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Situ P, Begley C, Simpson T. The roles of neural adaptation and sensitization in contact lens discomfort. Ocul Surf 2024; 34:132-139. [PMID: 39047906 DOI: 10.1016/j.jtos.2024.07.003] [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: 04/08/2024] [Revised: 07/03/2024] [Accepted: 07/11/2024] [Indexed: 07/27/2024]
Abstract
PURPOSE To investigate the roles of neural adaptation and sensitization in contact lens discomfort (CLD). METHODS Cooling stimuli (20 °C) were applied to the cornea in a group comprising 24 symptomatic and 25 asymptomatic contact lens (CL) wearers as well as 15 non-CL wearing controls, using a computerized Belmonte esthesiometer. The adaptation paradigm consisted of 20 repetitive stimuli at threshold, sub- and supra-threshold levels. The sensitization paradigm involved five levels of suprathreshold stimuli ranging between 1x to 2x threshold. Following each stimulus, participants rated the sensation magnitude regarding intensity, coolness and irritation. Measurements were taken with habitual CL (BL_CL), after 2 weeks of no-CL (No_CL) and after restarting habitual CL wear (ReSt_CL). RESULTS The symptomatic subjects exhibited a lower threshold but reported enhanced sensations during the adaptation and sensitization paradigm, compared to the asymptomatic and control groups (all p ≤ 0.021). At the BL_CL and ReSt_CL visits, they showed increased ratings to repeated subthreshold stimuli (p = 0.025) and greater irritation during the sensitization paradigm (p ≤ 0.032). Ratings in asymptomatic and control groups were relatively unchanged over time (p ≥ 0.181). Logistic regression revealed a link between the augmented sensory responses and increased likelihood with CLD. CONCLUSION The maladaptive sensory responses seen in CLD subjects, with reduced adaptation and heightened sensitization to ocular surface stimulation, suggest an imbalance between sensitization and adaptation in CLD. As CLD may represent a reversible subcategory of dry eye, it can serve as a human dry eye model for studying the neurosensory effect of ocular surface stimulation.
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Affiliation(s)
- Ping Situ
- School of Optometry, Indiana University, Bloomington, IN, USA.
| | - Carolyn Begley
- School of Optometry, Indiana University, Bloomington, IN, USA
| | - Trefford Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
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Pastor-Zaplana JÁ, Gallar J, Acosta MC. Functional Changes of the Ocular Surface Sensory Nerves Due to Contact Lens Use in Young Symptomatic and Asymptomatic Users. Invest Ophthalmol Vis Sci 2023; 64:12. [PMID: 37938935 PMCID: PMC10637199 DOI: 10.1167/iovs.64.14.12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 10/18/2023] [Indexed: 11/10/2023] Open
Abstract
Purpose The purpose of this study was to analyze the differences in corneal sensory nerve functionality in young asymptomatic (CL-A) and symptomatic (CL-S) contact lens (CL) users. Methods CL wearers (23.8 ± 1.0 years, n = 31) were classified as CL-S with an Ocular Surface Disease Index (OSDI) ≥ 13 (n = 14) or CL-A. Users of eye glasses (EG; 24.5 ± 0.8 years, n = 29) with OSDI < 13 participated as controls. The sensations evoked by mechanical, chemical (gas esthesiometer), and cold (4°C saline drops) stimuli were measured using the Visual Analogue Scales (VASs). Moreover, tear volume, tear break up time (TBUT), blinking frequency (BF), and ocular surface temperature (OST; IR thermography) were also measured. Results Mechanical and chemical stimuli produced similar scores in the CL-A and EG participants, although the CL-A subjects referred to stronger irritation (p < 0.05). Likewise, the VAS intensity in response to cold stimuli did not differ between CL-A and EG subjects, while the ability to detect cold was significantly worse in CL-S users (p < 0.05). CL-A users had a similar tear volume, a higher BF (p < 0.01) and shorter TBUT (p < 0.001) to EG wearers, and blinking and TBUT were also altered significantly in CL-S users (p < 0.01). Interestingly, the OST was significantly lower in CL-A users (p < 0.05) than in EG wearers, but not in CL-S users. Conclusions Using CLs modifies corneal sensitivity, blinking and tearing in young volunteers. Even if they have yet to develop clinical signs of inflammation, they display changes in corneal sensitivity consistent with the sensitization of corneal nociceptors and the inhibition cold thermoreceptors, phenomena that occur under inflammatory conditions. The differences in corneal sensitivity and OST between CL-A and CL-S users could reflect the extent of nerve damage and inflammation at the ocular surface.
