Neuropathic ocular pain: an important yet underevaluated feature of dry eye

Is there a rational basis for cannabinoids research and development in ocular pain therapy? A systematic review of preclinical evidence

BACKGROUND

Purpose of the present systematic review is to investigate preclinical evidence in favor of the working hypothesis of efficacy of cannabinoids in ocular pain treatment.

METHODS

Literature search includes the most relevant repositories for medical scientific literature from inception until November, 24 2021. Data collection and selection of retrieved records adhere to PRISMA criteria.

RESULTS

In agreement with a priori established protocol the search retrieved 2471 records leaving 479 results after duplicates removal. Eleven records result from title and abstract screening to meet the inclusion criteria; only 4 results are eligible for inclusion in the qualitative synthesis impeding meta-analysis. The qualitative analysis highlights the antinociceptive and anti-inflammatory efficacy of Δ8-tetrahydrocannabinol, cannabidiol and its derivative HU-308 and of new racemic CB1 allosteric ligand GAT211 and its enantiomers GAT228 and GAT229. Moreover, CB2R agonists RO6871304 and RO6871085 and CB2R ligand HU910 provide evidence of anti-inflammatory efficacy. CB2 agonist HU308 reduces of 241% uveitis-induced leukocyte adhesion and changes lipidome profile. Methodological and design issues raise concern of risk of bias and the amount of studies is too small for generalization. Furthermore, the ocular pain model used can resemble only inflammatory but not neuropathic pain.

CONCLUSIONS

The role of the endocannabinoid system in ocular pain is underinvestigated, since only two studies assessing the effects of cannabinoid receptors modulators on pain behavior and other two on pain-related inflammatory processes are found. Preclinical studies investigating the efficacy of cannabinoids in ocular inflammatory and neuropathic pain models are needed to pave the way for clinical translation.

Assessment and Management of Dry Eye Disease and Meibomian Gland Dysfunction: Providing a Singapore Framework

ABSTRACT

The purpose of this article is to provide a framework for general ophthalmologists in Singapore to manage dry eye. This framework considers the evidence in the literature as well as recommendations from expert panels such as the Tear Film & Ocular Surface Society Dry Eye Workshop II and the Asia Cornea Society Workgroup.This article covers the assessment of patient medical history and ask triage questions to identify local and systemic causes of dry eye disease (DED), excluding other possible causes, as well as the risk factors for DED and ocular surface inflammation. Evaluation of clinical signs to establish the diagnosis of DED and differentiation from other causes of irritable, red eyes are described. Tests for understanding the underlying disease processes and severity of DED are also presented.Management of dry eye should involve patient education and engagement. Information about the natural history and chronic nature of DED should be provided to improve long-term management of the disease and enhance compliance. Aggravating factors should be removed or lessened.We provide a guide to determine the most appropriate treatment (or combination of treatments) based on the severity and cause(s) of the disease, as well as the patient's needs and preferences. The aim of the management is to relieve ocular discomfort and prevent worsening of symptoms and signs, as well as to optimize visual function and minimize structural ocular damage. We also discuss the systematic follow-up and assessment of treatment response, as well as monitoring side effects of treatment, bearing in mind continuous support and reassurance to patients.

Corneal Nerve Abnormalities in Painful Dry Eye Disease Patients

Background: This study aimed to compare the corneal nerve structural abnormalities detected using in vivo confocal microscopy (IVCM) in patients with neuropathic corneal pain (NCP) secondary to primary meibomian gland dysfunction (MGD) or autoimmune dry eye (AIDE). Methods: A two-stage retrospective nested case-control study was conducted. First, data from patients with either MGD or AIDE were assessed, selecting only cases with no corneal pain (VAS = 0) or severe pain (VAS ≥ 8). Ocular signs and symptoms of the 238 selected patients were compared between painful and painless cases. Next, painful patients with no corneal damage (Oxford score ≤ 1) were selected within each study group, defining the cases with NCP (i.e., "pain without stain"). IVCM images from all groups were compared with prospectively-recruited healthy controls, focusing on dendritiform cell density and nerve abnormalities (density, tortuosity, microneuromas). Results: AIDE patients had more ocular signs/symptoms than MGD patients. Compared with healthy controls, AIDE-related NCP patients showed increased nerve tortuosity and number of neuromas, whereas MGD-related NCP patients had reduced nerve density and increased number, perimeter, and area of microneuromas. Microneuromas were also observed in healthy controls. Furthermore, a higher number of microneuromas was found in MGD-related NCP compared to AIDE-related NCP or painless MGD. Conclusions: MGD-related NCP was associated with significantly more corneal nerve abnormalities than AIDE-related NCP or healthy controls. Although IVCM can be useful to detect NCP-related corneal nerve changes in such patients, the diagnosis of dry eye disease-related NCP will require an association of several IVCM-based criteria without relying solely on the presence of microneuromas.

Concurrent ocular pain in patients with neurotrophic keratopathy

PURPOSE

To illustrate that ocular pain may occur in patients with neurotrophic keratopathy (NK) that typically are thought to lack symptoms of discomfort, and that aa subset of these patients may also present with neuropathic corneal pain (NCP).

METHOD

Retrospective Case series of 7 stage 1 NK patients who presented with concurrent ocular pain, as confirmed by clinical examination, proparacaine challenge test, and in vivo corneal confocal microscopy (IVCM). Records were assessed for results of ocular surface disease index (OSDI), pain on visual analog scale (VAS), ocular pain assessment survey (OPAS), best-corrected visual acuity (BCVA), corneal fluorescein staining (CFS) score, and IVCM findings. IVCM findings were compared to that of 20 healthy reference controls.

RESULTS

Mean age of patients was 63.7 ± 11.6 (range 44-76) years and 56.9 ± 8.6 (range 42-74) years in reference controls (p = 0.11). At presentation, ocular discomfort was 8.0 ± 1.3 (range 7-10) on VAS and mean OSDI scores were 72.26 ± 6.81 (range 62.50-79.54). Mean BCVA was 20/40, and mean CFS scores were 3.43 ± 0.79 (range 2-4) on the Oxford scale. IVCM analysis showed significant decrease in mean total, main and branch nerve densities in ranges consistent with NK as compared to normal controls (p < 0.001 for all), increased dendritiform cell density in three patients (p < 0.001), and the presence of microneuromas in six of the patients.

CONCLUSION

Patients with NK are thought to present with hypoesthesia. However, nerve damage and inflammation, which play a role in the development of NK may result in the development of chronic ocular pain, such as NCP, resulting in potential underdiagnosis of either disease.

The transcriptome of rabbit conjunctiva in dry eye disease: Large-scale changes and similarity to the human dry eye

The pathophysiology of dry eye disease (DED) remains largely unknown, accounting in part for the lack of successful treatments. We explored the pathophysiology of DED using a rabbit model of chronic DED induced with 3 weekly injections of Concanavalin A into the periorbital lacrimal glands. The transcriptome of full-thickness's conjunctival tissue from rabbits with DED and from normal controls was determined using microarrays and, as needed, confirmatory real-time polymerase chain reactions. Results were subjected to bioinformatic analysis. DED induced large-scale changes in gene transcription involving 5,184 genes (22% of the total). Differentially expressed genes could be segregated into: functional modules and clusters; altered pathways; functionally linked genes; and groups of individual genes of known or suspected pathophysiological relevance to DED. A common feature of these subgroups is the breadth and magnitude of the changes that encompass ocular immunology and essentially all aspects of cell biology. Prominent changes concerned innate and adaptive immune responses; ocular surface inflammation; at least 25 significantly altered signaling pathways; a large number of chemokines; cell cycle; and apoptosis. Comparison of our findings to the limited extant transcriptomic data from DED patients associated with either Sjogren's syndrome or non-Sjogren's etiologies revealed a significant correlation between human and rabbit DED transcriptomes. Our data, establishing the large-scale transcriptomic changes of DED and their potential similarity to the human, underscore the enormous complexity of DED; establish a robust animal model of DED; will help expand our understanding of its pathophysiology; and could guide the development of successful therapeutic strategies.

Chemokines and Pain in the Trigeminal System

Chemotactic cytokines or chemokines are a large family of secreted proteins able to induce chemotaxis. Chemokines are categorized according to their primary amino acid sequence, and in particular their cysteine residues that form disulphide bonds to maintain the structure: CC, CXC, CX3C, and XC, in which X represents variable amino acids. Among their many roles, chemokines are known to be key players in pain modulation in the peripheral and central nervous systems. Thus, they are promising candidates for novel therapeutics that could replace current, often ineffective treatments. The spinal and trigeminal systems are intrinsically different beyond their anatomical location, and it has been suggested that there are also differences in their sensory mechanisms. Hence, understanding the different mechanisms involved in pain modulation for each system could aid in developing appropriate pharmacological alternatives. Here, we aim to describe the current landscape of chemokines that have been studied specifically with regard to trigeminal pain. Searching PubMed and Google Scholar, we identified 30 reports describing chemokines in animal models of trigeminal pain, and 15 reports describing chemokines involved in human pain associated with the trigeminal system. This review highlights the chemokines studied to date at different levels of the trigeminal system, their cellular localization and, where available, their role in a variety of animal pain models.

