Abstract
Purpose::
We previously reported the quantitative analysis of tear film lipid layer spreading using the rheological model of Voigt (Yokoi N, et al., ARVO 2005); however analysis was labor intensive. In the present study, we therefore developed an automated program for the analysis of tear film lipid layer spreading using the cross-correlation method and applied it clinically.
Methods::
34 eyes from 20 subjects including normal volunteers and patients with aqueous tear-deficient dry eye [5 males and 15 females; mean age: 53.3 years] were enrolled. In all subjects, the radius (R: mm) of the central lower tear meniscus, reflecting total tear volume at the ocular surface (Yokoi N, et al., Arch Ophthalmol 2004), was measured by meniscometry (Yokoi N, et al., BJO, 1999) and interference images from the tear film lipid layer were recorded digitally using a DR-1TM interferometer (Kowa Co., Ltd., Japan). Next, a rectangular area [coordinates (x0, y0)~(x1, y1)] was selected on a captured image of the spreading lipid layer. Then, its transitional shift (dx, dy), 0.05 seconds after the last capture, was automatically calculated using a program based on the cross-correlation method, which recognizes the area [coordinates (x0+dx, y0+dy)~(x1+dx, y1+dy)] having the pattern most similar to the selected rectangular area. After that, the transitional shift along the y-direction, dy, was summed over time and incorporated into the Voigt model {H(t) = ρ[1-exp(-t/)]; H(t): transitional shift along y-direction (mm), ρ: a constant, t: second (sec),: relaxation time (sec)}. The relationship between the initial speed of lipid layer spreading along y-direction [H’(0) = dS(t)/dt|t=0] (mm/sec) and R were analyzed.
Results::
In all cases, time-dependent spreading of the tear film lipid layer was appropriately analyzed using the Voigt model and a significant correlation was found between H’(0) and R [r=0.614, p=0.0001].
Conclusions::
Automated rheological analysis using the cross-correlation method allows less labor, quantitative assessment of lipid layer spread, and is expected to give information about tear volume.
Keywords: cornea: tears/tear film/dry eye • cornea: clinical science • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)