Dynamic assessment of the tear film muco-aqueous and lipid layers using a novel tear film imager (TFI)

The Short-term Effects of Artificial Tears on the Tear Film Assessed by a Novel High-Resolution Tear Film Imager: A Pilot Study

PURPOSE

The purpose of this study was to investigate the effects of artificial tears (AT) on the sublayers of the tear film assessed by a novel tear film imaging (TFI) device.

METHODS

The mucoaqueous layer thickness (MALT) and lipid layer thickness (LLT) of 198 images from 11 healthy participants, 9 of whom had meibomian gland disease, were prospectively measured before and after exposure to 3 different AT preparations (Refresh Plus; Retaine [RTA]; Systane Complete PF [SYS]), using a novel nanometer resolution TFI device (AdOM, Israel). Participants were assessed at baseline and at 1, 5, 10, 30, and 60 minutes after instilling 1 drop of AT during 3 sessions on separate days. Repeated-measures analysis of variances were used for comparisons with P < 0.05 considered significant.

RESULTS

For all ATs, the mean MALT was greatest 1 minute after drop instillation, with an increase of 67%, 55%, and 11% above the baseline for SYS, Refresh Plus, and RTA, respectively. The SYS formulation demonstrated the highest percentage increases in mean MALT and LLT at most postdrop time points. The MALT differences were significantly higher in the SYS than in the RTA ( P = 0.014). After 60 minutes, no AT group demonstrated statistically significant changes in MALT or LLT compared with baseline.

CONCLUSIONS

We report, for the first time, the effects of AT on MALT and LLT using a high-resolution TFI. A substantial acute mean MALT increase occurs 1 minute after AT instillation with all agents tested, but there were clear differences in response and durability, suggesting the benefits of choosing specific AT according to the needs of each patient.

Contact lens fitting and changes in the tear film dynamics: mathematical and computational models review

PURPOSE

This review explores mathematical models, blinking characterization, and non-invasive techniques to enhance understanding and refine clinical interventions for ocular conditions, particularly for contact lens wear.

METHODS

The review evaluates mathematical models in tear film dynamics and their limitations, discusses contact lens wear models, and highlights computational mechanical models. It also explores computational techniques, customization of models based on individual blinking dynamics, and non-invasive diagnostic tools like high-speed cameras and advanced imaging technologies.

RESULTS

Mathematical models provide insights into tear film dynamics but face challenges due to simplifications. Contact lens wear models reveal complex ocular physiology and design aspects, aiding in lens development. Computational mechanical models explore eye biomechanics, often integrating tear film dynamics into a Multiphysics framework. While different computational techniques have their advantages and disadvantages, non-invasive tools like OCT and thermal imaging play a crucial role in customizing these Multiphysics models, particularly for contact lens wearers.

CONCLUSION

Recent advancements in mathematical modeling and non-invasive tools have revolutionized ocular health research, enabling personalized approaches. The review underscores the importance of interdisciplinary exploration in the Multiphysics approach involving tear film dynamics and biomechanics for contact lens wearers, promoting advancements in eye care and broader ocular health research.

Immune-Mediated Ocular Surface Disease in Diabetes Mellitus-Clinical Perspectives and Treatment: A Narrative Review

Diabetes mellitus (DM) is a chronic metabolic disorder marked by hyperglycemia due to defects in insulin secretion, action, or both, with a global prevalence that has tripled in recent decades. This condition poses significant public health challenges, affecting individuals, healthcare systems, and economies worldwide. Among its numerous complications, ocular surface disease (OSD) is a significant concern, yet understanding its pathophysiology, diagnosis, and management remains challenging. This review aims to explore the epidemiology, pathophysiology, clinical manifestations, diagnostic approaches, and management strategies of diabetes-related OSD. The ocular surface, including the cornea, conjunctiva, and associated structures, is vital for maintaining eye health, with the lacrimal functional unit (LFU) playing a crucial role in tear film regulation. In DM, changes in glycosaminoglycan metabolism, collagen synthesis, oxygen consumption, and LFU dysfunction contribute to ocular complications. Persistent hyperglycemia leads to the expression of cytokines, chemokines, and cell adhesion molecules, resulting in neuropathy, tear film abnormalities, and epithelial lesions. Recent advances in molecular research and therapeutic modalities, such as gene and stem cell therapies, show promise for managing diabetic ocular complications. Future research should focus on pathogenetically oriented therapies for diabetic neuropathy and keratopathy, transitioning from animal models to clinical trials to improve patient outcomes.