Are there Clinical Ways to Assess Inflammation in Dry Eye Disease?

In the diagnostic process of dry eye disease, the detection of inflammatory activity is critical in order to evaluate the risk of progression and immunologic shift of the disease, to predict patient response to treatment, and to design an efficient therapeutic strategy, including artificial tear replacement, punctal occlusion or anti-inflammatory therapy.Even if it is difficult to quantify, some indicators of the presence of inflammation are collectible during the examination of the ocular surface in a first-line clinical setting. This review presents and critically discusses the assessment of inflammation in dry eye disease in clinical practice.

Neuropathic Corneal Pain Following LASIK Surgery: A Retrospective Case Series

Introduction

Transient dry eye symptoms have been reported following laser in situ keratomileusis (LASIK). Very rarely, patients may present with debilitating symptoms of dry eye syndrome (DES) with limited or no evidence of ocular surface disease. These patients are diagnosed with a form of DES known as neuropathic corneal pain (NCP).

Patients and Methods

This study is a retrospective medical record review of a case series of 18 patients who developed NCP post-LASIK over the years 1996–2021. All patients who developed severe ocular pain following LASIK consistent with NCP were included. Patients with severe ocular pain who had evidence of severe ocular surface disease or other ophthalmic etiology to explain their debilitating symptoms were not included.

Results

The average age of patients in our study was 39.5 years. The majority of our patients were female (72.2%) and of Caucasian ancestry (83.3%). The average onset of symptoms was 9.6 months post-LASIK. Patients had past medical histories significant for neuropsychiatric conditions (50%), functional pain syndromes (22.2%), autoimmune diseases (33.3%), and hypothyroidism (27.8%), and the occurrence of these was higher than the national prevalence of these diseases. Symptoms were consistent with the severity and characteristics defining NCP. Treatment was multimodal, involved topical and systemic therapies, and was unique to each patient. Overall, the majority of patients had clinical improvement in symptoms following treatment with regular follow-up.

Conclusion

Although rare, the 26-year prevalence of NCP post-LASIK in our study was roughly 1 in 900 cases. The mean time to onset after surgery was delayed at 9.6 months. Certain risk factors such as neuropsychiatric conditions, history of functional pain syndromes, history of autoimmune conditions, and hypothyroidism may predispose patients to the development of this condition. Patients benefited from proper diagnosis and a multimodal approach to treatment.

Evaluation of dry eye subtypes and characteristics using conventional assessments and dynamic tear interferometry

BACKGROUND/AIMS

To evaluate subtypes and characteristics of dry eye (DE) using conventional tests and dynamic tear interferometry, and to investigate determinants of disease severity in each DE subtype.

METHODS

309 patients diagnosed with DE and 69 healthy controls were prospectively enrolled. All eyes were evaluated using Ocular Surface Disease Index (OSDI), Schirmer's test I (ST1) and Meibomian gland dysfunction (MGD) grade were analysed. The tear interferometric pattern and lipid layer thickness were determined using DR-1α and LipiView II, respectively.

RESULTS

Dynamic interferometric analysis revealed 56.6% of patients with DE exhibited Jupiter patterns, indicative of aqueous-deficiency, while 43.4% exhibited crystal patterns, indicative of lipid deficiency. These findings were in accordance with classification based on ST1 scores and MGD grade. Conventional assessment indicated 286 patients exhibited evidence of evaporative DE (EDE) due to MGD, while only 11 exhibited signs of pure aqueous-deficient DE (pure ADDE, only ST1 ≤5 mm). Interestingly, of 286 patients with EDE, 144 were categorised into the mixed-ADDE/EDE group, in which ST1 was identified as a strong negative determinant of OSDI. In contrast, 72.2% of patients with mixed-ADDE/EDE exhibited Jupiter patterns (Jupiter mixed), while 27.8% exhibited crystal patterns (crystal mixed). OSDI values were significantly higher in the crystal-mixed group than in the Jupiter mixed, in which OSDI scores were independently associated with ST1 values only.

CONCLUSIONS

Our findings indicate that majority of EDE patients also exhibit aqueous deficiency, which can aggravate symptoms even in patients with lipid-deficient mixed-ADDE/EDE. Conventional assessments should be combined with interferometric tear analysis to determine the most appropriate treatment for each DE patient.

Effects of Topical Gabapentin on Ocular Pain and Tear Secretion

Neuropathic ocular pain is a frequent occurrence in medium to severe dry eye disease (DED). Only palliative treatments, such as lubricants and anti-inflammatory drugs, are available to alleviate patients’ discomfort. Anesthetic drugs are not indicated, because they may interfere with the neural feedback between the cornea and the lacrimal gland, impairing tear production and lacrimation. Gabapentin (GBT) is a structural analog of gamma-amino butyric acid that has been used by systemic administration to provide pain relief in glaucomatous patients. We have already shown in a rabbit model system that its topic administration as eye drops has anti-inflammatory properties. We now present data on rabbits’ eyes showing that indeed GBT given topically as eye drops has analgesic but not anesthetic effects. Therefore, opposite to an anesthetic drug such as oxybuprocaine, GBT does not decrease lacrimation, but–unexpectedly–even stimulates it, apparently through the upregulation of acetylcholine and norepinephrine, and by induction of aquaporin 5 (AQP5) expression in the lacrimal gland. Moreover, data obtained in vitro on a primary human corneal epithelial cell line also show direct induction of AQP5 by GBT. This suggests that corneal cells might also contribute to the lacrimal stimulation promoted by GBT and participate with lacrimal glands in the restoration of the tear film, thus reducing friction on the ocular surface, which is a known trigger of ocular pain. In conclusion, GBT is endowed with analgesic, anti-inflammatory and secretagogue properties, all useful to treat neuropathic pain of the ocular surface, especially in case of DED.

Quantification of Increased Corneal Subbasal Nerve Tortuosity in Dry Eye Disease and Its Correlation With Clinical Parameters

Purpose

This study quantified corneal subbasal nerve tortuosity in dry eye disease (DED) and investigated its correlation with clinical parameters by proposing an aggregated measure of tortuosity (Tagg).

Methods

The sample consisted of 26 eyes of patients with DED and 23 eyes of healthy volunteers, which represented separately the dry eye group and the control group. Clinical evaluation of DED and in vivo confocal microscopy analysis of the central cornea were performed. Tagg incorporated six metrics of tortuosity. Corneal subbasal nerve images of subjects and a validation data set were analyzed using Tagg. Spearman's rank correlation was performed on Tagg and clinical parameters.

Results

Tagg was validated using 1501 corneal nerve images. Tagg was higher in patients with DED than in healthy volunteers (P < 0.001). Tagg was positively correlated with the ocular surface disease index (r = 0.418, P = 0.003) and negatively correlated with tear breakup time (r = -0.398, P = 0.007). There was no correlation between Tagg and visual analog scale scores, corneal fluorescein staining scores, or the Schirmer I test.

Conclusions

Tagg was validated for quantification of corneal subbasal nerve tortuosity and was higher in patients with DED than in healthy volunteers. A higher Tagg may be linked to ocular discomfort, visual function disturbance, and tear film instability.

Translational Relevance

Corneal subbasal nerve tortuosity is a potential biomarker for corneal neurobiology in DED.

Neuropathic corneal pain and dry eye: a continuum of nociception

Throughout the body, damage to peripheral nerves normally involved in nociception may produce a constellation of symptoms-including irritation, itchiness and pain. The neurobiological processes involved in corneal symptoms of dry eye (DE) and neuropathic corneal pain (NCP) have not been clearly considered in terms of nociceptive processing. The conventional underlying presumption is that a labelled line principle is responsible; that these distinct perceptions are hard coded by primary afferent inputs to the central nervous system. This presumption oversimplifies the neurobiological mechanisms underlying somatosensory perception. The labelled line perspective that DE represents a chronic pain condition does not make intuitive sense: how can an eye condition that is not painful in most cases be considered a pain condition? Does not chronic pain by definition require pain to be present? On the other hand, NCP, a term that clearly denotes a painful condition, has historically seemed to resonate with clinical significance. Both DE and NCP can share similar features, yet their differentiation is not always clear. As is often the case, clinical terms arise from different disciplines, with DE evolving from ophthalmological findings and NCP inspired by pain neurophysiology. This review evaluates the current definition of these terms, the rationale for their overlap and how the neurophysiology of itch impacts our understanding of these conditions as a continuum of the same disease. Despite the complexity of nociceptive physiology, an understanding of these mechanisms will allow us a more precise therapeutic approach.

