Study Design, Inclusion and Exclusion criteria
In this prospective non-comparison study, patients willing to undergo bilateral implantation of AcrySof ® IQ Vivity™ IOL from an experienced ophthalmic surgeon at a single center (Eye Day Clinic, Athens, Greece) were recruited and clinically assessed pre- and post-operatively. Eligible for inclusion in our study were patients aged ≥ 45 years old at the time of preoperative assessment, who had bilateral cataracts or clear intraocular media and were motivated to have spectacle independency, were in good general health and had the ability to perform the necessary pre- and post-operative examinations of the study. Additional inclusion criteria included potential postoperative visual acuity of Snellen ≥ 20/25 and keratometric astigmatism ≤ 0.75 D in both eyes. Exclusion criteria of our study included any ocular or systemic disease that could affect the visual outcomes, ocular trauma history, any condition increasing zonular instability, history of refractive surgery and the use of any medication with the potential of affecting vision.
The study was conducted in accordance with the tenets of Declaration of Helsinki for the use of human participants in biomedical research, as well as other applicable regulations of Greek law. Moreover, study methods were approved by an independent ethical committee and written informed consent was obtained from all patients, after the operating surgeon discussed with each patient the surgical complications of cataract surgery, the possibility of spectacles dependency and visual disturbances postoperatively.
Intraocular lens characteristics
AcrySof ® IQ Vivity™ IOL was bilaterally implanted in all eligible patients of our study. It is a single-piece EDOF IOL, consisted of a high-refractive index (n=1.55) hydrophobic acrylic material. The EDOF effect of this IOL is exerted by utilizing a novel patented technology, called Wavefront-Shaping technology (X-Wave technology) incorporated in the anterior aspheric IOL surface, while the posterior IOL surface is spherical. This technology is different from the ones used in other EDOF IOLs, which are based on diffraction or refraction of light. The AcrySof ® IQ Vivity™ has a central 2.2 mm zone consisting of two transitional elements: the first element stretches the incoming light that hits the retina in the myopic and hyperopic direction, while the second element moves the wavefront anteriorly, to the myopic direction, producing the EDOF effect and utilizing the maximum on incoming light energy . The positive spherical aberrations of the cornea are compensated from the negative spherical aberrations of the anterior surface. Moreover, AcrySof® IQ Vivity™ contains chromophores, which reduce the transmittance of ultraviolet and blue light, and as a result approximating the normal human crystalline lens . The optic zone diameter and overall length of the IOL is 6 mm and 13 mm, respectively.
Preoperative and Postoperative Assessment
All eligible participants underwent a complete ophthalmologic examination before phacoemulsification surgery, including slit lamp examination, assessment of monocular and binocular corrected distance visual acuity (CDVA), Goldmann applanation tonometry, fundoscopy, optical biometry (IOLMaster 500; Carl Zeiss Meditec AG, Jena, Germany) for measuring axial length, anterior chamber depth and keratometry indices and autorefraction (RT-5100; Nidek Co., Ltd., Gamagori, Japan).
Uncorrected distance (UDVA), intermediate (UIVA) and near visual acuities (UNVA) were measured at 6 meters, 66 cm and 33 cm, respectively, 1, 3 and 8 weeks postoperatively. UIVA and UNVA from the last follow up visit were measured using the University of Crete (UoC) chart, a modified Early Treatment Diabetic Retinopathy Study (ETDRS) chart for Europe-wide use for near and intermediate distance recordings . In order to reduce time of postoperative ophthalmological examinations at 1 and 3 weeks, UIVA and UNVA were assessed using Jaeger cards . Preoperative CDVA and postoperative UDVA were assessed using the Snellen acuity chart at 6 meters and all visual acuity assessments were performed under photopic conditions (85 cd/m2). Visual acuities assessed with Snellen charts were converted to logarithm of the minimum angle of resolution (LogMAR) values for analysis. Automated refraction (RT-5100; Nidek Co., Ltd., Gamagori, Japan), slit lamp examination, Goldmann applanation tonometry and fundoscopy were performed in all postoperative follow up visits of our study participants.
We employed the Freiburg Visual Acuity and Contrast Test (FrACT, version 3.10.5)  to assess uncorrected CS at the last follow up visit (8 weeks postoperatively), using a computer screen (1920 x 1080 pixels) at 2 meters. FrACT is a free software, available online at http://michaelbach.de, created by Michael Bach, which has been utilized and validated in several studies . The illumination of the LCD screen was calibrated at 100 cd/m2 and the gamma value of the system and FrACT was set to 1.0, according to the software developer instructions. CS thresholds were measured by presenting to the study participants single constant Landolt-C optotypes (50 arc-min in diameter corresponding to a dominant spatial frequency of 3 cycles per degree) over a range of CS and with the gap at eight possible positions. Every participant performed a practice test of about 5 trials before testing in order to clearly understand the task. The position of the gap was indicated verbally by the study participants and the examiner pressed the corresponding button on an 8-arrow keyboard. CS of the optotypes were adjusted real time to the participants according to their performance during the task, because FrACT employs a best parameter estimation by sequential testing (best PEST) algorithm, based on maximum likelihood estimation, in order to maximize information gain . The CS thresholds in FrACT are initially derived from the Weber CS formula (CSWeber = difference between surround and optotype luminance divided by the surround luminance) and converted to absolute Log10 values of CS (Log10[1/CSWeber]).
Finally, specific visual disturbances at night usually associated with multifocal and EDOF IOLs, including glare, haloes, starbursts, hazy vision, blurred vision, double vision, distortion, fluctuation of vision, focusing difficulties and depth perception difficulties were assessed using the Quality of Vision (QoV) questionnaire . QoV is an instrument to subjectively measure quality of vision by providing 30 questions on the frequency, severity and bothersome of specific visual disturbances.
All study participants underwent conventional phacoemulsification under topical anesthesia by a single experienced ophthalmic surgeon using the Centurion phacoemulsification device (Alcon Laboratories, Inc., Fort Worth, TX, USA). Phacoemulsification was performed through a sutureless clear corneal 2.2 mm incision created manually, after which AcrySof™ IQ Vivity™ IOL could be implanted in the capsular bag. The first Purkinje reflex was used to center the IOL. The required IOL power for each eye was determined preoperatively by combining the SRK/T formula with the “A” constant provided by the company. The lowest possible residual myopia was the refraction target for all participants. The postoperative medical regimen included topical chloramphenicol 0.1% with dexamethasone 0.5% eye drops (Nezefib, RAFARM, Greece) four times a day for 1 month and topical dorzolamide 2% (Optodrop, RAFARM, Greece) eye drops two times a day for 1 month.
Descriptive statistics of the study population preoperatively and postoperatively were reported using percentage values for categorical variables and mean ± standard deviation (SD) for continuous variables. We used Microsoft Excel to collect the data and all statistical analyses were performed with the statistical software R (version 3.5.1, Foundation for Statistical Computing, Vienna, Austria; package) . Additionally, the paired t-test was used to compare the differences preoperatively and postoperatively in continuous variables, while normality of our study variables was assessed with the Kolmogorov–Smirnov test. A P value less than 0.05 was considered as statistically significant and all statistical tests were two-sided.