[The lacrimal film, structure and stability]

Area of Science:

• Ophthalmology
• Biophysics
• Corneal Science

Background:

• The precorneal tear film is crucial for maintaining corneal epithelium integrity.
• Break-up time (BUT) is a clinical test for tear film evaluation, though its methodology is debated.
• Current bio-microscopic methods do not fully capture the nature of "dry spots".

Purpose of the Study:

• To introduce an innovative microscopic method for examining the tear film's wetting film on the cornea.
• To investigate the physico-chemical properties of thin wetting films on the ocular surface.
• To analyze the stability and rupture dynamics of the tear film.

Main Methods:

• Utilizing freshly enucleated eyes (rabbit/rat) immersed in physiological solution.
• Forming a thin wetting film by contacting an air bubble with the corneal epithelium.
• Employing a custom device for simultaneous air bubble delivery and microscopic observation of interference colors.
• Analyzing lipid droplet characteristics on the tear film surface.

Main Results:

• The innovative method reveals "dry spots" are actually thin fluid films (hundreds of nanometers thick).
• Corneal epithelium exhibits perfect wettability when epithelial cells are undamaged.
• Interference colors provide insights into the tear film's thickness and homogeneity.
• Lipid droplet behavior on the tear film surface can be observed.

Conclusions:

• The developed method offers a novel approach to studying tear film dynamics and corneal wetting.
• "Dry spots" are not an absence of fluid but a thin film layer.
• Corneal epithelial integrity is directly linked to tear film wettability.