Dry eye: why artificial tears are not always the answer

Dry eye disease (DED) is a multifactorial disease that manifests in patients with a variety of symptoms and signs such as ocular pain, visual issues, rapid tear evaporation and/or decreased tear production. It is a global health problem and is the leading cause of optometry and ophthalmology clinic visits. The mainstay therapy for DED is artificial tears (ATs), which mimics tears and improves tear stability and properties. ATs have been found to improve symptoms and signs of disease in all DED subtypes, including aqueous deficient DED and evaporative DED. However, given the heterogeneity of DED, it is not surprising that ATs are not effective in all patients. When AT fails to relieve symptoms and/or signs of DED, it is critical to identify the underlying contributors to disease and escalate therapy appropriately. This includes underlying systemic diseases, meibomian gland dysfunction, anatomical abnormalities and neuropathic dysfunction. Thus, this review will discuss the benefits and limitations of ATs and review conditions when escalation of therapy should be considered in DED.

Could contact lens dryness discomfort symptoms sometimes have a neuropathic basis?

Symptoms of dryness discomfort in soft contact lens wearers frequently lead to discontinuation from wear. The negative influence of pre-fitting tear dysfunctions appears likely to be exacerbated by the challenges to tear homeostasis caused by contact lenses. The corneal mechanisms for symptoms in contact lens wearers are different to those for dry eye disease because the cornea is insulated by the lens from ambient conditions as well as from lid wiper friction during blinking. Symptoms of dryness discomfort might be the consequence of increased lid wiper friction during blinking when the lens front surface becomes soiled and dry and exhibits very rapid tear break up. It is possible that some cases of contact lens intolerance and discontinuation could be a function of lid wiper neuropathy. In relation to the possibility of corneal neuropathy, a stagnant post-lens tear pool with the possibility of increased concentrations of metabolic by-products, cellular debris, and bacterial exotoxins, might have the potential to disturb the corneal epithelial and sub-basal nerves. Contributions by contact lens-induced inflammation to any neuropathic changes may partly depend on the degree to which inflammatory mediators are concentrated in a stagnant post-lens tear pool. It does not appear to be known if corneal neuropathic changes could develop under these conditions. The chances of neuropathic involvement may be greater if discomfort develops after a significant period of successful wear and there is a history of comorbid pain conditions. Esthesiometry and in vivo confocal microscopy in discontinued contact lens wearers may support a diagnosis of contact lens-related corneal neuralgia.

Is gabapentin effective in dry eye disease and neuropathic ocular pain?

This study aims to evaluate the efficacy of gabapentin treatment in dry eye disease (DED) and neuropathic ocular pain. Our study was performed with 72 patients. The painDETECT questionnaire was used for neuropathic pain screening. Patients who were thought to have severe DED according to ocular surface disease index (OSDI) questionnaire, Schirmer's test type 1 and tear break up time test results were treated with artificial tear and cyclosporine drops. Gabapentin treatment was also initiated in addition to artificial tear and cyclosporine drops treatments to the patients with neuropathic component and DED findings. We divided the patients into two groups: group 1 (n: 36), patients treated with artificial tear and cyclosporine drops and group 2 (n: 36), patients treated with artificial tear, cyclosporine drops and gabapentin. In the first evaluation, no significant differences were found between groups in terms of OSDI score, Schirmer's test result and TBUT. After the 6 weeks of treatment, in both groups OSDI score, Schirmer's test result and TBUT statistically significantly improved. OSDI score, Schirmer's test result and TBUT significantly improved after the 6 weeks of gabapentin treatment than artificial tear and cyclosporine treatment group (p < 0.001). Dry eye patients should be screened for neuropathic ocular pain symptoms and individualized treatment has to be applied. Our study showed that the use of gabapentin is effective in severe dry eye patients with neuropathic ocular pain.

Why the symptoms and objective signs of dry eye disease may not correlate

Cases of dry eye disease involving a neuropathic basis for symptoms and a poor correlation between symptoms and objective signs of dry eye disease can be associated with unsatisfactory responses to treatments which are limited to attempts to restore lacrimal function unit deficiencies. This review examines a wider range of circumstances under which the same kind of poor correlation between signs, symptoms and treatment results can be found. Some cases of computer vision syndrome can present for examination at times when objective signs related to reported symptoms have dissipated. A thorough history should explain this type of presentation for which symptoms might otherwise appear to be unexplained. However, mental health disorders can also be the basis for apparently unexplained levels of symptoms of dry eye disease. Anxiety, depression, hypochondriasis, stress, sleep and mood disorders as well as neuroticism for example, may be associated with exacerbation of symptoms to degrees that are not consistent with the levels of tear homeostasis anomalies that are assessed. The conclusion is drawn that failure to consider mental health comorbidities may result in symptomatic patients being exposed to less successful attempts to remediate tear dysfunctions when, for example, the symptoms have a somatic basis. Appropriate screening and referral to a psychologist or psychiatrist may be the key to managing some patients whose symptoms do not correlate with objective evidence of dry eye disease.

Abnormal Spontaneous Brain Activities of Limbic-Cortical Circuits in Patients With Dry Eye Disease

Whether brain function is altered in patients with dry eye disease (DED) remains unclear. Twenty patients with DED and 23 healthy controls (HCs) were scanned using resting-state functional magnetic resonance imaging. Regional homogeneity (ReHo) and support vector machine (SVM) were used to analyze the imaging data. Relative to the HCs, the patients with DED showed significantly increased ReHo values in the left inferior occipital gyrus (IOG), left superior temporal gyrus, and right superior medial prefrontal cortex, and significantly decreased ReHo values in the right superior frontal gyrus/middle frontal gyrus and bilateral middle cingulum (MC). SVM results indicated that the combination of ReHo values in the left MC and the left IOG in distinguishing patients with DED from HCs had a sensitivity of 95.00%, a specificity of 91.30%, and an accuracy of 93.02%. The present study found that the patients with DED had abnormal ReHo values in the limbic-cortical circuits. A combination of ReHo values in the left MC and the left IOG could be applied as a potential imaging biomarker to distinguish patients with DED from HCs. The dysfunction of limbic-cortical circuits may play an important role in the pathophysiology of DED.

Defining Dry Eye from a Clinical Perspective

Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.

Cost utility analysis of cryopreserved amniotic membrane versus topical cyclosporine for the treatment of moderate to severe dry eye syndrome

BACKGROUND

The purpose is to perform a cost effectiveness analysis amniotic membrane vs. topical medications in the use of treating dry eye disease. A cost effectiveness analysis comparing amniotic membrane + other topical medications to topical cyclosporine A + other topical medications was evaluated using accepted decision tree modeling software.

METHODS

TreeAge Pro 2019 software was used to evaluate the base case costs over a one year timeframe. Sensitivity analysis was performed on those variables which had the greatest effect on choosing one therapy versus the other based on cost. Monte Carlo simulation was run 1,000 times to determine the most effective, least costly alternative. Costs were evaluated from a societal level (direct + indirect). Quality of life utility scores were evaluated using known time tradeoffs from prior studies (scale 0-1; with 1 being perfect vision).

RESULTS

Over a one year timeframe, the base case demonstrated that amniotic membrane + topical medications was the less expensive alternative and provided for incremental utilities versus topical cyclosporine + other medications (Cost/utility: $18,275/0.78 vs. $20,740/0.74). If examining direct costs only, topical cyclosporine was the least expensive option over a one year timeframe: $4,112 vs. $10,300. Sensitivity analysis demonstrated that in order for topical cyclosporine to be the less expensive alternative the following variables would need to be: < 68 days productivity lost; < $161 productivity lost/day; > 79% of amniotic membrane implants would need to be re-implanted at month 4 (for whatever reason); > $2677 per amniotic membrane implant procedure (Medicare reimbursement rate); > 96% positive response to topical cyclosporine A at month 4; > 58% positive response to topical cyclosporine A at month 6 and; < 54% probability clinical improvement with amniotic membrane. Monte Carlo simulation demonstrated that amniotic membrane was the less costly, most effective alternative 91.5% of the time.

CONCLUSION

Based on improved outcomes using amniotic membrane, patient productivity was improved resulting in lower societal costs (less days lost from work). When considering the untoward effects of dry eye disease on societal costs, an improvement of the dry eye disease condition was accomplished most often with amniotic membrane.

Treatment Response to Gabapentin in Neuropathic Ocular Pain Associated with Dry Eye

PURPOSE

To investigate the response to gabapentin treatment in patients with dry eye (DE) accompanied by features of neuropathic ocular pain (NOP), and to analyze the differences between clinical manifestations of the groups according to treatment response.

METHODS

We retrospectively reviewed the records of 35 patients with DE accompanied by NOP features and obtained information on their medical history and previous ocular history. The patients underwent clinical examinations of the tear film, ocular surface, and meibomian gland and completed the Ocular Pain Assessment Survey (OPAS). One month after treatment with topical eye drops, add-on of gabapentin treatment was determined according to the Wong-Baker FACES Pain Rating Scale (WBFPS). A reduction of 2 points or more on the WBFPS was considered a positive treatment response. Enrolled patients were divided into three groups according to the treatment response: topical treatment response group (group 1, n = 11); gabapentin response group (group 2, n = 13); and gabapentin non-response group (group 3, n = 11). The medical history, clinical parameters, and OPAS scores were compared between groups.

