Incomplete response to artificial tears is associated with features of neuropathic ocular pain

Nociplastic pain among individuals with chronic ocular surface pain: One cause for "pain without stain"?

Chronic ocular surface pain (COSP) refers to interrelated symptoms such as burning, aching, and irritation and can occur as an isolated condition or comorbid with numerous ocular disorders, including dry eye syndrome Treatments for COSP are largely aimed at the ocular surface and modulating pain arising from damaged corneal nerves; however, the average impact of these treatments on COSP are low to absent. A potential explanation for this is that, in a subset of patients with COSP, individuals have amplified and/or dysregulated neural signaling and sensory processing within the central nervous system (CNS). As in other chronic pain conditions, this might be the pathogenic mechanism primarily responsible for maintaining pain - a phenomenon now referred to as nociplastic pain. The key clinical features of nociplastic pain include symptoms out of proportion to signs, regional or widespread pain, the presence of other chronic pain conditions, and non-pain CNS mediated symptoms (e.g., sleep disorders). We provide an overview for eye care clinicians of nociplastic pain and delineate the emerging evidence for the presence of nociplastic pain among some individuals with COSP. We highlight gaps in our current understanding of nociplastic pain in COSP and provide clinicians with specific tools that may aid in the assessment and management of nociplastic pain.

Corneal Sensory Changes and Nerve Plexus Abnormalities in Chronic Neuropathic Ocular Pain and Dry Eye Post-Refractive Surgery

PURPOSE

Chronic neuropathic ocular pain (NOP) can develop alongside chronic dry eye (DE) post-laser-assisted in-situ keratomileusis (LASIK), yet its specific characteristics remain poorly understood. This study aims to compare the clinical characteristics of patients who developed both DE and NOP after LASIK to those with only DE and to asymptomatic LASIK patients, to facilitate the diagnosis of NOP.

METHODS

Prospective, cross-sectional "case-control" comparison study. An 89-subject post-LASIK study comprised three groups: 34 patients developing NOP and DE (NOP-DE group), 25 patients developing only DE (DE group), and 30 asymptomatic subjects (control group). Assessments included clinical history and symptom questionnaires (OSDI, mSIDEQ, NRS, WFPRS), anxiety and depression evaluation (HADS), tear film stability (osmolarity and TBUT) and production (Schirmer), and ocular surface integrity. Corneal mechanical and thermal sensitivity thresholds were measured using Belmonte's non-contact esthesiometer, whereas tactile sensitivity threshold was assessed pre/post-topical anesthesia using the Cochet-Bonnet esthesiometer. In vivo confocal microscopy (IVCM) was used to evaluate the sub-basal nerve plexus characteristics and dendritic cell density in the central cornea. Group comparisons and correlations were conducted.

RESULTS

Compared with DE group, patients in the NOP-DE group exhibited significantly more DE symptoms with mSIDEQ (p=0.019) higher level of pain with NRS and WFPRS, increased use of ocular lubrication (p=0.003), greater frequency of patients with pathological results on anxiety and depression questionnaires (p<0.001), and a higher prevalence of central sensitization syndromes (p<0.001). Additionally, NOP-DE patients demonstrated higher tactile corneal sensitivity post-topical anesthesia (p=0.002). IVCM revealed lower nerve density (p=0.049) and higher microneuroma density (p=0.008) in the sub-basal nerve plexus of NOP-DE patients compared to DE patients without NOP (p=0.008). Most nerve metrics correlated moderately to strongly with clinical parameters.

CONCLUSIONS

Persistent high corneal tactile sensitivity post-anesthesia, reduced nerve density and increased microneuroma density in the central cornea may serve as diagnostic indicators for confirming NOP in patients experiencing chronic DE post-LASIK. These findings underscore the potential utility of incorporating these measures into clinical assessments to improve diagnostic accuracy and guide management strategies in this patient population.

Tear Film and Dry Eye Characteristics as Predictors of Photophobia in 374 Patients with Dry Eye Disease

PURPOSE

To assess the tear film parameters associated with photophobia in dry eye disease (DED).

METHODS

Three hundred seventy-four patients with DED (mean age, 42.2 ± 12.8 years) had their tear film and OSDI scores evaluated using Oculus keratograph 5 M (TMH, NIBUT, Meibography), Lipiview interferometer (LLT), and TearLab osmolarity system. Photophobia scoring from OSDI sheets was used to calculate the odds ratio via multivariate logistic regression analysis. Data from the eye with severely affected NIBUT was used.

RESULTS

Of 374, 127 had aqueous deficient dry eye disease (ADDE), and 247 had evaporative DED. The mean age, female sex, Schirmer I, TMH, NIBUT, LLT, and tear osmolarity values in patients with photophobia versus no or mild photophobia were 42.2. vs. 40.9 years, 42% vs. 40%, 11.6 vs. 10.5 mm, 0.27 vs. 0.29 mm, 4.6 vs. 4.7s, 60.3 vs. 60.9 nm and 305 vs. 307 mOsm/L, respectively. Multivariate analysis revealed no tear film parameters predictive of photophobia in evaporative DED, whereas tear osmolarity had a weak negative association with photophobia (odds ratio of 0.96, 95% C.I, 0.92-1, p = .04) in ADDE patients.

CONCLUSION

Tear film parameters do not predict the presence or absence of photophobia in DED except for a weak inverse association with tear osmolarity in ADDE. This suggests the role of central sensitization in regulating photophobia in DED patients.

Impact of botulinum toxin type A on ocular pain with neuropathic features

PURPOSE

To investigate the impact of botulinum toxin type A (BoNT-A) on neuropathic/nociplastic ocular pain (NOP) and identify predictors of patient outcomes.

METHODS

A retrospective study of individuals with NOP symptoms (light sensitivity, wind/air sensitivity, persistent pain despite dry eye treatment) who received ≥1 BoNT-A injection. Primary outcome measures included if (responders vs. non-responders) and to what degree (none vs. mild vs. moderate vs. marked) individuals experienced pain improvement 4-6 weeks post-injection. Demographics and clinical exam information was compared between the groups.

RESULTS

27 individuals received BoNT-A for NOP symptoms. 74 % (n = 20) reported an improvement in pain and were classified as responders. Among responders, the degree of benefit varied, with 25 % reporting mild, 45 % moderate, and 30 % marked pain improvement. Improvements in light sensitivity (37 %), wind/air sensitivity (33 %), and quality of life (QoL) (59 %) were reported by fewer individuals. 80 % of responders and 0 % of non-responders reported QoL improvements afer BoNT-A. In a multivariable model that examined predictors of response (none to marked, 0-3), the presence of fibromyalgia (FM) (β = 0.50; p = 0.004) portended a better response, while shooting pain (β = -0.47; p = 0.007) portended a worse response to BoNT-A, (full model r2 = 0.53; p < 0.001). Degree of pain improvement significantly correlated with improvements in light sensitivity, wind/air sensitivity, and QoL (ρ range: 0.42-0.63; p < 0.05).

CONCLUSION

After BoNT-A, most individuals reported improved ocular pain and QoL, while fewer noted improved light and wind/air sensitivity. Some systemic and ocular factors predicted treatment response and may thus guide treatment.

Mental burden of ocular surface discomfort

OBJECTIVE

This research investigates the associations between Dry Eye Disease (DED), pain perception, and mental health, focusing on how neuropathic pain influences treatment efficacy and patients' quality of life.

METHODS AND RESULTS

The study delves into the complexity of DED by assessing the correlation between ocular pain, depression, PTSD, and systemic pain conditions. It highlights the role of chronic neuropathic pain in DED and the nociceptive hypothesis, which suggests that psychological stress can exacerbate DED symptoms. Additionally, it explores diagnostic and management strategies for DED, emphasizing the importance of considering psychological aspects to improve patient care.

