Optical performance of toric intraocular lenses in the presence of decentration

Abstract

Aim: To evaluate the optical performance of toric intraocular lenses (IOLs) after decentration and with different pupil diameters, but with the IOL astigmatic axis aligned.

Methods: Optical performances of toric T5 and SN60AT spherical IOLs after decentration were tested on a theoretical pseudophakic model eye based on the Hwey-Lan Liou schematic eye using the Zemax ray-tracing program. Changes in optical performance were analyzed in model eyes with 3-mm, 4-mm, and 5-mm pupil diameters and decentered from 0.25 mm to 0.75 mm with an interval of 5° at the meridian direction from 0° to 90°. The ratio of the modulation transfer function (MTF) between a decentered and a centered IOL (MTFDecentration/MTFCentration) was calculated to analyze the decrease in optical performance.

Results: Optical performance of the toric IOL remained unchanged when IOLs were decentered in any meridian direction. The MTFs of the two IOLs decreased, whereas optical performance remained equivalent after decentration. The MTFDecentration/MTFCentration ratios of the IOLs at a decentration from 0.25 mm to 0.75 mm were comparable in the toric and SN60AT IOLs. After decentration, MTF decreased further, with the MTF of the toric IOL being slightly lower than that of the SN60AT IOL. Imaging qualities of the two IOLs decreased when the pupil diameter and the degree of decentration increased, but the decrease was similar in the toric and spherical IOLs.

Conclusions: Toric IOLs were comparable to spherical IOLs in terms of tolerance to decentration at the correct axial position.

Keywords: artificial; astigmatism; cornea; decentration; lens; model.

Figure 1. The theoretical pseudophakic model eye in Zemax.

Figure 2. The MTF curves of the pseudophakic model eye with pupil diameters of 3, 4, and 5 mm. The MTF was decreased in both IOLs with decentrations from 0.25 mm to 0.75 mm

A: The MTF curves of the model eye with a 3 mm pupil. Although the MTF values for the toric IOL were slightly lower than those for the spherical IOL, the MTF of the toric IOL was not affected when decentration was along meridians in different directions; B: The MTF curves with a pupil diameter of 4 mm. The imaging quality of the toric IOL was not altered significantly when decentered in any direction; C: The MTF curves with a pupil diameter of 5 mm. The MTF values of the two IOLs were significantly lower than MTF values obtained at the 3 mm pupil diameter. The imaging quality of the toric IOL was not altered significantly when decentered in any direction.

Figure 3. The ratios of MTF_Decentration/MTF_Centration in the pseudophakic model eyes with 3, 4, and 5 mm pupil diameters, with decentrations from 0.25 mm and 0.75 mm at spatial frequencies of 20 cycles/mm and 40 cycles/mm, respectively

The ratios were decreased in both IOLs, but remained comparable to each other.