Human Tears Research Articles

Decipher 'Em All: A Profiling Study on the Effects of Acyl Groups in O-Acyl-ω-hydroxy Fatty Acids.

The O-acyl-ω-hydroxy fatty acids (OAHFAs) are an intriguing class of surface-active lipids which can be found in the human tear film lipid layer (TFLL). Recent studies have suggested that OAHFAs exist in the polar lipid layer and play a central role in TFLL function. Surprisingly, biophysical profiling studies have only shed light on the properties of OAHFAs bearing an oleate acyl group and insights on species with other acyl groups are scarce. Herein, we seek to address this issue through (1) focusing on the synthesis and characterization of a representative library of OAHFA analogues bearing a palmitate, palmitoleate, stearate, and linoleate acyl group, and (2) performing an in-depth mapping of their biophysical properties. Our results indicate that NMR-spectroscopic techniques can be utilized for rough estimation of the amounts of distinct acyl groups in a sample and more importantly, how the subtle variations in both parent chains and acyl groups influence the core properties of the OAHFAs. We reach the conclusion that the correlation between melting points and film properties is not as clear-cut as previously thought. Nevertheless, grouping of OAHFA species into three separate categories which display distinct behavior seems to be possible utilizing the melting points as a guiding parameter. Altogether, our study suggests that the properties of OAHFAs need to be assessed from a viewpoint which combines both the parent chain and acyl group instead of independent analysis based on either fragment alone.

A chorismate mutase-targeted, core-shell nanoassembly-activated SERS immunoassay platform for rapid non-invasive detection of Acanthamoeba infection

Contact lens care and early diagnosis of Acanthamoeba keratitis (AK) are very important to prevent progression to blindness due to AK, which develops when Acanthamoeba attaches to contact lens-damaged corneas. Therefore, we propose a novel, non-invasive, immuno-surface-enhanced Raman scattering (SERS) sensing platform for rapid and accurate detection of Acanthamoeba infection in the tears and contact lens solutions of humans. This optic analysis method was based on the proven biological performance of chorismate mutase (CM)-specific monoclonal and polyclonal antibodies on trophozoite and cyst forms of Acanthamoeba castellanii, and its conditioned media. SERS-based, ultra-low concentration detection was achieved by the anisotropic fanblade-shaped core-shell nanoassembly (Ag@AuFNP) embedded with 4-fluorobenzenethiol Raman reporter. The immuno-SERS platform combining Ag@AuFNP and CM-specific antibody complexes was evaluated in vitro and in vivo. The non-invasive SERS-activated biosensing platform indicates strong feasibility for AK detection in human tears and contact lens solutions.

Association Between Dry Eye Disease with Anxiety and Depression Among Medical Sciences Students in Qassim Region: Cortisol Levels in Tears as a Stress Biomarker.

This study aimed to investigate the relationships between anxiety, depression, and ocular surface health. Cortisol levels were detected in human tears, and their relationship with anxiety levels was determined using a validated questionnaire. In total, 112 participants were recruited for this study. All participants were healthy medical students at the Qassim University. Each participant signed an informed consent form after receiving detailed information about the study. Visual acuity examination, TBUT, Shirmer1 test were performed. Participants were asked to fill out three questionnaires: Taylor Manifest Anxiety Scale, Beck Depression Inventory, and The Ocular Surface Disease Index. Tear samples were extracted from the Schirmer strips and cortisol level was measured using ELISA kits. A total of 112 college students were included in the study, 58.9% of whom were females. The mean age was 21.9 ± 1.7 years. Subjective reported symptoms of anxiety levels were significantly correlated with depression scores, the OSDI, and reduced Schirmer test measurements. Moreover, cortisol levels detected in tears were positively associated with higher anxiety scores (r=0.328, P<0.05). Ocular surface health is associated with symptoms of anxiety and depression. The use of tears to measure cortisol levels could be an interesting way to serve as an anxiety biomarker.

