Tear film and ocular surface changes after closure of the meibomian gland orifices in the rabbit

To determine whether meibomian gland dysfunction can increase tear film osmolarity and produce ocular surface changes analogous to those seen with lacrimal gland disease (keratoconjunctivitis sicca [KCS]), the authors closed the meibomian gland orifices in the right eyes of 11 rabbits by light cautery and studied the changes for 20 weeks. Tear film osmolarity was increased throughout the observation period. Conjunctival goblet cell density and corneal epithelial glycogen levels declined progressively. Closure of the meibomian gland orifices thus increased tear film osmolarity in the presence of normal lacrimal gland function and caused ocular surface abnormalities similar to KCS.     

Stimulation of tear secretion by topical agents that increase cyclic nucleotide levels

The authors examined the effect of topical application of agents known to increase cyclic nucleotide levels on tear secretion by accessory lacrimal gland tissue in their rabbit model for keratoconjunctivitis sicca (KCS). Tear secretion was studied by changes in tear film osmolarity and tear volume caused by application of the agents relative to application of isotonic buffer solution alone. A decrease in tear film osmolarity or increase in tear volume was interpreted as an increase in tear secretion. Irritative stimulation was distinguished from pharmacologic stimulation by the prior use of topical proparacaine. The following agents significantly decreased tear film osmolarity and increased tear volume: vasoactive intestinal peptide (2 X 10(-8) to 2 X 10(-6) M); three pro-opiomelanocortin fragments alpha-, beta-, and gamma-melanocyte stimulating hormone at 10(-4), 10(-3), and 10(-3) M, respectively; the permeable cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) analogs 8-Br cAMP (0.3-3.0 X 10(-3) M) and 8-Br cGMP (1.0-10.0 X 10(-3) M); and the cyclic nucleotide phosphodiesterase inhibitor 1-isobutyl-3-methyl xanthine (0.3-3.0 X 10(-3) M). Forskolin (2 X 10(-4) M), which activates the catalytic subunits of adenyl cyclase, increased tear volume significantly. Secretin, adrenocorticotropic hormone, and pilocarpine were ineffective. The authors conclude that agents that increase either cAMP or cGMP levels pharmacologically stimulated tear secretion when applied topically to rabbit eyes with surgically induced KCS.     

Lacrimal gland, cornea, and tear film in the NZB/NZW F1 hybrid mouse

The NZB/NZW F1 hybrid mouse has been reported to contract a disease similar to Sj?gren's syndrome in man. We studied lacrimal gland morphology, corneal morphology, and tear osmolarity in this mouse as a function of age. Lacrimal glands of hybrid mice contained abnormal periductal infiltrates of lymphocytes and plasma cells. Maximum infiltration of the lacrimal gland occurred in the 29-week-old female hybrid mouse and was estimated to involve 12% of the gland, but was insufficient to alter tear osmolarity relative to DBA and Balb/c control mice. Nevertheless, both NZB/NZW F1 hybrid mice and DBA and Balb/c control mice had tear osmolarity and corneal surface morphology similar to that reported for keratoconjunctivitis sicca in man. Although the NZB/NZW F1 hybrid mouse may provide a valuable model for the study of lacrimal gland infiltration, since its tear osmolarity and ocular surface remain normal for a mouse, its usefulness as a model for ocular surface disease in human keratoconjunctivitis sicca may be more limited than previously thought.     

Tear diluents in the treatment of keratoconjunctivitis sicca

To determine the optimum solution concentration for lowering elevated tear film osmolarity in keratoconjunctivitis sicca (KCS), tear osmolarity was measured in four KCS patients before and after instillation of either an isotonic saline solution or one of four hypotonic saline solutions (range, 75-225 mOsm/L). Average tear osmolarity one minute after instillation was significantly lower with the hypotonic solutions than with the isotonic saline (mean +/- SEM, 290 +/- 3 mOsm/L vs. 317 +/- 1 mOsm/L, P less than 0.0005). Solutions 150 mOsm/L or less were most effective in lowering osmolarity; the 75 mOsm/L solution was occasionally associated with irritation. In 16 KCS patients, we then compared the therapeutic efficacy of the 150 mOsm/L solution with that of an otherwise identical isotonic solution in a two-week, double-masked, crossover study. The 150 mOsm/L solution was superior for symptom relief by nearly 2:1 (P = 0.01).     

