The pathology of dry eye: the interaction between the ocular surface and lacrimal glands

Ocular Mucosal Immunity

Mucosal immunity defends the ocular surface against antigenic challenge and microbial invasion. The principal effector site is the lacrimal gland, where immunoglobulin A (IgA) antibodies are produced. Nasal-associated lymphoid tissue and posterior cervical lymph nodes function as major inductive sites for tear IgA responses. Neural connections and systemic hormones maintain the integrity and function of the ocular surface. Neuroenzyme activities in the lacrimal gland are influenced by ocular infections, leading to reduced expression of acetylcholine and modulation of receptors on acinar cells and on plasma cells, thereby decreasing fluid and immunoglobulin secretion. T lymphocyte-dependent responses result in production of interleukin-4 in lacrimal glands, thereby influencing cholinergic enzyme activity affecting immune processes and lacrimal physiology. Furthermore, neuropeptides released into lymphoid structures or inflamed tissues are chemotactic for antigen-presenting cells and affect their interactions with T cells. Thus, in developing therapeutic approaches for treating dry-eye conditions and vaccination strategies to elicit protective ocular mucosal immune responses, the entire lacrimal functional unit should be considered.

Improvement in the signs and symptoms of dry eye disease with dobesilate eye drops

BACKGROUND

Dry eye is a multifactor disease of the tear film and ocular surface that substantially affects quality of life.

CASE PRESENTATION

Dobesilate administered as eye drops was well tolerated and effective in treating both the objective signs and subjective symptoms of dry eye disease in this 2-week study.

CONCLUSION

To the best of our knowledge, this is the first clinical report of using dobesilate in eye drops. Dobesilate may provide a novel approach to treating drying diseases of the eye.

A thermo-responsive protein treatment for dry eyes

Millions of Americans suffer from dry eye disease, and there are few effective therapies capable of treating these patients. A decade ago, an abundant protein component of human tears was discovered and named lacritin (Lacrt). Lacrt has prosecretory activity in the lacrimal gland and mitogenic activity at the corneal epithelium. Similar to other proteins placed on the ocular surface, the durability of its effect is limited by rapid tear turnover. Motivated by the rationale that a thermo-responsive coacervate containing Lacrt would have better retention upon administration, we have constructed and tested the activity of a thermo-responsive Lacrt fused to an elastin-like polypeptide (ELP). Inspired from the human tropoelastin protein, ELP protein polymers reversibly phase separate into viscous coacervates above a tunable transition temperature. This fusion construct exhibited the prosecretory function of native Lacrt as illustrated by its ability to stimulate β-hexosaminidase secretion from primary rabbit lacrimal gland acinar cells. It also increased tear secretion from non-obese diabetic (NOD) mice, a model of autoimmune dacryoadenitis, when administered via intra-lacrimal injection. Lacrt ELP fusion proteins undergo temperature-mediated assembly to form a depot inside the lacrimal gland. We propose that these Lacrt ELP fusion proteins represent a potential therapy for dry eye disease and the strategy of ELP-mediated phase separation may have applicability to other diseases of the ocular surface.

Corneal sensation and dry eye symptoms after conventional versus inverted side-cut femtosecond LASIK: a prospective randomized study

PURPOSE

To compare corneal sensation and self-reported dry eye symptoms after femtosecond-assisted LASIK with conventional versus inverted side cuts.

DESIGN

Prospective, randomized, eye-to-eye study.

PARTICIPANTS

A total of 120 eyes in 60 participants with myopia.

METHODS

Fellow eyes were randomized to receive femtosecond-assisted LASIK with a conventional 70-degree side cut made with the 60 kHz IntraLase FS (Abbott Medical Optics, Santa Ana, CA) or an inverted 130-degree side cut made with the 150 kHz IntraLase iFS (Abbott Medical Optics). Cochet-Bonnet aesthesiometry (Luneau Ophthalmologia, Chartes, France) measured corneal sensation (60 mm = normal sensation; <60 mm = depressed sensation) preoperatively and at postoperative months 1, 3, 6, and 12. Participants also completed serial dry eye surveys using the same subscales (frequency, severity, bothersome) as the validated, Rasch-tested, linear-scaled Quality of Vision questionnaire.

MAIN OUTCOME MEASURES

Objective corneal sensation and self-reported light sensitivity, dryness, foreign body sensation, and pain/discomfort.

RESULTS

Preoperative corneal sensation as measured by mean Cochet-Bonnet aethesiometry was equal between the inverted and conventional side cut groups but was better in eyes with an inverted side cut compared with a conventional side cut at all postoperative months (inverted vs. conventional: 1 month, 14.5 vs. 13.2 mm; 3 months, 24.9 vs. 18.4 mm; 6 months, 51.2 vs. 42.6 mm; 12 months, 59.8 vs. 58.3 mm; all P ≤ 0.02). None of the subjective dry eye parameters demonstrated statistically significant differences between the groups at any time point.

CONCLUSIONS

The LASIK flaps with an inverted side cut are associated with superior recovery of corneal sensation compared with flaps with a conventional side cut during the first postoperative year; however, this may not translate to significant improvements in subjective dry eye symptoms.

Evaluation of the efficacy of 50% autologous serum eye drops in different ocular surface pathologies

PURPOSE

This study evaluated the efficacy of 50% autologous serum eye drops in ocular surface diseases not improved by conventional therapy.

