The Human Lacrimal Gland: Historical Perspectives, Current Understanding, and Recent Advances

The lateral fornix orbitotomy: a novel surgical corridor to lacrimal gland lesions

PURPOSE

Current practice for diagnostic biopsy of lacrimal gland lesions entails an orbitotomy procedure via an upper eyelid crease or lateral canthotomy skin incision. We describe a novel surgical technique to address these lesions via the lateral conjunctival fornix.

METHODS

Retrospective case series of all patients who underwent a lateral fornix orbitotomy procedure for incisional or excisional diagnostic biopsy of lacrimal gland lesions. The procedure involves a conjunctival incision in the lateral fornix remote from the openings of the lacrimal ductules, and an intraperiosteal surgical corridor to access the lacrimal gland.

RESULTS

The study cohort included 16 patients (3 male, 13 female) with a mean age of 48.3 years (range, 24.0-78,9 years). The sampled lesions involved the orbital lobe in 14 patients, the palpebral lobe in 1 patient, and the entire gland in 1 patient. A histopathological diagnosis was obtained in all cases. Postoperatively, new moderate adduction deficit developed in one patient (6.3%) that recovered after adhesiolysis of the conjunctival scar. 3 patients (18.8%) experienced transient mild limitation of adduction or abduction. There was no new or worse ptosis or dry eye disease related to the surgery. The mean length of postoperative follow-up was 1.3 years (median 1.0 years, range, 0.6-4.7 years).

CONCLUSION

The lateral fornix orbitotomy approach was successful in obtaining biopsy specimens of histopathological diagnostic value. It provides transconjunctival access to the lacrimal gland without damage to the excretory lacrimal ductules or displacement of the eyelid support system.

Application of eye organoids in the study of eye diseases

The eyes are one of the most important sensory organs in the human body. Currently, diseases such as limbal stem cell deficiency, cataract, retinitis pigmentosa and dry eye seriously threaten the quality of people's lives, and the treatment of advanced blinding eye disease and dry eye is ineffective and costly. Thus, new treatment modalities are urgently needed to improve patients' symptoms and suffering. In recent years, stem cell-derived three-dimensional structural organoids have been shown to mimic specific structures and functions similar to those of organs in the human body. Currently, 3D culture systems are used to construct organoids for different ocular growth and development models and ocular disease models to explore their physiological and pathological mechanisms. Eye organoids can also be used as a platform for drug screening. This paper reviews the latest research progress in regard to eye organoids (the cornea, lens, retina, lacrimal gland, and conjunctiva).

Analysis of the heterogeneity and complexity of murine extraorbital lacrimal gland via single-cell RNA sequencing

PURPOSE

The lacrimal gland is essential for maintaining ocular surface health and avoiding external damage by secreting an aqueous layer of the tear film. However, a healthy lacrimal gland's inventory of cell types and heterogeneity remains understudied.

METHODS

Here, 10X Genome-based single-cell RNA sequencing was used to generate an unbiased classification of cellular diversity in the extraorbital lacrimal gland (ELG) of C57BL/6J mice. From 43,850 high-quality cells, we produced an atlas of cell heterogeneity and defined cell types using classic marker genes. The possible functions of these cells were analyzed through bioinformatics analysis. Additionally, the CellChat was employed for a preliminary analysis of the cell-cell communication network in the ELG.

RESULTS

Over 37 subclasses of cells were identified, including seven types of glandular epithelial cells, three types of fibroblasts, ten types of myeloid-derived immune cells, at least eleven types of lymphoid-derived immune cells, and five types of vascular-associated cell subsets. The cell-cell communication network analysis revealed that fibroblasts and immune cells play a pivotal role in the dense intercellular communication network within the mouse ELG.

CONCLUSIONS

This study provides a comprehensive transcriptome atlas and related database of the mouse ELG.

Magnetic resonance diffusion-weighted imaging in lacrimal gland lymphoma versus inflammation: A comparative study

PURPOSE

To determine the role of diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) in differentiating the inflammatory process and malignant lymphoma of the lacrimal gland.

METHODS

A retrospective analysis of all subjects who underwent lacrimal gland biopsy and magnetic resonance (MR) imaging with DWI sequences during a 10-year period at the Sheba Medical Center, Israel. The lacrimal glands' ADC values were documented bilaterally by blinded observers and correlated with the final histology verified diagnoses.

RESULTS

Twenty-eight patients were included, with 19 females (68%) with a mean ± SD age of 48.1 ± 25.7 years. The right orbit was involved in 14 cases (50%) and the left in 13 (46%); one patient (4%) had bilateral involvement. Seventeen cases (61%) had a final diagnosis of idiopathic inflammation or dacryoadenitis, and six cases (21%) were diagnosed with lymphoma. Additional diagnoses included pleomorphic adenoma in 3 (11%), adenoid cystic carcinoma, and solitary fibrous tumor. Lower mean ADC values were observed in the lymphoma versus inflammatory group (1.03 × 10-3 Vs. 1.45 × 10-3, P = 0.02).