Assessing the safety of new germicidal far-UVC technologies

The COVID-19 pandemic underscored the crucial importance of enhanced indoor air quality control measures to mitigate the spread of respiratory pathogens. Far-UVC is a type of germicidal ultraviolet technology, with wavelengths between 200 and 235 nm, that has emerged as a highly promising approach for indoor air disinfection. Due to its enhanced safety compared to conventional 254 nm upper-room germicidal systems, far-UVC allows for whole-room direct exposure of occupied spaces, potentially offering greater efficacy, since the total room air is constantly treated. While current evidence supports using far-UVC systems within existing guidelines, understanding the upper safety limit is critical to maximizing its effectiveness, particularly for the acute phase of a pandemic or epidemic when greater protection may be needed. This review article summarizes the substantial present knowledge on far-UVC safety regarding skin and eye exposure and highlights research priorities to discern the maximum exposure levels that avoid adverse effects. We advocate for comprehensive safety studies that explore potential mechanisms of harm, generate action spectra for crucial biological effects and conduct high-dose, long-term exposure trials. Such rigorous scientific investigation will be key to determining safe and effective levels for far-UVC deployment in indoor environments, contributing significantly to future pandemic preparedness and response.

Examining Tear Film Dynamics Using the Novel Tear Film Imager

PURPOSE

The purpose of this study was to examine Tear Film Imager (TFI, AdOM, Israel) generated parameters across controls and dry eye (DE) subgroups and examine the changes in TFI parameters with contact lens (CL) placement.

METHODS

The retrospective study (n = 48) was conducted at the Miami Veterans Hospital. Symptoms were assessed through validated questionnaires and signs of tear function by tear break-up time and Schirmer scores. Participants were grouped as 1) healthy, 2) evaporative, 3) aqueous deficient, and 4) mixed DE based on tear function. Seventeen individuals had a baseline scan and a repeat scan following CL placement. Descriptives were compared across groups and over time.

RESULTS

The median age was 27 years, 74% self-identified as White, 45% as male, and 51% as Hispanic. Subjects in the aqueous deficiency category had lower muco-aqueous layer thickness (MALT) (2672 vs. 3084 nm) but higher lipid layer thickness (47.5 vs. 38.3 nm), lipid break-up time (4.4 vs. 2 seconds), and interblink interval (13.9 vs. 5.4 seconds) compared with the evaporative group. Subjects in the evaporative group had the highest MALT values (3084 vs. 2988, 2672, 3053 nm) compared with healthy, aqueous-deficient, and mixed groups. Symptoms were not significantly correlated with TFI parameters. CL placement significantly decreased MALT values (2869 → 2175 nm, P = 0.001).

CONCLUSIONS

The TFI provides unique information regarding the dynamic function of the tear film not captured by clinical examination. TFI generated metrics demonstrate a thinner aqueous layer in individuals with aqueous deficiency but highlight a thicker aqueous layer in those with evaporative DE.

A comparative review of evaporative dry eye disease and meibomian gland dysfunction in dogs and humans

Dry eye disease is a complex ophthalmic disorder that consists of two main subtypes, aqueous deficient dry eye (ADDE) and evaporative dry eye disease (EDED). Due to the complex underlying physiology, human dry eye disease can be difficult to model in laboratory animal species. Thus, the identification and characterization of a spontaneous large animal model of dry eye disease is desirable. Dogs have been described as an ideal spontaneous model of ADDE due to the similar pathophysiology between dogs and humans. Recently, EDED and meibomian gland dysfunction (MGD) have been increasingly recognized and reported in dogs. These reports on EDED and MGD in dogs have identified similarities in pathophysiology, clinical presentations, and diagnostic parameters to humans with the comparable disorders. Additionally, the tests that are used to diagnose EDED and MGD in humans are more easily applicable to dogs than to laboratory species due to the comparable globe sizes between dogs and humans. The reported response of dogs to EDED and MGD therapies are similar to humans, suggesting that they would be a valuable preclinical model for the development of additional therapeutics. Further research and clinical awareness of EDED and MGD in dogs would increase their ability to be utilized as a preclinical model, improving the positive predictive value of therapeutics for EDED and MGD in both humans and dogs.

Characterization of the thickness of the Tear Film Lipid Layer in Meibomian Gland Dysfunction using high resolution optical microscopy

PURPOSE

To evaluate the thickness of the tear film lipid layer (TFLL) in meibomian gland dysfunction (MGD) using a high-resolution optical microscope.

METHODS

The Ocular Surface Disease Index (OSDI) and meibum grade score (MGS) were used to classify 190 subjects into four groups: normal (OSDI<13 and MGS<10), mixed (OSDI≥13 and MGS<10), asymptomatic MGD (OSDI<13 and MGS≥10), and MGD (OSDI≥13 and MGS≥10). The high-resolution optical microscope was used to capture TFLL images in vivo. The histograms of TFLL thickness were analyzed and curve-fitted using probability density functions (PDFs).

