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Sullivan BD, Smith GT, Gupta A, Harman F, Ansari E. Impact of Clinician Subjectivity on the Assessment of Dry Eye Disease Prevalence in a UK Public Health Care Patient Population. Clin Ophthalmol 2024; 18:743-753. [PMID: 38476359 PMCID: PMC10929644 DOI: 10.2147/opth.s452149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 02/15/2024] [Indexed: 03/14/2024] Open
Abstract
Purpose To understand the impact of subjectivity on diagnosis rates of dry eye disease (DED) in an unbiased population. Patients and Methods A multicenter study enrolled 818 subjects with complete report forms (465 females, 67.1 ± 16.7 years, 353 males, 65.0 ± 15.9 years). Subjects were evaluated for staining, TBUT, tear osmolarity, meibomian gland disease, and OSDI. Results Physicians diagnosed 48.7% of subjects as having DED, ranging from 42.9% to 62.3% between sites. Positivity rates for staining (≥ grade 1) ranged from 41.3% to 84.1% (mean = 0.8 ± 0.9 grade), TBUT (<10s) ranged from 39.1% to 61.6% (mean = 10.4 ± 6.6 seconds), osmolarity (>308 mOsm/L) ranged from 63.7% to 72.4% (mean = 319.7 ± 20.8), MGD grading ranged from 28.9% to 51.3% (mean = 0.5 ± 0.7), and symptoms measured by OSDI ranged from 57.6% to 71.0% (mean = 23.5 ± 20.5) between sites. Tear osmolarity was the most consistent between sites (max/min positivity = 114%), followed by OSDI (123%), TBUT (158%), MGD (178%), and staining (204%). DED markers were uncorrelated (average r2 = 0.05 ± 0.07). A substantial number of subjects (N = 110) exhibited positive symptoms (OSDI = 32.4 ± 15.7) and hyperosmolarity (338.1 ± 20.1 mOsm/L) but no other obvious signs of DED (MGD grade = 0.2 ± 0.4, TBUT = 13.5 ± 7.0 seconds, staining grade = 0.4 ± 0.5). Conclusion Subjective signs of DED varied considerably, whereas objective measurements of OSDI and osmolarity were the most consistent between sites. A large proportion of subjects exhibited high symptoms and hyperosmolarity but no other obvious signs of dry eye disease, most of whom were undiagnosed by clinical assessment without access to the osmolarity measurement.
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Affiliation(s)
| | - Guy T Smith
- The Great Western Hospital NHS Trust, Swindon, UK
| | - Arun Gupta
- Ashford and St Peters NHS Trust, Ashford, UK
| | | | - Ejaz Ansari
- Department of Ophthalmology, Maidstone & Tunbridge Wells Hospitals, Maidstone, Kent, UK
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2
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Asiedu K. Role of ocular surface neurobiology in neuronal-mediated inflammation in dry eye disease. Neuropeptides 2022; 95:102266. [PMID: 35728484 DOI: 10.1016/j.npep.2022.102266] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 06/07/2022] [Accepted: 06/08/2022] [Indexed: 01/18/2023]
Abstract
Inflammation is the consequence of dry eye disease regardless of its etiology. Several injurious or harmless processes to the ocular surface neurons promote ocular surface neurogenic inflammation, leading to the vicious cycle of dry eye disease. These processes include the regular release of neuromediators during the conduction of ocular surface sensations, hyperosmolarity-induced ocular surface neuronal damage, neuro-regenerative activities, and neuronal-mediated dendritic cell activities. Neurogenic inflammation appears to be the main culprit, instigating the self-perpetuating inflammation observed in patients with dry eye disease.
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Affiliation(s)
- Kofi Asiedu
- School of Optometry & Vision Science, Faculty of Medicine and Health, University of New South Wales, Sydney, Australia.
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3
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Benzalkonium chloride, a common ophthalmic preservative, compromises rat corneal cold sensitive nerve activity. Ocul Surf 2022; 26:88-96. [DOI: 10.1016/j.jtos.2022.07.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Revised: 07/25/2022] [Accepted: 07/29/2022] [Indexed: 11/15/2022]
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4
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Corneal nerves and their role in dry eye pathophysiology. Exp Eye Res 2022; 222:109191. [PMID: 35850173 DOI: 10.1016/j.exer.2022.109191] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 06/15/2022] [Accepted: 07/11/2022] [Indexed: 12/11/2022]
Abstract
As the cornea is densely innervated, its nerves are integral not only to its structure but also to its pathophysiology. Corneal integrity depends on a protective tear film that is maintained by corneal sensation and the reflex arcs that control tearing and blinking. Furthermore, corneal nerves promote epithelial growth and local immunoregulation. Thus, corneal nerves constitute pillars of ocular surface homeostasis. Conversely, the abnormal tear film in dry eye favors corneal epithelial and nerve damage. The ensuing corneal nerve dysfunction contributes to dry eye progression, ocular pain and discomfort, and other neuropathic symptoms. Recent evidence from clinical studies and animal models highlight the significant but often overlooked neural dimension of dry eye pathophysiology. Herein, we review the anatomy and physiology of corneal nerves before exploring their role in the mechanisms of dry eye disease.
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5
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Kim YH, Lin MC, Peng CC, Radke CJ. Prevention of localized corneal hyperosmolarity spikes by soft-contact-lens wear. Cont Lens Anterior Eye 2022; 45:101722. [PMID: 35718682 DOI: 10.1016/j.clae.2022.101722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 05/19/2022] [Accepted: 05/24/2022] [Indexed: 11/30/2022]
Abstract
PURPOSE To determine whether localized hyperosmotic spikes on the pre-lens tear film (PrLTF) due to tear break up results in hyperosmotic spikes on the ocular surface during soft-contact-lens (SCL) wear and whether wear of SCLs can protect the cornea against PrLTF osmotic spikes. METHODS Two-dimensional transient diffusion of salt was incorporated into a computationally designed SCL, post-lens tear film (PoLTF), and ocular surface and solved numerically. Time-dependent localized hyperosmolarity spikes were introduced at the anterior surface of the SCL corresponding to those generated in the PrLTF. Salt spikes were followed in time until spikes penetrate through the lens into the PoLTF. Lens-salt diffusivities (Ds) were varied to assess their importance on salt migration from the PrLTF to the ocular surface. SCL and PoLTF initial conditions and the lens anterior-surface boundary condition were varied depending on the value of Ds and on dry-eye symptomatology. Determined corneal surface osmolarities were translated into clinical pain scores. RESULTS For Ds above about 10-7cm2/s, it takes around 5-10 s for the PrLTF hyperosmotic break-up spikes to diffuse across the SCL and reach the corneal surface. Even if localized hyperosmotic spikes penetrate to the ocular surface, salt concentrations there are much lower than those in the progenitor PrLTF spikes. For Ds less than 10-7cm2/s, the SCL protects the cornea from hyperosmotic spikes for both normal and dry eyes. When localized corneal hyperosmolarity is converted into transient pain scores, pain thresholds are significantly lower than those for no-lens wear. CONCLUSIONS A cornea can be protected from localized PrLTF hyperosmolarity spikes with SCL wear. With regular blinking (e.g., less than 10 s), SCL wear shields the cornea from significant hyperosmotic pain. Decreasing Ds increases that protection. Low-Ds soft contact lenses can protect against hyperosmotic spikes and discomfort even during infrequent blinking (e.g., > 10 s).
