[Calculation of pseudophakic toric intraocular lenses].

BACKGROUND

A high corneal astigmatism limits the attainable visual acuity and the ability of correction with spectacles or contact lenses. The astigmatism can also be an impairment for visual rehabilitation, especially after penetrating keratoplasty. A pseudohakic toric intraocular lens (T-IOL) can correct high corneal astigmatism during cataract surgery. For the calculation of the correct power for the T-IOL several additional factors need to be considered, which are less relevant for spherical IOL calculation.

METHODS

With the matrix-based vergence transformation an elegant paraxial calculation scheme is available for calculating the optical system "pseudophakic eye" as a closed system. The basic elements of this method are explained in detail along with some clinical examples. The Java-based software JToricIOL is provided online to support comprehension of the examples and to enable readers to make their own calculations for teaching and experimental purposes. The examples mentioned in this article have been calculated with JToricIOL.

CONCLUSIONS

Toric intraocular lenses are an essential tool for correcting high corneal astigmatism if cataract surgery is needed. For preoperative calculation of the lens power and axis, the matrix method provides a qualified tool for precise calculations. The software JToricIOL enables surgeons and students to reproduce the examples in this paper and to experiment with their own calculations.