Eledoisin and lacrimal secretion in the rabbit

Eledoisin has been tried as a possible treatment for dry eye based on the hypothesis that it pharmacologically stimulates tear secretion when topically applied to the eye. To determine if topically applied eledoisin pharmacologically stimulates orbital lacrimal secretion, the orbital lacrimal gland excretory duct of normal rabbits was cannulated, and eledoisin was applied topically with and without prior administration of proparacaine. To determine if topically applied eledoisin stimulated accessory lacrimal gland secretion, isotonic buffer with and without eledoisin was tested in a rabbit model with only accessory lacrimal tissue remaining after the administration of proparacaine. Topically applied eledoisin did not pharmacologically stimulate lacrimal secretion but rather increased lacrimal gland secretion only in non-anesthetized eyes through a sensory reflex mechanism that is blocked by proparacaine.     

Comparison of enzymes of tears, lacrimal gland fluid and lacrimal gland tissue in the rat

A variety of enzymes were identified in rat tears and lacrimal gland fluid. The use of a tapered glass cannula in the opening of the excretory duct was found to be an useful method to collect samples of rat lacrimal gland fluid, i.e., the fluid directly originated from the main excretory duct of the lacrimal gland, uncontaminated by secretions from the Harderian gland and from desquamating conjunctival and corneal epithelial cells. Based upon comparison of the enzyme pattern in tears, lacrimal gland fluid and the lacrimal gland tissue, we concluded that the lacrimal gland is the primary tissue source for peroxidase (POD), amylase (AMY) and total protein in rat tears, while plasminogen activator and lactatedehydrogenase (LDH) may be present in tears primarily as secretion products from other ocular tissue sources. beta-hexosaminidase (beta-hex) is released from the lacrimal gland and from other ocular tissue sources as well.     

A mass and solute balance model for tear volume and osmolarity in the normal and the dry eye

Tear hyperosmolarity is thought to play a key role in the mechanism of dry eye, a common symptomatic condition accompanied by visual disturbance, tear film instability, inflammation and damage to the ocular surface. We have constructed a model for the mass and solute balance of the tears, with parameter estimation based on extensive data from the literature which permits the influence of tear evaporation, lacrimal flux and blink rate on tear osmolarity to be explored. In particular the nature of compensatory events has been estimated in aqueous-deficient (ADDE) and evaporative (EDE) dry eye.The model reproduces observed osmolarities of the tear meniscus for the healthy eye and predicts a higher concentration in the tear film than meniscus in normal and dry eye states. The differential is small in the normal eye, but is significantly increased in dry eye, especially for the simultaneous presence of high meniscus concentration and low meniscus radius. This may influence the interpretation of osmolarity values obtained from meniscus samples since they need not fully reflect potential damage to the ocular surface caused by tear film hyperosmolarity.Interrogation of the model suggests that increases in blink rate may play a limited role in compensating for a rise in tear osmolarity in ADDE but that an increase in lacrimal flux, together with an increase in blink rate, may delay the development of hyperosmolarity in EDE. Nonetheless, it is predicted that tear osmolarity may rise to much higher levels in EDE than ADDE before the onset of tear film breakup, in the absence of events at the ocular surface which would independently compromise tear film stability. Differences in the predicted responses of the pre-ocular tears in ADDE compared to EDE or hybrid disease to defined conditions suggest that no single, empirically-accessible variable can act as a surrogate for tear film concentration and the potential for ocular surface damage. This emphasises the need to measure and integrate multiple diagnostic indicators to determine outcomes and prognosis. Modelling predictions in addition show that further studies concerning the possibility of a high lacrimal flux phenotype in EDE are likely to be profitable.     

AlphaB-crystallin in lacrimal gland duct and tears

PURPOSE: To investigate alphaB-Crystallin expression and localization in the lacrimal gland and tear fluid. METHODS: Mouse, rat, porcine, monkey and human lacrimal gland samples were immuno-histochemically and immuno-electron-microscopically stained with various antibodies against alphaB-crystallin. Western- and Northern-blotting was performed to demonstrate the presence of alphaB-crystallin mRNA and protein. Human tear fluid was analyzed for the presence of alphaB-crystallin using dot blotting. RESULTS: alphaB-Crystallin is located in the lacrimal gland duct cells but not in the acini. Electron microscopically, the protein was frequently found in apical electron-dense granules of lacrimal duct cells, occasionally also in the duct lumina. Western blotting confirmed the presence of alphaB-crystallin in the lacrimal gland, Northern blot samples revealed the presence of alphaB-crystallin mRNA. In the human tear fluid, alphaB-crystallin was present in all samples investigated. CONCLUSIONS: We demonstrate for the first time that alphaB-crystallin is present in the lacrimal gland. Presence of the protein in apical secretory granules as well as presence in the tear fluid might indicate secretion of alphaB-crystallin into the tear fluid.     