CONCLUSION

Restricted diffusion on MR imaging can serve as a diagnostic tool in the differentiation between inflammatory processes of the lacrimal gland and lymphoma.

Is Orbital Lobe of the Lacrimal Gland Dispensable? Tear Volume, Ocular Surface, and MRI Volumetric Analysis

PURPOSE

To investigate the effects of lacrimal gland reduction surgeries on the tear volume and ocular surface.

METHODS

This is a cohort study of patients post 2 lacrimal gland reduction surgeries: partial orbital lobe dacryoadenectomy for refractory epiphora (4 patients, mean age: 31 ± 13.6 years, 3 males) and complete orbital lobe dacryoadenectomy for lacrimal gland pleomorphic adenoma (15 patients, mean age: 41 ± 12 years, 7 females). Changes in Schirmer I, ocular surface staining, symptomatology, and lacrimal gland volumetrics (MRI) were assessed before and after the surgical procedure.

RESULTS

The median Schirmer value reduction following partial orbital lobe dacryoadenectomy was 5 mm at a mean follow-up of 18 ± 4.9 months. None of them developed dry eye disease or positive ocular staining. The gland volume was reduced by 45.9% to 53.5% in 3 patients and 13.3% in 1 patient. The epiphora improved moderately in 93% of patients. Of 15 patients with lacrimal gland pleomorphic adenoma excision, the median reduction in Schirmer I was 4 mm at a mean follow-up of 12.8 months.

CONCLUSION

Partial or complete removal of the orbital lobe of the lacrimal gland does not induce dry eye disease in otherwise healthy individuals. However, gland volume does not recover following partial reduction, and it seems unlikely that the lacrimal gland regenerates following partial removal.

Frozen Section Histoanatomy of the Peritarsal Eyelid

BACKGROUND

Mohs surgery of eyelid skin cancers requires detailed knowledge of anatomy for precise surgery and accurate evaluation of histology.

OBJECTIVE

To review the histology of the peritarsal eyelid using frozen sections as encountered intraoperatively by Mohs surgeons.

METHODS

The authors review the literature describing the anatomy and histology of the peritarsal eyelid from the lens of a Mohs surgeon. Histology from select Mohs cases is used to frame the discussion of the microanatomy of this region.

RESULTS

The peritarsal eyelids contain a unique mixture of skin, muscle, tarsus, glandular tissue, and conjunctiva. The histologic appearance of many of these structures differs from skin found outside of this anatomic region. Tumors of the eyelid and periocular region may mimic normal histologic structures found within the peritarsal eyelid.

CONCLUSION

The peritarsal eyelids have unique anatomy and associated histologic structures. Knowledge of the detailed histoanatomy is required for confident execution of Mohs surgery in this anatomic region.

Lacrimal gland activity in lacrimal drainage obstruction: exploring the potential cross-talk between the tear secretion and outflow

PURPOSE

To investigate the effects of lacrimal drainage obstructions on the lacrimal gland activity and if there exists a potential link between the two.

METHODS

Direct assessment of the lacrimal gland activity from the palpebral lobe was performed in consecutive patients diagnosed with unilateral primary acquired nasolacrimal duct obstruction (PANDO), along with Ocular Surface Disease Index (OSDI), non-invasive tear break up time (NIBUT; Oculus K5M), tear meniscus height and Schirmer I. The primary outcome measure was the difference in the tear flow rate between the eye with PANDO and the contralateral uninvolved eye.

RESULTS

Thirty patients (median age, 45.5 years; 25 females) with unilateral PANDO had epiphora for a mean duration of 20 months. The mean OSDI score was 6.3. NIBUT (mean 11.56 vs 11.58 s; p=0.49) and Schirmer I values (mean 18.83 vs 19.4 mm; p=0.313) were not significantly different between PANDO and non-PANDO eyes. The morphology of the palpebral lobe (size 29.3 vs 28.6 mm2, p=0.41) and the number of lacrimal ductular openings (median 2 vs 2.5) were similar between the two eyes. The mean tear flow from the lacrimal glands of the PANDO side was significantly reduced compared with the contralateral uninvolved side (0.8 vs 0.99 µL/min; p=0.014)).

CONCLUSION

Tear flow rate from palpebral lobes of patients with unilateral lacrimal outflow obstruction shows a significant reduction compared with the contralateral side. The potential ways of communications between the tear drainage and the tear production mechanisms need to be explored further.

Internal vascular anatomy of the human lacrimal gland: A protocol based on cadaver dissection and three-dimensional micro-computed tomography

PURPOSE

To evaluate the feasibility of studying the vascular supply of the orbital and palpebral lobes of the human lacrimal gland using micro-computed tomography (micro-CT) and microscopic dissection.

METHODS

The lacrimal gland artery of a fresh parasagittalized cadaver head (male, aged 76 years) was infused with a lead oxide-latex mixture near the occipital pole of the gland. The entire lacrimal gland was imaged using micro-CT and 3D cinematic rendering (CR) and then dissected under a surgical microscope.