Rapid tear screening of diabetic retinopathy by a detachable surface acoustic wave enabled immunosensor

BackgroundDiabetic retinopathy (DR), a chronic and progressive microvascular complication of diabetes mellitus, substantially threatens vision and is a leading cause of blindness among working-age individuals worldwide. Traditional diagnostic methods, such as ophthalmoscopy and fluorescein angiography are nonquantitative, invasive, and time consuming. Analysis of protein biomarkers in tear fluid offers noninvasive insights into ocular and systemic health, aiding in early DR detection. This study introduces a surface acoustic wave (SAW) microchip that rapidly enhances fluorescence in bead-based immunoassays for the sensitive and noninvasive DR detection from human tear samples. ResultsThe device facilitated particle mixing for immunoassay formation and particle concentration in the droplet, resulting in an enhanced immunofluorescence signal. This detachable SAW microchip allows the disposal of the cover glass after every use, thereby improving the reusability of the interdigital transducer and minimizing potential cross-contamination. A preliminary clinical test was conducted on a cohort of 10 volunteers, including DR patients and healthy individuals. The results demonstrated strong agreement with ELISA studies, validating the high accuracy rate of the SAW microchip. SignificanceThis comprehensive study offers significant insights into the potential application of a novel SAW microchip for the early detection of DR in individuals with diabetes. By utilizing protein biomarkers found in tear fluid, the device facilitates noninvasive, rapid, and sensitive detection, potentially revolutionizing DR diagnostics and improving patient outcomes through timely intervention and management of this vision-threatening condition.

Succinimide-Functionalized Reduced Graphene Oxide Nanosheets: A High-throughput Resistive Sensing Platform for Age-Related Macular Degeneration Biomarker Determination Using Human Tears.

Age-related macular degeneration (AMD) is a well-recognized affliction among the elderly, causing vision impairment ranging from blurred vision to complete blindness. This underscores the critical need for accurate, precise, and early detection methods. Herein, we developed a noninvasive, label-free electrical biosensor, constructed on an economical printed circuit board (PCB) substrate, designed specifically for the precise quantification of AMD biomarker: complement component III (C3). The hydrothermally reduced graphene oxide (rGO) was deposited between gold-interdigitated microelectrodes, forming a conductive channel. The fabricated C3 biosensor exhibits a low detection limit of 0.4342 ng/mL and an impressive sensitivity of 9.238 ((ΔR/R)/ng.mL-1)/cm2 with a regression coefficient of 0.9815 calibrated within the clinical C3 range of 10-30 ng/mL. This excellent performance is ascribed to the synergistic effects of 1-pyrenebutanoic acid succinimidyl ester (PBASE) linker and conducting properties of rGO as they generate large active sites for higher anti-C3 antibody immobilization, thereby enhancing sensitivity and specificity. Furthermore, the performance of this proposed C3 sensor chip was validated with enzyme-linked immunosorbent assay (ELISA) using five human tear samples exhibiting an outstanding correlation of a regression value of 0.9774. The unparalleled merits of this newly crafted C3 biosensor transcend those of preceding platforms, boasting superior accuracy and precision in quantifying C3 levels in human tears, accelerated operational speed with results attainable within a mere 15 min, cost-effectiveness, and excellent sensitivity.

Highly Efficient Dopamine Sensing with Carbon Nanotube Encapsulated Metal Chalcogenide Nanostructure

Carbon nanotube encapsulated nickel selenide composite nanostructures were used as a non-enzymatic electrochemical sensor for dopamine detection. These composite nanostructures were synthesized through a simple, one-step, and environmentally friendly chemical vapor deposition method, wherein the CNTs were formed in situ from pyrolysis of carbon-rich metallo-organic precursor. The composition and morphology of these NiSe2 filled hybrid nanostructures were confirmed by powder X-ray diffraction, Raman, XPS, and HRTEM images. Electrochemical tests demonstrated that the as-synthesized nanostructures exhibited outstanding electrocatalytic performance toward dopamine oxidation, with a high sensitivity of 19.62 μA μM−1 cm−2, low detection limit, broad linear range of (5 nM – 640 μM), and high selectivity. The synergistic effects of enhanced electrochemical activity of nickel selenide along with enhanced conductivity of carbon nanotubes leads to the high efficiency for these nanostructured composites. The high sensitivity and selectivity of this nano-structured composite could be exploited to develop simple, selective, and sensitive electrochemical sensor to detect and quantify dopamine in human tear samples with high reliability. This nanotube encapsulated sensor hence paves the way for new discoveries in the development of novel dopamine sensors with low cost and high stability than can be used for non-invasive dopamine detection in peripheral fluids.

