title: Corneal Sensitivity to Hyperosmolar Eye Drops: A Novel Behavioral Assay to Assess Diabetic Peripheral Neuropathy.
abstract: Diagnosis of peripheral neuropathy (PN), which affects approximately 50% of the diabetic population, is subjective, with many patients seeking a diagnosis only after presenting with symptoms. Recently, in vivo confocal microscopy of subepithelial corneal nerve density has been promoted as a surrogate marker for early detection of PN, but imaging of corneal nerves requires sophisticated instrumentation, expertise in confocal imaging, cooperative patients, and automated analysis tools to derive corneal nerve density. As an alternative, we developed a simple screening method that is based on the sensitivity of corneal nerves to cause reflex eyelid squinting in response to hyperosmolar eye drops.
  
  
  
  Eyes of control and type 2 diabetic rats were given an eye drop of a 290- to 900-mOsm solution, and the ocular response was video recorded. Other neuropathic end points including nerve conduction velocity and subepithelial cornea nerve density were determined.
  
  
  
  Motor and sensory nerve conduction velocity and total nerve fiber length of corneal nerves in the subepithelial layer were significantly decreased in diabetic rats. Applying the hyperosmotic solutions to the ocular surface caused an osmolarity-dependent increase in squinting of the treated eye in control rats. Squinting was almost totally blocked by preapplication of proparacaine or N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide, a transient receptor potential melastatin-8 channel blocker. Squinting in response to the 900-mOsm solution was significantly reduced in diabetic rats.
  
  
  
  Preclinical studies show that evaluation of corneal sensitivity may be an alternative method for the early detection of PN and has potential for translation to clinical studies.
authors.affiliation: Department of Veterans Affairs Iowa City Health Care System, Iowa City, Iowa, United States 2Veterans Affairs Center for the Prevention and Treatment of Visual Loss, Iowa City, Iowa, United States.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Yorek
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Eric P
authors.initials: EP
authors.lastname: Davidson
authors.affiliation: Department of Veterans Affairs Iowa City Health Care System, Iowa City, Iowa, United States 2Veterans Affairs Center for the Prevention and Treatment of Visual Loss, Iowa City, Iowa, United States 4Department of Ophthalmology and Visual Sciences, Universi.
authors.forename: Pieter
authors.initials: P
authors.lastname: Poolman
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Coppey
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Obrosov
authors.affiliation: Department of Veterans Affairs Iowa City Health Care System, Iowa City, Iowa, United States.
authors.forename: Amey
authors.initials: A
authors.lastname: Holmes
authors.affiliation: Department of Veterans Affairs Iowa City Health Care System, Iowa City, Iowa, United States 2Veterans Affairs Center for the Prevention and Treatment of Visual Loss, Iowa City, Iowa, United States 4Department of Ophthalmology and Visual Sciences, Universi.
authors.forename: Randy H
authors.initials: RH
authors.lastname: Kardon
authors.affiliation: Department of Veterans Affairs Iowa City Health Care System, Iowa City, Iowa, United States 2Veterans Affairs Center for the Prevention and Treatment of Visual Loss, Iowa City, Iowa, United States 3Department of Internal Medicine, University of Iowa, Iowa.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Yorek
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D003315:Cornea / Q000187:drug effects / Q000294:innervation*; D003921:Diabetes Mellitus, Experimental; D003929:Diabetic Neuropathies / Q000175:diagnosis* / Q000503:physiopathology; D042241:Early Diagnosis; D008297:Male; D018613:Microscopy, Confocal; D009412:Nerve Fibers / Q000187:drug effects; D059225:Nociception / Q000502:physiology*; D009883:Ophthalmic Solutions / Q000008:administration & dosage; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage*
chemical_list: D009883:Ophthalmic Solutions; D012462:Saline Solution, Hypertonic