Keratoconjunctivitis sicca in male patients infected with human immunodeficiency virus type 1

Keratoconjunctivitis sicca (KCS) has not been reported as occurring as a single entity in the acquired immune deficiency syndrome (AIDS) population. In a survey of human immunodeficiency virus type 1 (HIV-1) infected male patients, the authors found that 21% (9/42) had signs and symptoms compatible with KCS with positive Schirmer test results. Tear osmolarity determinations were obtained from this group and from an age- and sex-matched group of HIV-infected patients without symptoms of KCS and with negative Schirmer test results. Eighty-nine percent of the suspect group had increased tear osmolarity, whereas none of the control patients had a hyperosmolar tear film (P less than 0.0001). Results strongly suggest that KCS occurs at a significantly greater rate in male individuals infected with HIV-1 than in the general population.     

Open-label crossover study of vitamin A ointment as a treatment for keratoconjunctivitis sicca

The authors evaluated the efficacy of all-trans retinoic acid (vitamin A) ointment as a treatment for keratoconjunctivitis sicca (KCS) in a group of 11 patients selected on the basis of clinical history, slit-lamp examination results, rose Bengal staining, and tear film osmolarity. In this open-label crossover study, vitamin A ointment was no more effective than placebo in increasing tear secretion, as indicated by Schirmer test with proparacaine or tear film osmolarity, or in decreasing ocular surface disease, as indicated by rose Bengal staining. Seven patients stated some preference for the placebo ointment, two patients for the vitamin A ointment, and two patients had no preference.     

关于泪液系统的概念及意义

应激性泪液（感情泪、刺激泪）、平常性泪液的来源、机制、功用、排除路径有所差异。基础泪液生成机制一直存在争议,我们提出“周期性瞬目是基础泪液分泌产生的动力源”假说。本文叙述了以周期性瞬目运动启动基础泪液分泌机制,阐述了泪液功能运作包括：睑缘推动两条泪河合二为一再一分为二,周期性地涂布与更新前泪膜;同时瞬目运动周期地挤压和放松挤压泪囊,拉动泪小管壁产生泪泵作用,在前泪膜汽化性排除的同时,驱动泪河有序地移行到泪湖,此为泪道非管性段;泪泵作用令泪点主动吸取泪湖泪液进入管性泪道以排出。在泪囊和泪小管、鼻泪管衔接处以及鼻泪管下口,均有黏膜皱褶样瓣膜,且鼻泪管纤毛定向摆动,使基础泪液移行致鼻泪管下口,泪液再汽化进入呼吸气流,排出或吸入。强调了将泪液、结膜、结膜囊、眼睑和眼睑瞬目运动纳入泪液系统的必要性。文中首次提出“平常性泪液、汽化性泪道、泪道非管性段与管性段以及这两段的衔接点”等新概念。（眼科, 2014, 23： 226-229）     

New experimental method to study acid/base transporters and their regulation in lacrimal gland ductal epithelia

PURPOSE: The main function of the lacrimal gland is to produce the most aqueous component of the tear film covering the surfaces of the cornea and the conjunctiva. Studies have been conducted that characterize the mixed fluid and protein secretion of isolated acini, but no methods have been developed to characterize lacrimal gland ductal cell (LGDC) secretion. Secretory mechanisms of ductal epithelia may play physiological roles in the maintenance of the standard environments for the cornea and the conjunctiva. METHODS: In this study, the authors developed a rapid method to isolate large quantities of intact lacrimal ducts. The preparation of isolated intact lacrimal gland ducts for the first time enabled the performance of real-time functional experiments on cleaned ducts. Electron microscopy and fluorescence measurements were used to evaluate the viability of lacrimal ducts. RESULTS: Fluorescence measurements showed that LGDCs express functionally active Na(+)/H(+) exchanger (NHE) and Cl(-)/HCO(3)(-) exchanger (AE). Parasympathomimetic stimulation by carbachol stimulated NHE and AE through the elevation of intracellular calcium concentration. This mechanism can play a role in the regulation of ion and water secretion by LGDCs. CONCLUSIONS: The authors have described a lacrimal gland duct isolation technique in which the intact ducts remain viable and the role of duct cells in tear film secretion can be characterized. These data combined with the novel isolation facilitated understanding of the regulation mechanisms of ductal cell secretion at cellular and molecular levels under normal and pathologic conditions.     

