A Randomised, Subject-masked Evaluation of Stability After Implantation of Two Different Lens Models: FEMTIS-study

Cataract is a clouding of the crystalline lens which causes vision loss and blindness if untreated. Cataract surgery is the most frequently performed surgical intervention in medicine with an incidence of 880 surgeries per 100.000 population in 2010 amounting to a total number of over 160.000 surgeries per year in the Netherlands.1,3 The number of individuals with cataracts is predicted to reach 30 million by the year 2020.2 Due to aging of the general population this number of cataracts will only grow in the future.

For the last decade conventional phacoemulsification cataract surgery (CPCS) is the dominant form of cataract surgery in developed countries, accounting for over 90 percent of these procedures.4 The basic phacoemulsification procedure has remained largely unchanged over the past 20 years, including a series of steps: creating corneal incision, capsulorhexis and lensfragmentation.4 Although highly successful, each of the steps mentioned above are created manually which affects the safety and effectiveness of the procedure.

Since the first human eye was treated by femtosecond laser cataract surgery in 2008, the femtosecond-laser assisted cataract surgery (FLACS) became an innovative growing new technology in the world of cataract surgery.4-7 Femtosecond-lasers are capable of performing some of the most delicate and essential key steps during cataract surgery: capsulotomy, lens fragmentation, and corneal incisions. 'Automating' these steps and performing them with increased precision could lead to an improved quality of capsulotomy, easier lens fragmentation, and more precisely positioned corneal incisions, which in turn, lead to improved visual and refractive outcomes, a decrease in intra- and postoperative complication rates, and increased quality of life.

In order to remove the crystallized human lens, a circular opening in the capsular lens bag, capsulotomy, needs to be created. After removing the lens an intraocular lens (IOL) can be inserted in the empty capsule bag. However, one of the factors affecting postoperative achieved visual acuity and refraction, is the behaviour of this IOL in the capsular bag. Preoperative measurements need to be obtained in order to calculate the required IOL. One of the challenges of these IOL calculations is determining exactly where in the eye the IOL will end up, the effective lens position (ELP). The position of the IOL is crucial for the IOL's general performance because it influences the postoperative IOL tilt, decentration, and posterior capsule opacification (PCO). Considering the anatomical variety between patients, the predictability of an individual's ELP remains an educated guess.

The ELP, and therefore the amount of IOL tilt, decentration and PCO, of an IOL is mainly influenced by the interaction between the IOL and the lens capsule, especially during the time of capsule shrinkage. Theoretically, the positive optical effect of an IOL is lost when there is more than 7 degrees of tilt or more than 0.4 mm of decentration.8 Furthermore, studies have shown the effect of axial displacement of an IOL on refractive error. There is approximately 1.25 D change per millimetre of the IOL's longitudinal displacement.9 This reflects the importance of a stable and predictable ELP.