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Affiliation(s)
- Young Hyun Kim
- Herbert Wertheim School of Optometry & Vision Science, University of California, Berkeley, CA 94720, United States; Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States; Clinical Research Center, University of California, Berkeley, CA 94720, United States
| | - Meng C Lin
- Herbert Wertheim School of Optometry & Vision Science, University of California, Berkeley, CA 94720, United States; Clinical Research Center, University of California, Berkeley, CA 94720, United States
| | | | - Clayton J Radke
- Herbert Wertheim School of Optometry & Vision Science, University of California, Berkeley, CA 94720, United States; Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
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6
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Puja G, Sonkodi B, Bardoni R. Mechanisms of Peripheral and Central Pain Sensitization: Focus on Ocular Pain. Front Pharmacol 2021; 12:764396. [PMID: 34916942 PMCID: PMC8669969 DOI: 10.3389/fphar.2021.764396] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 11/09/2021] [Indexed: 12/14/2022] Open
Abstract
Persistent ocular pain caused by corneal inflammation and/or nerve injury is accompanied by significant alterations along the pain axis. Both primary sensory neurons in the trigeminal nerves and secondary neurons in the spinal trigeminal nucleus are subjected to profound morphological and functional changes, leading to peripheral and central pain sensitization. Several studies using animal models of inflammatory and neuropathic ocular pain have provided insight about the mechanisms involved in these maladaptive changes. Recently, the advent of new techniques such as optogenetics or genetic neuronal labelling has allowed the investigation of identified circuits involved in nociception, both at the spinal and trigeminal level. In this review, we will describe some of the mechanisms that contribute to the perception of ocular pain at the periphery and at the spinal trigeminal nucleus. Recent advances in the discovery of molecular and cellular mechanisms contributing to peripheral and central pain sensitization of the trigeminal pathways will be also presented.
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Affiliation(s)
- Giulia Puja
- Department of Life Sciences, University of Modena and Reggio Emilia, Emilia-Romagna, Italy
| | - Balazs Sonkodi
- Department of Health Sciences and Sport Medicine, University of Physical Education, Budapest, Hungary
| | - Rita Bardoni
- Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Emilia-Romagna, Italy
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7
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Protection against corneal hyperosmolarity with soft-contact-lens wear. Prog Retin Eye Res 2021; 87:101012. [PMID: 34597771 DOI: 10.1016/j.preteyeres.2021.101012] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 09/18/2021] [Accepted: 09/21/2021] [Indexed: 01/03/2023]
Abstract
Hyperosmotic tear stimulates human corneal nerve endings, activates ocular immune response, and elicits dry-eye symptoms. A soft contact lens (SCL) covers the cornea preventing it from experiencing direct tear evaporation and the resulting blink-periodic salinity increases. For the cornea to experience hyperosmolarity due to tear evaporation, salt must transport across the SCL to the post-lens tear film (PoLTF) bathing the cornea. Consequently, limited salt transport across a SCL potentially protects the ocular surface from hyperosmotic tear. In addition, despite lens-wear discomfort sharing common sensations to dry eye, no correlation is available between measured tear hyperosmolarity and SCL-wear discomfort. Lack of documentation is likely because clinical measurements of tear osmolarity during lens wear do not interrogate the tear osmolarity of the PoLTF that actually overlays the cornea. Rather, tear osmolarity is clinically measured in the tear meniscus. For the first time, we mathematically quantify tear osmolarity in the PoLTF and show that it differs significantly from the clinically measured tear-meniscus osmolarity. We show further that aqueous-deficient dry eye and evaporative dry eye both exacerbate the hyperosmolarity of the PoLTF. Nevertheless, depending on lens salt-transport properties (i.e., diffusivity, partition coefficient, and thickness), a SCL can indeed protect against corneal hyperosmolarity by reducing PoLTF salinity to below that of the ocular surface during no-lens wear. Importantly, PoLTF osmolarity for dry-eye patients can be reduced to that of normal eyes with no-lens wear provided that the lens exhibits a low lens-salt diffusivity. Infrequent blinking increases PoLTF osmolarity consistent with lens-wear discomfort. Judicious design of SCL material salt-transport properties can ameliorate corneal hyperosmolarity. Our results confirm the importance of PoLTF osmolarity during SCL wear and indicate a possible relation between PoLTF osmolarity and contact-lens discomfort.
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Hwang DDJ, Lee SJ, Kim JH, Lee SM. The Role of Neuropeptides in Pathogenesis of Dry Dye. J Clin Med 2021; 10:4248. [PMID: 34575359 PMCID: PMC8471988 DOI: 10.3390/jcm10184248] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2021] [Revised: 09/07/2021] [Accepted: 09/14/2021] [Indexed: 12/29/2022] Open
Abstract
Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.
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Affiliation(s)
- Daniel Duck-Jin Hwang
- Department of Ophthalmology, HanGil Eye Hospital, Incheon 21388, Korea;
- Department of Ophthalmology, College of Medicine, Catholic Kwandong University, Incheon 21388, Korea
| | - Seok-Jae Lee
- Fight against Angiogenesis-Related Blindness (FARB) Laboratory, Clinical Research Institute, Seoul National University Hospital, Seoul 03080, Korea; (S.-J.L.); (J.-H.K.)
- Department of Biomedical Sciences, College of Medicine, Seoul National University, Seoul 03080, Korea
| | - Jeong-Hun Kim
- Fight against Angiogenesis-Related Blindness (FARB) Laboratory, Clinical Research Institute, Seoul National University Hospital, Seoul 03080, Korea; (S.-J.L.); (J.-H.K.)
- Department of Biomedical Sciences, College of Medicine, Seoul National University, Seoul 03080, Korea
- Department of Ophthalmology, College of Medicine, Seoul National University, Seoul 03080, Korea
- Advanced Biomedical Research Center, Korea Research Institute of Bioscience & Biotechnology, Daejeon 34141, Korea
| | - Sang-Mok Lee
- Department of Ophthalmology, HanGil Eye Hospital, Incheon 21388, Korea;
- Department of Ophthalmology, College of Medicine, Catholic Kwandong University, Incheon 21388, Korea
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9
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Rolando M, Barabino S. Are there Clinical Ways to Assess Inflammation in Dry Eye Disease? Ocul Immunol Inflamm 2021; 29:1183-1189. [PMID: 34227903 DOI: 10.1080/09273948.2021.1916540] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
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.
