Optical Quality Degradation Caused By Astigmatism In Model Eyes With Toric And Non-Toric Monofocal Intraocular Lenses

To analyse the influence of astigmatism on the degradation of the optical image quality in a model eye implanted with a monofocal intraocular lens (IOL). The toric and non-toric versions of the same IOL are considered for a range of uncorrected astigmatism. In addition, the effect of a rotation error between the astigmatism axes of the cornea and the toric IOL is also evaluated.

Group of Applied Optics and Image Processing, Optics & Optometry Department, Universitat Politècnica de Catalunya-BarcelonaTech, Spain.

The optical image quality was measured in vitro using an on-bench model eye with an adaptive optics system for induced corneal astigmatism control. Corneal astigmatism ranged from 0.0D to 2.0D. The metric was the area under the modulation transfer function (MTFa) in a through-focus (TF-MTFa) analysis. Two 20-diopters (D) EnVista (Bausch+Lomb) lenses were studied: a non-toric MX60PL IOL and a MX60T toric IOL (cylinder = 1.25D). The toric IOL was used to further analyze the effect of a rotation error between the astigmatism axes of the cornea and the lens. The rotation error ranged from 0° to 35°. A pupil diameter of 3.0mm was set in all the experiments.

In the conditions of this study, the presence of uncorrected astigmatism degraded the optical image quality at the plane of the spherical equivalent in a similar way in both cases, that is, with the toric and non-toric monofocal IOLs. The image degradation caused by a rotation error between the astigmatism axes of the cornea and the toric IOL was relatively low in the range 0°-10°, moderate up to 20°, and severe beyond. In addition, some residual astigmatism remained uncorrected.

The objective analysis carried out in this study shows the influence of uncorrected astigmatism (either preoperatory, induced by surgery, or residual) in the optical image degradation of an eye implanted with either the toric or non-toric version of a monofocal IOL. The image degradation produced by uncorrected astigmatism at the spherical equivalent plane is similar in both cases.

A rotation error in the axis of a toric IOL (20 D spherical, 1.25 D cylinder) up to 10° with respect to the corneal astigmatism condition has a low degrading effect.