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Affiliation(s)
- José Ángel Pastor-Zaplana
- Instituto de Neurociencias, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Spain
- Departamento de Patología y Cirugía, Universidad Miguel Hernández de Elche, Sant Joan d'Alacant, Spain
| | - Juana Gallar
- Instituto de Neurociencias, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Spain
- Instituto de Investigación Biomédica y Sanitaria de Alicante, Alicante, Spain
| | - M. Carmen Acosta
- Instituto de Neurociencias, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Spain
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Jones L, Efron N, Bandamwar K, Barnett M, Jacobs DS, Jalbert I, Pult H, Rhee MK, Sheardown H, Shovlin JP, Stahl U, Stanila A, Tan J, Tavazzi S, Ucakhan OO, Willcox MDP, Downie LE. TFOS Lifestyle: Impact of contact lenses on the ocular surface. Ocul Surf 2023; 29:175-219. [PMID: 37149139 DOI: 10.1016/j.jtos.2023.04.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 04/10/2023] [Indexed: 05/08/2023]
Abstract
Several lifestyle choices made by contact lens wearers can have adverse consequences on ocular health. These include being non-adherent to contact lens care, sleeping in lenses, ill-advised purchasing options, not seeing an eyecare professional for regular aftercare visits, wearing lenses when feeling unwell, wearing lenses too soon after various forms of ophthalmic surgery, and wearing lenses when engaged in risky behaviors (e.g., when using tobacco, alcohol or recreational drugs). Those with a pre-existing compromised ocular surface may find that contact lens wear exacerbates ocular disease morbidity. Conversely, contact lenses may have various therapeutic benefits. The coronavirus disease-2019 (COVID-19) pandemic impinged upon the lifestyle of contact lens wearers, introducing challenges such as mask-associated dry eye, contact lens discomfort with increased use of digital devices, inadvertent exposure to hand sanitizers, and reduced use of lenses. Wearing contact lenses in challenging environments, such as in the presence of dust and noxious chemicals, or where there is the possibility of ocular trauma (e.g., sport or working with tools) can be problematic, although in some instances lenses can be protective. Contact lenses can be worn for sport, theatre, at high altitude, driving at night, in the military and in space, and special considerations are required when prescribing in such situations to ensure successful outcomes. A systematic review and meta-analysis, incorporated within the review, identified that the influence of lifestyle factors on soft contact lens dropout remains poorly understood, and is an area in need of further research. Overall, this report investigated lifestyle-related choices made by clinicians and contact lens wearers and discovered that when appropriate lifestyle choices are made, contact lens wear can enhance the quality of life of wearers.
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Affiliation(s)
- Lyndon Jones
- Centre for Ocular Research & Education (CORE), School of Optometry and Vision Science, University of Waterloo, Waterloo, ON, Canada.
| | - Nathan Efron
- School of Optometry and Vision Science, Queensland University of Technology, Kelvin Grove, Queensland, Australia
| | - Kalika Bandamwar
- Department of Ophthalmology, New Zealand National Eye Centre, The University of Auckland, Auckland, New Zealand
| | - Melissa Barnett
- University of California, Davis Eye Center, Sacramento, CA, USA
| | - Deborah S Jacobs
- Massachusetts Eye & Ear, Harvard Medical School, Boston, MA, USA
| | - Isabelle Jalbert
- School of Optometry and Vision Science, UNSW Sydney, NSW, Australia
| | - Heiko Pult
- Dr Heiko Pult Optometry & Vision Research, Weinheim, Germany
| | | | - Heather Sheardown
- Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada
| | | | - Ulli Stahl
- Centre for Ocular Research & Education (CORE), School of Optometry and Vision Science, University of Waterloo, Waterloo, ON, Canada
| | | | - Jacqueline Tan
- School of Optometry and Vision Science, UNSW Sydney, NSW, Australia
| | - Silvia Tavazzi
- Department of Materials Science, University of Milano-Bicocca, Milan, Italy
| | | | - Mark D P Willcox
- School of Optometry and Vision Science, UNSW Sydney, NSW, Australia
| | - Laura E Downie
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
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Evaluation of Ocular Surface Characteristics in Dry Eye Disease With and Without Soft Contact Lens Wear: A Comparative Study. Eye Contact Lens 2022; 48:377-383. [PMID: 35583308 DOI: 10.1097/icl.0000000000000904] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/21/2022] [Indexed: 11/25/2022]
Abstract
OBJECTIVES To investigate ocular surface alterations and in vivo confocal microscopic characteristics of the cornea in dry eye disease (DED) with contact lens wear (CLW). METHODS Sixty participants were divided into three groups: DED with CLW (n=20), DED without CLW (n=20), and normal control (n=20). Ocular surface parameters were evaluated. Basal tears and in vivo confocal microscopy images of the cornea were collected. Multiplex bead analysis was used to assess interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, nerve growth factor (NGF), and substance P (SP) in tears. Nerve morphology and dendritic cell density in corneal subbasal nerve images were calculated. RESULTS The DED with CLW group showed significantly higher ocular surface staining scores (P=0.022) and higher levels of IL-1β, NGF, and SP in tears (P=0.014, P=0.004 and P=0.025) than the DED without CLW group. Corneal dendritic cell density in the DED with CLW group was significantly higher than that in the normal controls (P=0.001) and DED without CLW group (P=0.043). Tear cytokine levels of IL-1β, NGF, and SP were correlated with ocular surface parameters in the DED with CLW group. Moreover, the years of CLW were positively correlated with corneal dendritic cell density (r=0.527, P=0.017) and negatively correlated with corneal nerve density (r=-0.511, P=0.021). CONCLUSIONS Patients with DED with CLW showed greater epithelial damage, elevated inflammatory cytokines and neuromediators in tears, and higher corneal dendritic cell density than patients with DED without CLW. The immune and nervous systems may be involved in contact lens-related DED.