METHODS

We analyzed two groups: (1) acute eye pathologies (e.g., chemical burns) and (2) chronic eye pathologies (e.g., recurrent corneal erosion, neurotropic keratitis, and keratoconjunctivitis sicca). The patients were treated for surface instability after conventional therapy. The patients received therapy 5 times a day until stabilization of the framework; they then reduced therapy to 3 times a day for at least 3 months. We analyzed the best corrected visual acuity, epithelial defects, inflammation, corneal opacity, and corneal neovascularization. We also analyzed symptoms such as tearing, burning, sense of foreign body or sand, photophobia, blurred vision, and difficulty opening the eyelids.

RESULTS

We enrolled 15 eyes in group 1 and 11 eyes in group 2. The average therapy period was 16 ± 5.86 weeks in group 1 and 30.54 ± 20.33 weeks in group 2. The epithelial defects all resolved. Signs and symptoms improved in both groups. In group 2, the defect recurred after the suspension of therapy in 2 (18%) patients; in group 1, no defects recurred.

CONCLUSIONS

Autologous serum eye drops effectively stabilize and improve signs and symptoms in eyes previously treated with conventional therapy.

Activation of HIF-1α (hypoxia inducible factor-1α) prevents dry eye-induced acinar cell death in the lacrimal gland

The pathogenesis of immune-mediated lacrimal gland (LG) dysfunction in Sjögren's syndrome has been thoroughly studied. However, the majority of dry eye (DE) is not related to Sjögren type, and its pathophysiology remains unclear. The purpose of this study was to determine and investigate the protective mechanisms against DE stress in mice. DE induced prominent blood vessel loss without apoptosis or necrosis in the LG. Autophagic vacuoles, distressed mitochondria, and stressed endoplasmic reticulum were observed via electron microscopy. Immunoblotting confirmed the increase in autophagic markers. Glycolytic activities were enhanced with increasing levels of succinate and malate that, in turn, activated hypoxia-inducible factor (HIF)-1α. Interestingly, the areas of stable HIF-1α expression overlapped with COX-2 and MMP-9 upregulation in LGs of DE-induced mice. We generated HIF-1α conditional knockout (CKO) mice in which HIF-1α expression was lost in the LG. Surprisingly, normal LG polarities and morphologies were completely lost with DE induction, and tremendous acinar cell apoptosis was observed. Similar to Sjögren's syndrome, CD3⁺ and CD11b⁺ cells infiltrated HIF-1α CKO LGs. Our results show that DE induced the expression of HIF-1α that activated autophagy signals to prevent further acinar cell damage and to maintain normal LG function.

New testing options for diagnosing and grading dry eye disease

PURPOSE

To describe new options for diagnosis and severity grading of dry eye disease.

DESIGN

Perspective on technological advancements to identify tear dysfunction and their value in diagnosing and grading dry eye disease.

METHODS

Evidence is presented on new and evolving technologies to measure tear stability, composition, and meniscus height and their role in dry eye diagnosis and therapeutic efficacy grading is assessed.

RESULTS

Evolving concepts regarding pathogenesis and new technologies to evaluate the tears and ocular surface have improved the ability to diagnose, classify, and grade the severity of dry eye disease. New technologies include noninvasive imaging of tear stability and tear meniscus height as a measure of tear volume and tear composition (osmolarity, lacrimal factors, inflammatory mediators, growth and differentiation factors). Approved tests, such as tear osmolarity and tear imaging, are being integrated into clinical practice and may eventually supplant certain traditional tests that have greater variability and less sensitivity. Other tests, such as molecular assays of tears and conjunctival cells, are currently being used in studies investigating pathogenesis and therapeutic mechanism of action. They may eventually translate to routine clinical practice.

CONCLUSIONS

New technologies have emerged that can noninvasively evaluate the tears and measure disease-associated compositional changes. These tests are being integrated into clinical practice and therapeutic trials for diagnosis, classification, and severity grading of dry eye disease.

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

PURPOSE

To investigate the effect of benzalkonium chloride (BAK) on corneal nerves.

METHODS

Fifty-four adult New Zealand Albino rabbits were randomly divided into 3 groups. BAK at concentrations of 0.005%, 0.01%, or 0.02% was applied once daily to 1 eye of each rabbit for 9 days. The contralateral untreated eyes were used as controls. Corneal mechanical sensitivity, aqueous tear production, tear break-up time (BUT), fluorescein, and Rose Bengal staining scores were compared with those of control values on days 3, 6, and 9. Corneal whole mounts were immunostained with a specific antitubulin βIII antibody to label nerve fibers. Epithelial superficial nerve terminal, subbasal, and stromal nerve fiber densities were quantified. The structure of the central cornea was examined by means of in vivo confocal microscopy on day 9.

RESULTS

The topical application of BAK resulted in lower corneal sensitivity and higher Rose Bengal staining scores on day 3, whereas there were no significant changes in the BUT, Schirmer, and corneal fluorescein scores. Decreased nerve densities in superficial and subbasal layers were observed in BAK-treated eyes on days 3 and 6, respectively. The eyes treated with 0.02% BAK exhibited significantly reduced Schirmer scores, BUT, and stromal nerve fiber density, and increased fluorescein staining scores on day 9. Corneal superficial epithelial cell size was significantly larger in all BAK-treated eyes compared with that in control eyes.

CONCLUSIONS

The topical application of BAK can quickly cause corneal hypoesthesia without tear deficiency. Changes in corneal innervation significantly correlate with BAK-induced ocular surface changes.

Effect of hypotonic 0.18% sodium hyaluronate eyedrops on inflammation of the ocular surface in experimental dry eye

PURPOSE

To investigate the efficacy of hypotonic 0.18% sodium hyaluronate (SH) eyedrops in a mouse model of experimental dry eye (EDE).