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Affiliation(s)
- Maurizio Rolando
- Ocular Surface and Dry Eye Clinic, ISPRE Ophthalmica, Genoa, Italy
| | - Stefano Barabino
- Ocular Surface and Dry Eye Center, ASST Fatebenefratelli-Sacco, Sacco Hospital-University of Milan, Milan, Italy
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10
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Awisi-Gyau D, Begley CG, Situ P, Simpson TL. Changes in Corneal Detection Thresholds After Repeated Tear Film Instability. Invest Ophthalmol Vis Sci 2019; 60:4234-4240. [PMID: 31618427 PMCID: PMC6795343 DOI: 10.1167/iovs.19-27802] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Purpose To use a human-based model to study the effects of repeated tear film instability on corneal detection thresholds to cold, mechanical, and chemical stimuli. Methods Twenty-five subjects participated in three study visits. A computer-controlled Belmonte esthesiometer was used to estimate corneal detection thresholds to cold, mechanical, and chemical stimuli before, after, and 30 minutes following 10 consecutive sustained tear exposure (STARE) trials. Subjects turned a pain knob (0–10) to indicate discomfort during STARE trials. The area of tear breakup and thinning in each trial was analyzed. Symptoms were evaluated by the Current Symptom Questionnaire (CSQ). Results There was a significant time effect on CSQ symptoms during both visits (Friedman test, P < 0.001), with immediately after repeated STARE and 30 minutes later significantly differing from before STARE (Wilcoxon, P < 0.017). Tear breakup occurred in every trial, ranging from 25% to 88% of the exposed corneal area and all subjects indicated discomfort during trials. There was a significant time effect on mechanical thresholds between before STARE mechanical thresholds and 30 minutes later (repeated measures analysis of variance [ANOVA] P < 0.001), but not cold (P = 0.057) or chemical (P = 0. 565) thresholds. Conclusions In this study, tear breakup during STARE trials was associated with discomfort, which when repeated, resulted in increased symptoms of ocular discomfort and alterations of mechanical sensory thresholds after 30 minutes. These results suggest that tear film instability, which is thought to occur repeatedly during normal blinking among dry eye patients over the day, can produce neurosensory alterations.
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Affiliation(s)
- Deborah Awisi-Gyau
- Indiana University School of Optometry, Bloomington, Indiana, United States
| | - Carolyn G Begley
- Indiana University School of Optometry, Bloomington, Indiana, United States
| | - Ping Situ
- Indiana University School of Optometry, Bloomington, Indiana, United States
| | - Trefford L Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
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11
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Situ P, Begley CG, Simpson TL. Effects of Tear Film Instability on Sensory Responses to Corneal Cold, Mechanical, and Chemical Stimuli. Invest Ophthalmol Vis Sci 2019; 60:2935-2941. [PMID: 31284310 PMCID: PMC6615367 DOI: 10.1167/iovs.19-27298] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Purpose To investigate the effects of tear film instability (TFI) induced by sustained tear exposure (STARE) on sensory responses to corneal cold, mechanical, and chemical stimuli. Methods Fifteen normal subjects were enrolled. TFI was induced during 10 repeated trials of STARE. Pneumatic cold, mechanical, and chemical stimuli were delivered using a computer-controlled Belmonte esthesiometer on three separate visits. The magnitude of the sensory responses to threshold and suprathreshold (1.25 and 1.50 times threshold levels) stimuli were assessed for intensity, coolness or warmness, irritation and pain, using a 0 (none) to 100 (very strong) scale, before and after STARE trials. Symptoms of ocular discomfort were evaluated using the Current Symptom Questionnaire (CSQ). Repeated measures ANOVA was used for data analysis. Results Following STARE trials, the intensity and coolness ratings to cooling stimuli decreased (P = 0.043 and 0.044 for intensity and coolness, respectively), while rated irritation to mechanical stimuli was increased (P = 0.024). The CSQ scores also increased regardless of visits (all P < 0.001). Intensity ratings, coolness to room temperature stimuli and irritation to mechanical and chemical stimuli increased for all suprathreshold stimuli with increasing stimulus levels (P ≤ 0.005). Conclusions Repeated TFI induced by STARE affects neurosensory function of the ocular surface. The decrease in reports of cooling and increase in irritation after repeated TFI suggest a complex interaction of neural mechanisms (particularly nonnociceptive cold and nociceptive mechanical) giving rise to ocular surface sensation in humans.
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Affiliation(s)
- Ping Situ
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Carolyn G Begley
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Trefford L Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
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12
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McKay TB, Seyed-Razavi Y, Ghezzi CE, Dieckmann G, Nieland TJF, Cairns DM, Pollard RE, Hamrah P, Kaplan DL. Corneal pain and experimental model development. Prog Retin Eye Res 2019; 71:88-113. [PMID: 30453079 PMCID: PMC6690397 DOI: 10.1016/j.preteyeres.2018.11.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Revised: 11/03/2018] [Accepted: 11/13/2018] [Indexed: 12/13/2022]
Abstract
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.
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Affiliation(s)
- Tina B McKay
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA
| | - Yashar Seyed-Razavi
- Center for Translational Ocular Immunology and Cornea Service, Department of Ophthalmology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA, USA
| | - Chiara E Ghezzi
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA
| | - Gabriela Dieckmann
- Center for Translational Ocular Immunology and Cornea Service, Department of Ophthalmology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA, USA
| | - Thomas J F Nieland
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA
| | - Dana M Cairns
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA
| | - Rachel E Pollard
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA
| | - Pedram Hamrah
- Center for Translational Ocular Immunology and Cornea Service, Department of Ophthalmology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA, USA
| | - David L Kaplan
- Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA.
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13
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Hirata H, Dallacasagrande V, Mizerska K, Ivakhnitskaia E, Rosenblatt MI. Ambient Air Currents Activate Corneal Nerves During Ocular Desiccation in Rats: Simultaneous Recordings of Neural Activity and Corneal Temperature. Invest Ophthalmol Vis Sci 2019; 59:4031-4043. [PMID: 30098191 PMCID: PMC6082328 DOI: 10.1167/iovs.18-24604] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Purpose Previously we found two types of corneal neurons that we hypothesized to play an important role in tearing. One type is called low threshold–cold sensitive plus dry sensitive (LT-CS + DS), and the other is termed high threshold–cold sensitive plus dry sensitive (HT-CS + DS). The present study examined critical stimuli influencing the activity of these neurons to elucidate environmental factors that may trigger this ocular reflex. Methods Single corneal neurons were extracellularly recorded from the trigeminal ganglia in response to ocular stimuli that mimic environmental conditions one encounters in daily life. They included an ocular desiccation and slight air currents and were presented while simultaneously monitoring the ocular surface temperatures (OST) in rats. Results The results showed that the changes in steady state (SS) activity of the neurons closely followed the changes in SS OST: during the sustained ocular desiccation, neural firing displayed numerous small sudden increases in activities (“spiking”); these “spiking” activities of LT-CS + DS neurons were replicated by a minute air current that induced slight ocular surface cooling of approximately 0.2–0.1°C; and the responses of HT-CS + DS neurons showed an inconsistent relationship to the changes in SS OST or exhibited little evidence for “spiking” activities. Conclusions These results suggest that LT-CS + DS neurons play a role in the afferent trigger of tearing as we face the environment, exposing the cornea to prevailing air currents that produce a slight cooling of the ocular surface. By contrast, HT-CS + DS neurons may serve to protect the eyes from extreme dryness by eliciting nociception-evoked tearing when the OST or osmolarity of tears becomes injurious.
