Related Experiment Videos
Structure and composition of rat precorneal tear film. A study by an in vivo cryofixation
H B Chen1, S Yamabayashi, B Ou
1Department of Ophthalmology, Yamanashi Medical University, Japan.
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.