Pre-wetted modified Schirmer's tear test to determine lacrimal tear-production rate from severe lacrimal-gland dysfunction patients.

Abstract

Significance: To determine basal tear-production rates from low tear-producing patients, we present a prewetted modified Schirmer's tear test (PW-MSTT). The improved method is an extension of the MSTT that provides a reliable method to investigate the relation between dry-eye symptoms and basal tear production rates.

Purpose: The MSTT quantifies basal tear-production rates from patients. However, the existing test does not allow measurement of basal tear-production rates from patients that do not wet past the 5-mm mark on the Schirmer strip within 5 minutes. We extended the MSTT with a prewetting technique to allow quantification of basal tear-production rates from patients that do not adequately wet the Schirmer strip within 5 minutes of strip insertion.

Methods: An in-vitro study was conducted with sheathed Schirmer strips to determine the volume of sterile nonpreservative saline solution necessary to prewet the Schirmer strip before insertion. This assessment determined that 1.6 µL of prewetting saline wets the Schirmer strip to 5.2 mm of the Schirmer strip, enough to allow basal tear production rate determination from subjects that do not adequately wet the Schirmer strip out to the 5-mm mark. Then, a clinical study was conducted with sheathed Schirmer strips with the prewetting technique to determine the basal tear-production rate from subjects that could not wet sufficiently to determine their basal tear-production rate.

Results: Eleven subjects completed the study; the basal tear production rates from these low tear-producing subjects were determined. The mean (SD) of the measured basal tear-production rate was 0.40 µL/min (0.28 µL/min) compared with normal subjects at 1.19 µL/min.

Conclusions: The developed PW-MSTT successfully quantifies basal tear production rates from subjects that do not adequately wet the Schirmer strip without the new prewetting technique. The determined basal tear-production rate from these low tear-producing subjects was three times less than that of those from a previous study where the subjects could adequately wet the Schirmer strip past the 5-mm line. Our improved methodology for low tear-producing patients sheds insight into how basal tear production rate is related to aqueous-deficient dry-eye symptoms.