Fat extrusion and septal reset in patients with the tear trough triad: a critical appraisal

Arcus marginalis release, fat extrusion, and septal reset were applied to 71 selected patients with a constellation of orbital deformities the authors term a "tear trough triad." Of the initial 71 patients, 59 had complete follow-up records. Evaluated by means of a proportional topographic scale, 95 percent of patients achieved significant improvement. Equally important, no incidence of middle lamella contracture occurred in the entire series. The authors conclude that the procedure is safe and effective in selected patients.     

Human tear lipocalin

Human tear prealbumin, now called tear lipocalin, was originally described as a major protein of human tear fluid, which was thought to be tear specific. However, recent investigations demonstrated that it is identical with lingual von Ebner's gland protein, and is also produced in prostate, nasal mucosa and tracheal mucosa. Homologous proteins have been found in rat, pig and probably dog and horse. Tear lipocalin is an unusual lipocalin member, because of its high promiscuity for relative insoluble lipids and binding characteristics that differ from other members. In addition, it shows inhibitory activity on cysteine proteinases similar to cystatins, a feature unique among lipocalins. Although it acts as the principal lipid binding protein in tear fluid, a more general physiological function has to be proposed due to its wide distribution and properties. It would be ideally suited for scavenging of lipophilic, potentially harmful substances and thus might act as a general protection factor of epithelia.     

The crocodile tear syndrome.

Gusto-lacrimation, or "crocodile tear syndrome," is a rare complication, with 95 cases reported in the literature. Two patients are presented here, one after a facial fracture which apparently extended into the temporal bone proximal to the optic ganglion, and one after a Bell's palsy. The mechanism appears to be a misdirection of regenerating gustatory fibers destined for the salivary glands, so that they become secretory fibers to the lacrimal gland and cause homolateral tearing while the patient is eating. A simple procedure, involving subtotal resection of the palpebral lobe of the involved lacrimal gland, proved to be an effective corrective measure in these cases. Although it was not done in these cases, it would perhaps be advisable to do a Schirmer's test to assist in determining the amount of gland to be removed.     

Dynamics of tear fluid desiccation on a glass surface: a contribution to tear quality assessment

Background

Fern-like crystalloids form when a microvolume of tear is allowed to dry out at ambient conditions on a glass surface. Presence of crystalloids in tear “microdesiccates” is used to evaluate patients with Dry-Eye disease. This study aims to examine morphologically the desiccation process of normal tear fluid and to identify changes associated with accelerated tear evaporation. Tear microdesiccates from healthy (Non-Dry Eye) and Dry Eye subjects were produced at ambient conditions. Microdesiccate formation was monitored continuously by dark-field video microscopy. Additionally, accelerated desiccation of tear samples from healthy subjects was conducted under controlled experimental conditions. Particular morphological domains of tear microdesiccates and their progressive appearance during desiccation were compared.

Results

In normal tear microdesiccates, four distinctive morphological domains (zones I, II, III and transition band) were recognized. Stepwise formation of those domains is now described. Experimentally accelerated desiccation resulted in marked changes in some of those zones, particularly involving either disappearance or size reduction of fern-like crystalloids of zones II and III. Tear microdesiccates from Dry Eye subjects may also display those differences and be the expression of a more synchronous formation of microdesiccate domains.

Conclusion

Morphological characteristics of tear microdesiccates can provide insights into the relative rate of tear evaporation.     

Interaction of ceramides and tear lipocalin

The distribution of lipids in tears is critical to their function. Lipids in human tears may retard evaporation by forming a surface barrier at the air interface. Lipids complexed with the major lipid binding protein in tears, tear lipocalin, reside in the bulk (aqueous) and may have functions unrelated to the surface. Many new lipids species have been revealed through recent mass spectrometric studies. Their association with lipid binding proteins has not been studied. Squalene, (O-acyl) omega-hydroxy fatty acids (OAHFA) and ceramides are examples. Even well-known lipids such as wax and cholesteryl esters are only presumed to be unbound because extracts of protein fractions of tears were devoid of these lipids. Our purpose was to determine by direct binding assays if the aforementioned lipids can bind tear lipocalin. Lipids were screened for ability to displace DAUDA from tear lipocalin in a fluorescence displacement assay. Di- and tri-glycerides, squalene, OAHFA, wax and cholesterol esters did not displace DAUDA from tear lipocalin. However, ceramides displaced DAUDA. Apparent dissociation constants for ceramide-tear lipocalin complexes using fluorescent analogs were measured consistently in the submicromolar range with 3 methods, linear spectral summation, high speed centrifugal precipitation and standard fluorescence assays. At the relatively small concentrations in tears, all ceramides were complexed to tear lipocalin. The lack of binding of di- and tri-glycerides, squalene, OAHFA, as well as wax and cholesterol esters to tear lipocalin is consonant with residence of these lipids near the air interface.     

Spectroscopic evaluation of human tear lipids

Infrared and fluorescence spectroscopies were applied to characterize the molecular conformational/structure and dynamics of human meibum (ML) and tear lipids (SSL). ML lipids contained more CC and CH3 moieties than SSL. SSL contained OH groups that were not apparent in the spectra of ML. The CO stretching band observed in the infrared spectra of SSL and ML revealed that the CO groups are not involved in hydrogen bonds. Bands due to the polar moieties CO and PO2- did not change significantly with increasing temperature, suggesting that they may not play an appreciable thermodynamic role in the lipid hydrocarbon chain phase transition. Components in tears bind to SSL and exclude water at the water-lipid boundary where the polar headgroups of phospholipids are located. If similar interactions occur in vivo at the tear film lipid-aqueous interface, they would reduce the rate of evaporation. The results provide a foundation for future studies to assess possible differences with age and sex in tears from normal and dry eye subjects.     