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Osae EA, Jones L, Nichols JJ. The impact of contact lenses on meibomian gland morphology. Ocul Surf 2022; 24:148-155. [PMID: 35395385 DOI: 10.1016/j.jtos.2022.04.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Revised: 02/22/2022] [Accepted: 04/02/2022] [Indexed: 11/28/2022]
Abstract
Despite years of experience with contact lenses, controversy remains as to whether contact lenses adversely impact the meibomian glands (MG). This review summarizes the present body of evidence, showing that contact lens wear is associated with alterations in MG morphology (up to 80% higher gland atrophy compared to non-wearers) and qualitative changes in MG secretion. Key factors such as duration of contact lens wear, contact lens type (e.g., soft vs. rigid), edge design, and material modulus of elasticity are discussed in relation to the extent of MG morphological changes, the quality of MG secretion and other ocular surface parameters. Longitudinal studies of sufficient statistical power are needed to better understand how contact lens wear affects the MG, risk factors, and the clinical sequelae of these changes.
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Affiliation(s)
| | - Lyndon Jones
- Centre for Ocular Research & Education (CORE), School of Optometry & Vision Science, University of Waterloo, Waterloo, Ontario, Canada; Centre for Eye and Vision Research (CEVR), 17W Hong Kong Science Park, Hong Kong
| | - Jason J Nichols
- The University of Alabama at Birmingham, School of Optometry, Birmingham, AL, 35233, USA.
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6
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CLEAR - Contact lens complications. Cont Lens Anterior Eye 2021; 44:330-367. [DOI: 10.1016/j.clae.2021.02.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2021] [Accepted: 02/01/2021] [Indexed: 12/20/2022]
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7
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Downie LE, Bandlitz S, Bergmanson JPG, Craig JP, Dutta D, Maldonado-Codina C, Ngo W, Siddireddy JS, Wolffsohn JS. CLEAR - Anatomy and physiology of the anterior eye. Cont Lens Anterior Eye 2021; 44:132-156. [PMID: 33775375 DOI: 10.1016/j.clae.2021.02.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 02/01/2021] [Indexed: 02/06/2023]
Abstract
A key element of contact lens practice involves clinical evaluation of anterior eye health, including the cornea and limbus, conjunctiva and sclera, eyelids and eyelashes, lacrimal system and tear film. This report reviews the fundamental anatomy and physiology of these structures, including the vascular supply, venous drainage, lymphatic drainage, sensory innervation, physiology and function. This is the foundation for considering the potential interactions with, and effects of, contact lens wear on the anterior eye. This information is not consistently published as academic research and this report provides a synthesis from all available sources. With respect to terminology, the report aims to promote the consistent use of nomenclature in the field, and generally adopts anatomical terms recommended by the Federative Committee for Anatomical Terminology. Techniques for the examination of the ocular surface are also discussed.
