An improved method for measuring human tear lysozyme concentration.

Previously described methods for measuring human tear lysozyme are fraught with shortcomings. A new method has been devised. Tear fluid was collected on Whatman filter paper discs. Each disc was placed in a tightly capped tube containing sodium phosphate buffer. Fluid from each tube was placed directly into a well of the lysozyme immunodiffusion plate. After the precipitation rings had reached maximum size, their diameters were measured. A linear standard curve was constructed, and lysozyme concentration was expressed as micrograms per milliliter. The tear lysozyme concentration was obtained from the standard curve and corrected for the assay dilution factor. The mean tear lysozyme concentration in 15 normal patients was 1.4 +/- 0.5 mg/mL. In ten patients with dry eyes, the mean was 0.7 +/- 0.5 mg/mL. The method used to collect, store, and transport tears is easily performed in the clinic and readily tolerated by patients. The technique of radial immunodiffusion is reliable and simple, compared with other assays.