Cornea; Sense Loss Clinical Trial
Official title:
Investigation in Variability and Repeatability of Corneal Sensation in a Normal Population
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.
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.
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