Temperatures of the Ocular Surface, Lid, and Periorbital Regions of Sjögren's, Evaporative, and Aqueous-Deficient Dry Eyes Relative to Normals

Association between dryness sensation and ocular surface temperature and conjunctival blood flow in soft contact lens wearers

PURPOSE

To investigate the association between dryness, ocular surface temperature (OST), and conjunctival blood flow (CBF) in soft contact lens (SCL) wearers after airflow stimulation.

METHODS

After recruiting 21 SCL wearers (mean age, 25.3 ± 4.2 years), subjects used two different daily disposable silicone hydrogel SCLs (narafilcon A and delefilcon A lenses). On three of four measurement days, excluding the first, OST, CBF, tear meniscus height (TMH), and non-invasive tear break-up time (NIBUT) were measured after airflow stimulation at a rate of 3 m/s for 10 min. The measurements were conducted without SCLs on the first and second days, and with different SCLs on the third and fourth days. Dryness was evaluated using the visual analogue scale (VAS). These parameters were compared between the two types of SCLs, and their association with the dryness sensation was then investigated.

RESULTS

Dryness was significantly weakly correlated with OST (r = -0.375, p < 0.05) and CBF (r = 0.339, p < 0.05). TMH, NIBUT, and VAS scores for dryness with the delefilcon A lens (0.15 ± 0.05 mm, 3.7 ± 01.7 s and 29.4 ± 16.9) were significantly higher, longer, and lower, respectively, than those with the narafilcon A lens (0.12 ± 0.05 mm, 2.3 ± 1.7 s and 35.9 ± 17.0; p < 0.05, p < 0.01 and p < 0.01). The changes in the OST and CBF between with and without the delefilcon A lens (-0.36 ± 0.35 °C and 0.99 ± 0.19) were significantly small compared to the narafilcon A lens (-0.60 ± 0.42 °C and 1.11 ± 0.21; p < 0.01 for both comparisons).

CONCLUSION

Dryness was correlated with OST and CBF, which indicates that when dryness was high, OST was low and CBF was high. These results suggest that OST and CBF assessments are effective for evaluating dryness sensation.

Safety and Efficacy of Dry Eye Intelligent Therapeutic Device in the Treatment of Meibomian Gland Dysfunction in Rabbits

PURPOSE

To assess the safety and efficacy of the dry eye intelligent therapeutic device in rabbits with meibomian gland dysfunction.

METHODS

The meibomian gland dysfunction-afflicted rabbits were subjected to treatment using the dry eye intelligent therapeutic device. Various parameters, including eyelid margin, meibomian gland opening, redness, meibomian gland area, keratoconjunctival fluorescence staining, and intraocular pressure, were examined and analyzed using an ocular surface comprehensive examination instrument, slit lamp, and tonometer at corresponding times points. Hematoxylin and eosin staining was performed to examine the mucosal epithelium and meibomian gland.

RESULTS

In this study, eyelid margin congestion and meibomian gland opening obstruction were significantly improved after 3 weeks and 4 weeks of treatment, respectively (p < .01, p < .05). The treatment group showed a significant increase in tear meniscus height after 2 weeks, 3 weeks and 4 weeks of treatment (p < .001, p < .01, p < .05). No significant changes were noted in meibomian gland area, redness, intraocular pressure, and keratoconjunctival fluorescence staining of rabbits before and after treatment. Hematoxylin and eosin staining revealed a complete structure of mucosal epithelium and meibomian gland in the treatment group and that the expansion of the blocked meibomian gland duct was reduced.

CONCLUSION

The utilization of the dry eye intelligent therapeutic device in treating meibomian gland dysfunction-afflicted rabbits exhibits potential promising safety, efficacy, and overall benefits, thereby offering a novel alternative for managing meibomian gland dysfunction patients in clinical settings.

Comparing the ocular surface temperature and dry eye condition of keratoconus with normal eyes using infrared thermal imaging

PURPOSE

This study was conducted to compare the ocular surface temperature in keratoconus eyes with that in normal eyes.

METHODS

A total of 27 participants were enrolled, with 10 and 17 participants in the keratoconus and control groups, respectively. Participants in the control group underwent an ophthalmic slit lamp examination and ocular thermography, while an additional corneal tomography was performed for those in the keratoconus group.