Paper-based Electrochemical Sensor Integrated with Gold Nanoparticle-Decorated Carbon Cloth as a Working Electrode for Nitric Oxide Detection in Artificial Tears.

Nitric oxide (NO) in human tears regulates numerous ocular surface processes, such as tear generation, corneal wound healing, conjunctival vascular tone, and so forth. Any deviation from its normal concentration is linked to various ocular syndromes, including microbial keratitis, conjunctivitis, pterygium, dry eye, retinitis, glaucoma, and so forth. Therefore, precise monitoring of NO in tears can be considered as a potential biomarker for ocular diseases. Here, we report a highly sensitive and selective electrochemical NO sensor using carbon ink-based electrodes. Counter, working (WE), and reference electrodes have been designed and painted on a butter paper by using carbon ink. To improve the sensing performance, the WE has been modified with a gold nanoparticle (Au NP)-deposited carbon cloth (CC). Such a paper-based sensor demonstrated high sensitivity of ∼0.34 μA μM-1 cm-2, ultralow detection limit of ∼2.35 nM, wide linear range of 10 nM-0.4 mM, and fast response time (0.35 s). The sensor also showed excellent stability and selectivity toward the interfering agents in human body fluids. Such a low-cost, flexible paper-based sensor was employed for the detection of NO in artificial tears.

Tear Fluid as a Matrix for Biomonitoring Environmental and Chemical Exposures.

Exposures to hazardous chemicals have been linked to many detrimental health effects and it is therefore critical to have effective biomonitoring methods to better evaluate key environmental exposures that increase the risk of chronic disease and death. Traditional biomonitoring utilizing blood and urine is limited due to the specialized skills and invasiveness of collecting these fluid samples. This systematic review focuses on tear fluid, which is largely under-researched, as a promising complementary matrix to the traditional fluids used for biomonitoring. The objective is to evaluate the practicability of using human tear fluid for biomonitoring environmental exposures, highlighting potential pitfalls and opportunities. Tear fluid biomonitoring represents a promising method for assessing exposures because it can be collected with minimal invasiveness and tears contain exposure markers from both the external and internal environments. Tear fluid uniquely interfaces with the external environment at the air-tear interface, providing a surface for airborne chemicals to diffuse into the ocular environment and interact with biomolecules. Tear fluid also contains molecules from the internal environment that have travelled from the blood to tears by crossing the blood-tear barrier. This review demonstrates that tear fluid can be used to identify hazardous chemicals from the external environment and differentiate exposure groups.

Exploring tear viscosity with quartz crystal microbalance technology.

Tear viscosity is a critical property affecting tear distribution and ocular surface stability. While not widely established as a primary diagnostic marker, deviations from normal viscosity can impact ocular health, potentially contributing to conditions such as dry eye syndrome. Despite their importance, traditional viscometers require sample volumes that are not feasible to use with tear volume. This research introduces a novel Quartz Crystal Microbalance (QCM)-based method for tear viscosity measurement, offering a viscometer prototype that operates with minimal sample volumes. Human tear samples, solutions used in artificial eye drops, and various commercial eye drop brands were evaluated. Results show that the QCM method aligns with established viscosity ranges. The average viscosity of healthy human tears was found to be 1.73 ± 0.61 cP, aligning with the typical range of 1-10 cP. Variability in the viscositiesof eye drop can be attributed to differences in their chemical compositions. The QCM method offers benefits such as reduced sample consumption and rapid results, enhancing understanding of tear dynamics for ocular health. Further research with larger sample sizes is needed to establish normative viscosity values in healthy individuals and those with dry eye syndrome, which is crucial for validating the device's clinical efficacy.

