Tear sodium, potassium, chloride, and calcium at various flow rates: Children with cystic fibrosis and unaffected siblings with and without corneal staining

When compared to their unaffected siblings, children with cystic fibrosis in this study had: high tear Ca 2+ especially at slow flow rates, low tear Na + at slow flow rates but the same tear Na + at fast rates, the same tear K + and Cl − at all flow rates, and the same minimal and maximal flow rates. Age, sex, environmental factors, and ocular bacterial infection could not account for the greater incidence of superficial punctate fluorescein staining of the cornea in the patients with cystic fibrosis, none of whom had signs or symptoms of any ocular disease, including those associated with vitamin A deficiency.