Intraocular lenses, tilt and astigmatism

Concern has been expressed in the literature regarding the frequency and amount of astigmatism found in patients with intraocular lens implants. Postoperative tilting of the implants is one suggested cause. We have measured the effect of tilt on focal length in lenses supplied by two companies. The method used involved photographing the refractive effect of lenses on fine parallel laser beams as the lenses were tilted to varying degrees. The results show that: (a) drastic tilting (e.g. 20 degrees) is required to produce significant amounts of variation in focal length, (b) the effect on back vertex power is more important, (c) spherical aberration of the lenses is minimized.