Molybdenum Disulfide-Assisted Spontaneous Formation of Multistacked Gold Nanoparticles for Deep Learning-Integrated Surface-Enhanced Raman Scattering.

Several fabrication methods have been developed for label-free detection in various fields. However, fabricating high-density and highly ordered nanoscale architectures by using soluble processes remains a challenge. Herein, we report a biosensing platform that integrates deep learning with surface-enhanced Raman scattering (SERS), featuring large-area, close-packed three-dimensional (3D) architectures of molybdenum disulfide (MoS2)-assisted gold nanoparticles (AuNPs) for the on-site screening of coronavirus disease (COVID-19) using human tears. Some AuNPs are spontaneously synthesized without a reducing agent because the electrons induced on the semiconductor surface reduce gold ions when the Fermi level of MoS2 and the gold electrolyte reach equilibrium. With the addition of polyvinylpyrrolidone, a two-dimensional large-area MoS2 layer assisted in the formation of close-packed 3D multistacked AuNP structures, resembling electroless plating. This platform, with a convolutional neural network-based deep learning model, achieved outstanding SERS performance at subterascale levels despite the microlevel irradiation power and millisecond-level acquisition time and accurately assessed susceptibility to COVID-19. These results suggest that our platform has the potential for rapid, low-damage, and high-throughput label-free detection of exceedingly low analyte concentrations.

Light‐Processed 3D Bioprinting of Symblepharon Rings Fortified with l‐Ascorbic Acid for Ocular Tissue Engineering

AbstractThis study aims to develop gelatin methacryloyl (GelMA)‐based symblepharon rings fortified with l‐ascorbic acid (lAA), aiming for controlled release of vitamins for the treatment of the ocular surface, corneal healing, and acceleration of epithelial growth, while concurrently preventing potential inflammation. The human tears contain abundant IAA, which serves a protective role for ocular tissues. The utilization of 3D printing digital light processing technology not only navigating the manufacturing process of symblepharon rings, addressing challenges related to commercial production and expedited delivery to patients but also imparts enhanced flexibility compared to commercial products. This innovative approach also facilitates the production of rings that exhibit superior softness and are amenable to mechanical movements for ocular tissue engineering. The morphological, chemical, rheological, biological, thermal, and drug‐release characteristics of 3D‐printed lAA‐loaded symblepharon rings are investigated. In the morphological characterization, it is observed that the rings exhibit a porous structure. In biocompatibility tests, Gelas and Gelas‐low rings achieve over 75% viability. Following the cell test, scanning electron microscope images reveal fibroblasts adhering to Gelas and Gelas‐low rings, spreading across their surfaces. Drug release studies conducted in phosphate‐buffered saline at pH 7.4 reveal the complete release of lAA from Gelas‐low within a 5‐d incubation period.

An artificial intelligence-assisted microfluidic colorimetric wearable sensor system for monitoring of key tear biomarkers

The precise, simultaneous, and rapid detection of essential biomarkers in human tears is imperative for monitoring both ocular and systemic health. The utilization of a wearable colorimetric biochemical sensor exhibits potential in achieving swift and concurrent detection of pivotal biomarkers in tears. Nevertheless, challenges arise in the collection, interpretation, and sharing of data from the colorimetric sensor, thereby restricting the practical implementation of this technology. To overcome these challenges, this research introduces an artificial intelligence-assisted wearable microfluidic colorimetric sensor system (AI-WMCS) for rapid, non-invasive, and simultaneous detection of key biomarkers in human tears, including vitamin C, H+(pH), Ca2+, and proteins. The sensor consists of a flexible microfluidic epidermal patch that collects tears and facilitates the colorimetric reaction, and a deep-learning neural network-based cloud server data analysis system (CSDAS) embedded in a smartphone enabling color data acquisition, interpretation, auto-correction, and display. To enhance accuracy, a well-trained multichannel convolutional recurrent neural network (CNN-GRU) corrects errors in the interpreted concentration data caused by varying pH and color temperature in different measurements. The test set determination coefficients (R2) of 1D-CNN-GRU for predicting pH and 3D-CNN-GRU for predicting the other three biomarkers were as high as 0.998 and 0.994, respectively. This correction significantly improves the accuracy of the predicted concentration, enabling accurate, simultaneous, and quick detection of four critical tear biomarkers using only minute amounts of tears ( ~ 20 μL). This research demonstrates the powerful integration of a flexible microfluidic colorimetric biosensor and deep-learning algorithm, which holds immense potential to revolutionize the fields of health monitoring.

