[Difficulty in the implantation of intraocular lenses by "hidden" parallax]

Although this is not the intent of the surgeon, many posterior chamber lenses are nevertheless placed asymmetrically--one loop in the sulcus and the other in the capsular bag. Difficulties can arise during implantation of even the first loop, which is mostly done in the 6 o'clock position. In this situation, a deficit or loss in steroscopic vision is observed. According to the law of Garten, depth perception is increasingly disturbed as the angle between the connection line of the two observer eyes and two smooth, stretched contours being steroscopical objects diminishes to zero. The reason is not a loss of parallaxis, but the fact that there are no structures that can be matched for stereopsis in a horizontal direction. Thus, stereoscopic vision can be improved dramatically by: (1) twisting the axis of the IOL loops into the five to four o'clock direction; (2) enlarging the magnification of the operating microscope until the grain of the structures is visible. It will then be possible to implant the IOL into the capsular bag (or the ciliary sulcus), which is what was intended.