RESULTS

For patients with keratoconus, the mean upper eyelid temperature (UET) was 32.36 ± 1.02 °C, inner canthus temperature (ICT) was 34.25 ± 0.83 °C, outer canthus temperature (OCT) was 33.62 ± 0.96 °C, initial central corneal temperature (initial CCT) was 33.04 ± 1.03 °C, sixth-second CCT (6 s-CCT) was 32.67 ± 1.19 °C, and the mean change in CCT measured within 6 s (change in CCT within 6 s) was 0.36 ± 0.26 °C. For controls, the values for UET, ICT, OCT, initial CCT, 6 s-CCT, and change in CCT within 6 s were 32.35 ± 1.13 °C, 34.14 ± 0.91 °C, 33.51 ± 1.02 °C, 33.22 ± 1.01 °C, 32.99 ± 1.01 °C, and 0.22 ± 0.17 °C, respectively. Except for the change in CCT within 6 s (p = 0.022), no significant differences were observed in UET (p = 0.973), ICT (p = 0.659), OCT (p = 0.697), initial CCT (p = 0.556) or 6 s-CCT (p = 0.310) between the two groups.

CONCLUSION

The keratoconus eyes showed faster changes in CCT and evaporation of tear film after opening the eyes. Therefore, the keratoconus eyes had a higher incidence of dry eye conditions.

Relationship between ocular surface temperature and 0.1% cyclosporine a in dry eye syndrome with meibomian gland dysfunction

To determine the relationship between ocular surface temperature (OST) and 0.1% cyclosporine A in patients with dry eye syndrome and meibomian gland dysfunction (MGD). This study retrospectively analyzed 35 eyes from 18 patients with dry eye disease (DED) and MGD, who were divided into two groups. Group 1 was treated with artificial tears, and eyelid margin scrubs without anti-inflammatory eye drops, while group 2 received the same treatment as group 1 along with 0.1% cyclosporine A. The ocular surface disease index (OSDI), tear meniscus height (TMH), noninvasive tear breakup time (NIBUT), lipid layer thickness (LLT), meibum quality score (MQS), and OST were measured at baseline and 1 month later. Nineteen and 16 eyes were included in groups 1 and 2, respectively. Both groups showed a significant decrease in OSDI and OST; however, the decrease was more significant in group 2. No other significant differences in TMH, NIBUT, and LLT were observed; however, MQS significantly differed in group 2. This study found that 0.1% CsA administration can relieve symptoms in patients with DED and MGD although there were no definite keratitis clues, such as epithelial erosion. In addition, the conjunctival temperature showed a correlation with symptom improvement.

Dry eye disease and blinking behaviors: A narrative review of methodologies for measuring blink dynamics and inducing blink response

Dry eye disease (DED) is a leading cause of ophthalmology clinical encounters with prevalence ranging from 8.7% to 64% in various populations. Blinking is an endogenous process to refresh the tear film, clear debris and maintain quality vision. Altered blinking behavior is a common feature of DED and is implicated in the pathology of the disease. However, lack of a comprehensive review on the relationship between altered blinking behavior and DED is notable in the literature. Blinking behavior may be an effect of DED due to an unstable tear film sensitizing a motor response or be its cause due to destabilization of the tear film in conditions such as benign essential blepharospasm. In this comprehensive review, we summarize the current models and theories of tear film dynamics and blinking behavior to better understand their connection to DED and introduce contemporary technologies and measurement tools used in the evaluation and induction of blinking behavior. We also describe future directions of research to better understand the relationship between DED and blinking and explore therapies that address the abnormal blinking component of DED.

In Vitro Inhibition of Evaporation with Perfluorohexyloctane, an Eye Drop for Dry Eye Disease

Objective

Perfluorohexyloctane (PFHO) MIEBO^TM, formerly (NOV03) is a single component, water-free eye drop approved by the Food and Drug Administration in the United States for the treatment of dry eye disease. We evaluated the in vitro inhibitory effect of PFHO on the evaporation rate (R_evap) of saline.

Methods

Evaporation rates were measured gravimetrically at 25°C or 35°C. The evaporation rate (R_evap) of phosphate-buffered saline (PBS) was measured following the application of 11-200 µL PFHO or 100 µL artificial tears (Soothe XP [Bausch + Lomb, Bridgewater, New Jersey], Systane Balance [Alcon, Fort Worth, Texas], and Systane Ultra [Alcon]). The effect of PFHO on the R_evap of PBS was further evaluated following the addition of 50 mg/mL mucin to PBS and compared with that of meibum lipid collected from a 68 year-old White volunteer.

Results

At 25°C the mean (SEM) R_evap of PBS alone or PFHO alone was 4.06 (0.06) and 0.137 (0.004) µm/min, respectively. Layering 100 µL PFHO over PBS inhibited the R_evap of PBS by 81% (P < 0.0001), whereas artificial tears had no effect. The presence of mucin attenuated the inhibition of the R_evap of PBS by PFHO by 17% (P < 0.0001). At 35°C, the R_evap of PBS was inhibited by 88% when layering 100 µL PFHO over PBS and 28% when applying a single 11 µL drop of PFHO (P value < 0.0001 for both). Meibum lipid inhibited the R_evap of PBS by 8% at this temperature, whereas the combination of a drop of PFHO plus meibum inhibited the R_evap of PBS by 34%.

