between January and August 2018 and evaluated after one-month treatment with 20% autologous serum eye drops. Significant improvement was observed in symptoms (OSDI scores from 25.5 ± 20.9 to 10.5 ± 12.0; P = .039), TFBUT (from 3.1 ± 1.8 s to 5.4 ± 2.3 s; P = .025), corneoconjunctival staining scores (from 7.7 ± 1.8 to 1.8 ± 1.9 NEI scale; P = .005), corneal sensitivity (from 4.6 ± .9 cm to 5.8 ± .5 cm; P = .013), and metalloproteinase-9 levels (P = .013). There were no significant changes in Schirmer I values and tear cytokine levels on multiplex assays. Treatment-related side effects were not detected.

CONCLUSIONS

Topical instillation of 20% autologous serum is an effective treatment for toxic corneal epitheliopathy associated with anti-glaucoma eye drops.

TRIAL REGISTRATION NUMBER

KCT0003827.

The use of preservatives in dry eye drops

Topical ocular preparations are widely recommended by health care professionals, or chosen by patients, to help manage dry eye disease (DED). The chronic and progressive nature of DED may result in the administration of topical products several times a day, over a period of many years. Given DED is a condition that by definition affects the ocular surface, it is important to understand how the repeated use of eye drops may impact the ocular surface, influence clinical signs, affect symptoms, and impact the overall disease process of dry eye. The component in topical preparations with the greatest potential to adversely affect the ocular surface is the preservative. This paper reviews the literature in relation to the use of preservatives in formulations for dry eye. The ocular effects of benzalkonium chloride (BAK) are summarised and compared to the performance of alternative preservatives and preservative-free formulations. Use of preserved and preservative-free drops in relation to the management of varying stages of DED is discussed.

Ocular surface toxicity from glaucoma topical medications and associated preservatives such as benzalkonium chloride (BAK)

INTRODUCTION

This review discusses the evidence concerning the effect of topical medications and their preservatives on the ocular surface in glaucoma patients. The role of topical anti-glaucoma medication remains critical in the management of chronic glaucoma worldwide but the beneficial effects of treatment are counterbalanced by the adverse effects of corneal and conjunctival toxicity. Areas covered: This article covers the effect of topical ocular drops and preservatives, particularly benzalkonium chloride, on the cornea and conjunctiva. Both basic science and clinical evidence will be presented. The first part reviews the relationship between ocular surface disease and benzalkonium chloride and the evidence from non-benzalkonium chloride preserved drops. The second part discusses the effects of benzalkonium chloride on the histopathology of the conjunctiva and its impact on clinical care as well as quality of life. Expert opinion: Topical anti-glaucoma medication will continue to be used in the management of this blinding disease for the foreseeable future. Treatment outcomes will benefit from minimized exposure to benzalkonium chloride. The development of alternative preservatives, preservative-free topical options, and non-drop therapeutics such as drug-eluting systems for the delivery of ocular medications, will be very helpful in the care of glaucoma patients.

Ocular inflammation induces trigeminal pain, peripheral and central neuroinflammatory mechanisms

Ocular surface diseases are among the most frequent ocular pathologies, with prevalence ranging from 20% of the general population. In addition, ocular pain following corneal injury is frequently observed in clinic. The aim of the study was to characterize the peripheral and central neuroinflammatory process in the trigeminal pathways in response to cornea alteration induced by chronic topical instillations of 0.2% benzalkonium chloride (BAC) in male C57BL/6J mice. In vitro BAC induced neurotoxicity and increases neuronal (FOS, ATF3) and pro-inflammatory (IL-6) markers in primary mouse trigeminal ganglion culture. BAC-treated mice exhibited 7days after the treatment reduced aqueous tear production and increased inflammatory cell infiltration in the cornea. Hypertonic saline-evoked eye wipe behavior was enhanced in BAC-treated animals that exhibited increased FOS, ATF3 and Iba1 immunoreactivity in the trigeminal ganglion. Ocular inflammation is associated with a significant increase in IL-6 and TNF-α mRNA expression in the trigeminal ganglion. We reported a strong increase in FOS and Iba1 positive cells in particular in the sensory trigeminal complex at the ipsilateral interpolaris/caudalis (Vi/Vc) transition and Vc/upper cervical cord (Vc/C1) regions. In addition, activated microglial cells were tightly wrapped around activated FOS neurons in both regions and phosphorylated p38 mitogen-activated protein kinase was markedly enhanced specifically in microglial cells during ocular inflammation. Similar data were obtained in the facial motor nucleus. These neuroanatomical data correlated with the increase in mRNA expression of pro-inflammatory (TNF-α, IL-6, CCL2) and neuronal (FOS and ATF3) markers. Interestingly, the suppression of corneal inflammation 10days following the end of BAC treatment resulted in a marked attenuation of peripheral and central changes observed in pathological conditions. This study provides the first demonstration that corneal inflammation induces activation of neurons and microglial p38 MAPK pathway within sensory trigeminal complex. These results suggest that this altered activity in intracellular signaling caused by ocular inflammation might play a priming role in the central sensitization of ocular related brainstem circuits, which represents a significant factor in ocular pain development.