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Affiliation(s)
- Harumitsu Hirata
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York, United States
| | | | - Kamila Mizerska
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York, United States
| | - Evguenia Ivakhnitskaia
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, Chicago, Illinois, United States
| | - Mark I Rosenblatt
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, Chicago, Illinois, United States
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Pontelli RCN, Souza MCO, Fantucci MZ, de Andrade M, Rocha EM. The role of endocrine disruptors in ocular surface diseases. Med Hypotheses 2018; 122:157-164. [PMID: 30593402 DOI: 10.1016/j.mehy.2018.11.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 11/05/2018] [Accepted: 11/20/2018] [Indexed: 11/28/2022]
Abstract
Endocrine disruptors are a group of compounds that occur in increasing amounts in the environment. These compounds change the hormone homeostasis of the target organs regulated by those hormones, mostly by binding to their receptors and affecting their signaling pathways. Among the hormones altered by endocrine disruptors are sex hormones, thyroid hormones, and insulin. Studies have documented abnormalities in the reproductive and metabolic systems of various animal species exposed to endocrine disruptors. Endocrine disruptors can play a significant role in ocular diseases once hormone deficiency or excess are involved in the mechanism of that disease. Cataracts, dry eye disease and retinal diseases, such as macular hole and diabetic retinopathy, are some of the frequent problems where hormones have been implicated. We found that some compounds function as endocrine disruptors in the metabolism of body organs and systems. The increasing frequency of dry eye and other ocular diseases indicates the need to better investigate the potential relationships beyond the isolated associations mentioned by patients and documented as rare case reports. The evidence from case-control studies and experimental assays can provide the information necessary to confirm the endocrine effects of these chemicals in the pathophysiology of dry eye disease. We hypothesize that endocrine disruptors may contribute to the increase of ocular diseases, such as dry eye disease, in recent years.
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Affiliation(s)
- Regina C N Pontelli
- Department of Ophthalmology, Otorhinolaryngology and Head & Neck Surgery, Ribeirao Preto Medical School, University of Sao Paulo University of São Paulo, Ribeirão Preto, Sao Paulo, Brazil
| | - Marília C O Souza
- Department of Clinical, Toxicological and Bromatological Analyzes, ASTox - Laboratory of Analytical and Systems Toxicology, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Brazil
| | - Marina Z Fantucci
- Department of Ophthalmology, Otorhinolaryngology and Head & Neck Surgery, Ribeirao Preto Medical School, University of Sao Paulo University of São Paulo, Ribeirão Preto, Sao Paulo, Brazil
| | - Mônica de Andrade
- Department of Ophthalmology, Otorhinolaryngology and Head & Neck Surgery, Ribeirao Preto Medical School, University of Sao Paulo University of São Paulo, Ribeirão Preto, Sao Paulo, Brazil
| | - Eduardo M Rocha
- Department of Ophthalmology, Otorhinolaryngology and Head & Neck Surgery, Ribeirao Preto Medical School, University of Sao Paulo University of São Paulo, Ribeirão Preto, Sao Paulo, Brazil.
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Melik Parsadaniantz S, Rostène W, Baudouin C, Réaux-Le Goazigo A. [Understanding chronic ocular pain]. Biol Aujourdhui 2018; 212:1-11. [PMID: 30362450 DOI: 10.1051/jbio/2018017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2018] [Indexed: 11/15/2022]
Abstract
Dry eye disease (DED) is a common chronic condition with multifactorial etiologies that is increasing in prevalence worldwide, up to 20% in the elderly. The economic burden and impact of DED on vision, quality of life, work productivity, psychological and physical impact of pain, are considerable. Chronic ocular pain is the most common symptom of DED and there is currently no topical ocular analgesic therapy available to treat this debilitating disease. Eye pain can be perceived as itch, irritation, dryness, grittiness, burning, aching, and light sensitivity. Ocular pain is triggered by corneal nociceptors (cornea being the most sensory innervated tissue of the body). It was clearly established that repeated direct damage to ocular surface and per se corneal nerves can cause peripheral and central sensitization mechanisms explaining the ocular pain in some patients with DED. However, the brain regions and the neuronal pathways associated with ocular pain are still unclear. Thus, a better characterization of chronic ocular pain and an understanding of the peripheral and central molecular and cellular mechanisms involved are crucial issues for developing effective management and therapeutic strategy to alleviate ocular pain. In this review, we first describe the nociceptive corneal nerve pathways and the classification and the neurochemistry of primary afferents innervating the cornea. Then, an update of the fundamental and clinical studies related to the inflammatory processes linked to ocular pain is detailed. The last part of the review presents the diagnostic tools used in clinic for evaluating corneal sensitivity and corneal inflammation.
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Affiliation(s)
| | - William Rostène
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Christophe Baudouin
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France - Département d'Ophtalmologie III, Hôpital National des Quinze-Vingts, Paris, France - Département d'Ophtalmologie, Hôpital Ambroise Paré, APHP, Université de Versailles Saint-Quentin en Yvelines, Versailles, France
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Yi HC, Lee YP, Shin YJ. Influence of Nasal Tear Osmolarity on Ocular Symptoms Related to Dry Eye Disease. Am J Ophthalmol 2018; 189:71-76. [PMID: 29470972 DOI: 10.1016/j.ajo.2018.02.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2017] [Revised: 02/09/2018] [Accepted: 02/11/2018] [Indexed: 01/02/2023]
Abstract
PURPOSE To investigate relationships between local tear osmolarity and tear film characteristics and dry eye disease (DED) symptoms. DESIGN Prospective, cross-sectional, observational study. METHODS Nasal and temporal tear osmolarity were measured in subjects with DED. The difference between nasal and temporal tears (OSM difference) was then calculated. Ocular symptoms were evaluated and tear break-up time (TBUT), corneal fluorescein staining score (CFSS), eyelid hyperemia, and tear production were measured. Correlations between DED symptoms and nasal tear osmolarity, temporal tear osmolarity, OSM difference, and tear film characteristics were evaluated using Pearson correlation analyses. Subjects were divided into 3 groups based on OSM difference: the temporal group had a temporal osmolarity > nasal osmolarity, the nasal group had a temporal osmolarity < nasal osmolarity, and the equal group had an OSM difference < 10 mOsm/L. RESULTS Forty-eight eyes of 48 subjects were included. Eleven eyes were in the temporal group, 17 eyes were in the equal group, and 20 eyes were in the nasal group. Temporal osmolarity, nasal osmolarity, and OSM difference were not correlated with TBUT, CFSS, lid hyperemia, or tear production. Nasal tear osmolarity was correlated with cold sensitivity frequency (r = 0.298, P = .040), foreign body sensation severity (r = 0.293, P = .043), and light sensitivity severity (r = 0.293, P = .043). Additionally, OSM difference was correlated with daily symptom frequency (r = 0.339, P = .019). CONCLUSIONS Nasal tear osmolarity and OSM difference play an important role in DED symptoms. Lid hyperemia, TBUT, CFSS, and tear secretion volume are not significantly affected by tear osmolarity. It is important to measure both nasal and temporal tear osmolarity when evaluating patients with DED.
