Tear Function Index: A New Measure of Dry Eye

Objective: To develop an efficient way to evaluate tear dynamics clinically. Participants: Three hundred fifty-two patients with dry eye, 64 of whom had Sjögren syndrome, and 55 normal subjects. Design: Because various forces that affect tear drainage are reflected in the values of the Schirmer test with anesthesia and the tear clearance rate, we introduced a new measure of tear dynamics, the tear function index, which is the value obtained from dividing the value of the Schirmer test with anesthesia by the tear clearance rate. Results: The tear function index was more specific (91.8%) and sensitive (78.9%) in diagnosing dry eye associated with Sjögren syndrome than was the Schirmer or tear clearance rate test alone. Tear function indexes below 96 were consistent with dry eye and those below 34 were seen primarily in patients with Sjögren syndrome. Conclusions: The tear function index offers a new method to evaluate tear production with the Schirmer test, introduces an extended way to measure tear flow combining with tear drainage, and gives a practical measure to diagnose dry eye.