RESULTS

There were three obvious peaks in the distributions of TFLL across the groups. From the curve-fitting process, the main outcomes are displayed according to each Gaussian function with the position of peak (μ) and the summed percentage within the range of standard deviation (σ). The normal group had distribution as follows: 33.3 ± 0.005 nm, 26%; 53.9 ± 0.019 nm, 40%; 79.4 ± 0.064 nm, 12%. The mixed group had a distribution as follows: 33.8 ± 0.004 nm, 32%; 53.1 ± 0.115 nm, 21%; 71.7 ± 0.232 nm, 27%. The asymptomatic MGD group had a distribution as follows: 33.5 ± 0.004 nm, 20%; 49.2 ± 0.041 nm, 25%; 62.9 ± 0.063 nm, 47%. The MGD group had a distribution as follows: 34.3 ± 0.004 nm, 34%; 53.7 ± 0.022 nm, 28%; 74.9 ± 0.060 nm, 16%.

CONCLUSIONS

The MGD and mixed groups had the largest percentages of TFLL thicknesses fall within the thinnest modes (peak 34.3 and 33.8 nm, respectively). These data show that measures of central tendency (e.g., averages, medians) do not fully appreciate the variable distributions of TFLL across disease spectra.

Human precorneal tear film and lipid layer dynamics in meibomian gland dysfunction

PURPOSE

To evaluate the precorneal tear film (PCTF) and lipid layer (TFLL) thicknesses and thinning rates in meibomian gland dysfunction (MGD) using a combined ultra-high-resolution optical coherence tomography (OCT) and thickness dependent fringe (TDF) interferometry system.

METHODS

Based on the Tear Film and Ocular Surface Society (TFOS) International Workshop on Meibomian Gland Dysfunction diagnostic algorithm, the Ocular Surface Disease Index (OSDI) and meibum grade score (MGS) were used to classify subjects into four groups: Normal (OSDI<13 and MGS<10), MGD (OSDI≥13 and MGS≥10), Asymptomatic MGD (OSDI<13 and MGS≥10), and Mixed (OSDI≥13 and MGS<10). The OCT/TDF system was used to capture PCTF and TFLL thicknesses and thinning rates. Kruskal-Wallis was used to compare median PCTF and TFLL thicknesses and thinning rates.

RESULTS

There were 190 subjects categorized into four groups: Normal (n = 63), MGD (n = 51), Asymptomatic MGD (n = 29), and Mixed (n = 47). The PCTF was significantly thinner in the Mixed group (3.3 [1.2]) than in the Normal (p < 0.001), MGD (p < 0.001) and Asymptomatic MGD (p = 0.009) groups. Relative to the Normal (4.5 [4.5] μm/min) and Mixed (5.0 [2.0] μm/min) groups, the rate of PCTF thinning was faster in the MGD (8.1 [3.0] μm/min, both p < 0.001) and Asymptomatic MGD (6.9 [3.1] μm/min, p = 0.009 and p = 0.04, respectively) groups. The correlation between PCTF thinning rate and TFLL thickness was ρ = -0.46, p < 0.001.

CONCLUSIONS

Symptomatic and asymptomatic MGD shows rapid PCTF thinning rates (evaporation), while the PCTF thickness was reduced in mixed disease. Thicker lipid layers were associated with slower PCTF thinning.

The Association between Tear Film Thickness as Measured with OCT and Symptoms and Signs of Dry Eye Disease: A Pooled Analysis of 6 Clinical Trials

Purpose: To determine the association between tear film thickness (TFT) as measured with ultra-high resolution optical coherence tomography (UHR-OCT) and signs and symptoms of dry eye disease (DED). Methods: A total of 450 eyes from 225 patients with DED from six different randomized clinical trials were included in this pooled analysis. In all subjects, TFT was measured with a custom-built UHR-OCT system. Symptoms of DED were quantified using a standardized Ocular Surface Disease Index (OSD)I questionnaire and clinical signs including tear film break up time (TFBUT) and Schirmer I test were assessed. Associations of the average TFT with OSDI, TFBUT, and Schirmer I test were calculated using a linear regression analysis. Results: The average TFT of the included sample (mean age, 45.0 ± 13.3 years; 65% female) was 4.2 ± 0.5 µm and the OSDI 36.2 ± 10.4. A significant negative correlation was found between TFT and OSDI (r = −0.36 to −0.31; p < 0.001). Tear break up time and Schirmer I test were not correlated with OSDI. Significant albeit weak correlations were found between TFT and TFBUT (r = 0.17 to 0.25; p < 0.01) as well as Schirmer I (r = 0.36 to 0.37; p < 0.001). Subgroup analysis revealed that the correlation was stronger in the subjects with abnormal Schirmer I (<15 mm; r = 0.50 to 0.54; p < 0.001). Conclusions: The present study demonstrates an objective measurement of TFT using a novel OCT approach for DED that correlates with symptoms and signs of DED. Our data are consistent with the idea that TFT represents the aqueous-deficient component of DED.

