Rotational stability of a single-piece hydrophobic acrylic intra-ocular lens in myopic and emmetropic eyes.

Abstract

A toric intra-ocular len's (IOL) effect on astigmatism correction is dependent on rotational stability inside the capsular bag, and even relatively small amounts of rotation can have significant effects. Myopic eyes are characterized by a larger capsular bag compared with emmetropic eyes, which could partially explain the greater risk of IOL rotation in this specific subgroup. (Chang 2003; Weinand et al. 2007). We designed a study investigating the rotational stability of a monofocal IOL (SN60WF, Alcon, Switzerland) in two groups of patients characterized by axial length (AL) greater than 26 mm (myopic group) and patients with AL between 22.0 and 24.5 mm (control group). The monofocal IOL in study has an identical platform compared with toric lenses of the same manufacturer (SA60T3-9). We chose to study the monofocal lens in order to obtain a relatively large number of patients and to obtain a control group with average AL values. In this project, we recruited 48 eyes of 48 patients undergoing cataract phacoemulsification and monofocal IOL implantation at the San Raffaele Hospital (Milan, Italy) from November 2014 to February 2015. The Institutional Board required informed consent to be obtained from all patients, and the guidelines of the Declaration of Helsinki were followed. Phacoemulsification was performed under topical anaesthesia by the same surgeon (FF). At the end of surgery, a retroillumination photograph was taken with the operating microscope camera system (3CCD-HD camera head – Panasonic System Networks, Japan; Leica F40 microscope, Leica Microsystems, Germany). Patients were re-examined at 15 and 90 days postoperatively. High-quality retroillumination digital slit lamp images were obtained (CSO, Firenze, Italy). All images were then analysed using professional photoediting software (Adobe Photoshop-CC-2014-San Jose, CA, USA). A reference axis was traced using two episcleral vessels that remain unchanged through the various follow-ups, and another line was traced passing through the insertion of the two haptics and the IOL centre (Fig. 1). The angle between the two lines was then measured, and the difference between the angles at different time intervals was calculated to obtain the degrees of IOL rotation. We included 48 patients in this prospective study; none was lost to follow up. In the myopic group, average AL was 28.12 ± 1.66 mm compared with 23.18 ± 0.60 mm in the control group. In the myopic group, maximum rotation occurred between baseline and 2 weeks (p < 0.0001). Mean IOL rotation in the first 2 weeks was 2.52 ± 1.89 degrees with a maximal rotation of 9.2 degrees in one patient. Similarly, in the control group, IOL rotation was greater in the first 2 weeks (p < 0.0001) with a maximum rotation of 1.90 degrees. The mean IOL rotation at 90 days was significantly greater in the myopic group (3.0 ± 1.76 degrees) compared with the control group (1.44 ± 0.39 degrees, p < 0.0004). In our study, IOL rotation occurred mostly within 15 days postoperatively in both the myopic group and control group. From 15 days to 90 days, IOL rotation was practically inexistent (0.20 ± 0.22 in the control group and 0.48 ± 0.59 in the myopic group). The rotational stability of the AcrySof ®IQ SN60WF IOL was very encouraging in the myopic population of our study, and our results confirm the good results described by other authors. (Kwartz & Edwards 2010; Mencucci et al. 2013, 2014) IOL rotation after 90 days was significantly greater in the myopic group compared with the emmetropic control group (p < 0.0004). Also in the first 15 days, IOL rotation was greater in the myopic group compared with the control group (p < 0.0156). When analysing the data from the myopic group, we did not find a significant correlation between IOL rotation (measured at 90 days) and AL, indicating that AL is not a good predictor of postoperative IOL rotation.