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King-Smith PE, Begley CG, Braun RJ. Mechanisms, imaging and structure of tear film breakup. Ocul Surf 2017; 16:4-30. [PMID: 28935579 DOI: 10.1016/j.jtos.2017.09.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2016] [Revised: 08/10/2017] [Accepted: 09/15/2017] [Indexed: 12/14/2022]
Abstract
Tear film breakup (BU) is an important aspect of dry eye disease, as a cause of ocular aberrations, irritation and ocular surface inflammation and disorder. Additionally, measurement of breakup time (BUT) is a common clinical test for dry eye. The current definition of BUT is subjective; here, a more objective concept of "touchdown" - the moment when the lipid layer touches down on the corneal surface - is proposed as an aid to understanding processes in early and late stages of BU development. Models of BU have generally been based on the assumption that a single mechanism is involved. In this review, it is emphasized that BU does not have a single explanation but it is the end result of multiple processes. A three-way classification of BU is proposed - "immediate," "lid-associated," and "evaporative." Five different types of imaging systems are described, which have been used to help elucidate the processes involved in BU and BUT; a new method, "high resolution chromaticity images," is presented. Three directions of tear flow - evaporation, osmotic flow out of the ocular surface, and "tangential flow" along the ocular surface - determine tear film thinning between blinks, leading to BU. Ten factors involved in BU and BUT, both before and after touchdown, are discussed. Future directions of research on BU are proposed.
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Réaux-Le Goazigo A, Labbé A, Baudouin C, Melik Parsadaniantz S. La douleur oculaire chronique : mieux la comprendre pour mieux la traiter. Med Sci (Paris) 2017; 33:749-757. [DOI: 10.1051/medsci/20173308020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Abstract
PURPOSE To examine the cooling thresholds and the estimated sensation magnitude at stimulus detection in controls and symptomatic and asymptomatic contact lens (CL) wearers, to determine whether detection thresholds depend on the presence of symptoms of dryness and discomfort. METHODS Forty-nine adapted CL wearers and 15 non-lens wearing controls had room temperature pneumatic thresholds measured using a custom Belmonte esthesiometer, during Visits 1 and 2 (Baseline CL), Visit 3 (2 weeks no CL wear), and Visit 4 (2 weeks after resuming CL wear). CL wearers were subdivided into symptomatic and asymptomatic groups based on comfortable wearing time (CWT) and CLDEQ-8 score (<8 hours CWT and ≥14 CLDEQ-8 stratified the symptom groups). Detection thresholds were estimated using an ascending method of limits and each threshold was the average of the three first-reported flow rates. The magnitude of intensity, coolness, irritation, and pain at detection of the stimulus were estimated using a 1-100 scale (1 very mild, 100 very strong). RESULTS In all measurement conditions, the symptomatic CL wearers were the most sensitive, the asymptomatic CL wearers were the least sensitive, and the control group was between the two CL wearing groups (group factor p < 0.001, post hoc asymptomatic vs. symptomatic group, all p's < 0.015). Similar patterns were found for the estimated magnitude of intensity and irritation (group effect p = 0.027 and 0.006 for intensity and irritation, respectively) but not for cooling (p > 0.05) at detection threshold. CONCLUSIONS Symptomatic CL wearers have higher cold detection sensitivity and report greater intensity and irritation sensation at stimulus detection than the asymptomatic wearers. Room temperature pneumatic esthesiometry may help to better understand the process of sensory adaptation to CL wear.
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20
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Abstract
Pain associated with mechanical, chemical, and thermal heat stimulation of the ocular surface is mediated by trigeminal ganglion neurons, while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of meibomian gland secretion or mucin release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.
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Bron AJ, de Paiva CS, Chauhan SK, Bonini S, Gabison EE, Jain S, Knop E, Markoulli M, Ogawa Y, Perez V, Uchino Y, Yokoi N, Zoukhri D, Sullivan DA. TFOS DEWS II pathophysiology report. Ocul Surf 2017; 15:438-510. [PMID: 28736340 DOI: 10.1016/j.jtos.2017.05.011] [Citation(s) in RCA: 949] [Impact Index Per Article: 135.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 05/26/2017] [Indexed: 12/18/2022]
Abstract
The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.
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Affiliation(s)
- Anthony J Bron
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK; Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK.
| | - Cintia S de Paiva
- Department of Ophthalmology, Baylor College of Medicine, Houston, TX, USA
| | - Sunil K Chauhan
- Schepens Eye Research Institute & Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, USA
| | - Stefano Bonini
- Department of Ophthalmology, University Campus Biomedico, Rome, Italy
| | - Eric E Gabison
- Department of Ophthalmology, Fondation Ophtalmologique Rothschild & Hôpital Bichat Claude Bernard, Paris, France
| | - Sandeep Jain
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA
| | - Erich Knop
- Departments of Cell and Neurobiology and Ocular Surface Center Berlin, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Maria Markoulli
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
| | - Yoko Ogawa
- Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
| | - Victor Perez
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami, Miami, FL, USA
| | - Yuichi Uchino
- Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
| | - Norihiko Yokoi
- Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan
| | - Driss Zoukhri
- Tufts University School of Dental Medicine, Boston, MA, USA
| | - David A Sullivan
- Schepens Eye Research Institute & Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, USA
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Hirata H, Mizerska K, Dallacasagrande V, Rosenblatt MI. Estimating the Osmolarities of Tears During Evaporation Through the "Eyes" of the Corneal Nerves. Invest Ophthalmol Vis Sci 2017; 58:168-178. [PMID: 28114576 PMCID: PMC5256685 DOI: 10.1167/iovs.16-20501] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose A population of corneal neurons in rats preferentially sense and monitor the hyperosmolar conditions of tears when the tears begin to evaporate during corneal dryness. The present study exploited this ability in an effort to estimate tear osmolarities by comparing the responses to corneal dryness to their responses to hyperosmolar stimuli. Methods Extracellular recordings were performed from single neurons in the trigeminal ganglia innervating the corneas of rats. To determine the extent to which the corneal neurons' responses to drying of the cornea were induced via the activation by hyperosmolar stimuli, we assessed the responses to ocular instillation of 500 and 600 mOsm/L, and a graded series of hyperosmolar stimuli ranging from 350 to 1000 mOsm/L. Results The magnitudes of the responses to drying of the cornea were matched almost exactly to those induced by the ocular instillation of the 600 mOsm/L stimuli but not the 500 mOsm/L solutions. The response magnitudes to a graded series of hyperosmolar solutions were nearly linear from the 350 to the 600 mOsm/L stimuli, but reached a plateau or declined slightly thereafter. Conclusions Our results demonstrate that the tear osmolarity in rats could reach 600 to 1000 mOsm/L during ocular dryness. Furthermore, a spontaneous eye blink could be generated at a tear osmolarity of approximately 400 mOsm/L if the blink is solely determined by hyperosmolar tears, but ocular surface cooling also can become a major factor if hyperosmolar tears occurring during ocular dryness lower the threshold of activation of the neurons.
