To determine the repeatability of the flush tear collection
technique and the Schirmer
strip for Substance P
The tears of 10 healthy non–contact-lens wearers were collected via Schirmer
strip and microcapillary following instillation of either 20 μL (F-20) or 60 μL (F-60) of saline. Each technique was conducted on two occasions and in a randomized order. Total protein content (TPC) and Substance P
concentrations were determined. The overall protein separation profile of each type of tears was examined using one-dimensional gel electrophoresis (1DGE).
Collection rates were significantly faster for the F-60 compared to F-20 (17.3 ± 6.9 μL/min and 11.9 ± 5.3 μL/min, respectively, P
< .001), with an average Schirmer
strip length of 1.5 ± 2.1 mm/min. The coefficient of repeatability between days and eyes was greatest for the Schirmer
strip, with eyes and days being significantly different (P
= .03 and P
= .03, respectively) for Schirmer
strip Substance P
. TPC was 3.8 ± 2.6 mg/mL, 3.3 ± 1.8 mg/mL, and 3.6 ± 3.0 mg/mL for F-20, F-60, and Schirmer
strip techniques, respectively, with no significant difference between techniques (P
= .85). Substance P
concentration was 13.1 ± 14.8 ng/mL, 9.1 ± 6.1 ng/mL, and 14.9 ± 10.6 ng/mL for F-20, F-60, and Schirmer
strip tears, respectively, with no significant difference between techniques (P
= .57). 1DGE profile showed similar electrophoresis patterns among F-20, F-60, and basal tears.
The F-60 method allows faster collection than F-20, but the latter results in better repeatability than both the F-60 and Schirmer
sampling techniques. All three techniques return the same concentrations of TPC and Substance P
. This indicates that tear collection
using the F-20 may be more appropriate when conducting comparative analysis, whereas the F-60 may be more appropriate when more volume is required.