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Affiliation(s)
- Laura E Downie
- Department of Optometry and Vision Sciences, The University of Melbourne, Australia.
| | - Stefan Bandlitz
- Höhere Fachschule für Augenoptik Köln, Cologne School of Optometry, Germany; School of Optometry, Aston University, Birmingham, UK
| | - Jan P G Bergmanson
- Texas Eye Research and Technology Center, University of Houston College of Optometry, United States
| | - Jennifer P Craig
- Department of Ophthalmology, New Zealand National Eye Centre, The University of Auckland, New Zealand
| | - Debarun Dutta
- School of Optometry, Aston University, Birmingham, UK
| | - Carole Maldonado-Codina
- Eurolens Research, Division of Pharmacy and Optometry, Faculty of Biology, Medicine and Health, The University of Manchester, UK
| | - William Ngo
- Centre for Ocular Research & Education, School of Optometry & Vision Science, University of Waterloo, Waterloo, Canada; Centre for Eye and Vision Research (CEVR), 14W Hong Kong Science Park, Hong Kong
| | | | - James S Wolffsohn
- School of Optometry, Aston University, Birmingham, UK; Department of Ophthalmology, New Zealand National Eye Centre, The University of Auckland, New Zealand
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8
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Jayakumar V, Simpson TL. Detectability and Bias Indices of Pneumatic Corneal Stimuli Using Signal Detection Theory. Transl Vis Sci Technol 2020; 9:17. [PMID: 33240570 PMCID: PMC7671863 DOI: 10.1167/tvst.9.12.17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 10/09/2020] [Indexed: 12/04/2022] Open
Abstract
Purpose To evaluate the feasibility of using signal detection theory (SDT) in estimating criterion and detectability indices for corneal pneumatic stimuli and test corneal psychophysical data against linking hypotheses from nonprimate physiology using Bayesian analysis. Methods Corneal pneumatic stimuli were delivered using the Waterloo Belmonte esthesiometer. Corneal thresholds were estimated in 30 asymptomatic participants and 1.5× threshold stimuli were used as signals (with 0.4 probability). There were 100-trial mechanical and cold stimulus experiments and 50-trial chemical experiments. Trials were demarcated auditorily and “yes” or “no” recorded after each trial. Cold stimulus experiments were conducted with 0.6 signal probability. Criterion (c), likelihood ratio (lnβ), and d′ were calculated from the yes-no responses. Results Average d′ was 0.59 ± 0.1, 1.65 ± 0.37, and 1.14 ± 0.3 units for cold, mechanical, and chemical stimuli, respectively. Bayes factors obtained using Bayesian analysis of variance mildly favored (BF10 = 1.55) differences between d′s of the stimulus types, with no support for differences in criteria between stimulus types. Multiple comparisons of d′ supported linking hypotheses based on nociception and nerve conductance theories. Conclusions Our experiments are the first to demonstrate the feasibility of estimating SDT indices and test different hypotheses. The conservative strategy (reporting “no” more often) chosen by participants was anticipated due to relatively large proportion of catch trials. Translational Relevance SDT when using pneumatic esthesiometry is vital to evaluate bias in responses of participants. Considering the varied forms of inherent noise in the corneal sensory system, SDT is critical to understand the sensory and decisional characteristics.
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Affiliation(s)
- Varadharajan Jayakumar
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
| | - Trefford L Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
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9
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Situ P, Simpson TL, Begley CG, Keir N. Role of diurnal variation of corneal sensory processing in contact lens discomfort. Ocul Surf 2020; 18:770-776. [PMID: 32828970 DOI: 10.1016/j.jtos.2020.08.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Revised: 08/06/2020] [Accepted: 08/14/2020] [Indexed: 02/07/2023]
Abstract
PURPOSE To examine the diurnal variation of corneal threshold and suprathreshold sensory processing, symptoms, and tear secretion in symptomatic and asymptomatic contact lens (CL) wearers and controls. METHODS 26 symptomatic and 25 asymptomatic CL wearers and 15 asymptomatic non-CL wearing controls participated. Cooling thresholds, symptoms and tear meniscus height (TMH) were measured on each of 3 measurement days (random order) on the following schedules; Day-1 within 1 h of awakening (Baseline) and 3, 6 and 9 h later, Day-2 baseline and 9 h later (CLs worn in CL group) and Day-3 baseline and 9 h later. Magnitudes estimates for threshold-scaled suprathreshold stimuli were also estimated on Day-3. Data were analyzed using mixed models and repeated measures ANOVA. RESULTS Cooling thresholds for the symptomatic group were lower and decreased over Day-1 (p < 0.008) and after 8 h of CL wear on Day-2 (p < 0.001) and were paralleled by increased symptoms (all p < 0.001), whereas minimal variations were found in the asymptomatic and control groups. Magnitude estimates for suprathreshold stimuli were higher (p ≤ 0.002) in the symptomatic group but did not differ significantly over the day. TMH varied little over time and was lower in the symptomatic group, but the difference was not statistically significant. CONCLUSION Corneal sensitivity and symptoms, but not TMH, increased diurnally irrespective of CL wear in symptomatic CL wearers. These results reveal the essential role of neurosensory abnormalities in CL discomfort and suggest involvement of a central mechanism in the diurnally increased symptoms of these patients.