Conclusions

PFHO significantly inhibited the R_evap of saline in this in vitro model. The data support the idea that PHFO may form an antievaporative layer on the tear film surface and may be a functional substitute for the native tear-film lipid layer in patients with dry eye disease.

Hot towels: The bedrock of Meibomian gland dysfunction treatment - A review

BACKGROUND

Meibomian gland dysfunction (MGD) reduces quality-of-life and hinders work productivity of millions of patients, with high direct and indirect societal costs. Thickened meibum obstructs the glands and disrupts ocular surface health. Heating the eyelids to soften and express meibum from the glands can be beneficial. The most accessible method for eyelid warming uses heated, wet towels. However, the efficacy of this treatment is reliant on the methodology, and evidence-based best-practice recommendations are needed.

PURPOSE

To evaluate the literature on hot towels in MGD treatment and recommend a best-practice protocol for future research and patient treatment.

METHODS

Studies were identified through PubMed on the May 28, 2021, with the search terms: (warm* OR heat* OR thermal* OR towel OR wet towel) AND (meibomian OR MGD OR eyelid OR "dry eye" OR DED). All relevant original articles with English full-text were included.

RESULTS

The search yielded 903 results, of which 22 met the inclusion criteria. Across studies, hot towels were found to be effective at reducing ocular symptoms. However, without reheating, the temperature quickly fell below the therapeutic range, which was deemed to be between 40 °C and 47 °C. Towels heated to around 45 °C and reheated every-two minutes were most effective at increasing eyelid temperature, comparable or better than several commercially available eyelid warming devices. No adverse effects were reported in the studies.

CONCLUSION

Hot towel treatment effectively warms the eyelids and reduces ocular symptoms, but must be standardized, and towels reheated to achieve maximum benefit. Future research should assess patient satisfaction with different hot towel treatment methods that reheat or replace the towel at least every-two minutes, to establish which methods yield the greatest compliance. Guidelines or clinical recommendations that do not mention the need for regular reheating during hot towel compress treatment should be updated to include this.

Applications of Infrared Thermography in Ophthalmology

Body temperature is one of the key vital signs for determining a disease’s severity, as it reflects the thermal energy generated by an individual’s metabolism. Since the first study on the relationship between body temperature and diseases by Carl Reinhold August Wunderlich at the end of the 19th century, various forms of thermometers have been developed to measure body temperature. Traditionally, methods for measuring temperature can be invasive, semi-invasive, and non-invasive. In recent years, great technological advances have reduced the cost of thermographic cameras, which allowed extending their use. Thermal cameras capture the infrared radiation of the electromagnetic spectrum and process the images to represent the temperature of the object under study through a range of colors, where each color and its hue indicate a previously established temperature. Currently, cameras have a sensitivity that allows them to detect changes in temperature as small as 0.01 °C. Along with its use in other areas of medicine, thermography has been used at the ocular level for more than 50 years. In healthy subjects, the literature reports that the average corneal temperature ranges from 32.9 to 36 °C. One of the possible sources of variability in normal values is age, and other possible sources of variation are gender and external temperature. In addition to the evaluation of healthy subjects, thermography has been used to evaluate its usefulness in various eye diseases, such as Graves’ orbitopathy, and tear duct obstruction for orbital diseases. The ocular surface is the most studied area. Ocular surface temperature is influenced by multiple conditions, one of the most studied being dry eye; other diseases studied include allergic conjunctivitis and pterygium as well as systemic diseases such as carotid artery stenosis. Among the corneal diseases studied are keratoconus, infectious keratitis, corneal graft rejection, the use of scleral or soft contact lenses, and the response to refractive or cataract surgery. Other diseases where thermographic features have been reported are glaucoma, diabetic retinopathy, age-related macular degeneration, retinal vascular occlusions, intraocular tumors as well as scleritis, and other inflammatory eye diseases.

Association between mask-associated dry eye (MADE) and corneal sensations

To determine the risk of mask-associated dry eye (MADE), we investigated the fluorescein tear break-up time (FBUT), ocular surface temperature and blood flow, along with corneal sensitivity, in mask wearers. We enrolled 60 mask wearers (mean age, 27.1 ± 5.2 years) and then measured FBUT, corneal temperature and conjunctival blood flow without wearing masks (no mask), with masks, and with taped masks. We defined MADE as the condition in which dry eye symptoms appeared and the FBUT with mask was less than 5 s. The FBUT with a mask was significantly shorter compared to the no mask and taped mask groups (P < 0.01 and P < 0.05). The corneal temperature difference and conjunctival blood flow difference were significantly higher after wearing a mask than after wearing a taped mask (P < 0.01). Of the 60 subjects, 13 were diagnosed with MADE. Pain sensitivity and the Ocular Surface Disease Index (P < 0.05 and P < 0.01) were significantly higher in the MADE group, with the FBUT without masks (P < 0.05) significantly shorter than in the non-MADE group. MADE may be associated with corneal hypersensitivity. Wearing masks decreased FBUT and increased ocular surface temperature and blood flow. Taping the top edge of masks prevented these changes. Fitting masks properly may reduce MADE risk.