METHODS

EDE was induced in C57BL/6 mice by a subcutaneous scopolamine injection and an air draft. The mice were divided into 4 groups according to topical treatment regimens: EDE control, isotonic 0.5% carboxymethycellulose (CMC), isotonic 0.1% SH, and hypotonic 0.18% SH. Tear volume, corneal smoothness, and corneal staining scores were measured at 5 and 10 days of EDE. Multiplex immunobead assay, immunohistochemistry, and flow cytometry for proinflammatory cytokines, chemokines, and inflammatory molecules were performed at 10 days of EDE.

RESULTS

The 0.18% SH group had a significantly lower corneal smoothness and staining scores than the 0.5% CMC and 0.1% SH groups at 10 days of EDE (P<0.05). The 0.18% SH group showed significantly low levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, monokine induced by interferon-γ, and interferon-γ-inducible protein 10 compared with the other groups (P<0.05). The mean percentages of CD4(+)CXCR3(+), CD40(+), and CD44(+) cells in the conjunctiva were significantly lower in the 0.18% SH group than in the other groups (P<0.05). In addition, the 0.1% SH group showed lower levels of TNF-α and IL-1β and percentages of CD40(+) and CD44(+) cells than the EDE and 0.5% CMC groups.

CONCLUSIONS

Hypotonic 0.18% SH eyedrops are more effective in improving ocular surface irregularity and staining and decreasing inflammatory cytokines, chemokines, and cells on the ocular surface compared with isotonic 0.5% CMC or 0.1% SH eyedrops in the treatment of EDE.

Sex hormones and the dry eye

The greater prevalence of dry eye in women compared to men suggests that sex hormones may have a role in this condition. This review aims to present evidence for how sex hormones may affect the ocular structures involved in the production, regulation and maintenance of the normal tear film. It is hypothesised that hormone changes alter the homeostasis of the ocular surface and contribute to dry eye. Androgens impact on the structure and function of the meibomian and lacrimal glands and therefore androgen deficiency is, at least in part, associated with the aetiology of dry eye. In contrast, reports of the effects of oestrogen and progesterone on these ocular structures and on the conjunctiva are contradictory and the mechanisms of action of these female-specific sex hormones in the eye are not well understood. The uncertainty of the effects of oestrogen and progesterone on dry eye symptoms is reflected in the controversial relationship between hormone replacement therapy and the signs and symptoms of dry eye. Current understanding of sex hormone influences on the immune system suggests that oestrogen may modulate a cascade of inflammatory events, which underlie dry eye.

Dry eye exacerbation in patients exposed to desiccating stress under controlled environmental conditions

PURPOSE

To determine if controlled environmental conditions can induce acute exacerbations of signs and symptoms in dry eye and asymptomatic subjects.

DESIGN

Prospective cross-sectional study.

METHODS

Nineteen patients with dry eye and 20 asymptomatic controls were exposed to controlled low humidity (5% relative humidity, desiccating environment) for 2 hours in our Controlled Environmental Research Laboratory at the University of Valladolid. The patients completed the Single-Item Score Dry Eye Questionnaire and the following diagnostic tests were performed before and after exposure: tear osmolarity, phenol red thread test, conjunctival hyperemia, fluorescein tear film break-up time, Schirmer test, and ocular surface vital staining. Sixteen molecules in the tears samples were analyzed by multiplex bead analysis.

RESULTS

After exposure, the patients and controls had a significant (P ≤ .003) increase in corneal staining (from 0.68 ± 0.15 to 1.16 ± 0.14 and from 0.50 ± 0.15 to 1.30 ± 0.19, respectively), significantly decreased (P ≤ .01) fluorescein tear film break-up time values (from 2.78 ± 0.56 seconds to 1.94 ± 0.24 seconds and from 2.81 ± 0.24 seconds to 2.13 ± 0.19 seconds, respectively), and significantly increased (P ≤ .03) matrix metalproteinase 9 tear levels (from 10 054.4 ± 7326.6 pg/mL to 25 744.5 ± 13 212.4 pg/mL and from 10 620.5 ± 4494.3 pg/mL to 16 398.7 ± 5538.3 pg/mL, respectively). In the control group, the epidermal growth factor tear levels decreased significantly (P = .007; from 1872.1 ± 340.7 pg/mL to 1107.1 ± 173.6 pg/mL), and interleukin 6 levels increased significantly (P < .001; from 29.6 ± 5.8 pg/mL to 54.3 ± 8.3 pg/mL) after exposure.

CONCLUSIONS

Adult patients with mild-to-moderate dry eye and asymptomatic subjects of similar ages can experience acute exacerbation in an environmental chamber that resembles the sudden worsening that patients with dry eye experience daily.

Effect of macrophage migration inhibitory factor on corneal sensitivity after laser in situ keratomileusis in rabbit

Purpose

To investigate the effect of macrophage migration inhibitory factor (MIF) on corneal sensitivity after laser in situ keratomileusis (LASIK) surgery.

Methods

New Zealand white rabbits were used in this study. A hinged corneal flap (160-µm thick) was created with a microkeratome, and -3.0 diopter excimer laser ablation was performed. Expressions of MIF mRNA in the corneal epithelial cells and surrounding inflammatory cells were analyzed using reverse transcription polymerase chain reaction at 48 hours after LASIK. After LASIK surgery, the rabbits were topically given either 1) a balanced salt solution (BSS), 2) MIF (100 ng/mL) alone, or 3) a combination of nerve growth factor (NGF, 100 ug/mL), neurotrophine-3 (NT-3, 100 ng/mL), interleukin-6 (IL-6, 5 ng/mL), and leukemia inhibitory factor (LIF, 5 ng/mL) four times a day for three days. Preoperative and postoperative corneal sensitivity at two weeks and at 10 weeks were assessed using the Cochet-Bonnet esthesiometer.

