Investigation in Corneal Sensation
Condition: Cornea; Sense Loss
Study type: Interventional

Summary: 
      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: 
      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.
    

Intervention name(s): Liquid Jet Esthesiometer Prototype; Tactile Esthesiometer Prototype; Cochet Bonnet esthesiometer
Intervention type(s): Device; Device; Device
Intervention description(s): Balanced salt solution with a pH value similar to the tear film uesd as a liquid jet stimulus for corneal sensation threshold measurement; A round plastic nozzle (1.8mm diameter) used as a stimulus for corneal sensation threshold measurement; A nylon thread (0.12mm diameter) used as a stimulus for corneal sensation threshold measurement
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: corneal sensation; subbasal nerve plexus