Basal and Reflex Human Tear Analysis: I. Physical Measurements: Osmolarity, Basal Volumes, and Reflex Flow Rate

Abstract

Minimally stimulated, retained “basal” tears and stimulated reflex tears were collected from normal controls, keratoconjunctivitis sicca (KCS) patients, and contact lens (CL) wearers. Basal tear samples were collected on small filter paper strips (Periopaper®) over a five-second period, and volume was measured by means of an electronic device (Periotron®). Collected basal tear volumes for KCS patients (0.84 ± 0.42 μl) were significantly lower (P <; 0.01) than normal controls (1.18 ± 0.36) and CL wearers (1.24 ± 0.27). Reflex tear flow rates were measured over a five-minute period on Schirmer strips. Volume was calculated by comparison of wet length with known volumes of 1% egg white lysozyme solution. The reflex tear flow rates in KCS patients (3.29 ± 3.57 μl/minute) were significantly lower than normal controls (5.71 ± 5.86) and CL wearers (6.96 ± 6.07). The elevation in CL wearers was not statistically significant when compared to normals. KCS patients are deficient in both basal and reflex tears compared to normals but have a more significant deficiency of basal tears. Female normals and CL wearers over 40 years of age have a higher tear osmolarity than those under 41 years of age. Female KCS patients over 40 years of age have a tear osmolarity that is not significantly different from female KCS patients under 41 years of age.