CONCLUSIONS

The intricate nature of DED, closely linked to mental health issues, requires a comprehensive diagnostic and therapeutic approach. Addressing neuropathic pain and psychological factors is crucial for effective DED management. Future efforts should focus on developing specific interventions targeting DED's physical and emotional impacts to enhance overall patient well-being.

Review of Hydroxypropyl Methylcellulose in Artificial Tears for the Treatment of Dry Eye Disease

Dry eye disease (DED) is a highly prevalent condition, resulting in reduced quality of life, lower participation in social life and impaired work efficiency. Hydroxypropyl methylcellulose (HPMC) is a cellulose-based viscosity-enhancing agent and is one of the most popular therapeutic ingredients in artificial tears. This review aims to evaluate the literature on the efficacy and safety of HPMC used in the treatment of DED. Literature searches were conducted in PubMed and Cochrane CENTRAL. A total of 28 clinical trials from 26 publications are included in this review, including 21 clinical intervention studies evaluating the effect of HPMC treatment over time and seven single instillation studies evaluating the short-term physical and symptomatic effects of HPMC after drop-instillation. The duration of clinical intervention studies ranged from 2 weeks to 5.5 months. DED severity ranged from mild to severe. Drop frequency ranged from two to up to 16 drops per day. HPMC concentration in artificial tears ranged from 0.2% to 0.5%. No major complications or adverse events were reported. Artificial tears containing HPMC were effective at improving symptoms and some signs of DED. However, combination drops with HPMC plus other therapeutic ingredients seem more effective than HPMC alone. HPMC appears to be equally effective or inferior to hyaluronic acid (HA). There is no evidence of superiority or inferiority to either carboxymethylcellulose (CMC) or polyethylene glycol 400/propylene glycol (PEG/PG). No single study explained the choice of drop frequency or HPMC concentration. More well-designed studies are needed to determine an evidence-based standard for HPMC treatment, including drop frequency, concentration and molecular weight for different DED severity and subgroups.

Effect of Acupuncture Treatment on the Ocular Pain, Mental State and Ocular Surface Characteristics of Patients with Dry Eye Disease: A Non-Randomized Pilot Study

Background

Ocular pain is a prevalent symptom of dry eye disease (DED), which often accompanies potential psychological issues. The study aimed to explore whether acupuncture could improve ocular pain, mental state, and dry eye parameters in patients with DED.

Methods

The non-randomized pilot study included 48 patients divided into two groups: the acupuncture group (n=27) and the 0.3% sodium hyaluronate (SH) group (n=21). Participants in the acupuncture group underwent treatments on six bilateral acupuncture points (BL1, BL2, ST1, LI 20, SI1 and SI3) 3 times per week for 4 weeks. Patients in the SH group received 0.3% SH 4 times per day for 4 weeks. Ocular pain was assessed using the numerical rating scale (NRS), and mental state was evaluated through the self-rating anxiety scale (SAS) and self-rating depression scale (SDS). Ocular surface parameters, concentrations of inflammatory cytokines, and corneal nerve morphological indicators were measured at baseline, the first week, and the fourth week. Randomization procedures were not used in this study, and outcome assessors and statistical analysts were blinded.

Results

Compared with baseline, both NRS scores (from 5.91 ± 1.52 to 1.94 ± 1.57) and ocular surface discomfort index (OSDI) scores (from 49.75 ± 14.92 to 29.64 ± 18.79) were decreased after 1 and 4 weeks of treatment in both groups (all p < 0.05). At 4 weeks, the acupuncture group showed significant improvements, including increased tear break-up time (TBUT) and corneal perception, decreased SAS and SDS scores, and reduced concentrations of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α concentration in tears (all p < 0.05). These changes were not observed in the SH group (all p > 0.05).

Conclusion

Acupuncture treatment could improve ocular surface characteristics in patients with DED, and more importantly, it alleviates their ocular pain and depressive state. The anti-inflammatory effect of acupuncture may be involved in this process. Future research with larger, randomized controlled trials (RCTs) is necessary to confirm these findings and clarify the mechanisms involved.

Corneal neuropathic pain: a review to inform clinical practice

Corneal neuropathic pain (CNP) is a poorly defined disease entity characterised by an aberrant pain response to normally non-painful stimuli and categorised into having peripheral and central mechanisms, with the former responding to instillation of topical anaesthetic. CNP is a challenging condition to diagnose due to numerous aetiologies, an absence of clinical signs and ancillary tests (in vivo confocal microscopy and esthesiometry), lacking the ability to confirm the diagnosis and having limited availability. Symptomatology maybe mirrored by severe and chronic forms of dry eye disease (DED), often leading to misdiagnosis and inadequate treatment. In practice, patients with suspected CNP can be assessed with questionnaires to elicit symptoms. A thorough ocular assessment is also performed to exclude any co-existent ocular conditions. A medical and mental health history should be sought due to associations with autoimmune disease, chronic pain syndromes, anxiety and depression. Management begins with communicating to the patient the nature of their condition. Ophthalmologists can prescribe topical therapies such as autologous serum eyedrops to optimise the ocular surface and promote neural regeneration. However, a multi-disciplinary treatment approach is often required, including mental health support, particularly when there are central mechanisms. General practitioners, pain specialists, neurologists and psychologists may be needed to assist with oral and behavioural therapies. Less data is available to support the safety and efficacy of adjuvant and surgical therapies and the long-term natural history remains to be determined. Hence clinical trials and registry studies are urgently needed to fill these data gaps with the aim to improve patient care.

Genome Wide Association Study of Neuropathic Ocular Pain

Purpose

To conduct a genome-wide association study (GWAS) of individuals with neuropathic ocular pain (NOP) symptoms to identify genomic variants that may predispose to NOP development.

Design

Prospective study of individuals with NOP.

Participants

Three hundred twenty-nine patients recruited from the Miami Veterans Affairs eye clinic.

Methods

The Neuropathic Pain Symptom Inventory modified for the eye (NPSI-Eye) was completed to calculate a NPSI-Eye-Sub-Score (summed ratings of burning and wind sensitivity) as an indicator of NOP severity. A GWAS was performed for the NPSI-Eye-Sub-Score with a significance threshold of P < 5 × 10-8. A gene-based analysis was performed using the multimarker analysis of genomic annotation software (in the functional mapping and annotation of GWAS online platform). The 13 865 778 single nucleotide polymorphisms (SNPs) from our GWAS analysis were mapped to 10 834 protein coding genes, and significant genes were run through gene set enrichment analysis.

Main Outcome Measures

Identification of SNPs and protein products that may be associated with the development of NOP.

Results

One hundred seventy-one SNPs reached a threshold of P < 10-5, of which 10 SNPs reached the suggestive level of significance of P < 5 × 10-7 and 1 SNP met our genome-wide significance threshold of P < 5 × 10-8. This lead SNP, rs140293404 (P = 1.23 × 10-8), is an intronic variant found within gene ENSG00000287251 coding for transcript ENST00000662732.1. Rs140293404 is in linkage disequilibrium with exon variant rs7926353 (r2 > 0.8) within ENSG00000279046 coding for transcript ENST00000624288.1. The most significant genes from gene-based tests were matrix metalloproteinase-19 (MMP19) (P = 1.12 × 10-5), zinc finger RNA-binding motif and serine/arginine rich-1 (ZRSR1) (P = 1.48 × 10-4), CTC-487M23.8 (P = 1.79 × 10-4), receptor expression-enhancing protein-5 (REEP5) (P = 2.36 × 10-4), and signal recognition particle-19 (SRP19) (P = 2.56 × 10-4). From gene set enrichment analysis, the sensory perception (false discovery rate = 6.57 × 10-3) and olfactory signaling (false discovery rate = 1.63 × 10-2) pathways were enriched with the most significant genes.