RESULTS

Micro-CT and CR images showed well-demarcated internal vascular branches of the lacrimal artery and their distribution within the orbital and palpebral lobes. The entire course of the artery and its branches could be visualized by CR and microscopic dissection, with the former showing better spatial orientation and finer branching. The main artery runs along the free edge of the aponeurosis of the levator palpebrae superior muscle and lies in the isthmus portion of the gland (between the orbital and palpebral lobes). The branches of the main lacrimal artery include one branch to the orbital adipose tissue just before entering the gland, two branches to the orbital lobe (medial and lateral), and two branches to the palpebral lobe (medial and lateral). The main artery terminates as palpebral and orbital lobe branches in the lateral half of the lacrimal gland.

CONCLUSION

Latex and contrast-enhanced micro-CT is very well suited to visualize the vascular anatomy of the lacrimal artery within the gland. A large number of lacrimal gland examinations using the method presented here are required to demonstrate and understand the variability of the vascular anatomy of the human lacrimal gland.

[Cell technologies as a basis for the development of regenerative principles for the treatment of lacrimal gland diseases]

The lacrimal gland (LG) is a tubuloacinar exocrine gland composed of acinar, ductal, and myoepithelial cells. Three-dimensional distribution of acinar lobules, ducts, and myoepithelial cells is necessary for the effective functioning of the organ. LG is the main organ of immune surveillance of the ocular surface system. The embryogenesis of the gland is regulated by the interaction of genetic mechanisms, internal epigenetic (enzyme systems, hormones) and exogenous factors. There is no doubt that there is a clear genetic program for the implementation of the complex process of embryonic development. The mechanisms regulating LG organogenesis initiate the work of a huge number of structural oncogenes, transcription and growth factors, etc. Studying the expression and selective activity of regulatory genes during organ development, their participation in the differentiation of different cell types is a current trend at the nexus of clinical genetics, molecular biology, embryology and immunocytochemistry. Due to its relatively simple structure and accessibility, human LG is a suitable object for potential application in regenerative medicine. Development of a universal protocol for obtaining functional differentiated secretory epithelium of LG capable of expressing tissue-specific markers is an urgent task. Determining the nature and origin of stem cells and progenitor cells will allow the isolation and multiplication of these cells in culture. After obtaining a functionally active culture of LG cells, it is possible to create a model of autoimmune diseases.

Advances in imaging of the lacrimal gland in Sjögren's syndrome: A narrative review

Due to lymphocytic infiltration of the salivary and lacrimal glands, Sjogren's syndrome (SS), a systemic autoimmune illness that mostly affects the exocrine glands, causes dry mouth (xerostomia) and dry eyes (xerophthalmia). Additionally, SS is associated with various comorbidities such as cardiovascular diseases, infections, musculoskeletal diseases, and cancers. Among patients with SS, xerophthalmia frequently arises as a complication, leading to insufficient tear production or rapid tear evaporation, thereby causing discomfort, irritation, and a gritty sensation in the eyes. This article aims to examine recent advancements in the imaging of the lacrimal gland in Sjögren's syndrome and briefly discusses the utilization of various imaging examinations for the lacrimal gland in this particular disease.

Aquaporins in lacrimal glands and their role in dry eye disease

Aging is the most important known risk factor for dry eye is aging, which is associated with changes in the structure and function of the lacrimal gland (LG) and characterized by atrophy, duct blocking lymphocyte infiltration, and reduced protein secretion. Aquaporins (AQP) have been proposed as a potential producer of exocrine gland fluids since exocrine secretion depends on the mobility of water. Therefore, the main topics of this review will be the expression, localization, and function of AQPs in LG. In addition, we review the mechanisms of fluid transport in exocrine gland fluid secretion and discuss the potential role of AQPs in dry eye.

Tear inflammatory cytokines as potential biomarkers for myopic macular degeneration