Results

Expression of MIF mRNA was 2.5-fold upregulated in the corneal epithelium and 1.5-fold upregulated in the surrounding inflammatory cells as compared with the control eyes. Preoperative baseline corneal sensitivity was 40.56 ± 2.36 mm. At two weeks after LASIK, corneal sensitivity was 9.17 ± 5.57 mm in the BSS treated group, 21.92 ± 2.44 mm in the MIF treated group, and 22.42 ± 1.59 mm in the neuronal growth factors-treated group (MIF vs. BSS, p < 0.0001; neuronal growth factors vs. BSS, p < 0.0001; MIF vs. neuronal growth factors, p = 0.815). At 10 weeks after LASIK, corneal sensitivity was 15.00 ± 9.65, 35.00 ± 5.48, and 29.58 ± 4.31 mm respectively (MIF vs. BSS, p = 0.0001; neuronal growth factors vs. BSS, p = 0.002; MIF vs. neuronal growth factors, p = 0.192). Treatment with MIF alone could achieve as much of an effect on recovery of corneal sensation as treatment with combination of NGF, NT-3, IL-6, and LIF.

Conclusions

Topically administered MIF plays a significant role in the early recovery of corneal sensitivity after LASIK in the experimental animal model.

Wounding the cornea to learn how it heals

Corneal wound healing studies have a long history and rich literature that describes the data obtained over the past 70 years using many different species of animals and methods of injury. These studies have lead to reduced suffering and provided clues to treatments that are now helping patients live more productive lives. In spite of the progress made, further research is required since blindness and reduced quality of life due to corneal scarring still happens. The purpose of this review is to summarize what is known about different types of wound and animal models used to study corneal wound healing. The subject of corneal wound healing is broad and includes chemical and mechanical wound models. This review focuses on mechanical injury models involving debridement and keratectomy wounds to reflect the authors' expertise.

Effects of eye drops containing a mixture of omega-3 essential fatty acids and hyaluronic acid on the ocular surface in desiccating stress-induced murine dry eye

PURPOSE

To investigate the efficacy of the topical application of omega-3 essential fatty acids (EFAs) and hyaluronic acid (HA) mixtures in a mouse model of experimental dry eye (EDE).

METHODS

Eye drops consisting of 0.1% HA, 0.02%, or 0.2% omega-3 EFAs alone and mixture of 0.02%, or 0.2% omega-3 EFAs and 0.1% HA were applied in desiccating stress-induced murine dry eye. Corneal irregularity scores and fluorescein staining scores were measured 5 and 10 days after treatment. Levels of interleukin (IL)-1β, -17, and interferon gamma-induced protein (IP)-10 were measured in the conjunctiva at 10 days using a multiplex immunobead assay. The concentrations of hexanoyl-lys (HEL) and 4-hydroxynonenal (4-HNE) in conjunctiva tissue were measured with enzyme-linked immunosorbent assays.

RESULTS

Mice treated with the mixture containing 0.2% omega-3 EFAs showed a significant improvement in corneal irregularity scores and corneal fluorescein staining scores compared with EDE, HA, 0.02% or 0.2% omega-3 EFAs alone, and 0.02% omega-3 EFAs mixture-treated mice. A significant decrease in the levels of IL-1β, -17, and IP-10 were observed in the 0.2% EFAs mixture-treated group, compared with the other groups. In the mice treated with the mixture containing 0.2% omega-3 EFAs, the concentration of 4-HNE was also lower than the other groups. Although 0.2% omega-3 EFAs alone group also had a significant improvement in corneal irregularity scores and IL-17, IL-10, and 4 HNE levels compared with the other groups, the efficacy was lower than 0.2% omega-3 mixture group.

CONCLUSIONS

Topically applied eye drops containing a mixture of omega-3 EFAs and HA could improve corneal irregularity and corneal epithelial barrier disruption, and decrease inflammatory cytokines and oxidative stress markers on the ocular surface. Topical omega-3 EFAs and HA mixture may have a greater therapeutic effect on clinical signs and inflammation of dry eye compared with HA artificial tears.

Tear meniscus dimensions in tear dysfunction and their correlation with clinical parameters

PURPOSE

To evaluate relationships between tear meniscus dimensions and parameters of ocular surface disease in a variety of tear dysfunction conditions.

DESIGN

Single-institution prospective observational study.

METHODS

This study from the Baylor College of Medicine included 128 eyes of 64 subjects. Cross-sectional lower tear meniscus height and tear meniscus area were measured using optical coherence tomography and were compared with tear break-up time (TBUT), corneal staining, conjunctival staining, and an irritation symptom questionnaire (Ocular Surface Disease Index). Study groups included meibomian gland disease (MGD), aqueous tear deficiency (ATD), Sjögren syndrome, non-Sjögren syndrome ATD, and control subjects. Statistical analyses were performed using the Pearson correlation and Student's t test.

RESULTS

When compared with mean tear meniscus height in controls (345 μm), mean tear meniscus height was lower in all tear dysfunction (234 μm; P = .0057), ATD (210 μm; P = .0016), and Sjögren syndrome groups (171 μm; P = .0054). For tear meniscus height ≤210 μm, relative risk ratio for developing corneal staining ≥10 was 4.65. Tear meniscus height correlated with corneal staining for all subjects (R = -0.32; P = .0008), MGD (R = +0.40; P = .059), and ATD (R = -0.36; P = .04). Tear meniscus area showed similar trends in MGD (R = +0.55; P = .006) and ATD (R = -0.40; P = .018). Tear meniscus height correlated with TBUT for all subjects (R = +0.39; P < .0001) and ATD (R = +0.37; P = .018).