Conclusions

Our GWAS revealed genes with protein products that may impact sensory perception, lending biological plausibility to a role for SNPs identified by our GWAS in the development of NOP. A better understanding of the biological relevance of these genes and pathways in the pathophysiology associated with NOP may facilitate future novel mechanism-based treatments.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Relationship between ocular surface pain and corneal nerve loss in dry eye diabetics: a cross-sectional study in Shenyang, China

BACKGROUND

Diabetes mellitus has been associated with increased dry eye disease (DED) and exacerbates DED pathology.

OBJECTIVE

To investigate the potential relationship between corneal nerve loss and ocular pain among diabetic patients with dry eye (DE).

DESIGN

A cross-sectional study.

SETTING

He Eye Specialist Hospital, Shenyang, China.

PARTICIPANTS

This study recruited 124 eyes of 62 diabetic patients diagnosed with DED between August and October 2022.

MAIN OUTCOME MEASURES

Best-corrected visual acuity, intraocular pressure, non-invasive tear breakup time, tear meniscus height, tear film lipid layer, conjunctival hyperaemia (redness score), conjunctivocorneal epithelial staining (CS score), central corneal sensitivity and vitro confocal corneal microscopy was assessed in all subjects. The Ocular Surface Disease Index Questionnaire assessed DE symptoms and ocular pain.

RESULTS

The study's final analysis included 26 patients (52 eyes) without ocular pain and 36 patients (72 eyes) with ocular pain. The corneal nerve fibre density (CNFD), corneal nerve branch density (CNBD) and corneal nerve fibre length (CNFL) in patients with ocular pain were significantly lower than those without (p<0.001, p=0.004, and p<0.001, respectively). CNFD, CNBD and CNFL negatively correlated with ocular pain (r=-0.385, r=-0.260, r=-0.358, respectively). Moreover, CNFD, CNBD and CNFL have a significant (p<0.05) positive correlation with corneal sensitivity (r=0.523, r=0.330, r=0.421, respectively).

CONCLUSIONS

Corneal nerve loss was associated with ocular pain and decreased corneal sensitivity in diabetic patients with DE. Further studies into the neurological role of ocular surface diseases can elaborate diagnostics, prognosis and treatment of diabetic patients with DE.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT05193331).

Ocular nociception and neuropathic pain initiated by blue light stress in C57BL/6J mice

To elucidate the physiological, cellular, and molecular mechanisms responsible for initiating and sustaining ocular neuropathic pain, we created a blue-light-exposure model in C57BL/6 mice. Mice were exposed to 12 h of blue or white light followed by 12 h of darkness. Before blue light exposure, baseline tear secretion, stability, and ocular hyperalgesia were assessed by measuring hyper- or hypo-osmotic solution-induced eye wiping, wind-induced eye closing, and cold-induced eye blinking. At 1 day post-blue light exposure, alterations in hypotonic/hypertonic-induced eye-wiping, and tear film abnormalities were observed. Eye-wiping behaviors were abolished by topical anesthesia. The cold-stimulated eye-blinking and wind-stimulated eye-closing behaviors began after day 3 and their frequency further increased after day 9. Blue-light exposure reduced the density of nerve endings, and increased their tortuosity, the number of beadlike structures, and the branching of stromal nerve fibers, as assessed by whole-mount confocal microscopy. Blue-light exposure also increased TRPV1, but not TRPV4 staining intensity of corneal-projecting neurons in the trigeminal ganglia, as detected by Fluorogold retrograde labeling and immunohistochemistry. TRPV1 and substance P expression was increased, whereas CGRP expression deceased at the mRNA level in isolated corneal projecting neurons. Hence, our blue-light exposure B6 mouse model for assessing tearing and ocular hyperalgesia is useful for studying ocular pain and its underlying mechanisms. Blue-light-induced alterations in tearing and ocular hyperalgesia may be related to the elevated expression of TRPV1, SP, and/or the suppressed expression of CGRP at the ocular surface.

Corticosterone mediates FKBP51 signaling and inflammation response in the trigeminal ganglion in chronic stress-induced corneal hyperalgesia mice

Stress-induced hyperalgesia is a health-threatening condition that lacks effective therapeutic intervention, impairing the quality of life. Interestingly, a high prevalence of corneal pain symptoms was also found in patients experienced severe stressors. Excessive secretion corticosterone in rodents has been shown to contribute to the development of visceral and mechanical hyperalgesia under stressful conditions. The co-chaperone protein FK506-binding protein 5 (FKBP5) was reported to modulate steroid sensitivity and inhibition of FKBP51 possessed anxiolytic and anti-hyperalgesic in the stressed-mice model. However, whether corticosterone and FKBP5 play a role in chronic stress-induced corneal hyperalgesia remains unknown. The aim of this study was to evaluate the corneal sensitivity after exposure to chronic restraint stress (CRS) and investigate the potential role of corticosterone and FKBP5 mediated proinflammatory cytokines release in trigeminal ganglion (TG) in corneal hyperalgesia under chronic stressful situations. Firstly, mice displayed increased corneal sensitivity without changes in tear production and corneal injury after CRS for 4 hours/day for 14 days. Meanwhile, corticosterone deficiency via adrenalectomy could prevent CRS-induced corneal hyperalgesia, whereas chronic corticosterone feeding increased the corneal sensitivity accompanied by increasing proinflammatory cytokines levels of phospho-NF-κB (p-NF-κB), tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the TG on d14. Notably, we found that FKBP51 was significantly upregulated in the TG in the stressed-mice. Intraperitoneal injection of FKBP51 inhibitor significantly alleviated CRS-induced corneal hyperalgesia, and reversed calcitonin gene related peptide (CGRP) increase and proinflammatory cytokines production in the TG. Moreover, FKBP51 inhibitor could also exert its anti-hyperalgesic effect on corneal pain through intra-TG injection. Our study proves that CRS can induce corneal hyperalgesia in mice and uncovers the role of corticosterone and FKBP51 in modulating corneal sensitivity, providing a novel treatment strategy for stress-induced corneal hyperalgesia. AVAILABILITY OF DATA AND MATERIALS: All data and additional file are available upon request from the corresponding author.

Botulinum toxin A decreases neural activity in pain-related brain regions in individuals with chronic ocular pain and photophobia

Introduction

To examine the effect of botulinum toxin A (BoNT-A) on neural mechanisms underlying pain and photophobia using functional magnetic resonance imaging (fMRI) in individuals with chronic ocular pain.

Methods

Twelve subjects with chronic ocular pain and light sensitivity were recruited from the Miami Veterans Affairs eye clinic. Inclusion criteria were: (1) chronic ocular pain; (2) presence of ocular pain over 1 week recall; and (3) presence of photophobia. All individuals underwent an ocular surface examination to capture tear parameters before and 4-6 weeks after BoNT-A injections. Using an event-related fMRI design, subjects were presented with light stimuli during two fMRI scans, once before and 4-6 weeks after BoNT-A injection. Light evoked unpleasantness ratings were reported by subjects after each scan. Whole brain blood oxygen level dependent (BOLD) responses to light stimuli were analyzed.