An LC-MS/MS method for the determination of Lifitegrast in human plasma and tear and its application in the pharmacokinetic study.

Aim: A new, selective and simple UPLC-MS/MS method was developed and validated for the determination of lifitegrast in human plasma and tear in order to obtain PK data. Materials & methods: Lifitegrast-d4 solutions were added in the samples, and then were extracted and transferred to a UPLC vial. Results: The respective working ranges were 25.00-2000.00pg/ml in plasma and 4.00-1000.00μg/ml in tear. The fully validated method complied with existing regulatory criteria for accuracy and precision, recovery, etc. It was applied to plasma and tear samples, which were from a clinical study, successfully. Conclusion: This method is useful in the evaluation of lifitegrast in plasma and tear.

Physical properties of soft contact lens multipurpose solutions commercially available in Ghana

PurposeTo investigate the physical properties of commercially available multipurpose soft contact lens solutions in Ghana. MethodspH (Kelilong ICL-099 pH meter, China), osmolality (OSMOMAT 3000, GONOTEC, Germany), surface tension (Sigma 700 Tensiometer, Sweden), and viscosity (CFOC-200 Viscometer, Cannon Company, USA) of various soft contact lens multipurpose solutions (MPS) were measured in triplicates at room temperature. Viscosity measurements were also taken at 34 °C ocular surface temperature. The solutions examined were Opti-Free Replenish (OFR), Trufresh (TF), Avizor (AV), Freshlook (FL), and Refresh (RF). ResultsSeveral solutions were largely hypo-osmotic in the range of 108–231 mOsm/kg, the exception being Avizor, which had osmolality values that were closer to human tears (301 ± 0.58 mOsm/kg). The range of pH values of the solutions (6.33–8.24, mean (SD) = 7.53 ± 0.18) fell within the reported tolerable range for the ocular surface (6.20–9.00). Surface tension values ranged from 35.86 to 42.27 mNm with a mean of 38.49 ± 2.32 mNm. The average viscosity of most solutions at room temperature (25 °C) was 1.44 ± 0.49 cP with a range of 1.04–2.15 cP. Significantly lower values ranging from 0.79 to 1.58 cP were obtained at ocular surface temperature (34 °C), p = 0.0001). ConclusionsThe physical properties of many of the solutions used as MPS in Ghana are markedly variable. Nevertheless, pH, surface tension, and viscosity fall within the acceptable limits of ocular physiological tolerance; except for osmolality, which majority were outside the reported tolerable range for the ocular surface. This information may partly explain the reason some patients exhibit strong preferences for certain care systems and should aid clinical decision-making when prescribing eye care systems to patients.

What’s the situation with ocular inflammation? A cross-seasonal investigation of proteomic changes in ocular allergy sufferers’ tears in Victoria, Australia

BackgroundOcular allergy (OA) is a localized subset of allergy characterized by ocular surface itchiness, redness and inflammation. Inflammation and eye-rubbing, due to allergy-associated itch, are common in OA sufferers and may trigger changes to the ocular surface biochemistry. The primary aim of this study is to assess the differences in the human tear proteome between OA sufferers and Healthy Controls (HCs) across peak allergy season and off-peak season in Victoria, Australia.Methods19 participants (14 OA sufferers, 5 HCs) aged 18–45 were recruited for this study. Participants were grouped based on allergy symptom assessment questionnaire scoring. Proteins were extracted from human tear samples and were run on an Orbitrap Mass Spectrometer. Peaks were matched to a DIA library. Data was analyzed using the software MaxQuant, Perseus and IBM SPSS.Results1267 proteins were identified in tear samples of OA sufferers and HCs. 23 proteins were differentially expressed between peak allergy season OA suffers vs HCs, and 21 were differentially expressed in off-peak season. Decreased proteins in OA sufferers related to cell structure regulation, inflammatory regulation and antimicrobial regulation. In both seasons, OA sufferers were shown to have increased expression of proteins relating to inflammation, immune responses and cellular development.ConclusionTear protein identification showed dysregulation of proteins involved in inflammation, immunity and cellular structures. Proteins relating to cellular structure may suggest a possible link between OA-associated itch and the subsequent ocular surface damage via eye-rubbing, while inflammatory and immune protein changes highlight potential diagnostic and therapeutic biomarkers of OA.

