2. Materials and Methods
Fifteen consecutive patients (mean age: 65 ± 5 years) diagnosed with senile corticonuclear cataract and no other concurrent eye pathologies, including no corneal opacity, were recruited. The study followed the tenets of the Declaration of Helsinki and all patients signed an informed consent after full explanation of the procedure.
The femtosecond laser assisted cataract surgeries were performed by an experienced surgeon (Lucio Buratto) using two FS laser cataract platforms, which included the LenSx (Alcon Laboratories Inc., Fort Worth, TX, USA; n = 5) and the Victus (Bausch & Lomb Inc., Dornach, Germany; n = 5). The intended capsulotomy diameter was 5.50 mm in all cases. Integrated real time OCT was used to plan and monitor the capsulotomy cut using both FS laser platforms.
The LenSx laser has a repetition rate of 33 kHz, pulse width of 600 to 800 fs, and central laser wavelength of 1030 nm. The proprietary rigid curved interface was used in all cases. The laser energy was set to 15 μJ with spot and layer separations of 3 and 4 μm, respectively. The Victus laser has a pulse frequency up to 80 kHZ, pulse duration of 400 to 500 fs, and central wavelength of 1040 nm. The curved patient interface provided by the manufacturer was used in all cases. The laser energy setting was 7.0 μJ with spot and layer separations of 6 and 4 μm, respectively.
The conventional phacoemulsification was performed by one experienced surgeon (Sebastiano Serrao). Manual capsulorhexis was created using a rhexis forceps (n = 5).
The fifteen anterior lens capsules, collected during cataract surgery, were immediately fixed in 2.5% glutaraldehyde solution and stored at 4°C for 24 hours. The specimens were then scanned by eSEM (FEI Quanta 400, OR, USA) without any further sample processing. Imaging was performed using 5.9 mbar vacuum and 3°C temperature in the eSEM chamber, after fixing each sample to the microscope holder with a drop of silver nitrate. The images were acquired at 10 kV voltage (HV), using magnifications (Mag) ranging from 400x to 6000x. The technician (Giovanni Desiderio) was masked as to which type of capsulorhexis was performed.
Image analysis was performed using ImageJ (https://imagej.net/ij/, NIH, USA). The irregularity measurements were performed on several reference areas of 7 × 7 μm along the capsular cutting edge in images acquired at 3000x Mag. The areas studied have been randomly chosen (at least 4 areas for capsule). Four quantitative parameters were used to characterize the cutting edge irregularity, which included the arithmetic mean deviation of the surface (Sa), the root-mean-square deviation of the surface (Sq), the skewness of the topography height distribution (Ssk), and the kurtosis of the topography height distribution (Sku). Detailed description of the above parameters has been given in previous work [16]. The surface skewness (Ssk) describes the asymmetry of the surface height distribution. Negative Ssk (Ssk < 0) indicates a predominance of valleys and positive Ssk (Ssk > 0) a predominance of peaks. If Ssk = 0, a symmetric height distribution is indicated (i.e., Gaussian like). In general, if the Ssk is >1 or <−1, the skewness is substantial and the distribution is far from symmetrical. The surface kurtosis (Sku) quantifies whether the shape of the data distribution matches the Gaussian distribution. Overall, kurtosis represents a measure of the randomness of surface heights. For normal height distributions, Sku = 3; for spiky distributions, Sku > 3; for bumpy distributions, Sku < 3.