Abstract
Purpose: :
The tear film lipid layer is known to spread over the aqueous layer after a blink. In a previous study, time required for the lipid layer to be stable after a blink (defined as spreading time) becomes shorter after punctal occlusion in aqueous tear–deficient dry eyes (Goto E, IOVS44, 2003). The purpose of this study is to analyze the dynamics of the tear film lipid layer rheologically, before and after punctual occlusion.
Subjects and Methods: :
Eight eyes from nine patients with aqueous tear–deficient dry eye [all female patients; aged 64.5 ± 12.0 (mean ± SD) years] were enrolled in this study. Punctal occlusion using punctal plugs was performed to both upper and lower puncta in all subjects. Before and after punctal occlusion, the radius (R: mm) of lower tear meniscus was measured by meniscometry (Yokoi N, BJO, 1999), and interference images from tear film lipid layer were recorded digitally by DR–1TM (Kowa). Areas of the lipid layer during spreading were sequentially calculated every 0.05 sec from the recorded interference images. The time–dependent changes of areas of the lipid layer during spreading were analyzed rheologically using the Voigt model {S(t) = ρ[1–exp(–t/)]; S(t): area (mm2), ρ: constant number, t: second (sec), : relaxation time (sec)}, and an initial speed of the lipid layer spread [S’(0) = dS(t)/dt | t=0] (mm2/sec) was calculated before and after the punctal occlusion.
Results: :
Before and after punctal occlusion, respective values for R were 0.18 ± 0.04 and 0.63 ± 0.22 and for S’(0) were 19.1 ± 10.6 and 212.5 ± 84.1. Both R and S’(0) were significantly increased after punctal occlusion (p<0.001).
Conclusions: :
By the rheological analysis of the tear film lipid layer, initial spread speed was demonstrated to increase after punctal occlusion. This facilitated increase in the lipid layer spread is considerably attributed to the increase of the aqueous tear volume as the carrier for the lipid layer.
Keywords: cornea: tears/tear film/dry eye