RESULTS

The incidence of systemic comorbidities was higher in group 2 than in other groups. The corneal staining scores were lower in groups 2 and 3 than in group 1. Among the treatment response groups, group 2 showed improvements in OPAS scores of ocular pain severity, pain other than eyes, and quality of life, while group 1 showed improved OPAS scores of ocular pain severity and ocular associated factors. Group 2 exhibited lower scores of pains aggravated by mechanical and chemical stimuli than group 3.

CONCLUSIONS

Gabapentin could be effective in patients who have systemic comorbidity and less pain evoked by mechanical and chemical stimuli for the treatment of DE patients with NOP, which is refractory to topical treatment.

Autoimmune Dry Eye without Significant Ocular Surface Co-Morbidities and Mental Health

Dry eye symptoms can negatively affect the psychological, physical, and social functioning, which can potentially impair the health-related quality of life. This review evaluated the association between autoimmune related dry eye in the absence of significant ocular surface co-morbidities and mental health. This review found a significantly higher prevalence of mental health disorders (such as depression and anxiety) in systemic lupus erythematous, rheumatoid arthritis, systemic sclerosis, Behcet’s disease, and primary Sjogren’s syndrome patients when compared to the general population. Moreover, patients with depression and anxiety interpret ocular sensations differently than healthy controls and the perception of dry eye symptoms can be influenced by their mood. Somatization is common in depression, and this could influence the perception of ocular discomfort. Anti-depressants and anxiolytics with their potential side effects on the tear film status may also contribute or aggravate the dry eye symptoms in these patients. Although ophthalmologists manage the dry eye disease, as per standardized algorithms, they should be mindful of different ocular sensation interpretation and coexistent mental health issues in a large number of this patient group and initiate a multidisciplinary management plan in certain cases. While rheumatologists look after their autoimmune condition, it may be worth liaising with GP and/or psychiatrist colleagues in order to address their neuropathic type pain and mental health co-morbidities.

Effectiveness of transcutaneous electrical stimulation combined with artificial tears for the treatment of dry eye: A randomized controlled trial

There is currently no available cure or universally effective treatment for dry eye (DE). The aim of the present study was to investigate the clinical efficacy of transcutaneous electrical stimulation (TES) combined with artificial tears in treating DE. Patients diagnosed with DE were referred for therapy with TES combined with sodium hyaluronate (SH)-containing artificial tears. A total of 52 patients (104 eyes) with DE were enrolled in this randomized controlled trial. The patients were randomized 1:1 to the TES + SH or SH group. The patients in the TES + SH group were treated with 20 sessions (5 sessions per week for 4 weeks), and each session lasted for 20 min. The treatment was continued for 4 weeks in all cases. The Ocular Surface Disease Index (OSDI), tear film breakup time (BUT), Schirmer's I test and corneal fluorescein scores were used to assess treatment efficacy. A total of 90 eyes of 45 patients completed all aspects of the study: 22 patients (44 eyes) in the TES + SH group and 23 patients (46 eyes) in the SH group. There was no statistically significant difference in sex, age or course between the two groups. The mean OSDI scores, BUT, Schirmer's I test and corneal fluorescein scores exhibited a significant improvement in the TES + SH group compared with the SH group after treatment. No serious adverse events were recorded during TES treatment. In conclusion, TES combined with artificial tears appeared to be an effective treatment for DE. Therefore, TES may represent a new therapeutic option with promising potential applications.

Ocular Neuropathic Pain: An Overview Focusing on Ocular Surface Pains

Objective

This paper reviews ocular pain with the main focus on ocular surface discomfort and dry eye pain. Anatomy, physiology, epidemiology, assessment, and treatment are discussed in this paper.

Methods

A PubMed search was conducted for studies published from 2000 to 2019 on the anatomy, pathophysiology, epidemiology, assessment, and treatment of ocular pain. Reviews, meta-analyses, and randomized clinical trials were included. Inclusion criteria focused on ocular surface discomfort, dry eye pain and neuropathic pain.

Results

A total of 112 articles were found through searches, 45 of which were selected and studied in this review.

Discussion

Pain in general can be acute or chronic. Acute pain is usually a physiologic response to a serious damage to the tissues and alleviates with pain relief treatments. Chronic pain is defined as the persistence of pain for more than three months. From another point of view, pain has been classified into either nociceptive or neuropathic. Nociceptive pain is a physiologic response to a noxious stimulus. Both central and peripheral nervous systems can be involved in the development of a neuropathic pain, which is characterized by positive or negative sensory signs, a pain perceived disproportionate to a noxious stimulus, and/or not responsive to analgesics. Chronic pain usually has a neuropathic component. Ocular surface pain is a well-known complaint after any corneal surgery. This is mainly due to abnormal regeneration of damaged corneal nerve endings and abnormal connections with adjacent nerve endings which produce spontaneous activity. Tear hyperosmolarity and the resultant ocular surface inflammation can also trigger voluntary activity of corneal nerve endings. Referral pain to the first and second division of the trigeminal nerve has been reported. Interference with vision and even sleep, which is out of proportion to the examination are among patients' complaints. All of these elements proposed the new concept of ocular neuropathic pain syndrome. The first step in conventional evaluation of ocular discomfort is search for tear insufficiency. Pathologies of lid and blinking as well as conjunctival irregularities should be addressed. Anti-inflammatory agents and, in resistant cases, systemic neuromodulators are shown to be helpful. Education on behavioral changes and reassurance are essential steps. Considering the neuropathic origin for the ocular pain, treatment modalities used for such pain in other parts of the body can be considered for this syndrome.

Characteristics of headaches among surgeons and associated factors: A cross-sectional study

BACKGROUND

Surgeons performing Minimally Invasive Surgery (MIS) report significant neck/shoulder problems and visual symptoms. Headache is another commonly reported symptom but publications about the characteristics and associated risk factors are limited.

PURPOSE OF THE STUDY

To determine the characteristics of headache among MIS surgeons and the associations of headache with neck/shoulder problems, visual symptoms and other associated factors.

DESIGN

A cross-sectional study.

METHODS

A comprehensive online survey was sent to MIS surgeons inclusive of 63 questions about individual and workplace physical factors, characteristics of headache, neck/shoulder problems and visual symptoms. Binary logistic regression models were conducted to determine the associations of the prevalence and severity of headache with risk factors.

THE MAIN FINDINGS

Headaches in the last 7 days were reported by 36% of surgeons, with 37% of these of moderate to severe intensity. Frequent intense headaches were often preceded by neck pain. Surgeons with headache were eight times more likely to also experience visual symptoms and four times more likely to experience neck/shoulder problems. Several factors (frequently adopting forward head movement, surgical specialty, sex and age) were significantly associated with headaches (p ≤ 0.05).

CONCLUSIONS

This study revealed headaches were present in one-third of MIS surgeons. During surgery, surgeons report adopting non-neutral neck/shoulder/head positions, which may explain headaches, neck/shoulder problems and visual symptoms. Evidence based strategies to assist surgeons better manage these symptoms are warranted.

Ocular Surface Pain: A Narrative Review

Ocular surface pain is a frequent cause of visits to an eye care provider and has a substantial impact on healthcare cost, yet a complete understanding of its causative factors and tools for diagnostic workup are notably missing in many eye clinics. The cornea has the densest sensory innervation in the human body and has the potential to be a powerful producer of pain. Pain can manifest as a result of a noxious stimulus or disruption in the ocular surface anatomy (nociceptive pain), or it can result from abnormalities in the ocular surface neurosensory apparatus itself (neuropathic pain). Novel advances in neurobiology have sought to differentiate the two entities, particularly to identify when chronic dry eye symptomatology is driven by neuropathic ocular pain. In this review, we seek to provide an overview of the prevalence, physiologic factors, and management of ocular surface pain complaints.

Efficacy and tolerability of nortriptyline in the management of neuropathic corneal pain

PURPOSE

Neuropathic corneal pain (NCP) is a recently acknowledged disease entity. However, there is no consensus in potential treatment strategies, particularly in patients with a centralized component of pain. This study aims to assess the efficacy and tolerability of the tricyclic antidepressant, nortriptyline, among NCP patients.

METHODS

Patients with clinically diagnosed NCP and a centralized component of pain, treated with oral nortriptyline, who had recorded pain scores as assessed by the ocular pain assessment survey at the first and last visit were included. Patients were excluded if they had any other ocular pathology that might result in pain or had less than 4 weeks of nortriptyline use. Demographics, time between visits, concomitant medications, systemic and ocular co-morbidities, duration of NCP, side effects, ocular pain scores, and quality of life (QoL) assessment were recorded.

RESULTS

Thirty patients with a mean age of 53.1 ± 18.5 were included. Male to female ratio was 8:22. Mean ocular pain in the past 24 h improved from 5.7 ± 2.1 to 3.6 ± 2.1 after 10.5 ± 9.1 months (p < 0.0001). Twelve patients (40.0%) had equal to or more than 50% improvement, 6 patients (20.0%) had 30-49% improvement, 6 patients (20.0%) had 1-29% improvement, 4 patients (13.3%) did not improve, while 2 patients (6.7%) reported increase in pain levels. Mean QoL improved from 6.0 ± 2.5 to 4.3 ± 2.4 (p = 0.019). Eight patients (26.6%) discontinued treatment due to persistent side effects, despite improvement by 22.4%.

