Investigation in Corneal Sensation

Study Overview
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Brief Summary
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The aim is to find out more about how corneal sensory fibres react to different types of stimuli (liquid / tactile / nylon thread) and how this can be consciously perceived by the individual. Is it possible to generate a stimulus that delivers a repeatable and reliable response within a useful stimulus force range which allows an interpretation / evaluation of normal / expected activity of superficial nerve fibres in the cornea? The study group will be divided into two age groups, as sensitivity changes are thought to occur in dependence of age. In vivo confocal microscopy has shown that the density of corneal nerve fibres in the sub-basal nerve plexus decreases with age, which consequently would suggest that sensitivity should also decrease. A very interesting research question is to find out, if such sensitivity differences can be detected with the nature of the stimuli applied in this study.

Detailed Description
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The aim of this study is to gain more physiological knowledge about ocular surface sensation (corneal sensitivity), with application of three different concepts employing different types of stimuli for triggering a response from the pain sensitive nerve endings in the superficial cornea: 1) liquid jet (consisting of isotonic saline solution; prototype), 2) tactile stimulus (round plastic nozzle, prototype) 3) commercially available Cochet Bonnet esthesiometer (nylon thread). Measurements will be carried out on healthy eyes of subjects in two different age groups. Current knowledge about human corneal sensitivity is limited, as applied methods for ocular surface sensation measurement are limited with regards to reproducibility / accuracy. Corneal sensitivity represents a neurological response from the free nerve endings within the epithelium. They are sensitive to mechanical, electrical, chemical or thermal stimuli and hence have a protective function for the cornea. Corneal nerves play an important role in cell growth and proliferation of epithelial cells, wound healing and repair. In experimental studies, corneal denervation has been reported to result in epithelial changes: increased permeability, decreased proliferation, changed appearance and delayed wound healing. Therefore, intact corneal innervation is required to maintain the integrity of a normal corneal epithelium. Corneal sensory nerves are believed to play an important role in maintaining the resting tear flow, as their afferent impulses from the ocular surface lead to a reflex response, best described by the lacrimal functional unit: an integrated system comprising the ocular surface tissues (cornea, corneal limbus, conjunctiva, conjunctival blood vessels, and eyelids), the tear secreting components (main and accessory lacrimal glands, meibomian glands, conjunctival goblet, and epithelial cells), and the sensory and motor nerves that connect them. Current knowledge about ocular surface sensitivity is insufficient, as currently available measurement possibilities lack repeatability and accuracy. Before a new instrument can be developed, more research is required, in order to find a suitable concept for precise sensitivity measurement. For this purpose, two new different concepts with different / new stimulus types will be applied repeatably on healthy eyes in this study. The aim is to find out more about how corneal sensory fibres react to different types of stimuli (liquid / tactile / nylon thread) and how this can be consciously perceived by the individual. Is it possible to generate a stimulus that delivers a repeatable and reliable response within a useful stimulus force range which allows an interpretation / evaluation of normal / expected activity of superficial nerve fibres in the cornea? The study group will be divided into two age groups, as sensitivity changes are thought to occur in dependence of age. In vivo confocal microscopy has shown that the density of corneal nerve fibres in the sub-basal nerve plexus decreases with age, which consequently would suggest that sensitivity should also decrease. A very interesting research question is to find out, if such sensitivity differences can be detected with the nature of the stimuli applied in this study.

Official Title
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Investigation in Variability and Repeatability of Corneal Sensation in a Normal Population

Conditions
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Cornea; Sense Loss

Intervention / Treatment
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* Device: Liquid Jet Esthesiometer Prototype
* Device: Tactile Esthesiometer Prototype
* Device: Cochet Bonnet esthesiometer


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Group 'young age': 18 - 30 years of age; healthy eyes with Ocular Surface Disease Index Score </= 13 Group 'advanced age': 50 - 70 years of age; healthy eyes with Ocular Surface Disease Index Score </= 13 Exclusion Criteria: Systemic disease that may affect ocular health, such as diabetes Injury and history of operations on the anterior segment of the eye regular application of systemic or ocular medication known to affect the tear film, specifically on the day of measurement rigid gas permeable contact lens wear soft contact lens wear less than 48 hours before study visit