Ocular Surface Temperature in DED under Natural Non-Controlled Blinking Conditions

Infrared (IR) thermography is a tool to non-invasively assess the tear film temperature. The aim was to analyze ocular surface temperature (OST) variations in dry eye disease (DED) and control eyes under natural non-controlled blinking conditions. Imaging was performed with a thermal camera (FLIR Systems Inc.) at 30 Hz framerate in 79 participants (39 DED (62.5% women, average age 48 ± 20 years) and 40 control (46.2 % women, average age 38 ± 13 years)) using non-contact IR thermography camera. Data acquisitions were performed in natural blinking conditions for 40 s. IR images were analyzed using a custom algorithm that calculates the OST indexes: mean OST, OST at the start and at the end, minimum and maximum OST, and tear evaporation rate (TER). No significant differences were found between groups in any thermal parameter analyzed (paired comparisons t-test, p > 0.05). In conclusion, the findings of this study did not reveal significant differences between DED and control eyes under natural non-controlled blinking conditions. However, the presence of clinical signs in the control group may affect the results, highlighting the role of DED diagnosis criteria.

Outcome Measures to Assess Dry Eye Severity: A Review

Outcome measures used to assess efficacy of dry eye therapeutics have not been consistently applied in clinical settings, nor have they been shown to correlate with functional outcomes. We propose that corneal staining, a clinically meaningful dry eye parameter, should be used as a standard objective outcome measure across all clinical trials evaluating dry eye treatments. We justify this based on evidence regarding its relationship to vision and vision related quality-of-life. In addition, corneal staining has been shown to correlate with ocular surface inflammation, a well elucidated aspect of dry eye pathophysiology and an active area in therapeutics research. No one outcome measure explored herein correlates perfectly to this heterogenous disease. However, there is mounting evidence showing the correlation between corneal staining and functional visual indices. We hope that future clinical trials will standardize corneal staining as a measure to determine the efficacy of interventions and justify their clinical utility.

A spectroscopic approach to measuring meibum lipid composition and conformation in donors with Sjӧgren's syndrome

Patients with Sjӧgren's syndrome (SS) have dry eye associated with meibomian gland dysfunction (MGD). The meibum from donors with dry eye due to MGD but without SS (MMGD) presents with lower levels of cholesteryl ester, less straight chains, and more ordered hydrocarbon chains compared with meibum from donors without MGD (Mn). The aim of the current study was to compare the composition and hydrocarbon chain conformation of meibum from donors with Sjögren's syndrome (Mss) to Mn and MMGD. Meibum was expressed from patients with SS using an ILUX instrument (Alcon Inc., Fort Worth TX). All of the nine meibum donors with SS were female. Meibum composition was characterized using 1H-NMR and meibum hydrocarbon chain conformation was measured using fourier transform infrared spectroscopy. Meibum from every donor with SS measured contained a significantly (P < 0.01) higher cholesteryl ester/wax ester ratio and more straight chains compared with donors without SS or dry eye. None of the nine phase transitional parameters were significantly different, P > 0.05, for Mss compared with Mn. Nor was the CH3/CH2 band height ratio used to estimate the number of hydrocarbon CH3 and CH2 moieties different, P = 0.22, for Mss compared with Mn. In conclusion, the compositional differences between Mss compared with Mn did not result in differences in any of the nine meibum lipid phase transitional parameters measured. The compositional differences observed between Mss and Mn could be markers for or contribute to SS as the differences could lead to tear film lipid packing differences other than conformational differences.

A spectroscopic study of the composition and conformation of cholesteryl and wax esters purified from meibum

Elucidating wax ester (WE) and cholesteryl ester (CE) compositional, structural and functional relationships is key to our understanding of how these lipids are involved in natural and pathological processes. Little is known about how CE and WE interact with one another. The focus of the present study is to bridge this gap of knowledge. CE and WE were collected from human meibum as a source of esters with complex hydrocarbon chains. MgO column chromatography was used to separate WE and CE. The esters were characterized using ¹H-NMR and Fourier transform infrared spectroscopy. The complexity of the hydrocarbon chains of native WE and CE influenced how changes in the ratio of WE and CE ester influenced some lipid phase transitional parameters but not others. Changes in CE content of WE/CE mixtures undoubtedly modifies the hydrocarbon chain conformation and packing of the mixture. The nature of the change depends on the conformation of the WE and CE. Differences in the complexity of the hydrocarbon chains are likely not to be a major influence on alterations in the order or phase transition temperature when more ordered WE is added to less ordered CE.