CONCLUSION

Nortriptyline was effective in relieving NCP symptoms in patients with centralized component and insufficient response to other systemic and topical therapies who tolerated the drug for at least 4 weeks. Nortriptyline may be used in the management of patients with NCP.

Capsaicin-induced pain sensitivity in short tear break-up time dry eye

PURPOSE

To evaluate transient receptor potential vanilloid 1 (TRPV1)-mediated pain sensitivity in patients with short tear break-up time (TBUT) dry eye (DE) by using the capsaicin stimulus test.

METHODS

This prospective cross-sectional comparative study included 22 eyes of 22 patients with short TBUT DE and 11 eyes of 11 non-DE control subjects. Patients were divided into two groups based on response to standard DE treatments: 10 non-responders (intractable DE) and 12 responders (responsive DE). Mechanical touch (M-touch) and mechanical pain (M-pain) were measured using a Cochet-Bonnet esthesiometer. Capsaicin-induced pain (C-pain) and C-pain duration (C-pain DT) were measured using a capsaicin stimulus test. Psychological distress was also assessed.

RESULTS

M-touch sensitivity was similar among all three groups. M-pain sensitivity was higher in the responsive DE group than in the intractable DE and control groups (P < .001). C-pain sensitivity was lower (P < .001) in the intractable DE group than in the responsive DE and control groups, and C-pain DT was shorter (P = .006) in the intractable DE group than in the responsive DE group. Psychological distress was higher in the intractable DE group than in the control group (P < .001).

CONCLUSIONS

Patients with intractable short TBUT DE were less sensitive to the effects of capsaicin than patients with responsive short TBUT DE and controls. Altered neural activation may contribute to the development of DE symptoms in the short TBUT DE subjects. The capsaicin stimulus test may be used to better understand pain sensitivity in short TBUT DE patients.

Comparison of clinical characteristics of post-refractive surgery-related and post-herpetic neuropathic corneal pain

Purpose:

To compare the clinical characteristics and in vivo confocal microscopy (IVCM) findings of patients with neuropathic corneal pain (NCP) due to refractive surgery (RS-NCP) and herpetic eye disease (H-NCP) to controls.

Methods:

Sixteen patients with RS-NCP and 7 patients with H-NCP, and 37 healthy reference age- and sex-matched healthy controls were included to the study. The medical records were reviewed for demographic features, detailed disease history, ocular surface disease index (OSDI), ocular pain assessment survey (OPAS) scores. IVCM images of patients were analyzed and compared to reference controls by two masked observers.

Results:

The mean pain intensity score for the last 24 h (5.1 ± 2.4 vs. 3.9 ± 1.2; p = 0.27), last 2 weeks (6.1 ± 2.5 vs. 4.8 ± 2.3; p = 0.13) for RS-NCP vs. H-NCP respectively, and quality of life scores (p = 0.23) were similar in both groups. Quality of life, especially mood (p = 0.06) and enjoying life/relations to others (p = 0.10) were affected in both groups, but were not statistically significant between groups. The mean total nerve density was lower in RS-NCP (5,702.4 ± 4,599.0 μm/mm²) compared to their respective controls (26,422.8 ± 4,491.0; p < 0.001) and in the H-NCP group (2,149.5 ± 2,985.9) compared to their respective controls (22,948.8 ± 3,169.0; p < 0.001). Alterations in DC density were similar between all groups (38.3 ± 48.0 cells/mm² in RS-NCP, 61.0 ± 76.9 in H-NCP, p = 0.95).

Conclusion:

Neuropathic corneal pain patients due to refractive surgery show similar clinical characteristics, pain levels, quality of life impact, and IVCM findings as patients with NCP due to herpetic eye disease.

Meibomian gland dysfunction is the primary determinant of dry eye symptoms: Analysis of 2346 patients

PURPOSE

To determine relative contributions of various ocular surface clinical signs and predisposing factors to the magnitude of dry eye symptoms.

METHODS

Clinical audit data were prospectively collected for newly referred dry eye patients. All 2346 patients had an initial visit evaluation of the Ocular Surface Disease Index (OSDI), and a detailed ophthalmic examination including tear breakup time (TBUT), ocular surface fluorescein staining, Schirmer's I test. Among the participants, 1414 had number of liquid meibum expressing glands (NLMEG) evaluated on standard force expression. Other variables collected included history of glaucoma or glaucoma surgery, and history of allergies.

RESULTS

In patients aged 46.2 ± 14.8 years, 77.4% were women and 87.1% Chinese. The mean ± SD OSDI was 35.2 ± 21.7. On univariate analysis, higher OSDI was associated with glaucoma diagnosis (p = 0.003), glaucoma surgery (p = 0.002), greater temporal corneal staining (p = 0.002), reduced NLMEG (p < 0.001), and higher inferior forniceal papillary grade (p < 0.001). OSDI was not significantly associated with gender, TBUT, Schirmer's I test values, or the use of cyclosporine eyedrops. On multivariate regression, higher OSDI scores were associated with fewer NLMEG (p = 0.002) and increased lower eyelid forniceal papillary grading (p = 0.002). Corneal staining, glaucoma status and glaucoma surgery were not significantly associated with OSDI. Logistic regression showed that severe symptoms (OSDI>32) was associated with <2 NLMEG [OR(95%CI): 1.34(1.08-1.66)], and presence of inferior eyelid forniceal papillae [1.50(1.17-1.91)].

CONCLUSIONS

Meibomian gland dysfunction (MGD) and lower forniceal papillary reaction had significant contributions to the severity of symptoms, in contrast to traditional dry eye signs. MGD should be objectively assessed and treated to improve symptoms.

Fibromyalgia syndrome and the eye-A review

Fibromyalgia is a chronic, widespread pain syndrome of unclear etiology characterized by fatigue, sleeping problems, cognitive disorders, somatic complaints, and severe pain in parts of the body at the time of physical activity, with no laboratory findings specific to the disease or diagnostic tests. Fibromyalgia can be associated with ocular symptoms (foreign body sensation, irritation) and visual disturbances (blurred vision), coexisting with dry eye syndrome and reduced corneal sensitivity. Cases of scleritis, including the necrotizing form, accompanying fibromyalgia have been reported. Changes in the eye may contribute to the pathogenesis of fibromyalgia. Research shows the choroid to be significantly thinner in patients with fibromyalgia, revealing changes in optic disc perfusion and a decreased retinal nerve fiber layer thickness. There are also thin corneal stromal nerves with diminished sub-basal plexus nerve density. Pathological changes and functional abnormalities of small nerve fibers are observed in patients with fibromyalgia. Corneal confocal bio-microscopy is a new noninvasive method to evaluate small nerve fiber morphology, serving as an alternative for skin biopsies, and reveals new possibilities in diagnostics and finding innovative therapies for this disease. Fibromyalgia remains a challenge for ophthalmologists, and further studies are required to evaluate ocular involvement. It may be that future diagnostic criteria for fibromyalgia will contain ophthalmic examination modalities. Observed ocular changes and their pathomechanisms may constitute new targets for therapy to improve the quality of life of patients with fibromyalgia.

Correlation between clinical and cytological parameters of dry eye among diabetics in a Nigerian tertiary hospital

PURPOSE

To correlate the clinico-cytological features of dry eye among diabetic patients attending Lagos University Teaching Hospital, Lagos.

METHODS

This was a cross-sectional, comparative study among 104 diabetic and 104 age-/sex-matched non-diabetic participants. Demographics were obtained using interviewer-administered questionnaire. Ocular Surface Disease Index (OSDI) questionnaire was used for subjective assessment of dry eye. All participants underwent ocular examination and dry eye assessment including Schirmer I test, tear film break-up time (TBUT) and ocular surface staining. In addition, conjunctival impression cytology (CIC) samples were taken for histological assessment. Data were analysed using IBM Statistical Package for the Social Sciences version 20.0 (IBM Corp., Armonk, NY USA).

RESULTS

The mean age was 58.5 ± 10.05 years and 58.32 ± 10.48 years among the diabetics and non-diabetics, respectively (p = 0.856). The male/female ratio was 1:1.4. Three hundred and ninety-seven (199 diabetic and 198 non-diabetic) eyes were assessed. Diabetics had a significantly higher median OSDI score and ocular surface staining grade compared to non-diabetics (p = 0.002 and 0.005, respectively). The TBUT was slightly lower, while the Schirmer test was slightly higher among the diabetics, but not significant (p = 0.058 and 0.033, respectively). The diabetics had a significantly higher CIC grade (p < 0.001). There was a moderate positive correlation between conjunctival cytology and ocular surface staining (r = 0.50, p < 0.01).

CONCLUSION

This study demonstrates worse ocular surface damage among diabetics characterised by ocular surface staining and abnormal CIC. Furthermore, it shows a positive correlation between ocular surface staining and CIC. Dry eye assessment should be incorporated in routine diabetic eye screening.