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Affiliation(s)
- Harumitsu Hirata
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York, United States
| | - Kamila Mizerska
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York, United States
| | | | - Mark I Rosenblatt
- Department of Ophthalmology and Visual Science, University of Illinois College of Medicine, Chicago, Illinois, United States
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Hirata H, Mizerska K, Dallacasagrande V, Guaiquil VH, Rosenblatt MI. Acute corneal epithelial debridement unmasks the corneal stromal nerve responses to ocular stimulation in rats: implications for abnormal sensations of the eye. J Neurophysiol 2017; 117:1935-1947. [PMID: 28250152 PMCID: PMC5411471 DOI: 10.1152/jn.00925.2016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 02/27/2017] [Accepted: 02/27/2017] [Indexed: 11/22/2022] Open
Abstract
It is widely accepted that the mechanisms for transducing sensory information reside in the nerve terminals. Occasionally, however, studies have appeared demonstrating that similar mechanisms may exist in the axon to which these terminals are connected. We examined this issue in the cornea, where nerve terminals in the epithelial cell layers are easily accessible for debridement, leaving the underlying stromal (axonal) nerves undisturbed. In isoflurane-anesthetized rats, we recorded extracellularly from single trigeminal ganglion neurons innervating the cornea that are excited by ocular dryness and cooling: low-threshold (<2°C cooling) and high-threshold (>2°C) cold-sensitive plus dry-sensitive neurons playing possible roles in tearing and ocular pain. We found that the responses in both types of neurons to dryness, wetness, and menthol stimuli were effectively abolished by the debridement, indicating that their transduction mechanisms lie in the nerve terminals. However, some responses to the cold, heat, and hyperosmolar stimuli in low-threshold cold-sensitive plus dry-sensitive neurons still remained. Surprisingly, the responses to heat in approximately half of the neurons were augmented after the debridement. We were also able to evoke these residual responses and follow the trajectory of the stromal nerves, which we subsequently confirmed histologically. The residual responses always disappeared when the stromal nerves were cut at the limbus, suggesting that the additional transduction mechanisms for these sensory modalities originated most likely in stromal nerves. The functional significance of these residual and enhanced responses from stromal nerves may be related to the abnormal sensations observed in ocular disease.NEW & NOTEWORTHY In addition to the traditional view that the sensory transduction mechanisms exist in the nerve terminals, we report here that the proximal axons (stromal nerves in the cornea from which these nerve terminals originate) may also be capable of transducing sensory information. We arrived at this conclusion by removing the epithelial cell layers of the cornea in which the nerve terminals reside but leaving the underlying stromal nerves undisturbed.
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Affiliation(s)
- Harumitsu Hirata
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York; and
| | - Kamila Mizerska
- Department of Ophthalmology, Weill Cornell Medical College, New York, New York; and
| | | | - Victor H Guaiquil
- Department of Ophthalmology and Visual Sciences, College of Medicine, University of Illinois-Chicago, Chicago, Illinois
| | - Mark I Rosenblatt
- Department of Ophthalmology and Visual Sciences, College of Medicine, University of Illinois-Chicago, Chicago, Illinois
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Cruzat A, Qazi Y, Hamrah P. In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease. Ocul Surf 2017; 15:15-47. [PMID: 27771327 PMCID: PMC5512932 DOI: 10.1016/j.jtos.2016.09.004] [Citation(s) in RCA: 207] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2016] [Revised: 09/19/2016] [Accepted: 09/25/2016] [Indexed: 12/20/2022]
Abstract
In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.
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Affiliation(s)
- Andrea Cruzat
- Cornea & Refractive Surgery Service, Department of Ophthalmology, Massachusetts Eye & Ear Infirmary, Harvard Medical School, Boston, MA, USA; Department of Ophthalmology, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Yureeda Qazi
- Cornea & Refractive Surgery Service, Department of Ophthalmology, Massachusetts Eye & Ear Infirmary, Harvard Medical School, Boston, MA, USA
| | - Pedram Hamrah
- Cornea & Refractive Surgery Service, Department of Ophthalmology, Massachusetts Eye & Ear Infirmary, Harvard Medical School, Boston, MA, USA; Boston Image Reading Center, Tufts Medical Center, Tufts University School of Medicine, Boston, MA; Cornea Service, New England Eye Center, Department of Ophthalmology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA.
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Kovács I, Dienes L, Perényi K, Quirce S, Luna C, Mizerska K, Acosta MC, Belmonte C, Gallar J. Lacosamide diminishes dryness-induced hyperexcitability of corneal cold sensitive nerve terminals. Eur J Pharmacol 2016; 787:2-8. [PMID: 27263827 DOI: 10.1016/j.ejphar.2016.05.044] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 05/26/2016] [Accepted: 05/31/2016] [Indexed: 10/21/2022]
Abstract
Lacosamide is an anti-epileptic drug that is also used for the treatment of painful diabetic neuropathy acting through voltage-gated sodium channels. The aim of this work was to evaluate the effects of acute application of lacosamide on the electrical activity of corneal cold nerve terminals in lacrimo-deficient guinea pigs. Four weeks after unilateral surgical removal of the main lachrimal gland in guinea pigs, corneas were excised and superfused in vitro at 34°C for extracellular electrophysiological recording of nerve terminal impulse activity of cold thermosensitive nerve terminals. The characteristics of the spontaneous and the stimulus-evoked (cooling ramps from 34°C to 15°C) activity before and in presence of lacosamide 100µM and lidocaine 100µM were compared. Cold nerve terminals (n=34) recorded from dry eye corneas showed significantly enhanced spontaneous activity (8.0±1.1 vs. 5.2±0.7imp/s; P<0.05) and cold response (21.2±1.7 vs. 16.8±1.3imp/s; P<0.05) as well as reduced cold threshold (1.5±0.1 vs. 2.8±0.2 Δ°C; P<0.05) to cooling ramps compared to terminals (n=58) from control animals. Both lacosamide and lidocaine decreased spontaneous activity and peak response to cooling ramps significantly (P<0.05). Temperature threshold was increased by the addition of lidocaine (P<0.05) but not lacosamide (P>0.05) to the irrigation fluid. In summary, the application of lacosamide results in a significant decrease of the augmented spontaneous activity and responsiveness to cold of corneal sensory nerves from tear-deficient animals. Based on these promising results we speculate that lacosamide might be used to reduce the hyperexcitability of corneal cold receptors caused by prolonged ocular surface dryness due to hyposecretory or evaporative dry eye disease.
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Affiliation(s)
- Illés Kovács
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain; Department of Ophthalmology, Semmelweis University, Budapest, Hungary
| | - Lóránt Dienes
- Department of Ophthalmology, Semmelweis University, Budapest, Hungary
| | - Kristóf Perényi
- Department of Ophthalmology, Semmelweis University, Budapest, Hungary
| | - Susana Quirce
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain
| | - Carolina Luna
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain
| | - Kamila Mizerska
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain
| | - M Carmen Acosta
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain
| | - Carlos Belmonte
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain
| | - Juana Gallar
- Instituto de Neurociencias, Universidad Miguel Hernández - CSIC, San Juan de Alicante, Spain.
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Hirata H, Mizerska K, Marfurt CF, Rosenblatt MI. Hyperosmolar Tears Induce Functional and Structural Alterations of Corneal Nerves: Electrophysiological and Anatomical Evidence Toward Neurotoxicity. Invest Ophthalmol Vis Sci 2016; 56:8125-40. [PMID: 26720465 DOI: 10.1167/iovs.15-18383] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE In an effort to elucidate possible neural mechanisms underlying diminished tearing in dry eye disease, this study sought to determine if hyperosmolar tears, a ubiquitous sign of dry eye disease, produce functional changes in corneal nerve responses to drying of the cornea and if these changes correlate with alterations in corneal nerve morphology. METHODS In vivo extracellular electrophysiological recordings were performed in rat trigeminal ganglion neurons that innervated the cornea before, and up to 3 hours after, the ocular application of continuous hyperosmolar tears or artificial tears. In corollary experiments, immunohistochemical staining was performed to compare corneal nerve morphology in control and in eyes treated with hyperosmolar solutions. RESULTS Our previous studies identified a population of corneal afferents, dry-sensitive neurons that are strongly excited by corneal dessication ("dry response"), a response thought to trigger the lacrimation reflex. In the present study, we found that the dry responses of corneal dry-sensitive neurons were depressed or even completely abolished by hyperosmolar tears in a time- (30 minutes to 3 hours) and dose (450- to 1000-mOsm solutions)-dependent manner. Furthermore, eyes treated with hyperosmolar tears for 3 hours contained large numbers of morphologically abnormal (granular, fragmented, or prominently beaded) subbasal nerves that appeared to be undergoing degeneration. CONCLUSIONS These results demonstrate that tear hyperosmolarity, considered to be a "core" mechanism of dry eye disease, significantly decreases physiological sensitivity and morphologic integrity of the corneal nerves important in tear production. These alterations might contribute to the diminished tearing seen clinically in dry eye patients.