Previous studies have reported that inflammatory cytokine levels increase in the intraocular fluids (aqueous humor and vitreous) of highly myopic eyes, However, there has been currently no study revealing the levels of inflammatory cytokines in tear. Therefore, this study aimed to determine tear cytokine levels of highly myopic eyes, and their relationships with myopic macular degeneration (MMD). This case-control study screened inflammatory cytokines of tear samples from 132 highly myopic and 105 emmetropic eyes using a multiplex cytokine antibody array, and cytokines showing significant intergroup differences were further validated using ProQuantum immunoassays in tear samples from another 60 highly myopic and 60 emmetropic eyes. Ultra-widefield fundus photographs of eyes were classified according to the meta-analyses of the Pathologic Myopia Classification. Associations between tear cytokine levels and MMD category were investigated. As a result, tear levels of interleukin (IL)-6, IL-13 and monocyte chemoattractant protein (MCP)-1 were screened significantly higher in highly myopic eyes than in emmetropic controls (IL-6: 11.70 ± 16.81 versus 8.22 ± 10.76 pg/mL; MCP-1: 63.60 ± 54.40 versus 33.87 ± 43.82 pg/mL; both P < 0.05). Validation assays further demonstrated the elevated concentrations of IL-6 and MCP-1 (IL-6: 13.97 ± 8.41 versus 8.06 ± 7.94 pg/mL, P < 0.001; MCP-1: 32.69 ± 8.41 versus 18.07 ± 8.41 pg/mL, P = 0.003). Tear levels of IL-6 and MCP-1 differed significantly among MMD categories (both P < 0.05). The area under receiver operating characteristic curve were 0.783 and 0.682 respectively (both P < 0.05), when using tear IL-6 and MCP-1 levels to predict the presence of MMD (category ≥2). The ordered logistic regression model also indicated that longer axial length, and higher IL-6 and MCP-1 tear levels were independent predictors of higher MMD category. In our study, highly myopic eyes presented significantly higher levels of tear IL-6 and MCP-1, which may also serve as potential biomarkers for MMD.

New insights into lacrimal gland anatomy using 7T MRI and electron microscopy: Relevance for lacrimal gland targeted therapies and bioengineering

PURPOSE

To study the tissue architecture, isthmus (connection between two lobes) of the lacrimal gland using preclinical 7T MRI in combination with histology and electron microscopy.

METHODS

Ten lacrimal glands from Caucasian body donors (mean age 78.7 years) were studied using 7T-MRI (N = 5; scanned at 75-μm intervals), histology, and electron microscopy (N = 5) and 3D cinematic rendering (CR) techniques.

RESULTS

3D CR images showed uniform-sized lobules (widest lobule diameter, 1.68 ± 0.19 mm in orbital lobe, 1.68 ± 0.17 mm in palpebral lobe) in both lobes, separated by septae (size, 0.29 ± 0.09 mm). The internal framework of the gland resembled a honeycoomb pattern. In CR and histology, the isthmus contained glandular acini, large blood vessels, nerves, and no more than two ducts having a tortuous course towards the conjunctival surface. On assigning a color display to the rendered lacrimal gland, all glands showed a blood vessel originating from the main lacrimal artery just 5 mm beyond the hilum and making it course to the palpebral lobe via isthmus. The distance between the conjunctiva and the central substance of the orbital and palpebral lobe was 9.4 ± 0.2 mm and 2.8 ± 0.7 mm, respectively. Electron microscopy of the palpebral lobe revealed compact subepithelial layer in the overlying conjunctiva, followed by loosely scattered collagen bundles that contained the gland lobules.

CONCLUSION

3D-CR can be used to study the lacrimal gland microstructure, help fabricate a 3D scaffold for lacrimal gland bioprinting, and serve as guide for transconjunctival lacrimal gland targeted therapies i.e., 2.9 & 9 mm long needle to reach the orbital and palpebral lobe center, respectively in normal-size glands.

Correction of Lacrimal Gland Ptosis in Blepharoplasty: A Systematic Review

PURPOSE

Lacrimal gland ptosis has a prevalence of 10% to 15% in Caucasian patients, reaching up to 60% in older age. Its involuntary resection during blepharoplasty carries the potential risk of compromising corneal lubrication. The purpose of this systematic review is to check whether there is a consensus in the literature regarding the surgical procedure of choice and which outcomes and complications have been observed.

METHODS

A systematic review was carried out following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A search was carried out in the Medline, Scopus, and Cochrane databases in March 2022.

RESULTS

A total of 16 studies involving 483 patients with lacrimal gland ptosis have been included. In 90.06% of patients, resuspension or direct refixation of the gland to the lacrimal fossa with suture to the orbital periosteum was performed. Follow up has been inconsistent, with an average of 18 months. Regarding complications, 5 recurrences and only 2 patients with persistent dry eye were observed.

CONCLUSIONS

In general, the evidence is sparse. Nevertheless, repair of lacrimal gland ptosis is a relatively simple, reproducible, and safe surgical technique, with a low likelihood of recurrence, severe, or persistent complications. A classification is proposed for both the grading of ptosis and its treatment.

UHFUS: A Valuable Tool in Evaluating Exocrine Gland Abnormalities in Sjögren's Disease

Sjögren's Disease (SjD) is a chronic autoimmune disorder that affects the salivary and lacrimal glands, leading to xerostomia and xerophthalmia. Ultrasonography of Major Salivary Glands (SGUS) is a well-established tool for the identification of the salivary glands' abnormalities in SjD. Recently, a growing interest has arisen in the assessment of the other exocrine glands with ultrasonography: lacrimal glands (LGUS) and labial salivary glands (LSGUS). The objective of this study is to explore the practical applications of ultra-high frequency ultrasound (UHFUS) in the assessment of lacrimal glands and labial salivary glands. Indeed, UHFUS, with its improved spatial resolution compared to conventional ultrasonography, allows for the evaluation of microscopic structures and has been successfully applied in various medical fields. In lacrimal glands, conventional high-frequency ultrasound (HFUS) can detect characteristic inflammatory changes, atrophic alterations, blood flow patterns, and neoplastic lesions associated with SjD. However, sometimes it is challenging to identify lacrimal glands characteristics, thus making UHFUS a promising tool. Regarding labial salivary glands, limited research is available with conventional HFUS, but UHFUS proves to be a good tool to evaluate glandular inhomogeneity and to guide labial salivary glands biopsy. The comprehensive understanding of organ involvement facilitated by UHFUS may significantly improve the management of SjD patients.

