to reduce glare, halos, and other photic phenomena which occur with multifocal IOLs. A possible drawback is decrease in image quality due to aberrations. EDOF IOLs have often been combined with multifocus designs, which has caused some confusion. It has been suggested that lenses combining more than one optical design be termed "hybrid IOLs" The principle on which they work is to form a single, axially elongated focal point, unlike monofocal lenses which have a single focal point, and multifocal lenses which have two or more stacked discrete focal points. The elongated zone of focus is intended to prevent the overlapped out-of-focus images of the multifocal lens which cause the halo effect. When matched correctly to the eye, these lenses are intended to have little effect on distance vision, and improve middle distance and near vision. In practice they have been satisfactory for intermediate distances, but not good enough for near vision. Spherical aberration and the pinhole effect have been use to produce the elongated focal zone. Phakic IOLs Phakic IOLs (PIOLs) are intraocular lenses which are placed in an eye that still contains a natural human crystalline lens. PIOLs are sometimes referred to as an 'implantable contact lenses' (ICLs). As with other IOLs, PIOLs can be either spheric or toric. Toric PIOLs have to be aligned with the meridian of astigmatism; toric IOL misalignment or rotation can lead to residual or even greater astigmatism postoperatively. Depending on their attachment site to the eye, PIOLs can be divided into three categories: Angle-supported PIOLs, placed in the anterior chamber. They are notorious for their negative impact on the corneal endothelial lining, which is vital for maintaining a healthy clear cornea. Iris-fixated PIOLs, attached by claws to the mid-peripheral iris by a technique called enclavation. It is believed to have a lesser effect on corneal endothelium. The main complication with this type is their tendency to cause endothelial cell reduction. Sulcus-supported PIOLs, placed in the posterior chamber in front of the natural crystalline lens. This type of PIOLs is gaining more and more popularity. They have special vaulting so as not to be in contact with the normal lens. The main complication with older versions was a small possibility of cataract formation. Blue-light filtering IOLs Blue light filtering IOLs filter the UV and high-energy blue light present in natural and artificial light, both of which can cause vision problems; however too much