Results

At baseline, all subjects reported unpleasantness with light stimulation (average: 70.8 ± 32.0). Four to six weeks after BoNT-A injection, unpleasantness scores decreased (48.1 ± 33.6), but the change was not significant. On an individual level, 50% of subjects had decreased unpleasantness ratings in response to light stimulation compared to baseline ("responders," n = 6), while 50% had equivalent (n = 3) or increased (n = 3) unpleasantness ("non-responders"). At baseline, several differences were noted between responders and non-responders; responders had higher baseline unpleasantness ratings to light, higher symptoms of depression, and more frequent use of antidepressants and anxiolytics, compared to non-responders. Group analysis at baseline displayed light-evoked BOLD responses in bilateral primary somatosensory (S1), bilateral secondary somatosensory (S2), bilateral anterior insula, paracingulate gyrus, midcingulate cortex (MCC), bilateral frontal pole, bilateral cerebellar hemispheric lobule VI, vermis, bilateral cerebellar crus I and II, and visual cortices. BoNT-A injections significantly decreased light evoked BOLD responses in bilateral S1, S2 cortices, cerebellar hemispheric lobule VI, cerebellar crus I, and left cerebellar crus II. BoNT-A responders displayed activation of the spinal trigeminal nucleus at baseline where non-responders did not.

Discussion

BoNT-A injections modulate light-evoked activation of pain-related brain systems and photophobia symptoms in some individuals with chronic ocular pain. These effects are associated with decreased activation in areas responsible for processing the sensory-discriminative, affective, dimensions, and motor responses to pain.

Novel Treatments for Chronic Ocular Surface Pain

ABSTRACT

Several etiologies can contribute to ocular surface pain including nociceptive, peripheral neuropathic, and central neuropathic mechanisms. Clinical clues can help identify contributors to ocular surface pain in a patient. In individuals whose pain persists despite targeting nociceptive contributors, neuropathic mechanisms should be considered and addressed using oral, topical, and/or adjuvant agents.

Artificial Tears: A Systematic Review

Artificial tears are the mainstay of dry eye disease management, but also have a role in corneal abrasion and wound healing, pain and inflammation management, conjunctivitis, keratitis, contact lens rewetting and removal, and foreign body removal. A systematic review of randomized controlled trials (PROSPERO registration CRD42022369619) comparing the efficacy of artificial tears in patients with dry eye to inform prescribing choices using Web of Science, PubMed and Medline databases identified 64 relevant articles. There is good evidence that artificial tears improve symptoms of dry eye disease within a month of regular use, applied about four times a day, but signs generally take several months to improve. Not all patients with dry eye disease benefit from artificial tears, so if there is no benefit over a month, alternative management should be considered. Combination formulations are more effective than single active ingredient artificial tears. Artificial tears containing polyethylene glycol are more effective than those containing carboxymethylcellulose/carmellose sodium and hydroxypropyl methylcellulose. Those classified as having evaporative dry eye disease, benefit from artificial tears with liposomes, especially of higher concentration. The data available is limited by the definition of dry eye disease applied in published studies being variable, as well as the disease severity examined and compliance with artificial tears being rarely quantified.

Diquafosol sodium reduces neuronal activity in trigeminal subnucleus caudalis in a rat model of chronic dry eye disease

Patients with persistent and severe dry eye disease (DED) have corneal hypersensitivity, resulting in ocular pain, and diquafosol sodium, a potent P2Y₂ receptor agonist, is commonly used to improve the resultant tear film stability. This study determined the effects of diquafosol instillation on the suppression of trigeminal subnucleus caudalis (Vc) neuronal activity and ocular pain by enhancing tear film stability in the model for chronic DED. The effects of diquafosol on the ocular surface were assessed by the topical application for 28 days, starting from the 14th day since unilateral exorbital gland removal (chronic DED). Loss of tear volume secretion in chronic DED rats was significantly reversed by diquafosol instillation after 28 days, compared with saline treatment. The number of eyeblinks and pERK-IR neurons in the superficial laminae of Vc following hypertonic saline administration to the ocular surface was lower in diquafosol-treated chronic DED rats than in saline-treated rats. The neuronal activity evoked by hypertonic saline and mechanical stimulation along with the spontaneous neuronal activity in the superficial laminae of the Vc were suppressed in diquafosol-treated chronic DED rats. These findings suggest that ocular surface instillation of diquafosol for 28 days attenuates the neuronal hyperactivity in the Vc and the ocular pain that often occurs in chronic DED.

Footedness for scratching itchy eyes in rodents

The neural bases of itchy eye transmission remain unclear compared with those involved in body itch. Here, we show in rodents that the gastrin-releasing peptide receptor (GRPR) of the trigeminal sensory system is involved in the transmission of itchy eyes. Interestingly, we further demonstrate a difference in scratching behaviour between the left and right hindfeet in rodents; histamine instillation into the conjunctival sac of both eyes revealed right-foot biased laterality in the scratching movements. Unilateral histamine instillation specifically induced neural activation in the ipsilateral sensory pathway, with no significant difference between the activations following left- and right-eye instillations. Thus, the behavioural laterality is presumably due to right-foot preference in rodents. Genetically modified rats with specific depletion of Grpr-expressing neurons in the trigeminal sensory nucleus caudalis of the medulla oblongata exhibited fewer and shorter histamine-induced scratching movements than controls and eliminated the footedness. These results taken together indicate that the Grpr-expressing neurons are required for the transmission of itch sensation from the eyes, but that foot preference is generated centrally. These findings could open up a new field of research on the mechanisms of the laterality in vertebrates and also offer new potential therapeutic approaches to refractory pruritic eye disorders.

Neuropathic pain and itch: mechanisms in allergic conjunctivitis

PURPOSE OF REVIEW

Allergic conjunctivitis is highly prevalent and affects up to one third of the general population. The current understanding of the pathophysiology and therapeutic strategies center around the type 2 inflammatory pathway. However, there is an increasing body of evidence that suggests neurogenic mechanisms also play a role in allergic inflammation, with a substantial proportion of allergic conjunctivitis patients experiencing both ocular itch and pain.

RECENT FINDINGS

Unmyelinated C fibres on the ocular surface transmit histaminergic itch and can be directly activated by mast cell mediators. The conjunctival mucosa also contains TRPV1+ (histamine-dependent) and TRPA1+ (histamine-independent) neurons that enhance ocular pain and itch in allergic conjunctivitis. Allergen-complexed IgE also binds directly to FcεRI expressed on peripheral neurons. Environmental aeroallergens can also directly stimulate neuronal nociceptors to release inflammatory substances. Allergic inflammation thus stimulates nerve terminals to release vasoactive and inflammatory neuropeptides, leading to a cyclical neuronal dysregulation that augments mast cell activity. These repetitive cycles lead to both peripheral and central sensitization and neuronal plasticity, resulting in decreased itch/pain thresholds and a heightened itch/pain response.

SUMMARY

Neurogenic mechanisms including peripheral and central sensitization may drive chronic ocular itch and pain secondary to allergic inflammation. Research into these pathways may help to identify therapeutic targets in allergic conjunctivitis patients with refractory symptoms.

The Utility of Oral Vitamin B1 and Mecobalamin to Improve Corneal Nerves in Dry Eye Disease: An In Vivo Confocal Microscopy Study

Our purpose is to demonstrate the changes in cornea nerve parameters and symptoms and signs in dry eye disease (DED) patients after oral vitamin B1 and mecobalamin treatment. In this randomized double-blind controlled trial, DED patients were randomly assigned to either the treatment group (oral vitamin B1 and mecobalamin, artificial tears) or the control group (artificial tears). Corneal nerve parameters via in vivo confocal microscopy (IVCM), DED symptoms, and signs were assessed at baseline and 1 and 3 months post-treatment. In total, 398 eyes from 199 patients were included. In the treatment group, there were significant improvements in corneal nerve length, width, and neuromas, the sign of conjunctival congestion score (CCS), symptoms of dryness, pain, photophobia, blurred vision, total symptom score, and OSDI (OSDI) at 1/3 months post-treatment (all p < 0.05). Patients who received vitamin B1 and mecobalamin showed greater improvement in CCS, dryness scores at 1 month (p < 0.05), corneal fluorescein staining (CFS) (p = 0.012), photophobia (p = 0.032), total symptom scores (p = 0.041), and OSDI (p = 0.029) at 3 months. Greater continuous improvement in CFS (p = 0.045), dryness (p = 0.033), blurred vision (p = 0.031) and total symptom scores (p = 0.023) was demonstrated at 3 months than at 1 month post-treatment in the treatment group. We found that oral vitamin B1 and mecobalamin can improve corneal nerve length, width, reflectivity and the number of neuromas in IVCM, thereby repairing epithelial cells and alleviating some ocular symptoms. Thus, vitamin B1 and mecobalamin are potential treatment options for patients with DED.