Novel Approaches for Imaging-Based Diagnosis of Ocular Surface Disease

Imaging has become indispensable in the diagnosis and management of diseases in the posterior part of the eye. In recent years, imaging techniques for the anterior segment are also gaining importance and are nowadays routinely used in clinical practice. Ocular surface disease is often synonymous with dry eye disease, but also refers to other conditions of the ocular surface, such as Meibomian gland dysfunction or keratitis and conjunctivitis with different underlying causes, i.e., allergies or infections. Therefore, correct differential diagnosis and treatment of ocular surface diseases is crucial, for which imaging can be a helpful tool. A variety of imaging techniques have been introduced to study the ocular surface, such as anterior segment optical coherence tomography, in vivo confocal microscopy, or non-contact meibography. The present review provides an overview on how these techniques can be used in the diagnosis and management of ocular surface disease and compares them to clinical standard methods such as slit lamp examination or staining of the cornea or conjunctiva. Although being more cost-intensive in the short term, in the long term, the use of ocular imaging can lead to more individualized diagnoses and treatment decisions, which in turn are beneficial for affected patients as well as for the healthcare system. In addition, imaging is more objective and provides good documentation, leading to an improvement in patient follow-up and education.

Objective Imaging Diagnostics for Dry Eye Disease

Traditional diagnostic tests for dry eye disease (DED), such as fluorescein tear film break-up time and the Schirmer test, are often associated with poor reproducibility and reliability, which make the diagnosis, follow-up, and management of the disease challenging. Advances in ocular imaging technology enables objective and reproducible measurement of changes in the ocular surface, tear film, and optical quality associated with DED. In this review, the authors will discuss the application of various imaging techniques, such as, noninvasive tear break-up time, anterior segment optical coherence tomography, in vivo confocal microscopy, meibography, interferometry, aberrometry, thermometry, and tear film imager in DED. Many studies have shown these devices to correlate with clinical symptoms and signs of DED, suggesting the potential of these imaging modalities as alternative tests for diagnosis and monitoring of the condition.

Impact of Attrition, Intercellular Shear in Dry Eye Disease: When Cells are Challenged and Neurons are Triggered

The mechanical component in the pathophysiology of dry eye disease (DED) deserves attention as an important factor. The lubrication deficit induced impaired mechano-transduction of lid pressure to the ocular surfaces may lead to the dysregulation of homeostasis in the epithelium, with sensations of pain and secondary inflammation. Ocular pain is possibly the first sign of attrition and may occur in the absence of visible epithelial damage. Attrition is a process which involves the constant or repeated challenge of ocular surface tissues by mechanical shear forces; it is enhanced by the thinning of corneal epithelium in severe DED. As a highly dynamic process leading to pain and neurogenic inflammation, the identification of the impact of attrition and its potential pathogenic role could add a new perspective to the current more tear film-oriented models of ocular surface disease. Treatment of DED addressing lubrication deficiencies and inflammation should also consider the decrease of attrition in order to stimulate epithelial recovery and neural regeneration. The importance of hyaluronic acid, its molecular characteristics, the extracellular matrix and autoregulative mechanisms in this process is outlined. The identification of the attrition and recognition of its impact in dry eye pathophysiology could contribute to a better understanding of the disease and optimized treatment regimens.

Diagnostic tests in dry eye

INTRODUCTION

Dry Eye (DE) is a multifactorial condition with a variable clinical presentation. This highly prevalent disease has multiple symptoms and signs that often do not correlate with one another. As such, the diagnosis of DE can be challenging to make, and a systematic approach must be taken.

AREAS COVERED

We review the different methods commonly utilized to evaluate a patient complaining of DE symptoms. Included in this review are clinical examination techniques, point of care tests, and imaging techniques.

EXPERT OPINION

DE is an umbrella term that encompasses different etiologies and pathophysiological mechanisms. The current definition recognizes tear instability, high osmolarity, inflammation, and neuro-sensory dysfunction as causative entities. The approach to DE begins with a systematic assessment of symptoms and signs, evaluating for both nociceptive and neuropathic sources of symptoms. Future research is needed to develop tests that assess neurosensory status in DE and couple point of care tests with therapeutic algorithms.