Associations between the menstrual cycle, lifestyle factors and clinical assessment of the ocular surface: a prospective observational study

BACKGROUND

Little is known about the ocular surface changes over the menstrual cycle in young women and the interactions with lifestyle factors. Therefore, the purpose of this study was to explore the associations between modifiable lifestyle factors and menstrual cycle phases on the ocular signs and symptoms of dry eye in young healthy women.

METHODS

This was a prospective 1-month observational study. Thirty young healthy women with regular, 24 to 32-day menstrual cycles were recruited. Participants attended three visits at day 7, 14, and 21 (± 1) of their menstrual cycle. At baseline, general health questionnaire was conducted. At each visit, symptomology was quantified using Ocular Surface Disease Index (OSDI) and overall ocular comfort (OOC, visual analogue scale). Ocular signs were assessed using Efron scales, tear break-up time (TBUT) and phenol red thread (PRT). Pearson's correlation was used to determine associations between variables at each visit.

RESULTS

A total of 26 participants (mean age = 22.3 ± 3.7 years) with an average menstrual cycle of 28.3 ± 1.3 days completed the 3 visits. The interaction between signs/symptoms and lifestyle factors changed over the cycle. At the follicular phase (day 7), lifestyle factors such diet and levels of stress were correlated with PRT and OSDI, (r = - 0.4, p = 0.022; r = 0.4, p = 0.045 respectively). At the ovulation phase (day 14), the general health score was correlated with OOC scores (r = 0.4, p = 0.047). At day 14, exercise frequency correlated with PRT (r = - 0.4, p = 0.028) and caffeine intake was positively correlate with both; TBUT (r = 0.5, p = 0.020) and PRT (r = 0.5, p = 0.014). At the luteal phase (day 21), we found no correlations between lifestyle factors and dry eye signs or symptoms.

CONCLUSIONS

The associations between lifestyle factors and objective and subjective ocular surface assessment appeared to be more pronounced during the ovulation phase of the menstrual cycle compared to the follicular and luteal phases. Misalignment of these factors with the ocular health during the luteal phase could be attributed to central sensitization and changes in levels of luteinising hormone. Natural hormonal changes during menstrual cycle should be considered for diagnosis and treatment of dry eye in young healthy women.

Dysregulated Tear Fluid Nociception-Associated Factors, Corneal Dendritic Cell Density, and Vitamin D Levels in Evaporative Dry Eye

Purpose

The purpose of this study was to study the status and association among tear-soluble factors, corneal dendritic cell density, vitamin D, and signs and symptoms in dry eye disease (DED).

Methods

A total of 33 control subjects and 47 evaporative dry eye patients were included in the study. DED diagnosis and classification was based on the 2017 Report of the Tear Film & Ocular Surface Society International Dry Eye Workshop (TFOS DEWS II). DED workup, including tear film break-up time (TBUT), Schirmer's test I (STI), corneal and conjunctival staining, ocular surface disease index (OSDI) scoring, and in vivo confocal microscopy (to assess corneal dendritic cell density [cDCD] and subbasal nerve plexus [SBNP] features) was performed in the study subjects. Tear fluid using Schirmer's strip and serum were collected from the subjects. Multiplex ELISA or single analyte ELISA was performed to measure 34 tear-soluble factors levels including vitamin D.

Results

Significantly higher OSDI discomfort score, lower TBUT, and lower STI were observed in DED patients. cDCD was significantly higher in DED patients. No significant difference was observed in SBNP features. Tear fluid IL-1β, IL-17A, MMP9, MMP10, MMP9/TIMP ratio, and VEGF-B were significantly higher in DED patients. Significantly lower tear fluid IL-2, IP-10, NPY, VEGF-A, and vitamin D was observed in DED patients. These dysregulated tear factors showed significant associations with DED signs and symptoms.

Conclusions

Altered tear fluid soluble factors with potential to modulate nociception exhibited a distinct association with ocular surface discomfort status, TBUT, STI, and cDCD. This implies a functional relationship between the various tear-soluble factors and dry eye pathogenesis, indicating new molecular targets for designing targeted therapies.

Benzalkonium chloride-induced direct and indirect toxicity on corneal epithelial and trigeminal neuronal cells: proinflammatory and apoptotic responses in vitro

Benzalkonium chloride (BAK), a quaternary ammonium compound widely used as disinfecting agent as well as preservative in eye drops is known to induce toxic effects on the ocular surface with inflammation and corneal nerve damage leading to dry eye disease (DED) in the medium-to-long term. The aim of this study was to evaluate in vitro the toxicity of a conditioned medium produced by corneal epithelial cells previously exposed to BAK (BAK-CM) on trigeminal neuronal cells. A human corneal epithelial (HCE) cell line was exposed to 5.10^-3% BAK (i.e. 0.005% BAK) for 15 min and let recover for 5 h to prepare a BAK-CM. This BAK concentration is the lowest one found in eye drops. After this recovery period, BAK effect on HCE cells displayed cytotoxicity, morphological alteration, apoptosis, oxidative stress, ATP release, CCL2 and IL6 gene induction, as well as an increase in CCL2, IL-6 and MIF release. Next, a mouse trigeminal ganglion primary culture was exposed to the BAK-CM for 2 h, 4 h or 24 h. Whereas BAK-CM did not alter neuronal cell morphology, or induced neuronal cytotoxicity or oxidative stress, BAK-CM induced gene expression of Fos (neuronal activation marker), Atf3 (neuronal injury marker), Ccl2 and Il6 (inflammatory markers). Two and 4 h BAK-CM exposure promoted a neuronal damage (ATF-3, phospho-p38 increases; phospho-Stat3 decreases) while 24 h-BAK-CM exposure initiated a prosurvival pathway activation (phospho-p44/42, phospho-Akt increases; ATF-3, GADD153, active Caspase-3 decreases). In conclusion, this in vitro model, simulating paracrine mechanisms, represents an interesting tool to highlight the indirect toxic effects of BAK or any other xenobiotic on corneal trigeminal neurons and may help to better understand the cellular mechanisms that occur during DED pathophysiology.

Clinical and in vivo confocal microscopic features of neuropathic corneal pain

Aims

To describe clinical and in vivo confocal microscopy (IVCM) features of neuropathic corneal pain (NCP) without clinically visible signs.

Methods

Prospective, observational study of 27 eyes of 14 patients who had continuous severe ocular pain for one or more years, with minimal or no ocular surface signs and were non-responsive to topical lubricants, steroids and/or ciclosporin. All patients were evaluated using Ocular Surface Disease Index, Oxford grading scale, Schirmer test 1, Cochet Bonnet esthesiometry and response to topical anaesthesia. Central and paracentral regions of the cornea of patients and seven healthy controls were studied by IVCM. Corneal epithelial thickness and sub-basal nerve density were measured in patients and controls.

Results

Four patients responded to topical anaesthesia (responsive group (RG)), indicating peripheral NCP while 10 patients did not show any improvement (non-responsive group (NRG)), indicating central NCP. Schirmer-1 test was within normal limits in the RG but significantly greater in the NRG (p<0.001). None of the other clinical parameters nor corneal epithelial thickness were statistically significantly different. The sub-basal nerve density was significantly reduced (p<0.008) in patients compared with controls. Stroma of all patients demonstrated activated keratocytes and spindle, lateral and stump microneuromas. There was a statistically significant greater number of microneuromas (p<0.0001) and activated keratocytes in RG compared with NRG.

Conclusion

NCP without visible clinical signs does not represent typical dry eye disease. Distinct signs demonstrated on IVCM suggest that peripheral NCP, which responds to topical anaesthesia, and central NCP, which does not, are separate entities.

Pregabalin Failed to Prevent Dry Eye Symptoms after Laser-Assisted in Situ Keratomileusis (LASIK) in a Randomized Pilot Study

PURPOSE

Perioperative pregabalin administration has been found to reduce the risk of persistent pain after a variety of surgical procedures. However, this approach has not been tested in relation to eye surgery. As such, the purpose of this study was to evaluate whether perioperative pregabalin can reduce the presence of dry eye (DE) symptoms, including eye pain, six months after laser-assisted in situ keratomileusis (LASIK).

METHODS

Prospective, masked, randomized single-center pilot study. Patients were treated with either pregabalin (oral solution of pregabalin 150 mg twice daily, first dose prior to surgery, continued for a total of 28 doses over 14 days) or placebo solution. The primary outcome was dry eye symptoms as measured by the Dry Eye Questionnaire 5 (DEQ-5). Secondary outcome measures included pain-related eye symptoms.