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Affiliation(s)
- Harumitsu Hirata
- Department of Ophthalmology Weill Cornell Medical College, New York, New York, United States
| | - Kamila Mizerska
- Department of Ophthalmology Weill Cornell Medical College, New York, New York, United States
| | - Carl F Marfurt
- Department of Anatomy and Cell Biology, Indiana University School of Medicine-Northwest, Gary, Indiana, United States
| | - Mark I Rosenblatt
- Department of Ophthalmology and Visual Science, University of Illinois College of Medicine, Chicago, Illinois, United States
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Kovács I, Luna C, Quirce S, Mizerska K, Callejo G, Riestra A, Fernández-Sánchez L, Meseguer VM, Cuenca N, Merayo-Lloves J, Acosta MC, Gasull X, Belmonte C, Gallar J. Abnormal activity of corneal cold thermoreceptors underlies the unpleasant sensations in dry eye disease. Pain 2016; 157:399-417. [PMID: 26675826 PMCID: PMC4733818 DOI: 10.1097/j.pain.0000000000000455] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Revised: 10/09/2015] [Accepted: 10/28/2015] [Indexed: 12/23/2022]
Abstract
Dry eye disease (DED) affects >10% of the population worldwide, and it provokes an unpleasant sensation of ocular dryness, whose underlying neural mechanisms remain unknown. Removal of the main lachrymal gland in guinea pigs caused long-term reduction of basal tearing accompanied by changes in the architecture and density of subbasal corneal nerves and epithelial terminals. After 4 weeks, ongoing impulse activity and responses to cooling of corneal cold thermoreceptor endings were enhanced. Menthol (200 μM) first excited and then inactivated this augmented spontaneous and cold-evoked activity. Comparatively, corneal polymodal nociceptors of tear-deficient eyes remained silent and exhibited only a mild sensitization to acidic stimulation, whereas mechanonociceptors were not affected. Dryness-induced changes in peripheral cold thermoreceptor responsiveness developed in parallel with a progressive excitability enhancement of corneal cold trigeminal ganglion neurons, primarily due to an increase of sodium currents and a decrease of potassium currents. In corneal polymodal nociceptor neurons, sodium currents were enhanced whereas potassium currents remain unaltered. In healthy humans, exposure of the eye surface to menthol vapors or to cold air currents evoked unpleasant sensations accompanied by increased blinking frequency that we attributed to cold thermoreceptor stimulation. Notably, stimulation with menthol reduced the ongoing background discomfort of patients with DED, conceivably due to use-dependent inactivation of cold thermoreceptors. Together, these data indicate that cold thermoreceptors contribute importantly to the detection and signaling of ocular surface wetness, and develop under chronic eye dryness conditions an injury-evoked neuropathic firing that seems to underlie the unpleasant sensations experienced by patients with DED.
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Affiliation(s)
- Illés Kovács
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
- Department of Ophthalmology, Semmelweis University, Budapest, Hungary
| | - Carolina Luna
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
| | - Susana Quirce
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
| | - Kamila Mizerska
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
| | - Gerard Callejo
- Laboratory of Neurophysiology, Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain
- Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Ana Riestra
- Instituto Universitario Fernández-Vega, Universidad de Oviedo and Fundación de Investigación Oftalmológica, Oviedo, Spain
| | - Laura Fernández-Sánchez
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, San Vicente del Raspeig, Spain
| | - Victor M. Meseguer
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
| | - Nicolás Cuenca
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, San Vicente del Raspeig, Spain
| | - Jesús Merayo-Lloves
- Instituto Universitario Fernández-Vega, Universidad de Oviedo and Fundación de Investigación Oftalmológica, Oviedo, Spain
| | - M. Carmen Acosta
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
| | - Xavier Gasull
- Laboratory of Neurophysiology, Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain
- Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Carlos Belmonte
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
- Instituto Universitario Fernández-Vega, Universidad de Oviedo and Fundación de Investigación Oftalmológica, Oviedo, Spain
| | - Juana Gallar
- Instituto de Neurociencias, Universidad Miguel Hernández–CSIC, San Juan de Alicante, Spain
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Correlation of Tear Film Osmolarity and 2 Different MMP-9 Tests With Common Dry Eye Tests in a Cohort of Non-Dry Eye Patients. Cornea 2016; 34:739-44. [PMID: 25909238 DOI: 10.1097/ico.0000000000000449] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE Given that early-stage dry eye is difficult to diagnose, the purpose of this study was to evaluate the performance of matrix metalloproteinase 9 (MMP-9) and tear film osmolarity (TFO) in a cohort of elderly patients with potential dry eye disease (DED). METHODS A group of 20 patients, aged 60 years and above, previously undiagnosed with DED were selected. The following DED tests were performed: tear osmolarity, MMP-9 (InflammaDry), Schirmer test, tear film break-up time, Ocular Surface Disease Index (OSDI) questionnaire, corneal fluorescein staining, and conjunctival lissamine green staining. MMP-9 concentrations in tears collected through Schirmer strips were analyzed by an MMP-9 enzyme-linked immunosorbent assay [ELISA]. Subjects were classified by symptoms (classification A: OSDI ≥10, n = 9), based on suspected mild dry eye (classification B: n = 14), TFO difference >8 mOsm/L between both eyes (classification C: n = 13), and TFO cutoff at 308 mOsm/L (classification D: >308 mOsm/L, n = 11). RESULTS Eleven percent (1/9) of the symptomatic and 14% (2/14) of the suspected mild dry eye were positive for MMP-9. InflammaDry MMP-9 tests were confirmed to be accurate through an ELISA. Sixty-seven percent (6/9) of the symptomatic and 64% (9/14) of the suspected mild dry eye were positive for tear osmolarity. None of the evaluated tear film parameters showed a significant correlation, although tear osmolarity and symptoms trended toward significance (r = 0.433, P = 0.06), whereas MMP-9 and corneal staining showed a positive association (r = 0.376, P = 0.10). CONCLUSIONS Similar to corneal staining, the MMP-9 is likely a late-stage sign that is rarely overexpressed in mild subjects, whereas tear osmolarity tends to be a more frequent early indicator of ocular surface disequilibrium within mild subjects.