Epithelial-mesenchymal transition in the lacrimal gland morphogenesis, damage and repair

Epithelial-mesenchymal transition (EMT) constitutes an important pathway in organ fibrosis seen in the lungs, liver, eye, and salivary glands. This review summarizes the EMT observed within the lacrimal gland during its development, tissue damage and repair along with possible translational implications. Existing animal and human studies have reported the increased expression of EMT regulators i.e., transcription factors like Snail, TGF-β1 within the lacrimal glands, and a possible role of reactive oxygen species, which might be initiating the cascade of EMT. In these studies, EMT is typically detected by reduced E-cadherin expression in the epithelial cells and increased Vimentin and Snail expression within the lacrimal glands' myoepithelial or ductal epithelial cells. Other than specific markers, electron microscopic evidence of disrupted basal lamina, increased collagen deposition, reorganised cytoskeleton of myoepithelial cells also indicated EMT. Very few studies have shown myoepithelial cells to be the cells transitioning into mesenchymal cells with increased extracellular matrix deposition within the lacrimal glands. EMT in animal models seemed reversible as glands got repaired after damage with IL-1α injection or duct ligation and transiently used the EMT as a means for tissue repair. The EMT cells also expressed nestin, a marker for progenitor cells in a rabbit duct ligation model. However, lacrimal glands of ocular graft versus host disease and IgG4 dacryoadenitis demonstrate irreversible acinar atrophy along with signs of EMT-fibrosis, reduced E-cadherin, and increased Vimentin and Snail expression. Future studies exploring the molecular mechanisms of EMT and thereby developing targeted therapies capable of transforming the mesenchymal cells into epithelial cells or blocking the EMT might help in the restoration of the lacrimal gland function.

Delineation of the lacrimal vein: a magnetic resonance imaging study

PURPOSE

To our knowledge, anatomical knowledge about the lacrimal vein (LV) is missed. Therefore, this retrospective study aimed to explore them using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Eighty-one patients who underwent contrast-enhanced MRI and three donated bodies to science were enrolled.

RESULTS

On the sagittal images, the measured mean right long (LD) and short diameters (SD) of the lacrimal gland (LG) were 17.3 ± 2.4 mm and 13.7 ± 2.1 mm, while the left LD and SD were 17.0 ± 2.6 mm and 13.6 ± 2.6 mm, respectively. Laterality or sex differences were not found in the LD and SD groups. In addition, no specific age range was associated with a significantly longer LD or SD. LVs were identified in 94% of axial images. Their course was classified into as follows: three types: connecting to the superolateral cavernous sinus (CS), to the superior ophthalmic vein (SOV), and the diploic channels of the greater wing of the sphenoid bone (DCGW). The CS type was the most frequently identified, followed by the SOV and DCGW types. In dissected specimens, the LVs consistently coursed between the posterior margin of the LG and the superolateral part of the CS, above the upper margin of the lateral rectus muscle.

CONCLUSIONS

The LV may consistently emerge from the upper posterior margin of the LG. It commonly pours into the SOV or superolateral part of the CS.

Atavistic and vestigial anatomical structures in the head, neck, and spine: an overview

Organisms may retain nonfunctional anatomical features as a consequence of evolutionary natural selection. Resultant atavistic and vestigial anatomical structures have long been a source of perplexity. Atavism is when an ancestral trait reappears after loss through an evolutionary change in previous generations, whereas vestigial structures are remnants that are largely or entirely functionless relative to their original roles. While physicians are cognizant of their existence, atavistic and vestigial structures are rarely emphasized in anatomical curricula and can, therefore, be puzzling when discovered incidentally. In addition, the literature is replete with examples of the terms atavistic and vestigial being used interchangeably without careful distinction between them. We provide an overview of important atavistic and vestigial structures in the head, neck, and spine that can serve as a reference for anatomists and clinical neuroscientists. We review the literature on atavistic and vestigial anatomical structures of the head, neck, and spine that may be encountered in clinical practice. We define atavistic and vestigial structures and employ these definitions consistently when classifying anatomical structures. Pertinent anatomical structures are numerous and include human tails, plica semilunaris, the vomeronasal organ, levator claviculae, and external ear muscles, to name a few. Atavistic and vestigial structures are found throughout the head, neck, and spine. Some, such as human tails and branchial cysts may be clinically symptomatic. Literature reports indicate that their prevalence varies across populations. Knowledge of atavistic and vestigial anatomical structures can inform diagnoses, prevent misrecognition of variation for pathology, and guide clinical interventions.

