Silicone IOLs are widely used in ophthalmic surgery, because of the hydrophobic properties with high transparency and because of the low rate of posterior capsule opacification. Silicone IOLs are usually 3-piece, and only recently has a pre-loaded silicone IOL been developed, the Staar KS3 model. A further evolution of this lens is the Staar KS3-Ai, an IOL with negative spherical aberration, designed to compensate for the positive spherical aberration of the cornea. Currently, this lens is the only pre-loaded silicone aspheric IOL available for clinical use, so we conducted a study to assess the results obtained in implanted eyes. The AMO Tecnis Z9002 IOL was used for comparison (Figure 1).

Comparison design

Figure 1: Staar KS3 Ai.

The comparison was conducted on 46 eyes in 23 patients affected by senile cataracts. They accepted random implantation with one lens in one eye, and the other lens in the contralateral eye. The two sequential surgeries were conducted under topical anaesthesia, with 3.2 mm incisions. Rhexis diameter was about 5.5 mm. After phacoemulsification, irrigation/aspiration (I/A) of residual cortical material, and cohesive viscoelastic injection, the pre-loaded Staar lens was injected within the capsular bag after viscoelastic filling of the lens cartridge and without any contact with surgical instruments. By contrast, the Tecnis lens had to be loaded into the unfolder system, and was injected in a two-step procedure also avoiding conjunctival touch.

Figure 2: Total optical aberrations.

Two months after second eye surgery the relevant measurements took place. Uncorrected and best corrected visual acuity were measured for distance vision. The optical aberrations of the cornea and of the eye were studied using the Topcon KR9000PW topographer / aberrometer.¹ Besides measuring low and high order aberration, this instrument also gives the produced point spread function (PSF) value. Contrast sensitivity for near was assessed using the Ophtec 6500 system, with optical correction in place.² In addition, patients were asked to specify which lens was better and were interviewed about problems of halos, glare, and perceived quality of vision in bright and in dim light conditions.

Surgical procedure

Figure 3: Corneal optical aberrations.

Surgical implantation of the Staar KS3-Ai was easy and uneventful. The transparency of the injector allows precise control of every step of the procedure. The cartridge tip entered the corneal incision easily, and in no case was implantation less than smooth and gentle. The injector did not require any rotation during implantation, unlike the unfolder injector that had to be rotated for optimal IOL placement inside the capsular bag.