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Nam SW, Lim DH, Hyun J, Chung TY. Effects and Prognostic Factors of Automated Thermodynamic System Treatment for Meibomian Gland Dysfunction. JOURNAL OF THE KOREAN OPHTHALMOLOGICAL SOCIETY 2016. [DOI: 10.3341/jkos.2016.57.5.724] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Seung Wan Nam
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Dong Hui Lim
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Joo Hyun
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Tae-Young Chung
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
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Dutescu RM, Panfil C, Schrage N. Osmolarity of prevalent eye drops, side effects, and therapeutic approaches. Cornea 2015; 34:560-6. [PMID: 25789693 DOI: 10.1097/ico.0000000000000368] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE Little is known about how the osmolarity of ophthalmic formulations affects the ocular surface. Because hyperosmolar eye drops could be therapeutic for treating corneal edema, this article presents an ex vivo model of corneal edema for testing ophthalmic drugs based on their osmolarity. The respective osmolarity of common eye drops found in the German market is also analyzed here. METHODS For modeling corneal edema, an Ex Vivo Eye Irritation Test was used to simulate an ocular anterior chamber with a physiological corneal barrier. To induce corneal edema, the anterior chamber was supplied with a hypoosmolar medium (148 mOsm/L) for 24 hours. Preserved and preservative-free 5% sodium chloride (hyperosmolar Omnisorb and Ocusalin 5% UD) were used for 1 hour, on 5 corneas each, to test their efficiency to reduce corneal edema in this model. Corneal thickness was determined by optical coherence tomography. Osmolarity of 87 common eye drops was measured by freezing point osmometry. RESULTS Ex vivo, the tested hypoosmolar condition induced corneal edema from 450 μm (±50 μm) at baseline to 851 μm (±94 μm, P < 0.0001). Omnisorb and Ocusalin 5% UD significantly reduced the corneal thickness by 279 μm (±28 μm, P < 0.001) for Omnisorb and 258 μm (±29 μm, P < 0.001) for Ocusalin 5% UD. Forty-three (49%) of the tested products had an osmolarity below and 44 (51%) above the physiological tear osmolarity of 289 mOsm/L. Osmolarity values of less than 200 mOsm/L were found in lubricant drops. The highest osmolarity was detected in Omnisorb (1955 mOsm/L). CONCLUSIONS The Ex Vivo Eye Irritation Test has proven to be a reliable novel model of corneal edema for evaluating osmotic eye drops. Osmolarity measurements revealed a wide range from hypotonic to hypertonic formulations for commonly marketed ophthalmic drugs.
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Affiliation(s)
- Ralf M Dutescu
- *Aachen Centre of Technology Transfer in Ophthalmology (ACTO e.V.), An-Institute, RWTH Aachen University, Aachen, Germany; and †Department of Ophthalmology, RWTH Aachen University, Aachen, Germany
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Subjective Discomfort Symptoms Are Related to Low Corneal Temperature in Patients With Evaporative Dry Eye. Cornea 2015; 34:1079-85. [DOI: 10.1097/ico.0000000000000512] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Abstract
Eye pain is an unpleasant sensory and emotional experience including sensory-discriminative, emotional, cognitive, and behavioral components and supported by distinct, interconnected peripheral and central nervous system elements. Normal or physiological pain results of the stimulation by noxious stimuli of sensory axons of trigeminal ganglion (TG) neurons innervating the eye. These are functionally heterogeneous. Mechano-nociceptors are only excited by noxious mechanical forces. Polymodal nociceptors also respond to heat, exogenous irritants, and endogenous inflammatory mediators, whereas cold thermoreceptors detect moderate temperature changes. Their distinct sensitivity to stimulating forces is determined by the expression of specific classes of ion channels: Piezo2 for mechanical forces, TRPV1 and TRPA1 for heat and chemical agents, and TRPM8 for cold. Pricking pain is evoked by mechano-nociceptors, while polymodal nociceptors are responsible of burning and stinging eye pain; sensations of dryness appear to be mainly evoked by cold thermoreceptors. Mediators released by local inflammation, increase the excitability of eye polymodal nociceptors causing their sensitization and the augmented pain sensations. During chronic inflammation, additional, long-lasting changes in the expression and function of stimulus-transducing and voltage-sensitive ion channels develop, thereby altering polymodal terminal's excitability and evoking chronic inflammatory pain. When trauma, infections, or metabolic processes directly damage eye nerve terminals, these display aberrant impulse firing due to an abnormal expression of transducing and excitability-modulating ion channels. This malfunction evokes 'neuropathic pain' which may also result from abnormal function of higher brain structures where ocular TG neurons project. Eye diseases or ocular surface surgery cause different levels of inflammation and/or nerve injury, which in turn activate sensory fibers of the eye in a variable degree. When inflammation dominates (allergic or actinic kerato-conjunctivitis), polymodal nociceptors are primarily stimulated and sensitized, causing pain. In uncomplicated photorefractive surgery and moderate dry eye, cold thermoreceptors appear to be mainly affected, evoking predominant sensations of unpleasant dryness.
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Affiliation(s)
- Carlos Belmonte
- />Instituto de Neurociencias, Universidad Miguel Hernández-CSIC San Juan de Alicante, Avenida de la Universidad, s/n, 03202 Alicante, Spain
- />Instituto Fernandez Vega, Fundación de Investigación Oftalmológica, Av Doctores Fernández Vega, 34, 33012 Oviedo, Asturias Spain
| | - M. Carmen Acosta
- />Instituto de Neurociencias, Universidad Miguel Hernández-CSIC San Juan de Alicante, Avenida de la Universidad, s/n, 03202 Alicante, Spain
| | - Jesus Merayo-Lloves
- />Instituto Fernandez Vega, Fundación de Investigación Oftalmológica, Av Doctores Fernández Vega, 34, 33012 Oviedo, Asturias Spain
| | - Juana Gallar
- />Instituto de Neurociencias, Universidad Miguel Hernández-CSIC San Juan de Alicante, Avenida de la Universidad, s/n, 03202 Alicante, Spain
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Abstract
As the biological alarm of impending or actual tissue damage, pain is essential for our survival. However, when it is initiated and/or sustained by dysfunctional elements in the nociceptive system, it is itself a disease known as neuropathic pain. While the critical nociceptive system provides a number of protective functions, it is unique in its central role of monitoring, preserving and restoring the optical tear film in the face of evaporative attrition without which our vision would be non-functional. Meeting this existential need resulted in the evolution of the highly complex, powerful and sensitive dry eye alarm system integrated in the peripheral and central trigeminal sensory network. The clinical consequences of corneal damage to these nociceptive pathways are determined by the type and location of its pathological elements and can range from the spectrum known as dry eye disease to the centalised oculofacial neuropathic pain syndrome characterised by a striking disparity between the high intensity of symptoms and paucity of external signs. These changes parallel those observed in somatic neuropathic pain. When seen through the neuroscience lens, diseases responsible for inadequately explained chronic eye pain (including those described as dry eye) can take on new meanings that may clarify long-standing enigmas and point to new approaches for developing preventive, symptomatic and disease-modifying interventions for these currently refractory disorders.
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Affiliation(s)
- Perry Rosenthal
- Boston EyePain Foundation, Chestnut Hill, Massachusetts, USA
| | - David Borsook
- Center for Pain and the Brain, Boston Children's, MGH and McLean Hospitals, Harvard Medical School, Children's Medical Center, Boston, Massachusetts, USA
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