EVALUATION AND CLINICAL-SIGNIFICANCE OF THE MECHANICAL-PROPERTIES OF VARIOUS PALPEBRAL SPRINGS

Fourteen different wire materials were evaluated for use as palpebral springs. Three of these, stainless steel 0.010- and 0.012-in diameter, respectively, and Australian stainless steel 0.012-in diameter, fulfi lled the designated criteria for suitability. The physiologic deflecti on range of palpebral springs was determined by examining 20 normal in dividuals. Angles that a spring would subtend were measured with eyes closed (42 +/- 3 degrees), in primary position (20 +/- 3 degrees), and in upgaze (6 +/- 3 degrees). The effects of spring design on load-def lection (the force required for angular deflection) were evaluated for 0.010- and 0.012-in stainless steel wire within the physiologic defle ction range. Variations in spring design in addition to wire diameter (gauge) included alteration of external loop size, number of external loop coils, and resting spring angle. There was a direct linear relati onship between force and angular deflection (load-deflection). Larger wire diameter increased the load-deflection. Australian stainless stee l had a higher load deflection (stiffer) for a given gauge than regula r stainless steel. Smaller diameter external loops and fewer external loop coils increased load-deflection. Although definite conclusions co uld not be drawn regarding the effect of resting angle on load-deflect ion, it appeared that no relationship (zero correlation) existed over the angles tested (55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees). These findings were consistent with predictions based on sta ndard spring equations. The clinical significance of the findings is d iscussed with reference to surgical planning and evaluation of lid dyn amics.