Evaluation of standardized endodontic paper point tear test in New Zealand white rabbits and comparison between corneal sensitivity followed tear tests

OBJECTIVE

To evaluate endodontic paper point tear test (PPTT) in rabbits and compare changes in corneal touch threshold (CTT) induced by Schirmer tear test (STT) and PPTT. Normal corneal sensitivity recovery time after both tear tests was also measured. Also, mean PPTT and STT values were obtained.

METHODS

Tear production of 20 eyes, from 10 rabbits, was evaluated using STT and the PPTT. Central corneal touch threshold was measured by a Cochet-Bonnet esthesiometer before any tear test was performed (zero time), immediately after the test (1 min), and consecutively at 6, 11, 16, and 26 min. Tests were conducted on three consecutive days: Day 1 - control condition, no tear tests performed only the CTT; Day 2 - CTT before and after PPTT; and Day 3 - CTT before and after STT. CTT values were compared using repeated measures ANOVA.

RESULTS

Corneal touch threshold was significantly increased for at least 16 min after STT, indicating STT causes corneal discomfort. No difference was found between CTT following PPTT and controls, indicating PPTT caused minimal corneal discomfort. The mean (±SD) value for STT was 5.2 ± 1.0 mm/min and for PPTT was 13.8 ± 1.5 mm/min.

DISCUSSION

The aqueous fraction of rabbit's tears can be successfully measured by PPTT. This report established reference values for PPTT in rabbits. Additionally, the absence of a significant difference in CTT after PPTT compared with controls shows that PPTT is well tolerated by rabbits. Considering the improved comfort (compared with STT), accuracy, and low cost, PPTT is a bona fide method of measuring aqueous tear production in rabbits.

Corneal alterations induced by topical application of commercial latanoprost, travoprost and bimatoprost in rabbit

Prostaglandin (PG) analogs, including latanoprost, travoprost, and bimatoprost, are currently the most commonly used topical ocular hypotensive medications. The purpose of this study was to investigate the corneal alterations in rabbits following exposure to commercial solution of latanoprost, travoprost and bimatoprost. A total of 64 New Zealand albino rabbits were used and four groups of treatments were constituted. Commercial latanoprost, travoprost, bimatoprost or 0.02% benzalkonium chloride (BAK) was applied once daily to one eye each of rabbits for 30 days. The contralateral untreated eyes used as controls. Schirmer test, tear break-up time (BUT), rose Bengal and fluorescein staining were performed on days 5, 10, 20, and 30. Central corneal changes were analyzed by in vivo confocal microscopy, and the corneal barrier function was evaluated by measurement of corneal transepithelial electrical resistance on day 5. Whole mount corneas were analyzed by using fluorescence confocal microscopy for the presence of tight-junction (ZO-1, occludin) and adherens-junction (E-cadherin, β-catenin) proteins, actin cytoskeleton, proliferative marker Ki67 and cell apoptosis in the epithelium. Topical application of commercial PG analogs resulted in significant corneal epithelial and stromal defects while no significant changes in aqueous tear production, BUT, rose bengal and fluorescein staining scores on day 5. Commercial PG analogs induced dislocation of ZO-1 and occludin from their normal locus, disorganization of cortical actin cytoskeleton at the superficial layer, and disruption of epithelial barrier function. The eyes treated with 0.02% BAK and latanoprost exhibited significantly reduced Schirmer scores, BUT, and increased fluorescein staining scores on days 10 and 30, respectively. Topical application of commercial PG analogs can quickly impair the corneal epithelium and stroma without tear deficiency. Commercial PG analogs break down the barrier integrity of corneal epithelium, concomitant with the disruption of cell junction and actin cytoskeleton between superficial cells in the corneal epithelium in vivo.