Neuropathic ocular surface pain: Emerging drug targets and therapeutic implications

INTRODUCTION

Dysfunction at various levels of the somatosensory system can lead to ocular surface pain with a neuropathic component. Compared to nociceptive pain (due to noxious stimuli at the ocular surface), neuropathic pain tends to be chronic and refractory to therapies, making it an important source of morbidity in the population. An understanding of the options available for neuropathic ocular surface pain, including new and emerging therapies, is thus an important topic.

AREAS COVERED

This review will examine studies focusing on ocular surface pain, emphasizing those examining patients with a neuropathic component. Attention will be placed toward recent (after 2017) studies that have examined new and emerging therapies for neuropathic ocular surface pain.

EXPERT OPINION

Several therapies have been studied thus far, and continued research is needed to identify which individuals would benefit from specific therapies. Gaps in our understanding exist, especially with availability of in-clinic diagnostics for neuropathic pain. A focus on improving diagnostic capabilities and researching gene-modulating therapies could help us to provide more specific mechanism-based therapies for patients. In the meantime, continuing to uncover new modalities and examining which are likely to work depending on pain phenotype remains an important short-term goal.

Self-Report of Severity of Ocular Pain Due to Light as a Predictor of Altered Central Nociceptive System Processing in Individuals With Symptoms of Dry Eye Disease

Dry eye disease (DED) is a diagnosis given to individuals with a heterogeneous combination of symptoms and/or signs, including spontaneous and evoked ocular pain. Our current study evaluated whether and which ocular pain assessments could serve as screening tools for central sensitization in individuals with DED. A cohort of individuals with DED symptoms (n = 235) were evaluated for ocular pain, DED signs (tear production, evaporation), evoked sensitivity to mechanical stimulation at the cornea, and evidence of central sensitization. Central sensitization was defined for this study as the presence of pain 30 seconds after termination of a thermal noxious temporal summation protocol (ie, aftersensations) presented at a site remote from the eye (ventral forearm). We found that combining ratings of average intensity of ocular pain, ratings of average intensity of pain due to light, response to topical anesthetic eye drops, and corneal mechanical pain thresholds produced the best predictive model for central sensitization (area under the curve of .73). When examining ratings of intensity of ocular pain due to light alone (0-10 numerical rating), a cutoff score of 2 maximized sensitivity (85%) and specificity (48%) for the presence of painful aftersensations at the forearm. Self-reported rating of pain sensitivity to light may serve as a quick screening tool indicating the involvement of central nociceptive system dysfunction in individuals with DED. PERSPECTIVE: This study reveals that clinically-relevant variables, including a simple 0 to 10 rating of ocular pain due to light, can be used to predict the contribution of central sensitization mechanisms in a subgroup of individuals with DED symptoms. These findings can potentially improve patient stratification and management for this complex and painful disease.

Topical Therapeutic Options in Corneal Neuropathic Pain

Purpose of Review: Corneal neuropathic pain can be difficult to treat, particularly due to its lack of response to standard dry eye therapies. We describe a variety of topical therapeutic options that are available to treat corneal neuropathic pain with a significant or primary peripheral component. We also describe possible mechanisms of action for such topical therapies.

Recent Findings: Topical corticosteroids and blood-derived tear preparations can be helpful. Newer therapies, including topical lacosamide and low-dose naltrexone are emerging therapeutic options that may also be considered.

Summary: Corneal neuropathic pain with a significant peripheral component may be managed with a variety of topical therapeutic options.

Differential Effects of Treatment Strategies in Individuals With Chronic Ocular Surface Pain With a Neuropathic Component

Background: Dysfunction at the ocular system via nociceptive or neuropathic mechanisms can lead to chronic ocular pain. While many studies have reported on responses to treatment for nociceptive pain, fewer have focused on neuropathic ocular pain. This retrospective study assessed clinical responses to pain treatment modalities in individuals with neuropathic component ocular surface pain. Methods: 101 individuals seen at the University of Miami Oculofacial Pain Clinic from January 2015 to August 2021 with ≥3 months of clinically diagnosed neuropathic pain were included. Patients were subcategorized (postsurgical, post-traumatic, migraine-like, and laterality) and self-reported treatment outcomes were assessed (no change, mild, moderate, or marked improvement). One-way ANOVA (analysis of variance) was used to examine relationships between follow up time and number of treatments attempted with pain improvement, and multivariable logistic regression was used to assess which modalities led to pain improvement. Results: The mean age was 55 years, and most patients were female (64.4%) and non-Hispanic (68.3%). Migraine-like pain (40.6%) was most common, followed by postsurgical (26.7%), post-traumatic (16.8%) and unilateral pain (15.8%). The most common oral therapies were α2δ ligands (48.5%), the m common topical therapies were autologous serum tears (20.8%) and topical corticosteroids (19.8%), and the most common adjuvant was periocular nerve block (24.8%). Oral therapies reduced pain in post-traumatic (81.2%), migraine-like (73%), and unilateral (72.7%) patients, but only in a minority of postsurgical (38.5%) patients. Similarly, topicals improved pain in post-traumatic (66.7%), migraine-like (78.6%), and unilateral (70%) compared to postsurgical (43.7%) patients. Non-oral/topical adjuvants reduced pain in postsurgical (54.5%), post-traumatic (71.4%), and migraine-like patients (73.3%) only. Multivariable analyses indicated migraine-like pain improved with concomitant oral α2δ ligands and adjuvant therapies, while postsurgical pain improved with topical anti-inflammatories. Those with no improvement in pain had a shorter mean follow-up (266.25 ± 262.56 days) than those with mild (396.65 ± 283.44), moderate (652 ± 413.92), or marked improvement (837.93 ± 709.35) (p < 0.005). Identical patterns were noted for number of attempted medications. Conclusion: Patients with migraine-like pain frequently experienced pain improvement, while postsurgical patients had the lowest response rates. Patients with a longer follow-up and who tried more therapies experienced more significant relief, suggesting multiple trials were necessary for pain reduction.

Dry eye disease and psychiatric disorders: A systematic review and meta-analysis

The association between dry eye disease (DED) and psychiatric conditions is a highly researched topic. This work reviews the literature on this relationship, examining the prevalence and correlations of depression and anxiety with dry eye signs and symptoms. A comprehensive literature search of MEDLINE, EMBASE, PsycINFO, and gray literature was conducted, with keywords for dry eye and mood disorders, depression, anxiety, and suicide. Eligible studies underwent quality assessment using the Newcastle-Ottawa Scale. Meta-analysis was performed using STATA 15.0. Fixed- and random-effects models were computed based on the presence of heterogeneity. Thirty-two studies were included, with 31 reporting on depression and 19 on anxiety. Meta-analysis results found a depression prevalence of 40% (CI: [0.29, 0.52]) in DED patients, with 1.81 times higher odds of prevalence compared to controls (CI: [1.61, 2.02]). Prevalence of anxiety was 39% (CI: [0.15, 0.64]), with 2.32 times higher odds of prevalence compared to controls (CI: [1.67, 3.23]). Depression scores were significantly higher in patients with DED in all studies. Anxiety scores were significantly higher in DED patients in studies using all scales except the Hospital Anxiety and Depression Scale-Anxiety Subscale. DED symptom scores were significantly associated with depression (ES = 0.43; CI: [0.31, 0.55]) and anxiety (ES = 0.41; CI: [0.32, 0.50]) scores. In conclusion, depression and anxiety are more prevalent and severe in DED patients and are correlated with dry eye symptoms but not signs. These findings highlight the interrelationship between these disorders and have important implications for providing appropriate care to these patients.