Nonpolar Lipids Contribute to Midday Fogging During Scleral Lens Wear

Purpose

To determine correlations between lipids in the fluid reservoir (FR) and the severity of midday fogging (MDF) in scleral lens (SL) wear.

Methods

SL neophytes were recruited to wear custom SL for 4 days, examined after 8 hours on days 1 and 4. Lens vault and MDF were quantified from anterior segment optical coherence tomography (AS-OCT), and the FR was collected and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Relative abundance of lipids was compared to MDF scores using nonparametric correlation testing (Spearman rank). Ocular surface and SL fitting characteristics (lens vault, fitting curves) were likewise compared to MDF.

Results

Thirteen participants (26 eyes, 69% female, 28 ± 9 years old) were included in this study. MDF severity after 8 hours of SL wear was 33 ± 29 units on day 1 and 28 ± 24 units on day 4 (r = .94; P < 0.01). Twelve samples were analyzed using LC-MS/MS, and a total of 170 distinct lipid species were detected. The lipid classes with greatest correlation to MDF were the wax esters (r = .73, P = 0.01), cholesteryl esters (r = .59; P = 0.049), and triacylglycerols (r = .64, P = 0.03). Polar lipids were observed abundantly in all samples. None of the measured ocular surface or fitting outcomes were correlated to MDF.

Conclusions

Nonpolar lipids were the greatest contributors to MDF among these normal participants. Polar lipids may be due to cellular debris, although they do not appear contributory to MDF.

Histochemical Comparison of Human and Rat Lacrimal Glands: Implications for Bio-Engineering Studies

Purpose

The purpose of this study was to determine whether rodent lacrimal glands (LGs) represent a suitable surrogate for human tissue in bio-engineering research, we undertook a meticulous histological and histochemical comparison of these two tissues.

Methods

Histological techniques and immunohistochemistry were used to compare the structure of adult human and rat LG tissues and the expression of key functional tissue elements.

Results

Compared with humans, the rat LG is comprised of much more densely packed acini which are devoid of an obvious central lumen. Myoepithelial, fibroblasts, dendritic cells, T cells, and putative progenitor cells are present in both tissues. However, human LG is replete with epithelium expressing cytokeratins 8 and 18, whereas rat LG epithelium does not express cytokeratin 8. Furthermore, human LG expresses aquaporins (AQPs) 1, 3, and 5, whereas rat LG expresses AQPs 1, 4, and 5. Additionally, mast cells were identified in the rat but not the human LGs and large numbers of plasma cells were detected in the human LGs but only limited numbers were present in the rat LGs.

Conclusions

The cellular composition of the human and rat LGs is similar, although there is a marked difference in the actual histo-architectural arrangement of the tissue. Further variances in the epithelial cytokeratin profile, in tissue expression of AQPs and in mast cell and plasma cell infiltration, may prove significant.

Translational Relevance

The rat LG can serve as a useful surrogate for the human equivalent, but there exist specific tissue differences meaning that caution must be observed when translating results to patients.

Lacrimal Gland Insufficiency in Aqueous Deficiency Dry Eye Disease: Recent Advances in Pathogenesis, Diagnosis, and Treatment

BACKGROUND

Aqueous deficiency dry eye disease is a chronic and potentially sight-threatening condition, that occurs due to the dysfunction of the lacrimal glands. The aim of this review was to describe the various recent developments in the understanding, diagnosis and treatment of lacrimal gland insufficiency in aqueous deficiency dry eye disease.

METHODS

A MEDLINE database search using PubMed was performed using the keywords: "dry eye disease/syndrome", "aqueous deficient/deficiency dry eye disease", "lacrimal gland" and "Sjogren's syndrome". After scanning through 750 relevant abstracts, 73 eligible articles published in the English language from 2016 to 2021 were included in the review.

RESULTS

Histopathological and ultrastructural studies have revealed new insights into the pathogenesis of cicatrising conjunctivitis-induced aqueous deficiency, where the lacrimal gland acini remain uninvolved and retain their secretory property, while significant ultrastructural changes in the gland have been observed. Recent advances in diagnosis include the techniques of direct clinical assessment of the lacrimal gland morphology and secretion, tear film osmolarity, tear film lysozyme and lactoferrin levels, tear film interferometry and lacrimal gland confocal microscopy. Developments in the treatment of aqueous deficiency dry eye disease, apart from the nanoparticle-based tear substitutes, include secretagogues like diquafosol tetrasodium and rebamipide, anti-inflammatory topical agents like nanomicellar form of cyclosporine and lifitegrast, scleral contact lenses, neurostimulation, and acupuncture for increasing the amount of tear production, minor salivary gland transplantation, faecal microbial transplantation, lacrimal gland regeneration and mesenchymal stem cell therapy.