Ocular surface investigations in dry eye

Dry eye is a complex clinicopathological entity involving tear film, lacrimal glands, eyelids, and a wide spectrum of ocular surface cells, including epithelial, inflammatory, immune, and goblet cells. From the tightly regulated lacrimal film functions and structure, a large variety of investigations have been developed, including tear meniscus measurements, fluorophotometry, meibometry, interference pattern analysis, evaporation rate, tear osmolarity, and thermography. Dry eye conditions also interfere with the ocular surface, causing corneal irregularities that may be explored using the techniques of videokeratography and in vivo confocal microscopy, or optical impairment, as confirmed by aberrometry. At the level of ocular surface cells, impression cytology remains a standard for assessing cell alterations. It has greatly benefited from new confocal microscopy, molecular biology, and flow cytometry techniques. Biological assessment of tear proteins or other mediators is also useful. Major limits should be acknowledged, however, such as technical issues in tear film collection, especially in dry eyes, and the lack of standardization of most measurements. Tear osmolarity, electrophoresis, and dosage of normal tear proteins, such as lysozyme or lactoferrin, remain the most useful tests. Finally, some extraocular explorations such as accessory gland biopsy or serum antinuclear antibody dosage may be useful for assessing the diagnosis of Sj?gren's syndrome.     

Mechanisms Involved in Injury and Repair of the Murine lacrimal Gland: Role of Programmed Cell Death and Mesenchymal Stem Cells

The non-keratinized epithelia of the ocular surface are constantly challenged by environmental insults, such as smoke, dust, and airborne pathogens. Tears are the sole physical protective barrier for the ocular surface. Production of tears in inadequate quantity or of inadequate quality results in constant irritation of the ocular surface, leading to dry eye disease, also referred to as keratoconjunctivitis sicca (KCS). Inflammation of the lacrimal gland, such as occurs in Sjogren syndrome, sarcoidosis, chronic graft-versus-host disease, and other pathological conditions, results in inadequate secretion of the aqueous layer of the tear film and is a leading cause of dry eye disease. The hallmarks of lacrimal gland inflammation are the presence of immune cell infiltrates, loss of acinar epithelial cells (the secreting cells), and increased production of proinflammatory cytokines. To date, the mechanisms leading to acinar cell loss and the associated decline in lacrimal gland secretion are still poorly understood. It is also not understood why the remaining lacrimal gland cells are unable to proliferate in order to regenerate a functioning lacrimal gland. This article reviews recent advances in exocrine tissue injury and repair, with emphasis on the roles of programmed cell death and stem/progenitor cells.     

干眼病理损害中的炎症机制

干眼是一种泪液和眼表的多因素性疾病,可引起眼部不适、视觉障碍、泪膜不稳定和眼表损害,并伴有泪膜渗透性升高和眼表炎症。目前研究表明,炎症在干眼的发病和病理损害中起着重要作用。本文从炎症与泪液渗透压、眼表黏蛋白表达、角结膜上皮结构及功能、泪腺及睑板腺结构和功能等方面对炎症造成干眼眼表和泪液功能损害的可能机制进行综述。     

The diagnosis and management of dry eye: a twenty-five-year review

PURPOSE: To review the advances in the diagnosis, pathogenesis, and management of dry eye disease in the past 25 years. METHODS: Literature review. RESULTS: The preocular tear film is a hydrated mucus gel that contains soluble antimicrobial proteins and growth factors that protect and support the ocular surface. The final common pathway in dry eye is a perturbation of the integrated ocular surface/lacrimal gland reflex unit. Diagnostic tests evaluating tear composition and clearance appear to show stronger correlation with the severity of ocular irritation symptoms and keratoconjunctivitis sicca (KCS) than the conventional Schirmer tests. KCS is a condition of abnormal differentiation and mucus production by the ocular surface epithelium that results in a poorly lubricated, abnormally permeable ocular surface that has increased susceptibility to environmental insults. Chronic subclinical ocular surface inflammation appears to play a key role in the pathogenesis of KCS. New therapeutic strategies are aimed at reducing the ocular surface inflammation of dry eye disease. CONCLUSIONS: There has been a tremendous increase in knowledge regarding dry eye disease in the past 25 years that has resulted in improved diagnostic classification and new targeted therapies.     