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Affiliation(s)
- Ping Situ
- School of Optometry, Indiana University, Bloomington, IN, USA.
| | - Trefford L Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
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10
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López-de la Rosa A, Fernández I, García-Vázquez C, Arroyo-Del Arroyo C, González-García MJ, Enríquez-de-Salamanca A. Conjunctival Neuropathic and Inflammatory Pain-Related Gene Expression with Contact Lens Wear and Discomfort. Ocul Immunol Inflamm 2019; 29:587-606. [PMID: 31825696 DOI: 10.1080/09273948.2019.1690005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Purpose: To identify alterations in neuropathic and inflammatory pain gene expression associated with contact lens (CL) wear and CL discomfort (CLD).Methods: Eight non-wearers, eight asymptomatic CL wearers (CLWs) and eight symptomatic CLWs were included. Conjunctival cells were collected by impression cytology and the mRNA expression levels of 85 genes were analyzed. Differentially expressed genes between non-wearers and CLWs and between asymptomatic and symptomatic CLWs were analyzed. An enrichment analysis was also performed.Results: Twelve genes were upregulated (including IL10, PDYN and PENK) and 28 downregulated (CCL2, IL1A, IL1B, IL2 and NGF) in CLWs (p ≤ 0.050). Eleven genes were upregulated (CCL2, IL1A, IL1B, IL2 and NGF) and nine downregulated (PDYN and PENK) in symptomatic CLWs (p ≤ 0.035). Enriched overrepresented terms were related to pain, neuronal transmission and inflammation.Conclusion: Contact lens wear might produce a desensitization-like mechanism responsible for comfortable CL wear. A malfunction of this mechanism might contribute to CLD.
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Affiliation(s)
- Alberto López-de la Rosa
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain.,Department of Theoretical Physics, Atomic and Optics, University of Valladolid, Valladolid, Spain
| | - Itziar Fernández
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain.,Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), Valladolid, Spain
| | - Carmen García-Vázquez
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain
| | - Cristina Arroyo-Del Arroyo
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain.,Department of Theoretical Physics, Atomic and Optics, University of Valladolid, Valladolid, Spain
| | - María J González-García
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain.,Department of Theoretical Physics, Atomic and Optics, University of Valladolid, Valladolid, Spain.,Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), Valladolid, Spain
| | - Amalia Enríquez-de-Salamanca
- Institute of Applied Ophthalmobiology (IOBA), University of Valladolid, Valladolid, Spain.,Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), Valladolid, Spain
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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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12
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Jayakumar V, Simpson TL. A Method to Calibrate the Carbon Dioxide (Chemical) Stimuli of Pneumatic Esthesiometer Externally. Transl Vis Sci Technol 2019; 8:4. [PMID: 31572624 PMCID: PMC6756506 DOI: 10.1167/tvst.8.5.4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 06/25/2019] [Indexed: 12/05/2022] Open
Abstract
Purpose To determine the feasibility of using a portable carbon dioxide (CO2) sensor to calibrate a pneumatic esthesiometer and then to calibrate the chemical stimuli. Methods The chemical stimuli in ocular surface experiments are combinations of medical air and added CO2 (%CO2). These stimuli were calibrated using a portable CO2 sensor (COZIR CM-0041) and data logger, delivered for 100 seconds by using the Waterloo Belmonte esthesiometer. The distances between the sensor and esthesiometer tip were 0 (to measure feasibility), 3, 5, and 10 mm. In experiment I, 100% CO2 was tested using four different flow rates (50, 100, 150, and 200 mL/min) at three working distances. In experiment II, flow rates of 20 to 100 mL/min and concentrations of 20% to 100% CO2 were tested in 20 steps at 3 working distances. Results The CO2 sensor correctly reported the esthesiometer extremes of 0% and 100% CO2 when placed at the esthesiometer tip. There were progressive, systematic increases in concentrations reaching/reported by the sensor with increasing flow rates and nominal concentrations and progressive decreases in measurements with increases in working distance. Conclusions CO2 concentrations in pneumatic esthesiometers can be calibrated and, as expected, vary with flow rate and distance, highlighting the importance of calibration and standardization of CO2 stimuli in these instruments. Translational Relevance Calibrated CO2, a chemical sensory stimulus in humans, may be used in testing the surface of the eye as well as other membranes within which the CO2 can be dissolved (e.g., mucous) to produce an acidic stimulus.
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Affiliation(s)
| | - Trefford L. Simpson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario
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13
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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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14
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|