Capsular Bag Performance of Two Hydrophobic Intraocular Lenses of Different Design

Continuous improvements in cataract surgery technique, intraocular lens (IOL) materials, and design over the past few decades, have led to a more safe procedure with satisfactory refractive outcomes and a short rehabilitation time. By that, patients' expectations concerning their postoperative visual quality and refractive outcome are increasing. However, two main problems might occur after cataract surgery: instability of the IOL position in the capsular bag and formation of posterior capsule opacification (PCO). Both may decrease the optical performance of an IOL.

The performance of an IOL depends on its behaviour in the capsular bag, which has an influence on the anterior chamber depth (ACD), as well as the postoperative refractive shift, the tilt and decentration of the IOL. Several factors such as IOL design and material, capsulorhexis size, capsular bag diameter, and capsular fibrosis or shrinkage may lead to a suboptimal IOL position. Misalignment of an IOL away from the retina leads to a myopic shift, while towards the retina leads to a hyperopic outcome. This explains why inaccurate prediction of postoperative ACD remains the main source of error in IOL power calculation.

One main goal of modern cataract surgery is to yield a low and predictable ACD shift as well as low degrees of IOL tilt and decentration after surgery in order to achieve ideal optical performance of the IOL.

Another aspect of capsular bag performance of an IOL is posterior capsule opacification (PCO). PCO is one of the most frequent long-term complications after cataract surgery leading to dissatisfying results by decreased visual function. Source of PCO are lens epithelial cells from the equator of the lens capsule, which acquire the ability to migrate and proliferate, causing epithelial ingrowth between the IOL and the posterior capsule. It is estimated that PCO occurs at a rate of 12% one year, 21% three years, and 28% five years after cataract surgery. PCO can be treated with neodymium-doped yttrium aluminium garnet (Nd:YAG) laser capsulotomy. However, complications including an increase in intraocular pressure, ocular inflammation, cystoid macular edema, and retinal detachment may occur after this treatment. Hence lower rates of PCO would improve patients long term safety following cataract surgery. Moreover, it would increase patient satisfaction.

The material and design of an IOL may have an effect on the formation of PCO. Sharp optic edge design has been shown to be a major factor in the prevention of PCO. Furthermore, acrylic and silicone hydrophobic materials showed a lower risk for PCO formation and lower rates of postoperative Nd:YAG laser capsulotomy than hydrophilic IOLs.