To quantify the tear spreading velocity and stabilization time after blinks in healthy patients.
Video recordings (magnification, ×130) were made of the movements of naturally occurring particles in the tear film while patients blinked naturally. After each blink, tear spreading velocity was computed every 40 milliseconds from particle displacements determined from a frame-by-frame analysis of the records.
After a blink, tears moved rapidly upward over the cornea. Forty milliseconds after passage of the lid, the velocity was 7.34 ± 2.73 mm/s (mean ± standard deviation, n = 20). The time to tear stabilization (i.e., zero velocity) was 1.05 ± 0.30 seconds. The decay of spreading velocity with time was well described by a logarithmic function for all individual patient data (R2 range, 0.88–0.99;n = 20). We have shown that initial velocity and stabilization time are independent descriptors of tear spreading. Meibomian gland expression markedly reduced initial velocity leaving a normal stabilization time, whereas inhalation of an irritant reduced stabilization time leaving a normal initial velocity. In a patient with Sjögren syndrome, punctal plugs rapidly restored initial velocity and stabilization time from near zero values to normal values.
We provide normal values for two descriptors of tear spreading, namely initial velocity and time to stabilization. These values can be modified by manipulations that alter tear constituents. Consequently, these descriptors may provide a basis for quantitative, noninvasive tear assessment.
From the Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand.
Submitted October 16, 2000.
Revision received January 29, 2001.
Accepted January 31, 2001.
Address correspondence and reprint requests to Dr. H. Owens, Department of Optometry and Vision Science, University of Auckland, Private Bag 92019, Auckland, New Zealand.