title: Evidence suggesting that the keratinized portions of the upper and lower lid margins do not make complete contact during deliberate blinking.
abstract: OBJECTIVE
  To investigate whether the keratinized portions of the upper and lower eyelid margins make complete contact during deliberate blinking.
  
  
  METHODS
  Ten asymptomatic subjects (21.7 ± 1.5 years) with healthy eyelids were enrolled. A 0.1-μL drop of unpreserved 2% fluorescein placed in the temporal (T) third of the keratinized lower lid margin was observed for 10 deliberate blinks, under 16× magnification. If 10 complete blinks did not alter the drop, the subject squeezed their lids shut. The number of lid squeezes to alter the drop appearance was recorded and repeated for the central (C) and nasal (N) sections. Meibomian gland (MG) functionality was assessed with standardized diagnostic expression. Liquid fluorescein was used to assess the proximity of the line of Marx (LOM) to the lower lid MG orifices.
  
  
  RESULTS
  In all cases, 10 complete deliberate blinks did not alter the drop. The mean numbers of lid squeezes to alter the drop was: T = 1.5 ± 1.3, C = 1.9 ± 1.8, and N = 1.2 ± 0.8. The mean number of functional MGs per lid section was as follows: T = 0.8 ± 2.2, C = 4.3 ± 2.3, and N = 4.4 ± 0.8. The LOM relative to the MG orifices was as follows-T: LOM in 30% of eyes was posterior to the MG orifices and in 70% of eyes was mixed (a combination of the LOM posterior, touching, bisecting, or anterior to the MG orifices); C: 70% posterior, 30% mixed; and N: 90% posterior, 10% mixed.
  
  
  CONCLUSIONS
  Counterintuitively, the keratinized portions of the upper and lower eyelid margins frequently do not make full contact during what appears to be complete blinking.
authors.affiliation: TearScience Inc, Morrisville, NC, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Korb
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Blackie
authors.forename: Erin N
authors.initials: EN
authors.lastname: McNally
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001767:Blinking / Q000502:physiology*; D005143:Eyelids / Q000502:physiology*; D005260:Female; D019793:Fluorescein / Q000008:administration & dosage; D006801:Humans; D008297:Male; D008537:Meibomian Glands / Q000378:metabolism; D055815:Young Adult
chemical_list: D019793:Fluorescein