Research in dry eye: report of the Research Subcommittee of the International Dry Eye WorkShop (2007)

Members of the DEWS Research Subcommittee reviewed research into the basic mechanisms underlying dry eye disease. Evidence was evaluated concerning the tear film, lacrimal gland and accessory lacrimal glands, ocular surface epithelia (including cornea and conjunctiva), meibomian glands, lacrimal duct system and the immune system. Consideration was given to both animal and human research data. Results are presented as a series of information matrices, identifying what is known and providing supporting references. An attempt is made to identify areas for further investigation.     

New insight into lacrimal gland function: Role of the duct epithelium in tear secretion

Tear secretion is a complex process with the involvement of the main and accessory lacrimal glands, corneal and conjunctival epithelial cells and the Meibomian glands. The lacrimal gland is the main source of fluid, electrolytes and proteins in tear fluid. Deficient ion and water secretion results in aqueous deficient dry eye with serious consequences on the integrity of the ocular surface. Functions of acinar cells are widely studied, whereas less information is available about the duct system of the lacrimal gland. Secretory mechanisms of duct epithelium may play an important role in tear production, but only limited studies have tried to elucidate the role of the duct system in tear secretion. Significant progress has been made in the past few years, resulting in new insight into lacrimal gland duct function. New experimental techniques were introduced, which contributed to the exploration of the role of lacrimal gland ducts in more detail. Therefore, the aim of this review is to summarize our present knowledge about the role of ducts in lacrimal gland function and tear secretion, which appears to be the first review with a focus on this topic. Short outline of pancreatic and salivary gland duct functions is also given for the purposes of comparison.     

Basal and Reflex Human Tear Analysis: I. Physical Measurements: Osmolarity,Basal Volumes,and Reflex Flow Rate

Minimally stimulated, retained “basal” tears and stimulated reflex tears were collected from normal controls, keratoconjunctivitis sicca (KCS) patients, and contact lens (CL) wearers. Basal tear samples were collected on small filter paper strips (Periopaper®) over a five-second period, and volume was measured by means of an electronic device (Periotron®). Collected basal tear volumes for KCS patients (0.84 ± 0.42 μl) were significantly lower (P <; 0.01) than normal controls (1.18 ± 0.36) and CL wearers (1.24 ± 0.27). Reflex tear flow rates were measured over a five-minute period on Schirmer strips. Volume was calculated by comparison of wet length with known volumes of 1% egg white lysozyme solution. The reflex tear flow rates in KCS patients (3.29 ± 3.57 μl/minute) were significantly lower than normal controls (5.71 ± 5.86) and CL wearers (6.96 ± 6.07). The elevation in CL wearers was not statistically significant when compared to normals. KCS patients are deficient in both basal and reflex tears compared to normals but have a more significant deficiency of basal tears. Female normals and CL wearers over 40 years of age have a higher tear osmolarity than those under 41 years of age. Female KCS patients over 40 years of age have a tear osmolarity that is not significantly different from female KCS patients under 41 years of age.     

Antiinflammatory therapy for dry eye

PURPOSE: To present evidence establishing the relationship between inflammation and dry eye and supporting the use of antiinflammatory therapy for dry eye. DESIGN: Analysis of literature. METHODS: Research studies that evaluated inflammation in dry eye pathogenesis and clinical trials of antiinflammatory therapies for dry eye were reviewed. RESULTS: There is increasing evidence that decreased tear secretion, decreased tear turnover, and desiccation promote inflammation on the ocular surface. An increase in soluble mediators (cytokines and proteases) in the tear fluid, adhesion molecule expression by the conjunctival epithelium, and T-cell infiltration of the conjunctiva have been observed in dry eye patients. This inflammation appears to have a role in the pathogenesis of the ocular surface epithelial disease, termed keratoconjunctivitis sicca (KCS), that develops in dry eye. Clinical improvement of KCS has been observed after therapy with antiinflammatory agents including corticosteroids, cyclosporin and doxycycline. Cyclosporin A emulsion was approved by the Food and Drug Administration as therapy for dry eye. Randomized placebo-controlled FDA clinical trials showed that cyclosporine A was superior to vehicle in stimulating aqueous tear production, decreasing corneal punctuate fluorescein staining, reducing symptoms of blurred vision, and decreasing artificial tear use in patients with KCS. No ocular or systemic toxicity was observed from this medication. CONCLUSIONS: Ocular surface and lacrimal gland inflammation has been identified in dry eye that plays a role in the pathogenesis of KCS. Antiinflammatory therapy has efficacy for treating KCS. Cyclosporin A is the first FDA approved therapy for this indication. It improved signs and symptoms of KCS, and it is safe for long-term use.