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Group 'young age'<br>Group 'young age': 18 - 30 years of age; healthy eyes | Device: Liquid Jet Esthesiometer Prototype<br>* Balanced salt solution with a pH value similar to the tear film uesd as a liquid jet stimulus for corneal sensation threshold measurement<br>Device: Tactile Esthesiometer Prototype<br>* A round plastic nozzle (1.8mm diameter) used as a stimulus for corneal sensation threshold measurement<br>Device: Cochet Bonnet esthesiometer<br>* A nylon thread (0.12mm diameter) used as a stimulus for corneal sensation threshold measurement<br>|
| Other: Group 'advanced age'<br>Group 'advanced age': 50 - 70 years of age; healthy eyes | Device: Liquid Jet Esthesiometer Prototype<br>* Balanced salt solution with a pH value similar to the tear film uesd as a liquid jet stimulus for corneal sensation threshold measurement<br>Device: Tactile Esthesiometer Prototype<br>* A round plastic nozzle (1.8mm diameter) used as a stimulus for corneal sensation threshold measurement<br>Device: Cochet Bonnet esthesiometer<br>* A nylon thread (0.12mm diameter) used as a stimulus for corneal sensation threshold measurement<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Repeatability of mechanical corneal sensation thresholds with the Cochet Bonnet esthesiometer | Evaluation of repeatability of mechanical corneal sensation thresholds for the measurement with the Cochet Bonnet instrument (in mN): the corneal sensation thresholds will be obtained with the double staircase method (with forced choice) and the stimulus represents a nylon thread, whereby its force is proportional to the length of the nylon thread applied to the corneal surface. | two weeks | 
| Repeatability of mechanical corneal sensation thresholds with the liquid jet protoype esthesiometer | Evaluation of repeatability of mechanical corneal sensation thresholds for the measurement with the liquid jet esthesiometer prototype instrument (in mbar): the corneal sensation thresholds will be obtained with the double staircase method (with forced choice) and the stimulus represents a liquid jet (consisting of isotonic saline solution). | two weeks | 
| Repeatability of mechanical corneal sensation thresholds with the tactile prototype esthesiometer | Evaluation of variability / repeatability of mechanical corneal sensation thresholds for the measurement with the tactile esthesiometer prototype instrument (in mN): the corneal sensation thresholds will be obtained with the double staircase method (with forced choice) and the stimulus represents a small, round plastic ball. | two weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Correlation between corneal sensation thresholds with the Cochet Bonnet esthesiometer | Correlation between corneal sensitivity thresholds (in mN) obtained with the Cochet Bonnet esthesiometer | one day | 
| Correlation between corneal sensation thresholds with the liquid jet prototype esthesiometer | Correlation between corneal sensitivity thresholds (in mbar) obtained with the liquid jet prototype esthesiometer | one day | 
| Correlation between corneal sensation thresholds with the tactile prototype esthesiometer | Correlation between corneal sensitivity thresholds (in mN) obtained with the tactile prototype esthesiometer | one day | 
| Correlation between corneal sensitivity thresholds, obtained with the Cochet Bonnet esthesiometer, and general pain perception | Correlation between corneal sensitivity thresholds obtained with the Cochet Bonnet esthesiometer and general pain perception, obtained with three different stimulus types, for each of the two different age groups recruited. | within two weeks | 
| Correlation between corneal sensitivity thresholds, obtained with the liquid jet prototype esthesiometer, and general pain perception | Correlation between corneal sensitivity thresholds, obtained with the liquid jet prototype esthesiometer, and general pain perception | within two weeks | 
| Correlation between corneal sensitivity thresholds, obtained with the tactile prototype esthesiometer, and general pain perception | Correlation between corneal sensitivity thresholds, obtained with the tactile prototype esthesiometer, and general pain perception | within two weeks | 
| Comparison of corneal sensation thresholds, obtained with the Cochet Bonnet esthesiometer, between the two different age groups in the study population | Comparison of corneal sensation thresholds obtained with the Cochet Bonnet esthesiometer between the two different age groups in the study population | within two weeks | 
| Comparison of corneal sensation thresholds, obtained with the liquid jet prototype esthesiometer, between the two different age groups in the study population | Comparison of corneal sensation thresholds, obtained with the liquid jet prototype esthesiometer, between the two different age groups in the study population | within two weeks | 
| Comparison of corneal sensation thresholds, obtained with the tactile prototype esthesiometer, between the two different age groups in the study population | Comparison of corneal sensation thresholds, obtained with the tactile prototype esthesiometer, between the two different age groups in the study population | within two weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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corneal sensation, subbasal nerve plexus