Study Design
Fifty-two eyes of 52 consecutive patients with age-related cataract who underwent intraocular lens (IOL) implantation via either FLACS or CPS from August 2018 to July 2019 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.
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, presence of amblyopia, media opacities which prevented high-quality imaging, dense cataracts, and ocular hypertension; and a history of systemic diseases such as hypertension, diabetes mellitus and cardiovascular disease, which might interference the ocular circulation; 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.
Data Collection
Patient metrics
Each participant underwent a comprehensive preoperative ophthalmic examination. Assessed metrics included the best-corrected visual acuity (BCVA); the 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 counts were determined with a specular microscope (SP-1P, Topcon Europe Medical B.V., Netherlands). B-scan ultrasound recordings were also documented (AVISO, Quantel Medical, Clermont-Ferrand, France). The macula was examined using swept-source optical coherence tomography (SS-OCT, Topcon DRI OCT-1 Atlantis). Refraction data were converted to spherical equivalents (SE; SE = spherical component + 1/2 cylindrical component). Any performed procedures or analyses were conducted by an optometrist or technician.
OCTA image acquisition and processing
OCTA images were 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. A 4.5 × 4.5 mm angio disc mode was centred on the optic disc, and two repeated volumes comprised by 304 B-scans were captured. During image processing, the Motion Correction Technology function was used to correct the horizontal and vertical scans for eye movement [23]. Automatic segmentation was performed by the Optovue software to generate face projection images. All scans with layer segmentation errors, signal strength index < 50, or significant motion artefacts in images were excluded to ensure the accuracy of the measurement. Collection of data on BCVA and IOP and OCTA image acquisition and processing for this study occurred before the surgery and at day 1 and months 1 and 3 after the surgery.
The Optovue software, equipped with the density function, was used to analyse a 4.5 × 4.5 mm optic disc angiogram. The average vessel density was automatically captured from the optic disc segment that extended from the internal limiting membrane (ILM) to 150 μm below the ILM. The average peripapillary RPC density was automatically calculated in a 0.75-mm-wide elliptical annulus region that extended from the optic disc boundary. The peripapillary RPC density was separately processed in two regions (superior-hemi, inferior-hemi). The software further calculated the whole image vessel density. (Figure 1)
Femtosecond laser-assisted pre-treatment and cataract surgical procedures
The femtosecond laser-assisted pre-treatment for the FLACS group was performed by a surgeon, who had previously performed at least 30 FLACS procedures before operating in this study, using a femtosecond laser (Lensx, Alcon Laboratories, Inc.). Before the femtosecond laser pre-treatment trial, the same surgeon received comprehensive training. 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. In cases where issues with the laser treatment were noted (e.g., a repeated inability to dock, laser machine fault, etc.) and when it could not be operated, patients instead underwent CPS. 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 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. Within-subject comparisons of RPC density, BCVA, and IOP at follow-up and baseline were performed using the paired samples t-test. Between-group time-course differences of RPC density, BCVA, and IOP between the two treatment groups were assessed using a repeated measures analysis of variance. Statistical analyses were performed using SPSS version 22.0 (SPSS, Inc., Chicago, IL, USA). Probability values of P < 0.05 were considered statistically significant.