February 1997
Volume 38, Issue 2
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Articles  |   February 1997
Structure and composition of rat precorneal tear film. A study by an in vivo cryofixation.
Author Affiliations
  • H B Chen
    Department of Ophthalmology, Yamanashi Medical University, Japan.
  • S Yamabayashi
    Department of Ophthalmology, Yamanashi Medical University, Japan.
  • B Ou
    Department of Ophthalmology, Yamanashi Medical University, Japan.
  • Y Tanaka
    Department of Ophthalmology, Yamanashi Medical University, Japan.
  • S Ohno
    Department of Ophthalmology, Yamanashi Medical University, Japan.
  • S Tsukahara
    Department of Ophthalmology, Yamanashi Medical University, Japan.
Investigative Ophthalmology & Visual Science February 1997, Vol.38, 381-387. doi:
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      H B Chen, S Yamabayashi, B Ou, Y Tanaka, S Ohno, S Tsukahara; Structure and composition of rat precorneal tear film. A study by an in vivo cryofixation.. Invest. Ophthalmol. Vis. Sci. 1997;38(2):381-387.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

PURPOSE: To visualize the in vivo structure and to investigate the composition of rat precorneal tear film. METHODS: An in vivo cryofixation with freeze substitution method of electron microscopy was used for the study. For light and transmission electron microscopy, a small amount of aluminum powder was used as a tracer spread on the corneal surface. The eyeballs were immediately and quickly frozen by pouring an isopentane-propane mixture cooled by liquid nitrogen directly over the eyes. For scanning electron microscopy, the corneal surface was freeze-fractured after the cryofixation. The specimens were then freeze-substituted and prepared conventionally for microscopic observation. RESULTS: The tear film appeared as a layer of homogeneous and fine network-like structures varying from 2 to 6 microns in thickness on the corneal surface, with a membrane-like layer covering its surface. The aluminum powder was located on the surface of the tear film. The tear film could be removed completely by applying 10% or 20% acetylcysteine, but not by phosphate buffer. CONCLUSIONS: The in vivo structure of the rat tear film is composed primarily of mucus, with a lipid layer covering its surface but without a free aqueous layer. The "three layers theory" of tear film structure requires revisions.

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