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.

Topical Tacrolimus Progylcosomes Nano-Vesicles As a Potential Therapy for Experimental Dry Eye Syndrome

The present work aimed to evaluate the efficacy of topical tacrolimus (0.01%) loaded propylene glycol (PG) modified nano-vesicles (Proglycosomes Nano-vesicles, PNVs) for the treatment of experimental dry eye syndrome (DES) in rabbits. DES was induced by topical application of atropine (1.0%) and benzalkonium chloride (0.1%) aqueous solution. PNVs treatment (PNV group) was compared with tacrolimus solution 0.01% (TAC group) and untreated group and healthy group were used as controls. PNV treated animals showed improved clinical performance with marked increase in tear production and tear break-up time (TBUT). Further, PNVs also subside ocular inflammation as evident from absence of matrix metalloprotenaise-9 and normal ocular surface temperature (32.3 ± 0.34 °C). Additionally, PNVs have positive effect on ocular and epithelial damage observed through low ocular surface staining score and improved globlet cell density. The PNV treatment was found to more effectively compared to TAC solution and most of the parameters were close to those of healthy animals. In conclusion, tacrolimus PNV formulation (0.01%) could be a potential therapy for treatment of dry eye syndrome.

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.

Long-Term Trigeminal Nerve Stimulation as a Treatment for Ocular Pain

OBJECTIVES

Ocular pain symptoms (e.g., hypersensitivity to light and wind, "burning" sensations) can be debilitating and difficult to treat. Neuromodulatory therapies targeting sensory trigeminal and central pain pathways may help treat chronic ocular pain refractory to traditional therapies. The current study evaluates the long-term effects of a trigeminal neurostimulator (TNS) on ocular pain.

MATERIALS AND METHODS

Retrospective review of 18 individuals at the Miami Veterans Affairs Eye Clinic with chronic, severe ocular pain who were prescribed and used TNS at home for ≥3 months. The primary outcome measures were 1) ocular symptom intensity over a 24-hour recall period (dryness, pain, light sensitivity, wind sensitivity, burning; rated on 0-10 scales) captured pre-TNS and at monthly follow-up intervals and 2) side effects. The frequency and duration of TNS was a secondary outcome measure.

RESULTS

The mean age of the population (n = 18) was 57.5 years (range, 34-85 years) with a male majority (67%). Two individuals discontinued use due to lack of efficacy and one due to confounding health issues. Initial mean weekly frequency of TNS use was 3.7 ± 1.9 sessions of 25.8 min at month 1 and 2.7 ± 2.3 sessions of 28.0 min at month 6. At six months, pain intensity (↓ 31.4%), light sensitivity (↓ 36.3%), wind sensitivity (↓ 32.6%), and burning sensation (↓ 53.9%) were all decreased compared to baseline (p < 0.01 for all); greater decreases in ocular pain were noted in individuals with migraine (n = 10) than those without migraine (n = 8). No significant change was noted in mean dryness scores. Fifteen subjects experienced sedation with TNS use, persisting throughout the follow-up visits. No other adverse effects were communicated by any subjects.

CONCLUSION

Our study suggests TNS is a safe, adjunctive treatment option in individuals with severe, chronic ocular pain. Individuals demonstrated gradual, continual improvement in pain symptoms over time within a multimodal approach.

Altered ocular surface immune cell profile in patients with dry eye disease

PURPOSE

Aberrant inflammation and immune dysregulation are known pathogenic contributors in dry eye disease (DED). Aim of the study was to determine the proportions of immune cell subsets on the ocular surface (OS) of DED patients.

METHODS

15 healthy controls (22 eyes) and 48 DED subjects (36 eyes with evaporative DED - EDED; 60 eyes with aqueous deficient DED - ADED) were included in the study. Tear break up time (TBUT), Schirmer's test 1 (ST1), corneal staining (CS) and ocular surface disease index (OSDI) scoring were recorded. OS wash was used to collect immune cells on the OS of study subjects. The cells immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer-NK cells and T cell subsets (CD4; CD8; double positive-DP; gamma delta-γδ and NK T cells).

RESULTS

Significantly higher proportions of leukocytes, neutrophils, CD4 T cells, CD8 T cells, DP T cells and CD4/CD8 T cells ratio were observed in EDED and/or ADED patients. Significantly higher proportions of neutrophils and lower proportions of NK cells were observed in ADED subjects with corneal staining compared to those without and controls. Neutrophils/NK cells ratio was significantly higher in EDED and ADED subjects compared to controls. Correlation analysis revealed pathological relationships between proportions of leukocytes, neutrophils, CD4 T cells and Neutrophil/NK cells ratio with DED clinical parameters.

CONCLUSION

OS immune cell subset proportion changes in DED patients were associated with DED types and severity. The data suggests the potential for a new generation of therapies targeting immune cells on the ocular surface.

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.

Oral Gabapentinoids and Nerve Blocks for the Treatment of Chronic Ocular Pain

PURPOSE

There is a recognition that nerve dysfunction can contribute to chronic ocular pain in some individuals. However, limited data are available on how to treat individuals with a presumed neuropathic component to their ocular pain. As such, the purpose of this study was to examine the efficacy of our treatment approaches to this entity.

METHODS

A retrospective review of treatments and outcomes in individuals with chronic ocular pain that failed traditional therapies.

RESULTS

We started eight patients on an oral gabapentinoid (gabapentin and/or pregabalin) as part of their pain regimen (mean age 46 years, 50% women). Two individuals reported complete ocular pain relief with a gabapentinoid, in conjunction with their topical and oral medication regimen. Three individuals noted significant improvements, one slight improvement, and two others no improvement in ocular pain with gabapentin or pregabalin. We performed periocular nerve blocks (4 mL of 0.5% bupivacaine mixed with 1 mL of 80 mg/mL methylprednisolone acetate) targeting the periocular nerves (supraorbital, supratrochlear, infratrochlear, and infraorbital) in 11 individuals (mean age 54 years, 36% women), 10 of whom had previously used a gabapentinoid without ocular pain improvement. Seven individuals experienced pain relief after nerve blocks that lasted from hours to months and four failed to benefit. Five of the individuals who experienced pain relief underwent repeat nerve blocks, weeks to months later.

CONCLUSIONS

Approaches used to treat chronic pain outside the eye can be applied to ocular pain that is not responsive to traditional therapies.

High Molecular Weight Hyaluronan Promotes Corneal Nerve Growth in Severe Dry Eyes

The purpose of this study was to investigate the effect of high molecular weight hyaluronan (HMWHA) eye drops on subbasal corneal nerves in patients suffering from severe dry eye disease (DED) and to evaluate the damage of subbasal corneal nerves associated with severe DED. Designed as an international, multicenter study, 16 patients with symptoms of at least an Ocular Surface Disease Index (OSDI) score of 33, and corneal fluorescein staining (CFS) of at least Oxford grade 3, were included and randomized into two study arms. The control group continued to use their individual optimum artificial tears over the study period of eight weeks; in the verum group, the artificial tears were substituted by eye drops containing 0.15% HMWHA. At the baseline visit, and after eight weeks, the subbasal nerve plexus of 16 patients were assessed by confocal laser scanning microscopy (CSLM). The images were submitted to a masked reading center for evaluation. Results showed a significant increase of total nerve fiber lengths (CNFL) in the HMWHA group (p = 0.030) when compared to the control group, where the total subbasal CNFL did not significantly change from baseline to week 8. We concluded that in severe DED patients, HMWHA from topically applied eye drops could cross the epithelial barrier and reach the subbasal nerve plexus, where it exercised a trophic effect.