CONCLUSIONS

Significant advances in the understanding, diagnosis and management of lacrimal gland insufficiency and its role in aqueous deficiency dry eye disease have taken place within the second half of the last decade. Of which, translational breakthroughs in terms of newer drug formulations and regenerative medicine are most promising.

Exocrine gland structure-function relationships

Fluid secretion by exocrine glandular organs is essential to the survival of mammals. Each glandular unit within the body is uniquely organized to carry out its own specific functions, with failure to establish these specialized structures resulting in impaired organ function. Here, we review glandular organs in terms of shared and divergent architecture. We first describe the structural organization of the diverse glandular secretory units (the end-pieces) and their fluid transporting systems (the ducts) within the mammalian system, focusing on how tissue architecture corresponds to functional output. We then highlight how defects in development of end-piece and ductal architecture impacts secretory function. Finally, we discuss how knowledge of exocrine gland structure-function relationships can be applied to the development of new diagnostics, regenerative approaches and tissue regeneration.

Transdermal anti-inflammatory therapy for aqueous deficiency

PURPOSE

Lacrimal gland inflammation has been identified as an important limitation on aqueous production and associated dry eye disease. Ocular surface inflammation in dry eye disease can be a downstream response to reduced quantities of warmer hyperosmotic aqueous being delivered from an inflamed lacrimal gland with high concentrations of inflammatory mediators. This review examines evidence which shows how topical applications of anti-inflammatory drugs have very limited access to the lacrimal gland and an associated limited capacity to increase aqueous flow by reducing inflammation in the main lacrimal gland.

RECENT FINDINGS

Using cyclosporine as an exemplar immunomodulatory drug, this review examines problems associated with the topical administration of all anti-inflammatory drugs in the treatment of dry eye disease.

SUMMARY

Limited access to the lacrimal gland for topical applications and their very short on-eye residence times are compared with the therapeutic potential of prolonged therapeutic episodes that could be achieved with transdermal applications of a drug to the skin at the site of the lacrimal gland. Poor access to the lacrimal gland for topically administered drugs is a major barrier to the treatment of aqueous deficiency. While topical inflammatory drug access to the ocular surface is direct, poor access to the lacrimal gland is partly due to drop placement being downstream to the flow of aqueous (Eye Vis 2020;7:1; Eye Vis 2019;6:1). This barrier is much greater according to the degree that reflex tear flow is stimulated by irritation associated with adverse drop temperature, and/or pH and/or tonicity for example.

Non-infectious Dacryoadenitis

Dacryoadenitis is an inflammation of the lacrimal gland that may have various etiologies with similar presentations. Despite more recent elucidation of specific causes, the management has remained largely unchanged. Hence, the condition remains under biopsied with the rationale that empirical treatment with corticosteroids is effective for many of the causes. Dacryoadenitis, however, dacryoadenitis can be the presenting sign of an undiagnosed systemic disease and a mimick for lymphoma; hence, tissue diagnosis and systemic investigations play a vital role. A significant proportion of dacryoadenitis has a specific etiology, and IgG4-related dacryoadenitis is more frequently identified as a cause. We summarize the different types of immune-mediated dacryoadenitis, their clinical findings, histopathology, management, and prognosis. We have also highlighted and formulated practice guidelines for diagnosis and effective treatment based on the underlying systemic disease.

Rabbit models of dry eye disease: Current understanding and unmet needs for translational research

Dry eye disease (DED) is emerging as an eye health pandemic, affecting millions worldwide. The development of novel drugs, drug delivery systems, and targeted therapies for addressing the inflammation in DED necessitates progress in experimental models of DED. Animal models of DED have been created for simulating the two clinically described forms of DED: lacrimal insufficiency and the evaporative DED models. Although most DED models have relied upon rodents, the larger eye size and longer life span of rabbits and the closer resemblance to human lacrimal glands, render rabbits a promising near-ideal model for studying DED. Since the first rabbit DED model was described, numerous modifications including the use of topical epitheliotoxic drugs, neural abolition, activated lymphocytes injection, and surgical dacryoadenectomy have been introduced. The stability of these models, whether short-term or long-term, accordingly guides their experimental or therapeutic utility. A rabbit autoimmune dacryoadenitis model has successfully simulated DED signs and features of lacrimal gland inflammation, as observed in Sjogren's syndrome, that improved with mesenchymal stem cell therapy. This review summarizes the comparative microscopic anatomy of rabbit and human lacrimal glands, various existing rabbit DED models and their respective suitability for understanding pathogenetic mechanism of DED or for experimental drug testing. Also, the insights gained from animal models in dry eye management is described along with the future perspectives. There is still a pressing need of developing rabbit models for studying the pathogenesis of complex ocular surface changes in evaporative and aqueous deficiency DED other than autoimmune dacryoadenitis.

Tear secretion from the lacrimal gland: variations in normal versus dry eyes

Purpose

To investigate the secretory status of the main lacrimal gland in healthy and dry eye disease (DED) via fluorescein-assisted direct assessment of tear secretion from the palpebral lobes.