RESULTS

In total, 43 individuals were enrolled in the study and randomized to pregabalin (n = 21) or placebo (n = 22). Of those, 42 individuals completed the final visit after six months of follow-up. Some differences were noted between the two groups at baseline, including a higher frequency of females in the pregabalin group. At 6-months, there were no significant differences in the percentage of patients with DE symptoms (DEQ5 ≥ 6, 57% vs. 33%, p = 0.14), DE symptom severity (DEQ5, 6.6 ± 5.0 vs. 4.5 ± 4.2, p = 0.14), ocular pain intensity (numerical rating scale, 1.10 ± 1.48 vs. 0.38 ± 0.97, p = 0.08), or neuropathic pain complaints (Neuropathic Pain Symptom Inventory-Eye, 2.81 ± 4.07 vs. 3.14 ± 5.85, p = 0.83) between the pregabalin and control groups. Ocular signs were likewise similar between the groups, and of note, did not correlate with DE symptoms. The strongest predictor of DE symptoms six months post-surgery was the presence of DE symptoms prior to surgery.

CONCLUSIONS

Perioperative pregabalin did not reduce the frequency or severity of DE symptoms at a six month follow-up after LASIK in this small pilot study.

Role of TRPM8 Channels in Altered Cold Sensitivity of Corneal Primary Sensory Neurons Induced by Axonal Damage

The cornea is extensively innervated by trigeminal ganglion cold thermoreceptor neurons expressing TRPM8 (transient receptor potential cation channel subfamily M member 8). These neurons respond to cooling, hyperosmolarity and wetness of the corneal surface. Surgical injury of corneal nerve fibers alters tear production and often causes dry eye sensation. The contribution of TRPM8-expressing corneal cold-sensitive neurons (CCSNs) to these symptoms is unclear. Using extracellular recording of CCSNs nerve terminals combined with in vivo confocal tracking of reinnervation, Ca²⁺ imaging and patch-clamp recordings of fluorescent retrogradely labeled corneal neurons in culture, we analyzed the functional modifications of CCSNs induced by peripheral axonal damage in male mice. After injury, the percentage of CCSNs, the cold- and menthol-evoked intracellular [Ca²⁺] rises and the TRPM8 current density in CCSNs were larger than in sham animals, with no differences in the brake K⁺ current I _KD Active and passive membrane properties of CCSNs from both groups were alike and corresponded mainly to those of canonical low- and high-threshold cold thermoreceptor neurons. Ongoing firing activity and menthol sensitivity were higher in CCSN terminals of injured mice, an observation accounted for by mathematical modeling. These functional changes developed in parallel with a partial reinnervation of the cornea by TRPM8(+) fibers and with an increase in basal tearing in injured animals compared with sham mice. Our results unveil key TRPM8-dependent functional changes in CCSNs in response to injury, suggesting that increased tearing rate and ocular dryness sensation derived from deep surgical ablation of corneal nerves are due to enhanced functional expression of TRPM8 channels in these injured trigeminal primary sensory neurons.SIGNIFICANCE STATEMENT We unveil a key role of TRPM8 channels in the sensory and autonomic disturbances associated with surgical damage of eye surface nerves. We studied the damage-induced functional alterations of corneal cold-sensitive neurons using confocal tracking of reinnervation, extracellular corneal nerve terminal recordings, tearing measurements in vivo, Ca²⁺ imaging and patch-clamp recordings of cultured corneal neurons, and mathematical modeling. Corneal nerve ablation upregulates TRPM8 mainly in canonical cold thermoreceptors, enhancing their cold and menthol sensitivity, inducing a rise in the ongoing firing activity of TRPM8(+) nerve endings and an increase in basal tearing. Our results suggest that unpleasant dryness sensations, together with augmented tearing rate after corneal nerve injury, are largely due to upregulation of TRPM8 in cold thermoreceptor neurons.

Eye Pain and Dry Eye in Patients with Fibromyalgia

Objectives

The aim of this study was to examine visual function and eye symptoms in fibromyalgia patients, with a particular focus on dry eye syndrome and eye pain.

Methods

A tertiary care center-based cross-sectional study was carried out in chronic musculoskeletal pain patients diagnosed with fibromyalgia. Chronic musculoskeletal pain patients without fibromyalgia were enrolled as a comparison group. Self-reported eye pain was investigated with the McGill pain questionnaire and the numeric rating scale. In addition, we assessed corrected visual acuity, vision-related quality of life, and self-reported dry eye syndrome.

Results

A total of 90 musculoskeletal pain patients were included, with 66 patients fulfilling American College of Rheumatology 1990 criteria for fibromyalgia. Sixty-seven percent (95% confidence interval [CI] = 56%-78%) of the fibromyalgia patients reported eye pain, and 62% (95% CI = 43%-81%) of those were without fibromyalgia diagnosis. Sixty-seven percent (95% CI = 56%-78%) of the fibromyalgia patients reported an experience of dry eye compared with 76% (95% CI = 57%-95%) in the nonfibromyalgia group. Vision-related quality of life was noticeably reduced in both groups.

Conclusions

Eye pain and dry eye are common in chronic pain patients, with comparable prevalence in musculoskeletal pain patients with and without fibromyalgia.

Association between the levels of prostaglandin E2 in tears and severity of dry eye

AIM

To investigate the relationship between the levels of prostaglandin E2 (PGE2) in tears and dry eye disease severity based on both clinical symptoms and signs.

METHODS

Tear samples were collected from 36 non-Sjögren syndrome dry eye patients (10 males and 26 females, mean age 50.11±11.17y). All participants completed the Ocular Surface Disease Index (OSDI) questionnaire and underwent a detailed ophthalmic examination including, tear film breakup time (TBUT), ocular surface fluorescein staining, Schirmer I test, and meibomian gland assessment. The level of PGE2 in tears was measured using enzyme-linked immunosorbent assay (ELISA). The independent associations between tear PGE2 levels and other variables including demographics, OSDI scores, TBUT, Schirmer scores, ocular surface staining scores, and stage of meibomian gland dysfunction (MGD) were evaluated using linear regression analysis.

RESULTS

The mean PGE2 level in tears of dry eye patients was 537.85±234.02 pg/mL. The tear PGE2 levels significantly positively correlated with OSDI scores (R=0.608, P<0.001), however, they did not significantly associate with TBUT (R=0.153, P=0.373), Schirmer scores (R=-0.098, P=0.570), ocular surface staining scores (R=0.282, P=0.095), and stage of MGD (R=-0.107, P=0.535). Male sex was significantly negatively correlated with tear PGE2 levels.

CONCLUSION

The levels of PGE2 in tears are positively correlated with dry eye symptoms. However, no significant association was found between tear PGE2 levels and the results of other common dry eye diagnostic tests.

Corneal pain and experimental model development

The cornea is a valuable tissue for studying peripheral sensory nerve structure and regeneration due to its avascularity, transparency, and dense innervation. Somatosensory innervation of the cornea serves to identify changes in environmental stimuli at the ocular surface, thereby promoting barrier function to protect the eye against injury or infection. Due to regulatory demands to screen ocular safety of potential chemical exposure, a need remains to develop functional human tissue models to predict ocular damage and pain using in vitro-based systems to increase throughput and minimize animal use. In this review, we summarize the anatomical and functional roles of corneal innervation in propagation of sensory input, corneal neuropathies associated with pain, and the status of current in vivo and in vitro models. Emphasis is placed on tissue engineering approaches to study the human corneal pain response in vitro with integration of proper cell types, controlled microenvironment, and high-throughput readouts to predict pain induction. Further developments in this field will aid in defining molecular signatures to distinguish acute and chronic pain triggers based on the immune response and epithelial, stromal, and neuronal interactions that occur at the ocular surface that lead to functional outcomes in the brain depending on severity and persistence of the stimulus.

Sleep Disorders are a Prevalent and Serious Comorbidity in Dry Eye

Purpose

Sleep is an essential life habit and closely associated with lifespan, diabetes, hypertension, and mental health. Sleep disorders are a prominent, but overlooked problem in patients with dry eye disease (DED), characterized by a poor sleep index, short sleep duration, long sleep latency, and poor subjective sleep. DED and sleep disorders are more prevalent in women than men. Moreover, sleep quality in DED is worse than in other eye diseases, including glaucoma, retinal diseases, cataract, and allergic and chronic conjunctivitis.

Methods

We reviewed the literature for studies investigating sleep and health, eyes and sleep, and DED and sleep, in terms of systemic and eye health, especially in women.

Results

Two studies reported that approximately half of patients with DED suffer from poor sleep. The severity of mood disorders, including anxiety and depression, is correlated strongly with sleep disorders in DED, and the symptoms and signs of DED, especially pain, also are correlated with sleep quality. Sleep disorders are documented in primary Sjögren's syndrome and an association with sleep apnea and depression is suggested. Primary Sjögren's syndrome includes arthritis and other rheumatic disease causing pain and fatigue; however, how sicca contributes to sleep disorders is not known.

Conclusions

Possible explanations for sleep disorders in DED may be depression, pain, and eye exposure at night. Reciprocal effects may be expected and consultation-liaison psychiatry is recommended for the management of sleep disorders in DED. Topical medication and lid heating also may be advantageous for sleep quality in DED.

