title: [Ocular surface acidity and buffering system (by studying the conjunctival sac)].
abstract: As any mucous membrane the conjunctiva is characterized by a definite pH value which guarantees-physiological functioning of the ocular surface. The most commonly used method of assessment is potentiometric pH measurement with ion-specific glass microelectrodes. The results, however, can be affected by such factors, as conjunctival sac zoning, tissue acidity, epithelial trauma, and reflex tear secretion. Few data and hypotheses are available on mechanisms of maintaining the acid-base balance of the conjunctival sac (bicarbonate buffering system in particular).
  
  
  OBJECTIVE
  to study spatial variability of conjunctival tear fluid pH and possible mechanisms of its maintenance using original methods of acidity measurement and mineral content assessment.
  
  
  METHODS
  Tear pH was determined in 42 healthy participants (84 eyes) by means of litmus test strips and computer- aided colorimetry. Electron probe microanalysis in combination with energy dispersive spectrometry was performed in 8 healthy participants (8 eyes, 8 samples).
  
  
  RESULTS
  In the group of 42 healthy participants (84 eyes) the pH value of conjunctival tear fluid varied from 6.30 to 7.23 with the average of 6.76 and pH mode 6.74. The pH value of conjunctival mucous discharge was measured in 25 healthy participants (28 eyes) and varied from 7.00 to 8.00 with the average of 7.26 and pH mode 7.30. The main mineral components of tear fluid are chlorine, sodium, potassium, and boron. Borate buffer is regarded as a mechanism of maintaining the acid-base balance of the ocular surface.
  
  
  CONCLUSIONS
  The developed method of pH measurement ensuresreliable determination of conjunctival sac acidity in accordance with zoning and heterogeneity of its media as well as the complex structure of the tear film. In a healthy population, the acidity of tear significantly differs from that of conjunctival mucous discharge. Soluble chlorine, sodium, potassium, and boron compounds are the prevailing mineral components of tear fluid. Borate buffer appears to be the most stable of all mechanisms of maintaining the acid-base status of tear fluid.
authors.forename: S É
authors.initials: SÉ
authors.lastname: Avetisov
authors.forename: T N
authors.initials: TN
authors.lastname: Safonova
authors.forename: I A
authors.initials: IA
authors.lastname: Novikov
authors.forename: L S
authors.initials: LS
authors.lastname: Pateiuk
authors.forename: I G
authors.initials: IG
authors.lastname: Griboedova
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000137:Acid-Base Imbalance / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy; D000328:Adult; D001895:Boron; D002021:Buffers; D003228:Conjunctiva / Q000378:metabolism / Q000503:physiopathology; D003941:Diagnostic Techniques, Ophthalmological; D019468:Disease Management; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D013499:Surface Properties; D013666:Tears / Q000737:chemistry / Q000378:metabolism
chemical_list: D002021:Buffers; D001895:Boron