Pigment epithelium-derived factor (PEDF) plays anti-inflammatory roles in the pathogenesis of dry eye disease

PURPOSE

To investigate the expression of pigment epithelium-derived factor (PEDF) in ocular surface in dry eye disease (DED) and its anti-inflammatory roles and mechanisms, clinically and by experiments in vivo and in vitro.

METHODS

A cross-sectional study was conducted to detect the expression of PEDF in tears of dry eye patients by enzyme-linked immunosorbent assay (ELISA). Using dry eye mouse model and human corneal epithelial cells (hCECs) stimulated by hyperosmolarity or inflammatory cytokines, expression of PEDF in corneal epithelial cells, stroma and conjunctiva was quantified by real-time polymerase chain reaction, ELISA and Western blot. Next, either dry eye mice or hyperosmotic hCECs were treated with recombinant PEDF or neutralizing antibodies, and the expressions of inflammatory cytokines and immune cells were detected. Finally, Western blot was performed on MAPK and NF-κB to investigate the signaling pathways by which PEDF played its roles.

RESULTS

Concentrations of PEDF were increased in tears of dry eye patients. Increased PEDF was observed in corneal epithelial cells (CECs) rather than corneal stroma or conjunctiva in dry eye mice. Furthermore, hCECs exposed to hyperosmolarity showed upregulation of PEDF. In vivo and in vitro studies showed that PEDF suppressed the expression of inflammatory cytokines including IL-1β, IL-6, TNF-α and IL-17A, as well as the percentage of Th17 cells in DED. Further investigation showed that PEDF inhibited the phosphorylation of MAPK p38 and JNK in hyperosmotic hCECs.

CONCLUSIONS

CECs derived PEDF is increased in DED. PEDF plays anti-inflammatory and immunoregulatory roles in the pathogenesis of DED.

Impact of Ocular Surface Temperature on Tear Characteristics: Current Insights

Infrared (IR) thermographic assessment of ocular surface temperature (OST) is gaining interest as an adjuvant method to evaluate the ocular surface. It is a quick, non-invasive test that causes minimal, if any, discomfort to patients. The purpose of this article was to summarize research on how OST relates to tear film parameters and dry eye disease (DED). PubMed, Google Scholar, and Scopus searches for specific terms were carried out and eligible articles reviewed. OST of the central cornea is ~34-35°C when measured as a single time-point (typically right after a blink). Dynamically, OST values decrease over time at a rate of ~ -0.01 °C/s in healthy eyes. Single time-point OST values are impacted by temperature, with positive correlations noted with both ambient (1°C↓ results in ~0.16°C↓ in OST) and body (1°C↑ results in ~0.98°C↑ in OST) temperature. Single time-point OST values are also impacted by tear parameters, with negative correlations noted with tear break-up time (TBUT; r=-0.61) and positive correlations with lipid layer thickness (~r=0.50). Dynamically, the rate of OST cooling over the interblink period correlates with various tear parameters including Schirmer's test scores (r=-0.39), tear meniscus height (r=-0.52) and the rate of tear film break-up (r=-0.74). These data imply that OST decreases more rapidly in individuals with greater tear production, larger tear volumes, and shorter tear break-up times (faster rates of tear film break-up). There are discrepancies in relationships between OST and DED across studies, which is not surprising given that DED encompasses a number of different phenotypic presentations. However, most studies found that OST decreases at a more rapid rate in DED vs. control groups. As such, cooling rate may have utility as a screening tool in DED in combination with established point-of-care tests.

Lacritin proteoforms prevent tear film collapse and maintain epithelial homeostasis

Lipids in complex, protein-enriched films at air/liquid interfaces reduce surface tension. In the absence of this benefit, the light refracting and immunoprotective tear film on eyes would collapse. Premature collapse, coupled with chronic inflammation compromising visual acuity, is a hallmark of dry eye disease affecting 7 to 10% of individuals worldwide. Although collapse seems independent of mutation (unlike newborn lung alveoli), selective proteome and possible lipidome changes have been noted. These include elevated tissue transglutaminase and consequent inactivation through C-terminal cross-linking of the tear mitogen lacritin, leading to significant loss of lacritin monomer. Lacritin monomer restores homeostasis via autophagy and mitochondrial fusion and promotes basal tearing. Here, we discover that lacritin monomer C-terminal processing, inclusive of cysteine, serine, and metalloproteinase activity, generates cationic amphipathic α-helical proteoforms. Such proteoforms (using synthetic peptide surrogates) act like alveolar surfactant proteins to rapidly bind and stabilize the tear lipid layer. Immunodepletion of C- but not N-terminal proteoforms nor intact lacritin, from normal human tears promotes loss of stability akin to human dry eye tears. Stability of these and dry eye tears is rescuable with C- but not N-terminal proteoforms. Repeated topical application in rabbits reveals a proteoform turnover time of 7 to 33 h with gradual loss from human tear lipid that retains bioactivity without further processing. Thus, the processed C-terminus of lacritin that is deficient or absent in dry eye tears appears to play a key role in preventing tear film collapse and as a natural slow release mechanism that restores epithelial homeostasis.