Nanosurgical and Bioengineering Treatment of Human Anterior Cruciate Ligament Tears with Ultrasound-Guided Injection of Modified Platelet-Rich Plasma Using Human Cell Memory Based on Clinical, Ultrasound, MRI, and Nanoscope Analyses: A Double-Blind Randomized Trial.

Background: Anterior cruciate ligament (ACL) tears account for 40% to 50% of all ligamentous knee injuries. Most patients with ACL ruptures undergo surgical treatment. There is currently no objective, well-documented, repeatable, and standardized nonsurgical method for ACL tear treatment. This study aimed to investigate ACL outcomes in patients who underwent a novel nanosurgery and bioengineering treatment (NSBT) for an ACL tear. Methods: This was a double-blind randomized trial including 44 patients with a history of traumatic knee injury and a confirmed ACL tear. The final sample comprised 40 patients who met all the eligibility criteria. The patients were divided into two groups: the treatment group (n = 30) and the control group (n = 10). The treatment group underwent nanosurgery with an ultrasound-guided injection of modified platelet-rich plasma (PRP) using human cell memory (RP-hCM). The control group was treated with an ultrasound-guided PRP injection into the joint capsule. At baseline and post-treatment, all patients underwent both ultrasonography and magnetic resonance imaging (MRI), and the following clinical variables were assessed: the WOMAC score, the Lysholm knee score, the visual analog scale score, and knee instability. In most patients, the clinical outcome was verified using nanoscopy. Results: The median WOMAC, VAS, and LKS scores, as well as knee instability, improved significantly 12 weeks after the procedure in the treatment group (p < 0.001). We found a significantly larger improvement in the assessed parameters in the treatment group compared to the control group (p < 0.001). In the treatment group, all the patients had good and very good clinical outcomes, while 90% of the patients had a normal ACL signal in a follow-up MRI scan. In the control group, a physical examination revealed no changes in knee stability after treatment. Conclusions: This study showed that there is a significant difference in patient experience and the duration of recovery for patients with ACL tears treated with NSBT. The novel nonsurgical method was shown to be repeatable, objective, well documented, standardized, and highly effective.

Framework Nucleic Acids Combined with 3D Hybridization Chain Reaction Amplifiers for Monitoring Multiple Human Tear Cytokines.

Existing tear sensors are difficult to perform multiplexed assays due to the minute amounts of biomolecules in tears and the tiny volume of tears. Herein, the authors leverage DNA tetrahedral frameworks (DTFs) modified on the wireless portable electrodes to effectively capture 3D hybridization chain reaction (HCR) amplifiers for automatic and sensitive monitoring of multiple cytokines in human tears. The developed sensors allow the sensitive determination of various dry eye syndrome (DES)-associated cytokines in human tears with the limit of detection down to 0.1 pgmL-1, consuming as little as 3 mL of tear fluid. Double-blind testing of clinical DES samples using the developed sensor and commercial ELISA shows no significant difference between them. Compared with single-biomarker diagnosis, the diagnostic accuracy of this sensor based on multiple biomarkers has improved by ≈16%. The developed system offers the potential for tear sensors to enable personalized and accurate diagnosis of various ocular diseases.

The Plight of the Metabolite: Oxidative Stress and Tear Film Destabilisation Evident in Ocular Allergy Sufferers across Seasons in Victoria, Australia.