CONCLUSIONS

In tear dysfunction conditions, lower tear volume correlates with worse corneal epithelial disease in ATD and Sjögren syndrome, conditions with lacrimal gland dysfunction. In contrast, higher tear volume is associated with corneal epithelial disease in MGD. These findings may improve the ability to identify patients at risk for corneal epithelial disease.

Effects of vitamin B12 on the corneal nerve regeneration in rats

The study was designed to investigate the effects of a new ophthalmic solution containing 0.05% vitamin B12 0.05% on corneal nerve regeneration in rats after corneal injury. Eyes of anesthetized male Wistar rats were subjected to corneal injury by removing the corneal epithelium with corneal brush (Algerbrush). After the epithelial debridement, the right eye of each animal received the instillation of one drop of the ophthalmic solution containing vitamin B12 0.05% plus taurine 0.5% and sodium hyaluronate 0.5% four time per day for 10 or 30 days. Left eyes were used as control and treated with solution containing taurine 0.5% and sodium hyaluronate 0.5% alone following the same regimen. Fluorescein staining by slit-lamp and morphological analysis was used to determine corneal wound healing. Immunohistochemistry, immunoblot and confocal microscopy were used to examine corneal re-innervation. Slit-lamp and histological analyses showed that re-epithelization of the corneas was accelerated in rats treated with vitamin B12. A clear-cut difference between the two groups of rats was seen after 10 days of treatment, whereas a near-to-complete re-epithelization was observed in both groups at 30 days. Vitamin B12 treatment had also a remarkable effect on corneal re-innervation, as shown by substantial increased in the expression of neurofilament 160 and β-III tubulin at both 10 and 30 days. The presence of SV2A-positive nerve endings suggests the presence of synapse-like specialized structures in corneal epithelium of the eye treated with vitamin B12. Our findings suggest that vitamin B12 treatment represents a powerful strategy to accelerate not only re-epithelization but also corneal re-innervation after mechanical injury.

Post-LASIK dry eye

Laser-assisted in situ keratomileusis (LASIK) is a frequently performed corneal refractive surgery with excellent refractive outcomes. The most common complication of LASIK is dry eyes, with virtually all patients developing some degree of dryness in the immediate postoperative period. Identifying preoperative dry eyes, and conscientious attention and treatment in the perioperative time period, can lead to enhanced patient satisfaction and more accurate visual outcomes. Improved understanding of the development of dry eyes after LASIK will advance our understanding of the complex pathophysiology of dry eye disease.

Effect of desiccating stress on mouse meibomian gland function

PURPOSE

Mice exposed to standardized desiccating environmental stress to induce dry eye-like symptoms have been used as a model to study the underlying mechanisms of evaporative dry eye. While studies have shown marked inflammatory and immune changes, the effect of such stress on meibomian gland function remains largely unknown. We sought to evaluate the effects of desiccating stress on meibocyte proliferation and meibum quality.

METHODS

Ten mice were treated with scopolamine and subjected to a drafty low humidity environment (30-35%). Five and ten days after treatment, eyelids were harvested and cryosections stained with Ki67 antibody to identify cycling cells. Sections were also imaged using stimulated Raman scattering (SRS) microscopy to characterize the gland compositional changes by detecting the vibrational signatures of methylene (lipid) and amide-I (protein).

RESULTS

Desiccating stress caused a 3-fold increase in basal acinar cell proliferation from 18.3 ± 11.1% in untreated mice to 64.4 ± 19.9% and 66.6 ± 13.4% after 5 and 10 days exposure, respectively (P < .001). In addition, SRS analysis showed a wider variation in the protein-to-lipid ratio throughout the gland, suggesting alterations in meibocyte differentiation and lipid synthesis.

CONCLUSIONS

These data are consistent with a model that a desiccating environment may have a direct effect on meibomian gland function, leading to a significant increase in basal acinar cell proliferation, abnormal meibocyte differentiation, and altered lipid production.

Topical interferon-gamma neutralization prevents conjunctival goblet cell loss in experimental murine dry eye

Evidence suggests that the cytokine interferon (IFN)-γ released by natural killer and CD4(+) T cells contributes to the conjunctival goblet cell (GC) loss in dry eye. The purpose of this study was to investigate if topical neutralization of IFN-γ prevents or alleviates GC loss in an experimental desiccating stress (DS) model of dry eye. In this study, we found that topical IFN-γ neutralization significantly decreased DS-induced conjunctival GC loss. This was accompanied by decreased epithelial apoptosis, and increased IL-13 and decreased FoxA2 expression in the forniceal conjunctiva. To establish that IFN-γ produced by pathogenic CD4(+) T cells contributes to DS-induced GC loss, adoptive transfer of CD4(+) T cells isolated from DS exposed donors to naïve RAG-1(-/-) recipient mice was performed. Similar to the donor mice, topical IFN-γ neutralization decreased conjunctival GC loss, suppressed apoptosis and increased IL-13 expression in adoptive transfer recipients. In summary, this study demonstrated that topical neutralization of IFN-γ prevents GC loss via modulating apoptosis and maintaining IL-13 signaling.