Nonlinear theory of tear film rupture

Nonlinear thin film rupture has been analyzed by investigating the stability of tear films to finite amplitude disturbances. The dynamics of the liquid film is formulated using the Navier-Stokes equations, including a body force term due to van der Waals attractions. The governing equation was solved by the finite difference method as part of an initial value problem for spatial periodic boundary conditions. The rupture of the tear film covering the cornea and the formation of dry spots is an important phenomenon in various pathological states associated with a dry eye.     

Identification of hemopexin in tear film

Human tear fluid is a complex mixture of aqueous lipids, proteins, enzymes, and other biochemical and cellular elements. By conventional comparative proteomic approaches, we investigated the proteome in human tear fluid and compared the tear protein profile of normal control subjects with that of patients suffering from the ocular inflammatory disease vernal keratoconjunctivitis (VKC). Collected tear samples were directed to two-dimensional polyacrylamide gel electrophoresis protein separation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry peptide identification. Six differentially expressed proteins—interleukin 4, phospholipase A2, albumin, lactoferrin, hemopexin, and lipocalin—were displayed. Hemopexin had not been reported previously in tear film. Enzyme-linked immunosorbent assay confirmed that hemopexin concentrations were significantly higher in VKC tear samples and increased with disease stages. The results implied clinical interest of hemopexin in the tear proteome and eye diseases.     

Erythropoietin levels in human tear fluid

Erythropoietin level was evaluated in blood plasma and tear fluid of humans with normal functions of eye and normal blood characteristics. We examined 21 patients. Principle ability of erythropoietin level detection in patient's tear fluid ascertained.     

Diadenosine tetraphosphate contributes to carbachol-induced tear secretion

The purpose of this study is to investigate if the cholinergic stimulation by carbachol on tear secretion is a direct process or if it is also mediated by purinergic mechanisms. Experiments were performed in New Zealand male rabbits. The amount of tear secretion was measured with Schirmer’s test and then analyzed by a HPLC protocol in order to study the nucleotide levels. Animal eyes were instilled with carbachol (a cholinergic agonist), pirenzepine, gallamine and 4-DAMP (muscarinic antagonists), PPADS, suramin and reactive blue 2 (purinergic antagonists), and a P2Y₂ receptor small interfering RNA (siRNA). Tear secretion increased with the instillation of carbachol, approximately 84 % over control values 20 min after the instillation and so did Ap₄A and ATP release. When we applied carbachol in the presence of muscarinic antagonists, tear volume only increased to 4 % with atropine, 12 % in the case of pirenzepine, 3 % with gallamine, and 8 % with 4-DAMP. In the presence of carbachol and purinergic antagonists, tear secretion was increased to 12 % (all values compared to basal tear secretion). By analyzing tear secretion induced with carbachol in presence of a P2Y₂ receptor siRNA, we found that tear secretion was diminished to 60 %. The inhibition of tear secretion in the presence of carbachol and purinergic antagonists or P2Y₂ siRNA occurred with no apparent change in the tear amount of Ap₄A. These experiments demonstrated the participation of Ap₄A in lacrimal secretion process.     

Genetic polymorphism of human anodal tear protein

Electrophoresis of human tears on slab polyacrylamide gels showed five phenotypes among anodal tear proteins. These phenotypes are the expression of autosomal codominant alleles. Gene frequencies are as follows: for Caucasians, At ¹=0.99, At ³=0.01; for Negroes, At ¹=0.97, At ²=0.03; for Chinese, At ¹=0.98, and At ⁴ and At ⁵ are both approximately 0.008.This study was supported by a grant from the National Institutes of Dental Research (5-R01-DE-E-03658-10).     

Role of lactoferrin in the tear film

The surface of the eye provides an inert barrier against infection. Through its unique combination of antimicrobial action and anti-inflammatory activities lactoferrin (Lf) in the tear film plays an important role in the maintenance of ocular health. In order to maintain clarity the eye must provide immunological defense without immunopathology. Along with physical barriers, soluble plasma factors and other proteins such as lysozyme, Lf produced by the acinar cells of the lacrimal gland serves a number of roles in defense for this purpose. Lf in tears provides antimicrobial efficacy by binding free iron thus reducing the availability of iron necessary for microbial growth and survival as well as pathogenesis. Lf has been shown to inhibit biofilm formation and thus may play a role in protecting contact lens surfaces from colonization. Virus particles' entry into epithelial cells is inhibited by Lf while an excess of Lf in tear film is thought to limit the opportunistic Lf-mediated bridging of adenovirus and host cell that occurs in other tissues. Lf dampens the classical complement activation pathway by binding to markers of inflammation and immune activation while pathogen-associated molecular patterns such as lipopolysaccharide (LPS) are targeted by Lf for removal through tears and hydrodynamic flushing. This review focuses on the role of Lf in human tear film and its contribution to ocular health during contact lens wear.