Methods

Included were 25 healthy subjects (50 lobes) and 75 subjects with DED (cicatrising conjunctivitis (CC, n=27), evaporative dry eyes (EDE, n=25) and Sjogren’s syndrome (SS, n=23)). Analysed parameters included number and location of ductular openings, tear flow rate per gland and per ductule, and the time lag for the initiation of secretion.

Results

Ductular openings could be observed in all patients with EDE and healthy subjects whereas only 33% (18/54) glands of CC patients and 67% glands (31/46) patients with SS revealed ductules. The median number of ductules per lobe was 4 in normal (range 3–5), 3 in EDE (3–6), 1 in SS (0–3) and 0 in CC group (0–3) (p<0.000001). The median tear flow rate per lobe in CC (0.00 μL/min) and SS (0.21 μL/min) was significantly lesser than normal lobes (1.05 μL/min, and EDE (0.99 μL/min eyes. The tear flow rate differed significantly between SS and CC group (p<0.0001). The maximum time lag occurred in the CC group (median, 20 s), followed by the SS group (median, 1.5 s) whereas the EDE group had similar time lag (<1 s) as of normal glands (p<0.0001).

Conclusion

Direct assessment of tear secretion from the palpebral lobe demonstrates significant differences between EDE, aqueous deficient dry eye and dry eye in CC.

Immunohistological Study of Palpebral Lobe of the Lacrimal Gland in Severe Dry Eyes Secondary to Stevens-Johnson Syndrome

PURPOSE

To detect the immunohistochemical changes in the main lacrimal glands of patients suffering from chronic ocular sequelae of Stevens-Johnson syndrome (SJS).

METHODS

Histological sections of biopsies from the lacrimal gland of three chronic SJS patients (mean age, 33 years; 2 males) with severe dry eye disease (Schirmer = 0 mm) were assessed using double immunofluorescence techniques. Changes in the expression of secretory proteins lactoferrin (Lf), lysozyme (Ly), aquaporin 5 (AQP5), S-100, and early apoptosis marker (Annexin V) were studied.

RESULTS

Different morphological expressions of secretory proteins were present in the three samples. One sample had maintained the immunoreactivity for Lf, Ly, S-100, similar to healthy controls. Two samples had significantly reduced immunoreactivity for anti-Lf, anti-Ly, and S-100, the weakest being in the sample with distorted lobular architecture and mild interlobular fibrosis. AQP5 had a distinct vesicular intracytoplasmic immunoreactivity suggesting defective trafficking and integration of the protein to the apical membrane. There was no S-100 immunostaining in the acinar or ductal epithelium, whereas interstitial nerve fibers scattered in the periacinar region showed reduced immunoreactivity for S-100. There was strong Annexin V immunoreactivity in the nuclei of epithelial cells in the majority of acinar and ductal epithelia of all the samples, with distorted nuclear morphology in one sample.

CONCLUSION

Defective trafficking of AQP5 and variable expression of Ly, Lf, S-100 are the notable findings in the lacrimal glands of chronic SJS patients along with signs of early apoptosis. It suggests that the palpebral lobe of the lacrimal gland is involved in the pathological processes occurring in the conjunctiva of SJS patients.

Palpebral lobe of the human lacrimal gland: morphometric analysis in normal versus dry eyes

AIM

To study the morphological features of the palpebral lobe of the main lacrimal gland in normal and dry eyes.

METHODS

This cross-sectional study included 25 healthy subjects and 83 patients with dry eye disease (DED). The aetiological groups of DED were cicatrising conjunctivitis (CC, n=35), evaporative dry eyes (EDE, n=25) and Sjogren's syndrome (SS, n=23). The palpebral lobes in both eyes were evaluated using slit-lamp biomicroscopy and photography for size (exposed area in mm²), shape (convex or flat), presence of cicatrisation (scarring and/or symblepharon) and appearance of the overlying conjunctival vessels.

RESULTS

The palpebral lobes in the normal and EDE group were similar in terms of size (41.5±15.6 mm² vs 39±12.2 mm², p=0.203), convex shape (100%) and absence of cicatrisation or vascular engorgement (0%). However, as compared to normal controls, the size of the palpebral lobe was markedly reduced in the SS (27.9±12.3, p<0.0001) and CC (18.1±13.7, p<0.0001) groups. The size of the lobes was asymmetric in the CC group (p<0.0001) and differed significantly from the SS group (p=0.0003). Flat contour (79% vs 50%, p=0.0028), subepithelial scarring with or without symblepharon (52% vs 13%, p<0.0001) and engorged conjunctival vessels (96% vs 63%, p=0.00011) were seen in a significantly higher proportion of lobes in the CC as compared to the SS group.

CONCLUSION

The morphological features of the palpebral lobe of the main lacrimal gland are significantly distorted in aqueous deficient dry eyes due to CC and SS; however, the lobes in patients with EDE are similar to normal eyes.