Tear sample collection using cellulose acetate absorbent filters Marieh Esmaeelpour 1 , Jun Cai 3 , Patrick Watts 2 , Mike Boulton 3 and Paul J. Murphy 1 1 School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4LU, 2 University Hospital of Wales, Cardiff, UK, and 3 University of Florida College of Medicine Interdisciplinary Program in Biomedical Sciences, P.O. Box 100235 Gainesville, Florida 32610-0235, USA Abstract Purpose: To assess the use of cellulose acetate filter rods as a technique for tear collection. Method: The cellulose acetate rod (CR) was compared with the ÔstandardÕ glass capillary tube (CT), in a series of experiments, to assess: sample collection by collected volume size; the effect of tear stimulation on total tear protein concentration and major tear protein concentrations; and technique invasiveness. Results: No difference was found in concentrations for total protein, IgA (secretory immunoglobulin A), lactoferrin and lysozyme (p> 0.05) with no clinically significant increase in serum albumin to show serum leakage. Sample volume was higher for CR (p< 0.005) and sample volume increased for stimulated collection with CR (p= 0.001). Dilution effect of a stimulated sample size was reliably shown only with CR (r= )0.66, p= 0.011). Using bovine albumin standard with CR and CT, a smaller sample volume (p< 0.001) and a higher protein concentration (p< 0.001) were extracted with CR. Conclusion: The cellulose rod offers a suitable alternative to the glass CT. It is able to quickly absorb a sample, allowing use for a wide range of sample sizes, while being minimally invasive. Keywords: cellulose rod, glass capillary, tear collection, tear proteins Introduction The tear film can be assessed clinically for its stability, volume, lipid layer appearance or evaporation rate (Cho and Brown, 1993; Goto and Tseng, 2003; Mathers, 2004). However, tear collection is required to determine its physio-chemical properties with laboratory analysis (Webster and Kairys, 1984; Norn, 1992; Bjerrum and Prause, 1994). This can be achieved using narrow calibre glass capillaries, absorbent paper strips or polyester rods (Stuchell et al., 1984; Jones et al., 1997; Dumortier and Chaumeil, 2004). Glass capillaries are commonly used, but collect tears slowly and erratically, are not well accepted by patients and are not suited for children and special needs populations. The alternatives, such as Schirmer papers (Schirmer, 1903), irritate the ocular surface and induce reflex tearing (Clinch et al., 1983) and may require the use of anaesthetics (Bawazeer and Hodge, 2003). These difficulties have affected the number and quality of tear film research studies that have been carried out in children to date. The optimal safe collection technique should combine ease of use and minimal invasiveness, with rapid sample collection, and good extraction properties. This paper reports on a new tear collection method that uses cellulose acetate filter rods. A series of studies is presented that compares the cellulose rod with the capillary tube (CT) for sample collection and extraction; major tear protein concentration analysis; and technique invasiveness. Methods Subjects Subjects recruited were members of staff and students of Cardiff University. Exclusion criteria were: systemic or Received: 10 March 2008 Revised form: 2 June 2008; 18 August 2008 Accepted: 21 August 2008 Correspondence and reprint requests to: Marieh Esmaeelpour. Tel.: 44 2920 879048; Fax: 44 2920 874859. E-mail: EsmaeelpourM@cf.ac.uk Ophthal. Physiol. Opt. 2008 28: 577–583 ª 2008 The Authors. Journal compilation ª 2008 The College of Optometrists doi: 10.1111/j.1475-1313.2008.00603.x