Correlation between Blood Flow and Temperature of the Ocular Anterior Segment in Normal Subjects

Purpose: To determine a correlation between temperature and blood flow in the ocular anterior segment, and their effects on corneal temperature. Methods: In experiment 1, we recruited 40 eyes and measured the temperature and blood flow in the ocular anterior-segment (upper/lower eyelid skin, palpebral and bulbar conjunctiva, and cornea) before and after application of warm compresses. In experiment 2, we recruited 20 eyes and measured the same tissues before and during stimulation using water and capsaicin solution in the oral cavity. Results: In experiment 1, the temperatures of the upper/lower eyelid skin and cornea increased significantly until 15 min after the application of the warm compress; the temperatures of the palpebral and bulbar conjunctiva increased significantly until 10 min. The blood flow in the upper/lower eyelid skin and bulbar conjunctiva increased significantly until 10 min, and that of the palpebral conjunctiva increased significantly until 15 min. In experiment 2, the temperatures were correlated significantly with the blood flow in the upper and lower eyelid skin and palpebral and bulbar conjunctiva. The temperature of all locations and palpebral conjunctival blood flow contributed independently to the corneal temperature. Conclusions: In the ocular anterior segment, the temperature and blood flow were correlated significantly, and contributed to the corneal temperature.

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.

The clinical and experimental significance of blinking behavior

Evaluations of tear functions frequently involve some form of voluntary control over blink behaviour. To the degree that voluntary control of blinking risks departure from normal-range spontaneous blinking, the tear function findings from such studies may be confounded. Even subject awareness that blinking is being assessed may influence findings if such awareness results in any degree of voluntary control. Ideally, the influence on blink rate and tear functions induced by therapeutic or experimental interventions could be measured against a normal-range baseline spontaneous blink rate in order that any differences found could be validly attributed to those interventions. Sometimes pre-intervention 'rest-related' baseline blink rates have been incorrectly described as 'basal' blink rates without specification of pre-intervention conditions of 'rest' or consideration of any contributions from voluntary control. Also, studies which use only blink rates to measure blink efficiency ignore the critically important contribution of incomplete blinking to blink inefficiency. This review finds that the assessment of normal-range spontaneous blink rates depends on measurement conditions which have frequently been ignored previously. For example, normal-range spontaneous blink rates appear more likely to occur with fixation targets which have a disengaged affect and an associated neutral influence on and from dopamine activity. Ideally, fixation targets should also involve minimal cognitive loading and vision demands. In addition, normal-range (symptom free) spontaneous blink rates are more likely to be assessed in a comfortable ambient environment without subject awareness that blink behaviour is being assessed and when voluntary blinking is not involved.

Structural Differences in Meibum From Teenagers Without and With Dry Eye and Allogeneic Hematologic Stem Cell Transplantations

Although dry eye occurs mostly in adults, dry eye may be induced in teens receiving allogeneic hematologic stem cell transplantations (AHSCT). Changes in meibum composition and structure has been associated with dry eye. The structure of meibum from teens with dye eye or teens with dry eye and AHSCT has not been studied, so in this study, we compared the structure of meibum from teens receiving AHSCT that had a dry eye with meibum from teens without AHSCT and without dry eye symptoms.

Differences in Meibum and Tear Lipid Composition and Conformation

PURPOSE

The compositional, structural, and functional relationships of meibum may provide insights into the loss of tear film stability. Although the conformation of meibum lipids has been studied rigorously, that of tear lipids has not.

METHODS

Tear lipids (TLHSCT) and meibum (MHSCT) from patients who had hematopoietic stem cell transplantation were pooled prospectively. The infrared spectra of meibum from donors with (MMGD) and without (Mn) meibomian gland dysfunction were retrospectively analyzed to measure the lipid composition and structure. The infrared CH stretching region was used to measure the relative content of CH3 and CH2 moieties in the meibum.

RESULTS

The 3 major findings of the current study are as follows: 1) compared with Mn, MHSCT and MMGD had 18% fewer CH3 moieties; 2) compared with MHSCT, the phase transition temperature, cooperativity, and order were approximately 20% greater for TLHSCT; and 3) compared with Mn and MMGD, MHSCT and TLHSCT contained fewer double bonds.

