Modulation Transfer Function of a Toric Intraocular Lens: Evaluation of the Changes Produced by Rotation and Tilt

PURPOSE: To evaluate the changes in optical quality when toric intraocular lenses (IOL) are rotated or tilted and to demonstrate that IOL rotation produces an increasing effect of aberrations. METHODS: Modulation transfer function (MTF) and average modulation were used to analyze the image quality of a toric IOL. The axis of the toric IOL was rotated 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, and 30 degrees in successive MTF measurements. The tilt values were 0 degrees to 5 degrees, in increments of 1 degrees, plus a tilt of 15 degrees. Pupil diameters of 3 and 5 mm were used. RESULTS: The MTF decay due to aberrations was more sensitive to rotation than tilt. The main decrement in the average modulation, of approximately 50% in both pupils, occurs when the IOL rotates from 0 degrees to 5 degrees. Between 0 degrees and 1 degrees tilt, the average modulation decreases approximately 25% for both pupils; with tilt > 1 degrees, the average modulation remains virtually unchanged. The points representing average modulation versus rotation angle are satisfactorily fitted by an exponential function, R = 0.98. Average modulation versus tilt angle provides lower correlation degrees, R = 0.91 and R = 0.79, for 3- and 5-mm pupils, respectively. CONCLUSIONS: The MTF of the toric IOL decays with rotation and tilt, with greater decrement occurring in rotation from 0 degrees to 5 degrees. An asymptotic value exists in the average modulation decay, meaning that for angles higher than 15 degrees, the average modulation of the toric IOL remains virtually constant. [J Refract Surg. 2012; 28(5): 335-340.] doi: 10.3928/1081597X-20120321-01