A novel instrument to quantify the tension of upper and lower eyelids.

An instrument was developed for the objective measurement of passive lid tension of the upper and lower eyelid. Eyelid tension is defined as the first derivative of the force over elongation function. Lid tension was determined by gripping the eyelid at the eyelashes and displacing the lid while measuring the force exerted by the eyelid. Two motorised spindles provided motion control of the gripper in anterior/posterior and nasal/temporal directions. Each axis was fitted with a sensitive force transducer to record the force while stretching and relaxing the eyelid. Motion control, data collection and data analysis were computer controlled, with various user-selectable options for measurement speed, direction and end-of-measurement conditions. Calibration of the instrument reduced the maximum error of the recorded forces to +/- 10 mN. Repeatability for on-eye measurements was verified by multiple measurements on the same eye under identical conditions. Preliminary results from a pilot study, investigating differences between Asian and Caucasian lid tension showed no statistically significant difference between the two groups.