The Tear Film Breaks Up From the Lipid Tear Film by Condensation: Evidence Provided by Kinetic Tear Interference Analysis

Abstract

Abstract: : Purpose: To determine the time, pattern and location of the lipid tear film breakup (TBU) of normal subjects and patients with dry eyes by kinetic tear interferometry and to correlate these data with those measured by the conventional fluorescein staining. Methods: In 5 healthy volunteers and 5 patients with lipid tear deficiency and aqueous tear deficiency (LTD/ATD), we used our published method based on DR–1® (Kowa Inc., Japan) interference camera to perform kinetic analysis of tear interference images of the central 8 mm of the pre–corneal lipid tear film. Each analysis was carried out by asking them to hold the blink until an unbearable discomfort occured. The time (defined as non–invasive NTBUT), pattern and location of the lipid film breakup were compared and rendered into a 3D surface map between the two groups, and compared to that of the fluorescein–stained TBUT. Results: In all cases, NTBUT of the lipid film started significantly earlier than TBUT. In normal subjects, NTBUT was 7 ± 1 sec, while TBUT was 22 ± 11.2 sec (P=0.02). In LTD/ATD cases, NTBUT was 1.9 ± 1.3 sec, while TBUT was 3.9 ± 0.6 sec (P=0.007). NTBU started with condensation of lipids into thicker lipid spots or lines (formed between lipid waves) and evolved rapidly into thinning resulting in a breakup of the lipid tear film. The location of NTBU of dots or lines occurred randomly between different blinks and corresponded well with ensuing fluorescein TBU pattern. The location tended to be in the region near to the lower lid margin or the central cornea in normal subjects, but in LTD/ATD cases, the TBUT can be located in the upper, central or lower cornea. Conclusions: Kinetic analysis of tear interference images allows us to discover that TBU starts from the lipid film, much earlier than that detected by the conventional fluorescein method. NTBUT was significantly shorter in dry eye patients. TBU of the lipid film starts with lipid condensation followed by rapid thinning and rupture of the aqueous tear film.

Keywords: cornea: tears/tear film/dry eye • cornea: clinical science • cornea: surface mucins