Clinical characteristics of dry eye with ocular neuropathic pain features: comparison according to the types of sensitization based on the Ocular Pain Assessment Survey

BACKGROUND

To compare the clinical characteristics of dry eye patients with ocular neuropathic pain features according to the types of sensitization based on the Ocular Pain Assessment Survey (OPAS).

METHODS

Cross-sectional study of 33 patients with dry eye and ocular neuropathic pain features. All patients had a comprehensive ophthalmic assessment including detailed history, the intensity and duration of ocular pain, the tear film, ocular surface, and Meibomian gland examination, and OPAS. Patients with < 50% improvement in pain intensity after proparacaine challenge test were assigned to the central-dominant sensitization group (central group) and those with ≥50% improvement were assigned to the peripheral-dominant sensitization group (peripheral group). All variables were compared between the two groups.

RESULTS

No significant differences were observed in age, sex, underlying diseases, history of ocular surgery, duration of ocular pain, tear film, ocular surface and Meibomian gland parameters (all p > 0.05). Ocular pain and non-ocular pain severity and the percentage of time spent thinking about non-ocular pain were significantly higher in the central group than in the peripheral group (all p < 0.05). Central group complained more commonly of a burning sensation than did the peripheral group (p = 0.01).

CONCLUSIONS

Patients with central-dominant sensitization may experience more intense ocular and non-ocular pain than the others and burning sensation may be a key symptom in those patients.

The HYLAN M Study: Efficacy of 0.15% High Molecular Weight Hyaluronan Fluid in the Treatment of Severe Dry Eye Disease in a Multicenter Randomized Trial

The aim of the HYLAN M study was to investigate if symptoms and/or signs of patients suffering from severe dry eye disease (DED) can be improved by substituting individually optimized artificial tear therapy by high molecular weight hyaluronan (HMWHA) eye drops. In this international, multicenter study, patients with symptoms of at least ocular surface disease index (OSDI) 33 and corneal fluorescein staining (CFS) of at least Oxford grade 3 were included. A total of 84 per-protocol patients were randomized in two study arms. The control group continued to use their individual optimum artificial tears over the study period of eight weeks; in the verum group, the artificial tears were substituted by eye drops containing 0.15% HMWHA. At the week 8 visit, the average OSDI of the verum group had improved by 13.5 as compared to the control group (p = 0.001). The best corrected visual acuity (BCVA) had improved by 0.04 logMAR (p = 0.033). CFS, tear film break-up time (TBUT), Schirmer I, lid wiper epitheliopathy (LWE), mucocutaneous junction (Yamaguchi score), and tear osmolarity were not significantly different between the verum and control groups (p > 0.050). We conclude that for most patients with severe DED, 0.15% HMWHA eye drops provide excellent improvement of symptoms without impairment of dry eye signs.

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.

Modification of the Neuropathic Pain Symptom Inventory for use in eye pain (NPSI-Eye)

Chronic eye pain, which has previously been assumed to be due to ocular surface abnormalities (ie, "dry eye [DE] disease"), has recently garnered attention as a potential indicator of neuropathic ocular pain in some patients. The purpose of this study was to evaluate the psychometric properties of a modified version of the Neuropathic Pain Symptom Inventory in individuals with eye pain (NPSI-Eye). Enrolled participants (n = 397) completed the NPSI-Eye, general pain severity questionnaires, DE symptom report, and psychological health indices. Participants also underwent mechanical pain sensitivity testing of the cornea, tear film assessment, and evaluation of the efficacy of anesthetic eye drops to relieve pain. Short-term test-retest reliability of the NPSI-Eye was excellent (intraclass correlation coefficient = 0.98, P < 0.001). Correlations between the NPSI-Eye and indicators of general eye pain were ≥0.65 (P < 0.001), whereas correlations between the NPSI-Eye and DE symptom severity and psychological health indices were lower (rho = 0.56, 0.32, 0.37; all P < 0.001). Individuals who reported little or no decrease in pain after anesthetic eye drops (hypothesized to indicate eye pain with at least partial central involvement) had significantly higher NPSI-Eye scores than participants whose eye pain was completely relieved by anesthetic (P < 0.05). Overall, our results support preliminary validation of the NPSI-Eye, yielding similar metrics to those reported in Bouhassira et al.'s original NPSI publication (2004). However, additional evaluation and refinement of some questions may be desirable, including the potential elimination of items that were not highly endorsed.

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.

Effects of Vitamin A on Expressions of Apoptosis Genes Bax and Bcl-2 in Epithelial Cells of Corneal Tissues Induced by Benzalkonium Chloride in Mice with Dry Eye

Background

The apoptosis of corneal epithelial cells participates in the pathological processes of dry eye, which is expected to be a treatment target for dry eye. The aim of this study was to investigate the effects of vitamin A (VA) on apoptosis of corneal epithelial cells in a mouse model with dry eye induced by benzalkonium chloride (BAC).

Material/Methods

We randomly divided 60 male BALB/c mice aged 8–10 weeks into 3 groups: the blank control group, the dry eye+vehicle group, and the dry eye+drug group. On the 7^th day after the dry eye model successfully induced, the mouse eyeballs removed, and the mouse corneal tissues were isolated. The expression levels of Bax and Bcl-2 in corneal tissues were detected via reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. The apoptotic corneal epithelial cells were quantified using terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) staining technique.

Results

VA suppressed the upregulation of the Bax gene at the mRNA and protein levels, and upregulated the expression of the Bcl-2 gene (P<0.05). TUNEL results revealed that the number of apoptotic epithelial cells in the dry eye group was 40 times larger as that in the blank control group. After the intervention of VA at an appropriate concentration, the number of apoptotic corneal epithelial cells was remarkably reduced to about 10 times that in the blank control group (P<0.05).

Conclusions

VA can inhibit upregulation of the expressions of Bax and Bcl-2 in the epithelial cells of mice with dry eye induced by BAC, so as to suppress the apoptosis of epithelial cells in mice with dry eye.

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.

TRPV1 and TRPM8 Channels and Nocifensive Behavior in a Rat Model for Dry Eye

Purpose

Persistent ocular surface pain occurs in moderate to severe dry eye disease (DE); however, the mechanisms that underlie this symptom remain uncertain. The aim of this study was to determine if the transient receptor potential vanilloid ion channels play a role in hypertonic saline (HS)-evoked corneal reflexes in a model for aqueous tear deficient DE.

Methods

Eye wipe behavior and orbicularis oculi muscle activity (OOemg) were measured after ocular instillation of HS, capsaicin, or menthol 14 days after exorbital gland removal. Total RNA and protein were measured from anterior eye segment and trigeminal ganglia of sham and DE rats.

Results

Eye wipe behavior was enhanced in DE rats after HS and capsaicin instillation, but not after menthol when compared to sham rats. DE rats displayed greater OOemg activity after HS and capsaicin, but not after menthol, compared to sham rats. HS-evoked OOemg activity was reduced by selective TRPV1 antagonists and by coapplication of capsaicin plus QX-314, a charged lidocaine derivative. Menthol did not affect OOemg activity; however, selective antagonism of TRPM8 reduced HS-evoked OOemg activity. TRPV1 protein levels were increased in anterior eye segment and trigeminal ganglion samples from DE rats, whereas TRPM8 levels were not affected.

Conclusions

These results suggest that TRPV1 plays a significant role in mediating enhanced nocifensive behavior in DE, while TRPM8 may play a lesser role. Strategies to target specific transducer molecules on corneal nerves may prove beneficial as adjunct therapies in managing ocular pain in moderate to severe cases of DE.

