Purpose: To determine the repeatability of the flush tear collection technique and the Schirmer strip for Substance P tear analysis.
Methods: 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).
Results: 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.
Conclusions: 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.
*PhD, MOptom, FAAO
School of Optometry and Vision Science, University of New South Wales, Sydney, Australia (MM, JY); Deakin Optometry, Deakin University, Waurn Ponds, Victoria, Australia (MG); and University of Sydney, SaveSight Institute, Sydney, New South Wales, Australia (MM, JY).
Maria Markoulli School of Optometry and Vision Science The University of New South Wales Sydney, NSW 2052 Australia e-mail: firstname.lastname@example.org