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F Sistani, H Brewitt, G Daenecke, UH Steinhorst; Effects of Different Lipid-containing Artificial Tears on the Ocular Surface of Rabbits, a Scanning Electron Microscopic Study . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3115.
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Purpose: The function of the ocular epithelium depends on typical surface structures and the integrity of the tear film. The most desirable artificial tears would substitute all components of the tear film. Most of the artificial tears do not contain the typical lipid constituents of the tear fluid. We compared changes of the cornea and conjunctiva using a scanning electron microscope (SEM) after application of a new lipid-containing test substance ( F-Gel artificial tears), a commercially available preserved lipid-containing tear substitute (Liposic Gel), a commercially available preservative-free lipid-containing tear substitute (Liposic EDO) and a commercially available non-lipid-containing tear substituent (Liquigel). Methods: F-Gel, Liposic, Liposic EDO and Liquigel were examined in two sets of experiments: The surface compatibility and the surface protection. In surface compatibility test, the eye drops were instilled in the conjuctival sack of narcotized rabbits, spread over the entire ocular surface and left for 30 minutes. After this time, the animals were killed using an intracardial injection of T 61. The conjunctiva and cornea were then processed further for SEM. In the surface protection test, after application of the test substances, the lid closure was inhibited using lid retractors and exposing the ocular surface for 60 minutes to the air. After this time, the tissue was prepared for SEM. Results: Surface compatibility test (30 min. after application of one drop): The ocular surface of rabbits did not show any changes to the normal epithelium using the test substances. The characteristic microstructure of the rabbit cornea and conjunctiva was very well preserved in all of the preparations. Surface protection test (after application of one drop and exposure to the air for 60 min.) : All four substances preserved the ocular epithelium in comparison to the control groups, which were not treated with any artificial tears. Those ocular surfaces showed, extreme damage with desquamation of the epithelial cells, epithelial tears and loss of microvilli and microplicae. In contrary all of the test substances showed an acceptable degree of protection of the ocular surface. There was not a difference comparing the tested artificial tears. Conclusions: Our results support the hypothesis, that optimal artificial tears should structurally be as close to the natural tear fluid as possible. However, since the lipid layer of the tear film is very complex, future efforts are needed to develop tear substitutes with lipid constituents more similar to the natural lipid layer.
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