The role of corneal innervation in LASIK-induced neuropathic dry eye

Almost half the patients who undergo laser in situ keratomileusis (LASIK) experience dry eye following the procedure. However, the etiology of LASIK-induced dry eye is unclear. The purpose of this review is to examine and summarize the current evidence for the etiology of LASIK-induced dry eye, with a focus on ocular surface sensitivity and corneal innervation. Evidence suggests that the alteration of corneal nerves after LASIK is the most likely cause of the subjective symptoms of LASIK-induced dry eye, even though corneal sensitivity and the clinical indicators of dry eye return to apparently normal values within a year due to the partial recovery of the corneal nerve plexus. The hypothesis is explored that dry eye symptoms following LASIK may result from abnormal sensation due to LASIK-induced corneal neuropathy. Other factors, such as alterations in conjunctival goblet cell density, might also contribute to the symptoms and signs of LASIK-induced dry eye. Inter-relationships between nerve morphology, tear neuropeptide levels and dry eye require further investigation. A better understanding of this phenomenon may result in improved management of post-LASIK dry eye.

The TFOS International Workshop on Contact Lens Discomfort: report of the subcommittee on neurobiology

This report characterizes the neurobiology of the ocular surface and highlights relevant mechanisms that may underpin contact lens-related discomfort. While there is limited evidence for the mechanisms involved in contact lens-related discomfort, neurobiological mechanisms in dry eye disease, the inflammatory pathway, the effect of hyperosmolarity on ocular surface nociceptors, and subsequent sensory processing of ocular pain and discomfort have been at least partly elucidated and are presented herein to provide insight in this new arena. The stimulus to the ocular surface from a contact lens is likely to be complex and multifactorial, including components of osmolarity, solution effects, desiccation, thermal effects, inflammation, friction, and mechanical stimulation. Sensory input will arise from stimulation of the lid margin, palpebral and bulbar conjunctiva, and the cornea.

[Dry eye syndrome. Occupational risk factors, valuation and prevention]

Dry eye syndrome in the workplace is associated with new ways of working, with increasing use of screens and electronic devices and environmental conditions encountered in modern office designs and other environments. Also affect occupational exposure to ionizing radiation, chemicals or atmospheric dust with increased ocular dryness. The study of pathophysiological aspects and laboral causality of the dry eye, must be to develop joint task in Occupational Health, Public Health in coordination with and responsible for the national health system, which would involve primary and secondary preventive measures more effective and proper diagnosis, control and monitoring of the disease, A better knowledge of occupational hazards and actions agreed and coordinated between occupational physicians, preventers, primary care physicians and specialist physicians, such as ophthalmology, will get results much more effective when earlier and optimize available resources.

TearLab® Osmolarity System for diagnosing dry eye

Dry eye (DE) disease is an impairment of the lachrymal unit function and one the most frequent eye problems. A major challenge is to find accurate diagnostic criteria to be able to define DE severity, as symptoms poorly correlate with clinical signs. Tear osmolarity is considered a key factor in DE onset and perpetuation; its measurement is now possible in clinical setting by an innovative electrical impedance-based lab-on-a-chip technology. This article outlines the features of DE disease and the limitations of current clinical tests. The role of tear osmolarity in DE etiopathogenesis is surveyed, and the pitfalls in measurement are discussed. Diagnostic performance, accuracy and clinical applications of the technology in focus are critically reviewed. The instrument offers the possibility to measure tear osmolarity in a rapid and reliable way in daily practice. As scientific evidence grows, it is expected in the future that it will represent an objective indicator of ocular surface health in the management of DE disease and in clinical trials.

Bilateral nerve alterations in a unilateral experimental neurotrophic keratopathy model: a lateral conjunctival approach for trigeminal axotomy

To study bilateral nerve changes in a newly developed novel mouse model for neurotrophic keratopathy by approaching the trigeminal nerve from the lateral fornix. Surgical axotomy of the ciliary nerve of the trigeminal nerve was performed in adult BALB/c mice at the posterior sclera. Axotomized, contralateral, and sham-treated corneas were excised on post-operative days 1, 3, 5, 7 and 14 and immunofluorescence histochemistry was performed with anti-β-tubulin antibody to evaluate corneal nerve density. Blink reflex was evaluated using a nylon thread. The survival rate was 100% with minimal bleeding during axotomy and a surgical time of 8±0.5 minutes. The blink reflex was diminished at day 1 after axotomy, but remained intact in the contralateral eyes in all mice. The central and peripheral subbasal nerves were not detectable in the axotomized cornea at day 1 (p<0.001), compared to normal eyes (101.3±14.8 and 69.7±12.0 mm/mm² centrally and peripherally). Interestingly, the subbasal nerve density in the contralateral non-surgical eyes also decreased significantly to 62.4±2.8 mm/mm² in the center from day 1 (p<0.001), but did not change in the periphery (77.3±11.7 mm/mm², P = 0.819). Our novel trigeminal axotomy mouse model is highly effective, less invasive, rapid, and has a high survival rate, demonstrating immediate loss of subbasal nerves in axotomized eyes and decreased subbasal nerves in contralateral eyes after unilateral axotomy. This model will allow investigating the effects of corneal nerve damage and serves as a new model for neurotrophic keratopathy.