Short Tear Film Breakup Time-Type Dry Eye

Measurement of tear film breakup time (TBUT) has become a standard diagnostic procedure in the dry eye clinic. Short TBUT-type dry eye is characterized by TBUT of less than 5 seconds and dry eye symptoms such as ocular fatigue or dryness; the importance of this type has recently been gaining prominence. Patients with this condition show no reduction in tear production and no staining of the ocular surface. The severity of symptoms is almost the same as in dry eye in which the ocular surface is stained with rose bengal or fluorescein. In addition to discomfort, patients suffer from decreased vision due to the unstable tear film, which can be attributed to the relative abnormality of the lipid layer, aqueous layer, and/or mucin layer. The diagnosis should be performed carefully on the basis of the patient's symptoms and the TBUT test, because the ocular surface appears normal and remains unstained.

Individuals with migraine have a different dry eye symptom profile than individuals without migraine

BACKGROUND

Many individuals with migraine report symptoms of dry eye (DE). However, it is not known whether DE profiles are similar between individuals with and without migraine. To bridge this gap, we evaluated symptoms and signs of DE, including symptoms suggestive of nerve dysfunction, in a large group of individuals with DE symptoms, and compared profiles between individuals with migraine and those without migraine or headache.

METHODS

Prospective cross-sectional study of individuals with DE symptoms seen at the Miami VA.

RESULTS

Of 250 individuals, 31 met International Classification of Headache Disorders criteria for migraine based on a validated screen. Individuals with migraine were significantly younger (57 vs 62 years) and more likely to be female (26% vs 6%) than controls. Individuals with migraine had more severe DE symptoms and ocular pain compared with controls (mean Ocular Surface Disease Index 53.93 ± 21.76 vs 36.30 ± 22.90, p=0.0001; mean Neuropathic Pain Symptom Inventory modified for the Eye 39.39 ± 23.33 vs 21.86 ± 20.17, p=0.0001). The difference in symptom profile occurred despite similar ocular surface parameters between the groups.

CONCLUSIONS

Individuals with migraine had a different DE symptom yet a similar DE sign profile when compared with controls without migraine. This suggests that DE symptoms in individuals with migraine may be driven by nerve dysfunction as opposed to ocular surface abnormalities.

Latent Sensitization in a Mouse Model of Ocular Neuropathic Pain

Purpose

Chronic ocular pain is poorly understood and difficult to manage. We developed a murine model of corneal surface injury (CSI)-induced chronic ocular neuropathic pain. The study focuses on changes in corneal nerve morphology and associated short- and long-term pain-like behavior after CSI.

Methods

CSI was induced in mice by local application of an alkali solution (0.75 N NaOH). Corneal nerve architecture, morphology, density, and length were studied. Eye-wiping was evaluated before and after CSI in response to hypertonic saline (2 M NaCl). Naltrexone (NTX) or Naloxone-methiodide (NLX-me), opioid receptor antagonists, were given subcutaneously (s.c., 3 mg/kg) or topically (eye drop, 100 μM), and then an eye-wiping test was performed.

Results

CSI caused partial corneal deinnervation followed by gradual reinnervation. Regenerated nerves displayed increased tortuosity, beading, and branching. CSI enhanced hypertonic saline-induced eye-wiping behavior compared to baseline or sham-injury (P < 0.01). This hypersensitivity peaked at 10 days and subsided 14 days after CSI. Administration of NTX, or NLX-me, a selective peripheral opioid antagonist, reinstated eye-wiping behavior in the injury group, but not in the sham groups (P < 0.05).

Conclusions

This study introduces a model of chronic ocular pain and corneal neuropathy following CSI. CSI induces central and peripheral opioid receptor-dependent latent sensitization (LS) that is unmasked by systemic or topical administration of opioid antagonists.

Translational Relevance

This model of chronic ocular pain establishes LS as a new inhibitory mechanism in the oculotrigeminal system and may be used for potential diagnostic and therapeutic interventions for ocular neuropathy.

Unilateral recurrent periorbital pain: the role of the neuro-ophthalmologist

Unilateral recurrent periorbital pain is an aspecific symptom that may have originated from different orbital and ocular regions and structures that share the same innervation and can be provoked by different pathological disease. Since in some cases the patient is unable to associate with certainty the pain to a specific structure or region, a neuro-ophthalmological evaluation may be addressed to highlight signs useful to suspect the involvement of the eye, the optic nerve, the extra-ocular muscles, or intraorbital tissue or the cavernous sinus. This review describes the clinical patterns of periocular pain related to common ocular disease, orbital, or intracranial diseases.

Role of corneal nerves in ocular surface homeostasis and disease

Corneal nerves are key components of the physiological system that controls ocular surface homeostasis. The cornea is primarily innervated by the ophthalmic branch of the trigeminal nerves (cranial nerve V), which distend bilaterally from the pons. The nasociliary branch (afferent) of the ophthalmic nerve is sensory for cornea, eyelid and conjunctiva. These nerve fibres play a role in sensing temperature, chemical and mechanical stimuli, and pain, whereas, branches of the facial nerve (cranial nerve VII) contain motor nerves that control blinking and autonomic (sympathetic and a paucity of parasympathetic) fibres that stimulate tear production and secretion via feedback loops between the ocular surface, lacrimal glands and brain. Disruption of these nerves with interruption of neural feedback loops between the ocular surface and lacrimal glands can lead to corneal diseases such as dry eye disease (DED) and neurotrophic keratopathy (NK). Inversely, hypersensitivity of the nerve fibres and/or dysregulation of pain-controlling nervous centres may lead to neuropathic pain. Recently, medications that specifically target regeneration of corneal nerves have started to become available - and considering the high prevalence of diseases associated with corneal nerve dysfunction, these agents promise to fulfil a hitherto important unmet need. In this review, we explore the physiology of corneal nerves, the pathology of corneal nerve diseases and how these relate to neuropathic pain, NK and DED. We also discuss what novel treatments may be useful against diseases involving corneal nerves.

Resolution of pain with periocular injections in a patient with a 7-year history of chronic ocular pain

Purpose

We report a case of a male patient with chronic ocular pain that resolved completely following peripheral nerve blocks.

Observations

A 66-year-old male presented with a seven-year history of severe left eye pain and photophobia. The pain began after retinal detachment repair with scleral buckle placement. Previous treatments included topical (autologous serum tears, corticosteroids, diclofenac, cyclosporine) and oral (gabapentin, diclofenac) therapies with no pain relief. The patient's pain was so severe that he requested enucleation. After discussion, the decision was made to perform periocular nerve blocks. Prior to the procedure, the patient reported an average pain intensity of 8 out of 10 and photophobia daily. Following left supraorbital, supratrochlear, infraorbital and infratrochlear injections with bupivacaine and methylprednisolone, pain intensity and photophobia improved to 1–2 out of 10. One week later, repeat infraorbital and infratrochlear nerve blocks were given, after which time the patient reported complete resolution of symptoms that lasted for 7 months. Repeat nerve blocks were administered with repeat resolution of pain. There were no complications associated with the procedures.

Conclusions and Importance

Chronic ocular pain can be a debilitating condition. Periorbital nerve blocks can provide pain relief and should be considered as a potential treatment option after medical management has failed.

Efficacy of autologous serum tears for treatment of neuropathic corneal pain

OBJECTIVE

Corneal nerve damage may result in neuropathic corneal pain (NCP). Autologous serum tears (AST) have been shown to results in nerve regeneration and may help alleviate corneal pain. This study aimed to evaluate the efficacy of AST in the treatment of NCP.

METHODS

This was a retrospective case-control study. Sixteen patients suffering from severe NCP and no current ocular surface disease were compared to 12 controls. In vivo confocal microscopy (IVCM) (HRT3/RCM; Heidelberg Engineering GmbH, Germany) of the central corneas was performed bilaterally. Change in pain severity (scale of 0-10), corneal nerve density, tortuosity, reflectivity and presence of beading and micro-neuromas before and after treatment were recorded.

RESULTS

All patients had severe pain, with a mean of 9.1 ± 0.2 (range 8-10). Subbasal nerves were significantly decreased before treatment as compared to controls, including total nerve length (10,935.5 ± 1264.3 vs. 24,714.4 ± 1056.2 μm/mm²; p < 0.0001) and total number of nerves (10.5 ± 1.4 vs. 28.6 ± 2.0; p < 0.0001), respectively. Morphologically, significantly increased reflectivity (2.9 ± 0.2 vs. 1.2 ± 0.1; p = 0.00008) and tortuosity (2.4 ± 0.2 vs. 1.7 ± 0.1; p = 0.001), both graded on a scale of 0-4, were noted. After a mean of 3.8 ± 0.5 months (range 1-8 months) of AST treatment, pain severity decreased to 3.1 ± 0.3 (range 0-4), (p < 0.0001). Further, IVCM demonstrated a significant improvement (p < 0.005) in total nerve length (17,351.3 ± 1395.6  μm/mm²) and number (15.1 ± 1.6), as well as significant decrease in reflectivity (2.4 ± 0.2; p = 0.001) and tortuosity (2.2 ± 0.2; p = 0.001).

CONCLUSION

IVCM demonstrates underlying alterations of the subbasal corneal nerve plexus in patients suffering from debilitating NCP. AST-induced nerve regeneration is seen following treatment with AST, which correlates with improvement in patient symptoms of NCP.