Ocular allergy (OA) is characterised by ocular surface itchiness, redness, and inflammation in response to allergen exposure. The primary aim of this study was to assess differences in the human tear metabolome and lipidome between OA and healthy controls (HCs) across peak allergy (spring-summer) and off-peak (autumn-winter) seasons in Victoria, Australia. A total of 19 participants (14 OA, 5 HCs) aged 18-45 were recruited and grouped by allergy questionnaire score. Metabolites and lipids from tear samples were analysed using mass spectrometry. Data were analysed using TraceFinder and Metaboanalyst. Metabolomics analysis showed 12 differentially expressed (DE) metabolites between those with OA and the HCs during the peak allergy season, and 24 DE metabolites were found in the off-peak season. The expression of niacinamide was upregulated in OA sufferers vs. HCs across both seasons (p ≤ 0.05). A total of 6 DE lipids were DE between those with OA and the HCs during the peak season, and 24 were DE in the off-peak season. Dysregulated metabolites affected oxidative stress, inflammation, and homeostasis across seasons, suggesting a link between OA-associated itch and ocular surface damage via eye rubbing. Tear lipidome changes were minimal between but suggested tear film destabilisation and thinning. Such metabolipodome findings may pave new and exciting ways for effective diagnostics and therapeutics for OA sufferers in the future.

In vitro biomechanical properties of porcine perineal tissues to better understand human perineal tears during delivery.

Data concerning the mechanical properties of the perineum during delivery are very limited. Invivo experiments raise ethical issues. The aim of the study was to describe some of the biomechanical properties of each perineal tissue layer collected from sows in order to better understand perineal tears during childbirth. Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS), and the anal mucosa of fresh dead sows. They were tested in quasi-static uniaxial tension using the testing machine Mach-1®. Tests were performed at a displacement velocity of 0.1 mm·s-1. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled using a hyperelastic Yeoh model described by three coefficients: C1, C2, and C3. Pearson correlation coefficients were calculated to measure the correlation between the C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture for each perineal tissue layer. Pearson correlation was computed between C1 and the number of microfailures before complete rupture for each tissue. Ten samples of each perineal tissue layer were analyzed. Mean values of C1 and corresponding standard deviations were 46 ± 15, 165 ± 60, 27 ± 10, 19 ± 13, 145 ± 28 kPa for the perineal skin, the vagina, the EAS, the IAS, and the anal mucosa, respectively. According to this same sample order, the first microfailure in the population of 10 sows appeared at an average of 54%, 27%, 70%, 131%, and 22% of strain. A correlation was found between C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture (r = 0.7, p = 0.02) or the number of microfailures before complete rupture only for the vagina (r = 0.7, p = 0.02). In this population of fresh dead sow's perineum, the vagina and the anal mucosa were the stiffest tissues. The IAS and EAS were more extensible and less stiff. A significantly positive correlation was found between C1 and the duration between the first microfailure and the complete rupture of the vagina, and the duration between the first microfailure and the complete rupture of the vagina.

Usefulness of Schirmer's tear strips and borosilicate glass tubes in chemical analysis of human tear fluid: A practical check in VEGF detection.

Human tears contain a number of agents which may play an important role in diagnosing local eye disorders as well as systemic diseases. The small amount of fluid obtained during the collection and the consequent difficulty in analysing it are the main problems encountered in the diagnostic process. We decided to investigate the practical usefulness of two simple methods of collecting tear fluid for chemical analysis, i.e., glass tubes and Schirmer's strips. The substance analyzed was vascular endothelial growth factor (VEGF), a compound commonly recognized in ophthalmology. We used standard Schirmer's tear test and calibrated glass tubes for tear fluid collection in healthy volunteers. The standard ELISA assay was used to check the effectiveness of the tear sampling by estimating the VEGF level. The results of the study show that Schirmer's tear strip test is a more effective tool of the two. Moreover, using Schirmer's strips to obtain tear fluid was found to be more patient friendly and amounts of the tear fluid collected with that test were enough and better for the VEGF detection. Our study indicates that the widely used Schirmer tear test may be the best method of tear collection for chemical analysis. However, further studies on test calibration are needed.