Study Design
Fifty-six eyes of 56 consecutive patients with age-related cataract who underwent intraocular lens (IOL) implantation via either FLACS or CPS from August 2018 to July 2020 were included in this retrospective, interventional comparative case series. These procedures were performed uniformly at a single University Hospital (Tianjin Medical University Eye Hospital, Tianjin, China). Written informed consents were obtained from each subject based on their decision to proceed with either FLACS or CPS. The ethics committee of Tianjin Medical University approved the study, which is in accordance with the Declaration of Helsinki.
Patients who received monocular phacoemulsification for uncomplicated cataract with IOL implantation were enrolled. All patients were over 40 years old and had no other systemic pathology that would interfere with ocular or systemic circulation. The nuclear sclerosis grade was determined at the slitlamp biomicroscope using the Lens Opacities Classification System II (LOCS II). All patients were mild and moderate cataract (nuclear sclerosis grades 1 and 2). Exclusion criteria included the following: myopia or hyperopia to avoid the influence of magnification of the OCTA images, inflammatory cells in the anterior chamber > 5 postoperation, obvious postoperative corneal oedemas which prevented high-quality imaging and ocular hypertension; a history of previous ocular surgery; evidence of retinal pathologies, such as retinal vascular diseases; a history of trauma; and complications such as large fluctuation of blood pressure and posterior capsular rupture during operation. All scans with layer segmentation error, signal strength index < 50, or significant motion artefacts in images were excluded to ensure the accuracy of the measurement.
Data Collection
Each participant underwent a comprehensive preoperative ophthalmic examination. Assessed metrics included the best-corrected visual acuity (BCVA); the intraocular pressure (IOP), as measured by Goldmann applanation tonometry; a refractive status assessment, as determined by an automatic refractometer; slit-lamp examination; and fundoscopy. Axial length (AL) was measured using the IOL Master system (Carl Zeiss, Meditec, Germany). Corneal topography was measured with a Scheimpflug device (Pentacam, Oculus Optikger ate GmbH). Endothelial cell count was determined with a specular microscope (SP-1P, Topcon Europe Medical B.V., Netherlands). B-scan ultrasound recording was also documented (AVISO, Quantel Medical, Clermont-Ferrand, France). Any performed procedures or analyses were conducted by an optometrist or technician.
OCTA image acquisition and processing
OCTA image was obtained using RTVue XR OCT (Optovue, Inc., Fremont, CA, USA; Software V.2017.1.0.155). The split-spectrum amplitude decorrelation algorithm (SSADA) was used to extract OCTA images, which operates A-scan of 70, 000 HZ scans per second. During image processing, the Motion Correction Technology function was used to correct the horizontal and vertical scans for eye movement [10]. Automatic segmentation was performed by the Optovue software to generate en face projection images.
The ONH area was measured using a 4.5 × 4.5-mm OCTA scan. The RPC density was automatically captured from the optic disc segment that extended in a 0.75-mm-wide elliptical annulus from the ONH boundary [11]. The RNFL thickness measurements were obtained using a 3.45 mm radius ring centred on the optic disc (Fig.1). The macular area was covered using a 3.0 × 3.0-mm OCTA scan. The superficial capillary plexus (SCP) was automatically selected from 3 μm below the inner limiting membrane (ILM) to 15 μm below the inner plexiform layer (IPL) (Fig.2); the deep capillary plexus (DCP) was automatically selected from 15 μm to 70 μm below the IPL [12]. The macular thickness was measured from the ILM to the middle of the retinal pigment epithelium (RPE)-Bruch membrane complex. The measurement area of fovea was 1 mm diameter in the centre of macula. The measurement area of parafovea was 2 mm ring zone surrounding the fovea. Blood flow was calculated automatically in a selected area of 3144 mm2, which was centered on the fovea in the choriocapillary bed from 31 μm below RPE to 59 μm below the RPE [11].
Femtosecond laser-assisted pre-treatment and cataract surgical procedures
The femtosecond laser-assisted pre-treatment was performed by a surgeon, using a femtosecond laser (Lensx, Alcon Laboratories, Inc.). The LenSx system consists of a 50 kHz femtosecond infrared laser with a pulse width of 600-800 femtoseconds, a central laser wavelength of 1,030 nm, and a maximum pulse energy of 15 µJ. The laser pulse energy setting was 6 μJ for performing the anterior capsulotomy (diameter: 5.2 mm). This laser is combined with a 3D spectral-domain OCT system providing visualization of the entire anterior segment during the surgical procedure and a liquid-free curved patient interface (SoftFit). The femtosecond laser system was used for capsulotomy, lens fragmentation, and corneal incision. All cataract surgical procedures were performed under local anaesthesia.
After the femtosecond laser treatment, each participant was transferred to another operating room for the remainder of the procedure. Phacoemulsification was completed using torsional phacoemulsification on an active-fluidics-based platform (Centurion® Alcon Laboratories, Inc., USA). Patients undergoing CPS were prepared for surgery in the same way as those in the femtosecond laser arm. Instead of receiving laser pre-treatment, they directly underwent the operation. The default intraocular len (IOL) used in the capsular bag was a hydrophobic acrylic IOL (Alcon Laboratories, Inc., USA). Patients received levofloxacin (Cravit) and prednisolone acetate 1% (Pred Forte) eyedrops four times a day for 1-week after the surgery, followed by tapering for 3 weeks for both groups.
Statistical Analysis
The normality of data distribution was tested using the Kolmogorov-Smirnov test. After confirmation of the normality assumption, data are generally presented as mean ± standard deviation (SD) values. The comparisons of baseline were performed using t-test. The preoperative and postoperative measurements were compared using repeated measures analysis of variance tests with Bonferroni corrections. Pearson correlation analyses were performed to determine the relationships between the changes in peripapillary vessel density at each timepoint postoperatively and related clinical factors. Statistical analyses were performed using SPSS version 22.0 (SPSS, Inc., Chicago, IL, USA). Probability values of P < 0.05 were considered statistically significant.