Role of hyperosmolarity in the pathogenesis and management of dry eye disease: proceedings of the OCEAN group meeting

Dry eye disease (DED), a multifactorial disease of the tears and ocular surface, is common and has a significant impact on quality of life. Reduced aqueous tear flow and/or increased evaporation of the aqueous tear phase leads to tear hyperosmolarity, a key step in the vicious circle of DED pathology. Tear hyperosmolarity gives rise to morphological changes such as apoptosis of cells of the conjunctiva and cornea, and triggers inflammatory cascades that contribute to further cell death, including loss of mucin-producing goblet cells. This exacerbates tear film instability and drives the cycle of events that perpetuate the condition. Traditional approaches to counteracting tear hyperosmolarity in DED include use of hypotonic tear substitutes, which have relatively short persistence in the eye. More recent attempts to counteract tear hyperosmolarity in DED have included osmoprotectants, small organic molecules that are used in many cell types throughout the natural world to restore cell volume and stabilize protein function, allowing adaptation to hyperosmolarity. There is now an expanding pool of clinical data on the efficacy of DED therapies that include osmoprotectants such as erythritol, taurine, trehalose and L-carnitine. Osmoprotectants in DED may directly protect cells against hyperosmolarity and thereby promote exit from the vicious circle of DED physiopathology.

Dry eye as a mucosal autoimmune disease

Dry eye is a common ocular surface inflammatory disease that significantly affects quality of life. Dysfunction of the lacrimal function unit (LFU) alters tear composition and breaks ocular surface homeostasis, facilitating chronic inflammation and tissue damage. Accordingly, the most effective treatments to date are geared towards reducing inflammation and restoring normal tear film. The pathogenic role of CD4+ T cells is well known, and the field is rapidly realizing the complexity of other innate and adaptive immune factors involved in the development and progression of disease. The data support the hypothesis that dry eye is a localized autoimmune disease originating from an imbalance in the protective immunoregulatory and proinflammatory pathways of the ocular surface.

Intraglandular injection of botulinum toxin a reduces tear production in rabbits

PURPOSE

To develop an animal model and investigate the dose-dependent effect of an intraglandular injection of botulinum toxin A (BTX-A) on tear production.

METHODS

In a volume of 0.1-ml, 0.625-, 1.25-, or 2.5-U BTX-A was injected transconjunctivally in the superolateral lobe of the lacrimal gland of adult New Zealand white female rabbits. In the contralateral lacrimal gland, 0.1 ml of 0.9% sodium chloride was injected. Prior to injection and at 1-week postinjection, photographs were taken to evaluate pre- and postoperative eyelid position. Fluorescein and Rose Bengal stain were used to evaluate the corneal surface, and Schirmer test was used to assess tear production.

RESULTS

Glands injected with the intermediate (1.25 U) and the highest (2.5 U) doses of BTX-A displayed a statistically significant decrease in tear production (p = 0.002 and 0.007, respectively) compared with the contralateral saline-injected glands at 1 week. No corneal pathologic factors from excessive dryness were observed following the injection. While postinjection ptosis was observed (p = 0.025), no difference was seen between BTX-A and saline-injected eyes.

CONCLUSIONS

In rabbits, intraglandular injection of BTX-A resulted in decreased tear production at 1 week. No additional reduction in tear production was seen with a BTX-A dose greater than 1.25 U, suggesting glandular receptor saturation at this dose. Despite suppression of tear production, no corneal pathologic factors were observed. Further studies are needed to refine this animal model with the ultimate goal of determining optimum delivery route and concentration to reduction in tear production while minimizing side effects in patients.

Enzymes of urea synthesis are expressed at the ocular surface, and decreased urea in the tear fluid is associated with dry-eye syndrome

PURPOSE

The present study aims at determining whether enzymes of urea synthesis are expressed in the human lacrimal gland and in tissues of ocular surface (conjunctiva, cornea), to give evidence for the hypothesis that urea can be locally formed from ocular tissues and is important for the composition of the tear fluid.

METHODS

The presences of enzymes (arginase 1, 2 and agmatinase) that directly contribute to the formation of urea were investigated in the lacrimal gland and tissues of ocular surface by RT-PCR and immunohistochemistry. We collected tear fluid, aqueous humour, and blood samples from a total of 38 subjects, and tear fluid samples from a total of 78 subjects, with and without dry-eye syndrome (DES, keratoconjunctivitis sicca), and determined the urea concentration.

RESULTS

The enzymes arginase 1, 2 and agmatinase were expressed in all tissues examined except for arginase 1, which was not expressed in the cornea. There was no correlation of urea concentration in tear fluid with aqueous humour and blood plasma (r = 0.13, p = 0.58 and r = 0.45, p = 0.05 respectively). However, correlation of urea concentration between aqueous humour and blood plasma was highly significant (r = 0.7, p = 0.0001). The concentration of urea in the tear fluid of patients with DES compared to healthy control group was significantly reduced (p < 0.0001).

CONCLUSION

Enzymes that are directly involved in the formation of urea are expressed in ocular tissues. This may imply that in the ocular surface is a well-coordinated system of enzymes that can produce urea which might be independent of external urea supply.

Topical cyclosporine for severe dry eye disease in liver-transplanted Portuguese patients with familial amyloidotic polyneuropathy (ATTRV30M)

PURPOSE. Evaluation of the use of topical cyclosporine eyedrops in the treatment of severe dry eye disease in liver transplanted patients with familial amyloidotic polyneuropathy (FAP) unresponsive to therapy with artificial tears and lacrimal plugs.

METHODS

A prospective clinical study of 5 patients (10 eyes) admitted to the Ophthalmology Department of the Centro Hospitalar do Porto with severe dry eye disease refractory to artificial tears and lacrimal plug treatments. Evaluation of the patients included best-corrected visual acuity, corneal punctuate fluorescein staining, tear break-up time, Schirmer test without anesthesia, and Ocular Surface Disease Index. Patients were observed at time 0, and at 3, 7, and 11 months.

