Use of laser flare-cell photometry to count anterior chamber canine leukocytes and latex beads in vitro

Abstract

Objective - To determine whether the cell measuring function of a laser flare-cell photometer is accurate and reproducible, using an in vitro model. Sample Population - Leukocytes from 8 clinically normal Beagles. Procedure - Latex beads 11.9 and 6.4 μm in diameter were used to simulate canine WBC and RBC, respectively. Beads were diluted to known concentrations, placed in a model eye, and counted by use of the laser flare-cell photometer. A range of protein diluents from 0 to 2,000 mg/dl was used to suspend beads and simulate anterior uveitis, when cells and protein would be in the aqueous humor. A similar series of experiments were repeated, using leukocytes isolated from the blood of Beagles. Results - The laser flare-cell photometer can count 6.4-μm beads reproducibly and linearly up to a total of 510 cells/mm3, and 11.9-μm beads up to 1,300 cells/mm3 over a protein range of 0 to 2,000 mg/dl. The instrument can also count canine leukocytes reproducibly and linearly up to 1,300 cells/mm3 over that protein range. Conclusions and Clinical Relevance - Cell and bead sizes and concentrations and protein concentrations were chosen to mimic the range observed in dogs with uveitis. Because the laser flare-cell photometer accurately counted these cells in a range of protein concentrations in the model eye, it has the potential for use in noninvasive quantitative evaluation and monitoring of uveitis in dogs.