CONCLUSIONS

Tear lipids are more ordered than meibum lipids, which could have functional consequences. The human meibum peak height ratio of the CH3/CH2 bands is not a factor related to tear film stability with age or sex. The amount of CH3 moieties relative to CH2 moieties and saturation could contribute to a higher meibum lipid order associated with a younger age, meibomian gland dysfunction, and dry eye from hematopoietic stem cell transplantation. Therefore, the hydrocarbon order may be a marker of or contribute to an unstable tear film layer.

[Current methods of tear film stability assessment]

Dry eye syndrome (DES) is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles. The clinical manifestations of DES can be highly variable, so its diagnosing is typically based on a combination of symptoms, signs, and clinical tests. Majority of the techniques involved in the diagnosis of this disease has a large degree of subjectivity. The present article reviews current dry eye diagnostic tests and presents a new tear film stability assessment technique that may potentially become the objective method for establishing DES diagnosis.

Structural Differences in Meibum From Donors After Hematopoietic Stem Cell Transplantations

PURPOSE

Meibum is considered to be a key component of tears that serve to protect the eye, and conformational changes in meibum have not been studied extensively within the population of patients who had hematopoietic stem cell transplantation (HSCT). The aim of this study was to determine possible lipid conformational changes in the meibum of patients who had HSCT.

METHODS

Participants who had HSCT were randomly sampled for this prospective comparative study. Control participants did not have dry eye or had not undergone allogeneic or autologous stem cell transplantation. Fourier-transform infrared spectroscopy was used to measure meibum phase transition.

RESULTS

Meibum was collected from both eyes of 36 donors without dry eye (Mc) and from 22 patients who had undergone HSCT (MHSCT). There were no significant differences between the phase transition parameters based on gender or race. The following were the significant differences (P < 0.0001) between the parameters for Mc compared with MHSCT : lipid order (% trans) at 33.4°C increased from 40 (1) to 54 (2), cooperativity decreased from 7.9 (0.4) to 5.4 (0.3), the phase transition temperature (C) increased from 30.3 (0.4) to 34.2 (0.9), and the magnitude of the phase transition (cm) increased from 4.0 (0.1) to 4.7 (0.5) (standard error of the mean).

CONCLUSIONS

Conformational and thermodynamic differences were observed between Mc and MHSCT. The changes observed in the lipid conformation of meibum from patients receiving HSCTs suggest that meibum composition changes after stem cell transplantation, and clinicians should consider treating the meibomian glands to improve the ocular surface.

Characterization of the ocular surface temperature dynamics in glaucoma subjects using long-wave infrared thermal imaging

We evaluated the dynamics of ocular surface temperature using thermal imaging in 21 glaucoma subjects and 19 healthy subjects. On opening of the eye, subjects with glaucoma showed significantly cooler temperatures in the central cornea compared to the control group. The upper eyelid was also significantly cooler just before the eye opened. Immediately after opening the eye, the dynamic of temperature change was different in the two groups. In subjects with glaucoma, the eyes cooled significantly faster, with an average decrease of 0.49°C during the first second compared to 0.24°C in the control group. Our results support the hypothesis that both the stability of the tear film and changes in the ocular blood supply in subjects with glaucoma play an important role in thermal dynamics of the ocular surface.

The optimum temperature for the heat therapy for meibomian gland dysfunction

PURPOSE

Numerous devices have been developed to warm the eyelid as a therapy for Meibomian gland dysfunction. The optimum temperature for such therapy was determined.

METHODS

Meibum lipid disorder versus temperature was calculated from previously published phase transition parameters measured using infrared spectroscopy. Phase transitions parameters were calculated from meibum obtained from donors with Meibomian gland dysfunction (MMGD), donors who were susceptible to dry eye after hematopoietic stem cell transplantations (MHSCT) and meibum from donors without dry eye (Mn).

RESULTS

Heating Mn to 40 °C increases the lipid disorder by 20.4%-90%. Heating the meibum another 4° increases the disorder to 95%. MMGD is 73.2% disordered with no heating. Heating MMGD to 41.5 °C increases the disorder by 26.8%-90% disordered. Heating MMGD another 5.1 °C increases the disorder to 95%. As MHSCT is much more ordered, 56.9% disordered compared with Mn and MMGD, a higher temperature above safety limits, 52 and 59 °C is need to disorder MHSCT to 90 and 95% disorder.

CONCLUSIONS

Heating the eye lid above the phase transition temperature of meibum increases the disorder of meibum lipid which could ameliorate dry eye symptoms. The optimum temperature for disordering Mn and MMGD to 90% maximum disorder is 40 and 41.5 °C, respectively. Safety issues and discomfort should be considered in obtaining an optimal level of disorder, especially for severe cases of dry eye.

Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology

Babies have the most stable tears and people with dry eye have the least stable tears. Meibum may contribute to tear film stability, so in this study, the hydrocarbon chain conformation and rheology of meibum from babies was studied for the first time. Infrared spectroscopy was used to measure lipid phase transitions. Rheology was measured using Langmuir film technology. Meibum from 25 donors 1 to 13 years old was compared with meibum from 18 donors 13 to 25 years old. The phase transition temperature and lipid order (stiffness) increased with increasing age from 1 to 25 years. The increase in meibum lipid order from 1 to 25 years of age may contribute to the instability of the tear film with age and contribute to films with a higher reciprocal compressibility modulus that are not as compressible and not as viscoelastic. Changes in the lipid phase transition parameters of meibum lipid with dry eye are an exacerbation of the changes observed with age. The lower reciprocal compressibility moduli of meibum films from children and babies compared with meibum from adults reiterates higher stability in their films which spread better, resist deformation, and facilitates their ability to be quickly restored after blinking.

Physiological and behavioral reactivity to social exclusion: a functional infrared thermal imaging study in patients with psoriasis

Recent studies have shown that sympathetic nervous system (SNS) activity can be heavily impacted not only by basic threats to survival but also by threats to social bonds. In this study we explored the behavioral and physiological consequences of social exclusion/inclusion in patients with psoriasis, a disease frequently associated with the experience of being ostracized and with deficient emotion regulation skills. We employed a virtual ball-tossing game (Cyberball) to induce the experience of social exclusion/inclusion. We then used a Trust Game to measure the effects of this social modulation on trust. During Cyberball, infrared thermal imaging was used to record participants' facial temperature and thus obtain an online measure of SNS activation. Behavioral data showed that social exclusion shifted participants' trust toward unfamiliar players who had not previously excluded them. Physiological data indicated that in control participants, social exclusion triggered higher SNS activation than inclusion. No such effect was found in patients with psoriasis, whose SNS activity was the same during inclusion as it was during exclusion, suggesting that they benefit less from inclusive experiences than control participants. In addition, in patients but not in controls, higher SNS activation during social exclusion was linked to higher monetary investment toward unfamiliar players, a result in keeping with the social reconnection hypothesis, according to which emotions triggered by social rejection can be regulated by investing in new social interactions. We also found that an increase in periorbital temperature is accompanied by a decrease in happiness ratings after social exclusion was experienced during the Cyberball game. NEW & NOTEWORTHY Previous research on emotional processes in psoriasis has mainly employed self-report measures. In this study we used thermal imaging to obtain an online measure of the sympathetic nervous system (SNS) activity during social exclusion and tested how this experience influenced subsequent trust. We found that being included was a less positive experience for patients compared with controls and that SNS activity during exclusion had a stronger influence on subsequent trust in patients than in controls.

Cornea Thermography: Optimal Evaluation of the Outcome and the Resulting Reproducibility

Purpose

The aim of the study was to establish a standardized quantitative evaluation of corneal temperature (CT) that includes anchoring reference points in the topography and minimization of artifacts. We further investigated the distribution and the short- and long-term reproducibility of the CT values, as well as the influence of the core temperatures.

Methods

The CT values in both eyes of 40 healthy subjects were measured through thermography. These examinations took place over the course of four visits within 2 consecutive weeks. At each visit, the CTs were measured twice in both eyes with intervals of 15 minutes between measurements.

Results

CT values were not significantly different between the right and left eyes and their distribution was nearly normal. The CTs increased slightly when measured twice over the 15-minute intervals (short-term reproducibility) but remained stable over a period of 2 weeks (long-term reproducibility). In addition, the CT values depended on the core temperatures.

Conclusions

Ocular surface thermography is a fast and noninvasive examination. The methods of optimized and standardized evaluation of the CT values facilitate comparisons and follow-ups.

Translational Relevance

Thermography can be used clinically and scientifically only if both the measurement and its evaluation are efficient and standardized and if the outcomes are highly reproducible.

Blink: Characteristics, Controls, and Relation to Dry Eyes

Blink is a complex phenomenon that is profoundly affected by diverse endogenous and exogenous stimuli. It has been studied in the context of cognition, emotional, and psychological states, as an indicator of fatigue and sleepiness, particularly in the automobile and transportation industry, in visual tasking, and finally, as it relates to tear film stability and ocular surface health. The fact that it is highly variable and has input from so many sources makes it very difficult to study. In the present review, the behavior of blink in many of these systems is discussed, ultimately returning in each instance to a discussion of how these factors affect blink in the context of dry eyes. Blink is important to ocular surface health and to an individual's optimal functioning and quality of life. Disturbances in blink, as cause or effect, result in a breakdown of tear film stability, optical clarity, and visual function.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.