Abstract
BackgroundQuantification of lacrimal total protein content (TPC) is an important tool for clinical scientists to understand disease pathogenesis, identify potential biomarkers and assess response to therapy, among other applications. However, TPC is not only affected by disease state but also by the method used for tear collection. Thus, the purpose of this study is to determine the impact on TPC of two methods of tear collection in dogs and cats: Schirmer strips and polyvinyl acetal (PVA) sponges.Methods(i) In vivo - Ten healthy dogs and 10 healthy cats were examined. Each animal underwent two sessions, separated by 10 min, in which a Schirmer strip was placed in one randomly selected eye until the 20-mm mark was reached, while a strip of PVA sponge was placed in the other eye for 1 min. (ii) In vitro - Schirmer strips and PVA sponges were spiked with various volumes of four bovine serum albumin solutions (0.5, 4, 10, and 20 mg/mL).In both experiments, the wetted absorbent materials were centrifuged for 1 min, and the TPC was quantified on the extracted fluid using Direct Detect™ infrared spectroscopy.ResultsLacrimal TPC in dogs and cats ranged from 5.2 to 14.6 mg/mL and from 6.2 to 20.6 mg/mL, respectively. In cats, TPC was significantly lower with Schirmer strips vs. PVA sponges (P < 0.001). In dogs, the volume absorbed by PVA sponges was negatively correlated with TPC (r = − 0.48, P = 0.033). The inter-session coefficient of variation was significantly lower with Schirmer strips vs. PVA sponges in both species (P ≤ 0.010). In vitro, both absorbent materials resulted in a ‘concentrating effect’ of the TPC obtained post-centrifugation, which was most pronounced when the volume absorbed was low, especially for Schirmer strips.ConclusionSchirmer strips provide a repeatable method to quantify lacrimal TPC in dogs and cats, although care should be taken to absorb sufficient volumes of tears to minimize the concentrating effect from the absorbent material.
Highlights
Quantification of lacrimal total protein content (TPC) is an important tool for clinical scientists to understand disease pathogenesis, identify potential biomarkers and assess response to therapy, among other applications
The purpose of our study is to evaluate the effect of tear collection with two different absorbent materials on TPC in dogs and cats, namely Schirmer strips and polyvinyl acetal (PVA) ophthalmic sponges
Median (95% range) feline TPC in tears was 9.6 mg/mL (6.2–12.1 mg/mL) with Schirmer strips and 15.9 mg/mL (6.6–20.6 mg/mL) with PVA sponges, a difference that was statistically significant (P < 0.001, Fig. 1b)
Summary
Quantification of lacrimal total protein content (TPC) is an important tool for clinical scientists to understand disease pathogenesis, identify potential biomarkers and assess response to therapy, among other applications. TPC is affected by disease state and by the method used for tear collection. The purpose of this study is to determine the impact on TPC of two methods of tear collection in dogs and cats: Schirmer strips and polyvinyl acetal (PVA) sponges. Analysis of tear protein can help identify new biomarkers, better understand disease pathogenesis, and develop new diagnostic tools and therapeutics. It is often challenging to draw accurate conclusions and make crossstudy comparisons because the protein content in tears is affected by disease state, and largely by the method of tear collection used by each investigator
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