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.

Neuropathic-Like Ocular Pain and Nonocular Comorbidities Correlate With Dry Eye Symptoms

OBJECTIVE

To evaluate the association between dry eye (DE) symptoms and neuropathic-like ocular pain (NOP) features, chronic pain conditions, depression, and anxiety in patients presenting for routine ophthalmic examinations.

METHODS

Two hundred thirty-three consecutive patients ≥18 years of age presenting to a comprehensive eye clinic between January and August 2016 were included in this study. Information on demographics, chronic pain conditions, medication use, DE symptoms (dry eye questionnaire, DEQ5), NOP complaints (burning; wind, light, and temperature sensitivity), depression, and anxiety indices (patient health questionnaire 9, PHQ-9 and symptom checklist 90-revised, SCL-90-R) were collected for each individual. Pearson correlation was used to evaluate strengths of association. Logistic regression analysis examined risk factors for any (DEQ5≥6) and severe (DEQ5≥12) DE symptoms.

RESULTS

The mean age of the population was 46.3 years (±13.0); 67.8% (n=158) were female. Per the DEQ5, 40.3% (n=94) had mild or greater DE symptoms and 12% (n=24) had severe symptoms. Severity of DE symptoms correlated with NOP complaints: burning (Pearson r=0.37, P<0.001); sensitivity to wind (r=0.37, P<0.001), sensitivity to light (r=0.34, P<0.001), and sensitivity to temperature (r=0.30, P<0.001). Sex, race, and ethnicity were not significant risk factors for DE symptoms. Risk factors for mild or greater DE symptoms included a greater number of chronic nonocular pain conditions (odds ratio [OR]=1.38, P<0.001), arthritic pain (OR=6.34, P<0.001), back pain (OR=2.47, P=0.004), headaches (OR=2.14, P=0.02), depression (OR=1.17, P<0.001), and anxiety (OR=1.13, P=0.02).

CONCLUSION

Dry eye severity positively associated with NOP complaints, comorbid chronic pain conditions, and symptoms of depression and anxiety.

Epidemiology of Persistent Postsurgical Pain Manifesting as Dry Eye-Like Symptoms After Cataract Surgery

PURPOSE

To evaluate the epidemiology of persistent postsurgical pain (PPP) manifesting as dry eye (DE)-like symptoms 6 months after surgery.

METHODS

This single-center study included 119 individuals whose cataract surgeries were performed by a single surgeon at the Bascom Palmer Eye Institute and who agreed to participate in a phone survey 6 months after surgery. Patients were divided into 2 groups: the PPP group was defined as those with a Dry Eye Questionnaire-5 score ≥6 and without PPP as those with a Dry Eye Questionnaire-5 score <6 at 6 months after cataract surgery.

RESULTS

Mean age of the study population was 73 ± 8.0 years; 55% (n = 66) were female. PPP was present in 34% (n = 41) of individuals 6 months after surgery. Factors associated with an increased risk of PPP were female sex [odds ratio (OR) = 2.68, 95% confidence interval (CI) = 1.20-6.00, P = 0.01], autoimmune disorder (OR = 13.2, CI = 1.53-114, P = 0.007), nonocular chronic pain disorder (OR = 4.29, CI = 1.01-18.1, P = 0.06), antihistamine use (OR = 6.22, CI = 2.17-17.8, P = 0.0003), antireflux medication use (OR = 2.42, CI = 1.04-5.66, P = 0.04), antidepressant use (OR = 3.17, CI = 1.31-7.68, P = 0.01), anxiolytic use (OR = 3.38, CI = 1.11-10.3, P = 0.03), and antiinsomnia medication use (OR = 5.28, CI = 0.98-28.5, P = 0.047). PPP patients also reported more frequent use of artificial tears (P < 0.0001), higher ocular pain levels (P < 0.0001), and greater neuropathic ocular pain symptoms, including burning (P = 0.001), wind sensitivity (P = 0.001), and light sensitivity (P < 0.0001).

CONCLUSIONS

PPP in the form of persistent DE-like symptoms is present in approximately 34% of individuals 6 months after cataract surgery. The frequency of PPP after cataract surgery is comparable to that of other surgeries including laser refractive surgery, dental implants, and genitourinary procedures.

Comparison Between Viscous Teardrops and Saline Solution to Fill Orthokeratology Contact Lenses Before Overnight Wear

OBJECTIVE

To compare, in terms of efficacy, the differences between the use of saline solution and a viscous artificial tear to fill the lens during the first month of orthokeratology wear.

METHODS

A pilot, double-masked, crossed, randomized, and prospective study was conducted. In this study, 20 subjects (14 males and 6 females) with a mean age of 16.29±6.22 years (range, 10-26) were fitted with orthokeratology contact lenses. For the study, nonpreserved 0.9% NaCl commercial saline solution (Avizor, Madrid, Spain) and nonpreserved artificial teardrops with 0.3% of hyaluronic acid (Ocudry 0.3%; Avizor, Madrid, Spain) were used. Corneal staining, tear break up time (TBUT), topography, refraction, visual acuity, and subjective comfort and vision with the visual analog scale (score from 0 to 10, being 10 better comfort and vision) were evaluated at 1 day, 1 week, and 1 month of contact lens wear.

RESULTS

The corneal staining was statistically greater in the saline group than in the Ocudry group for the first day and during 1 week of wear (P<0.05). Comfort was found to be statistically better, with Ocudry 0.3% than saline solution, being 7.17±1.94 and 6.37±1.63, for the first day, and 8.78±0.43 and 8.15±0.62 for the day 28, respectively (P<0.05). However, no differences were found for subjective vision scores, TBUT, spherical equivalent, best-corrected visual acuity and uncorrected visual acuity, and mean keratometry between groups for any visit (P>0.05).

CONCLUSION

Viscous artificial tears improve the subjective comfort of patients and reduce the corneal staining, compared with saline solution during the orthokeratology lenses fitting process. However, no differences between solutions for the treatment efficacy, in vision and corneal topography, were found.

Photophobia and sensations of dryness in patients with migraine occur independent of baseline tear volume and improve following botulinum toxin A injections

BACKGROUND

To evaluate the efficacy of botulinum toxin A (BoNT-A) in reducing photophobia and dry eye symptoms in individuals with chronic migraine. Additionally, we aimed to evaluate tear film volume as a potential contributor to symptoms in these patients.

METHODS

Retrospective review of 76 patients who received BoNT-A for chronic migraine between 23 August 2017 and 13 December 2017 at the Miami Veterans Affairs Medical Center Neurotoxin Clinic. Demographic data and all comorbidities were queried via chart review. Standardised validated surveys were administered to assess symptoms prior to and after BoNT-A injection. Preinjection tear volumes were obtained using the phenol red thread (PRT) test.

RESULTS

Preinjection migraine, photophobia and dry eye symptom scores were all significantly correlated, p<0.05, and none were associated with preinjection PRT results. After BoNT-A, improvements in migraine, photophobia and dry eye symptoms were also significantly correlated, p<0.05 and similarly did not associate with preinjection PRT results. Photophobia scores significantly improved following BoNT-A, while dry eye symptoms significantly improved in those with severe symptoms at baseline (DEQ-5 score ≥12), p=0.027. In logistic regression analysis of all individuals with dry eye symptoms (DEQ-5 ≥6), individuals with more severe dry eye symptoms were more likely improve, OR 1.27, 95% CI 1.06 to 1.51, p<0.01.

CONCLUSIONS

BoNT-A significantly improved photophobia in patients being treated for migraine and also improved dry eye symptoms in patients with severe symptoms at baseline, independent of baseline tear film volume. These improvements may be due to modulation of shared trigeminal neural pathways.