Comparing aspherical IOLs: Tecnis remains on top

According to Alessandro Franchini, it is insufficient to design an aspheric lens that maintains a certain degree of spherical aberration simply to achieve a degree of pseudo-accommodation.

Tecnis from AMO, the first aspherical intraocular lens (IOL) to be launched, represented a leap forward in ophthalmic technology because, by reducing spherical aberration, an improvement in contrast sensitivity and quality of vision could be made. Since the success of Tecnis, a number of other manufacturers have proposed new forms of aspheric lenses, which vary in terms of the position of the aspheric surface and the extent of spherical aberration corrected.

Franchini, of the University of Florence Eye Institute, Italy, and colleagues conducted a study to evaluate the performance of four such models: the Tecnis silicone three-piece lens with the aspherical surface on the anterior of the lens; the Alcon IQ, an acrylic single-piece lens with the aspherical surface on the posterior of the lens and a yellow blue-blocker chromophore in the optic; the Bausch & Lomb SofPort, a three-piece silicone lens with the aspherical profile on the anterior and posterior surface; and the STAAR Surgical KS-3Ai three-piece silicone lens, that comes preloaded in an injector, with the aspherical profile on the anterior surface of the optic.

Using a ray tracing programme and a pseudophakic eye model, analysis was conducted through a pupil of 5.0 mm to simulate scotopic conditions of illumination. All lenses used for simulation had a power of 20 D. In each case, depth of focus was tested and further analysis was performed to determine the variation of Strehl ratio for the three colours (yellow, blue and red) in each of the four lenses. The larger the area in which single colour curves are overlapped, the better the depth of focus.

The IQ lens demonstrated high Strehl ratios but poor overlapping of blue and yellow curves, marginal overlapping between red and yellow and no overlapping between blue and red. In contrast, the SofPort had very low Strehl ratios with large overlapping of the three colours and the KS-3Ai showed intermediate Strehl ratios and poor overlapping. The Tecnis lens demonstrated the best results in depth of focus and overall was the most balanced.

Allowing a degree of spherical aberration to remain in order to obtain a certain level of pseudo-accommodation, is insufficient. According to Franchini, for now, the Tecnis IOL remains unsurpassed and the gold standard IOL when compared with its aspherical counterparts.

Ophthalmology Times Europe reporting from the XXIV Congress of the ESCRS, London, 9-13 September, 2006.