RESULTS

Treatment with topical cyclosporine improved all studied parameters from baseline, and in all the patients (p<0.001). The safety profile was excellent, without topical or systemic adverse events.

CONCLUSIONS

Topical cyclosporine was beneficial in the treatment of severe dry eye disease in liver transplanted patients with FAP.

Factors predicting the ocular surface response to desiccating environmental stress

PURPOSE

To identify factors predicting the ocular surface response to experimental desiccating stress.

METHODS

The ocular surfaces of both eyes of 15 normal and 10 dry eye subjects wearing goggles were exposed to a controlled desiccating environment (15%-25% relative humidity and 2-5 L/min airflow) for 90 minutes. Eye irritation symptoms, blink rate, tear meniscus dimensions, noninvasive (RBUT) and invasive tear break-up time, and corneal fluorescein and conjunctival lissamine green-dye staining were recorded before and after desiccating stress. Pre- and postexposure measurements were compared, and Pearson correlations between clinical parameters before and after desiccating stress were calculated.

RESULTS

Corneal and conjunctival dye staining significantly increased in all subjects following 90-minute exposure to desiccating environment, and the magnitude of change was similar in normal and dry eye subjects; except superior cornea staining was greater in dry eye. Irritation severity in the desiccating environment was associated with baseline dye staining, baseline tear meniscus height, and blink rate after 45 minutes. Desiccation-induced change in corneal fluorescein staining was inversely correlated to baseline tear meniscus width, whereas change in total ocular surface dye staining was inversely correlated to baseline dye staining, RBUT, and tear meniscus height and width. Blink rate from 30 to 90 minutes in desiccating environment was higher in the dry eye than normal group. Blink rate significantly correlated to baseline corneal fluorescein staining and environmental-induced change in corneal fluorescein staining.

CONCLUSIONS

Ocular surface dye staining increases in response to desiccating stress. Baseline ocular surface dye staining, tear meniscus height, and blink rate predict severity of ocular surface dye staining following exposure to a desiccating environment.

Discomfort symptoms reduction and ocular surface parameters recovery with Artelac Rebalance treatment in mild-moderate dry eye

PURPOSE

To evaluate Artelac Rebalance® eyedrops' efficacy in symptoms reduction, ocular surface parameters recovery, and tolerability in the treatment of mild to moderate dry eye.

METHODS

Fifteen patients were enrolled. Inclusion criteria were Ocular Surface Disease Index (OSDI) score >16, tear film break-up time (TFBUT) <10 seconds, Schirmer test I >10 mm/5 min, and mild ocular surface damage (Oxford grading) ≤3. Artelac Rebalance® eyedrops were administered 3 times daily for 2 months. Patients were evaluated at enrollment, after 2 days of washout (baseline), and after 1 and 2 months of treatment. Parameters for ocular discomfort (OSDI score), tear film quality (Schirmer test I, TFBUT, tear osmolarity), ocular surface damage (fluorescein staining, conjunctival imprint cytology), and inflammation (scraping cytology and exuded serum albumin) were measured. Tolerability and satisfaction were assessed by validated questionnaires.

RESULTS

At endpoint versus baseline, all variables showed a statistically significant improvement (paired Student t test, p<0.01 for all parameters) as follows: OSDI score (21.9 ± 10.6 vs 35.8 ± 12.2), TFBUT (6.5 ± 1.1 s vs 5.2 ± 2.3 s), Oxford grading of corneal and conjunctival damage (0.56 ± 0.50 vs 1.16 ± 0.37), tear osmolarity (294.6 ± 2.1 mOsm/L vs 303.1 ± 4.6 mOsm/L), conjunctival goblet cell density/mm2 (140.8 ± 43.3 cells/mm2 vs 115.1 ± 15.8 cells/mm2), scraping cytology score (2.9 ± 1.0 vs 4.2 ± 1.3), and percentage of serum albumin in tears (9.2% ± 4.8% vs 24.1% ± 10.8%). Tolerability and satisfaction were scored high, with no adverse events reported.

CONCLUSIONS

Application of Artelac Rebalance® eyedrops for 2 months in mild to moderate dry eye resulted in a reduction of ocular inflammation parameters, ocular surface damage, and subjective discomfort symptoms, with a parallel improvement in tear film quality (measured by TFBUT and osmolarity).

Molecular and cellular biomarkers in dry eye disease and ocular allergy

PURPOSE OF REVIEW

To summarize recent studies in biomarkers in dry eye disease (DED) and ocular allergy in the last 18 months.

RECENT FINDINGS

New significant correlations with clinical symptoms and signs have been described for some tear molecules (proteins, cytokines/chemokines, metalloproteinases, mucins and lipids). Correlation with disease severity has been shown for some of them. New proposed DED biomarkers include some proteins, such as S100A8, S100A9, lipocalin-1, secretory phospholipase A2 and some cytokines and chemokines; mucin-1 mRNA conjunctival expression levels are shown to be a very sensitive and specific DED diagnosis biomarker; metalloproteinase-9 tear level is confirmed as a good DED biomarker; cell parameters such as conjunctival cell viability and proliferative capacity have been also proposed as DED biomarkers. In ocular allergy, protein activated receptor-2, heat shock protein-70, eosinophil cationic protein and hemopexin have been pointed as potential biomarkers. Characterization of neuromediators tear levels confirmed the involvement of these molecules in both DED and ocular allergy.

SUMMARY

Biomarkers are essential to monitor health status. Several studies have proposed different molecules and/or cellular parameters as potential biomarkers for DED and ocular allergy. The knowledge presented in these studies will further add support to the discovery and development of new drugs and the establishment of personalized medicine.