Transitional conic toric intraocular lens evaluation after femtosecond laser-assisted cataract surgery using intraoperative aberrometry

In our study specifically, the good outcomes in refractive astigmatism were also shown in the vector analysis for J0 and J45 (see Figure 3 for each predictability graph) and in the distribution of points plotted in Figure 4 between pre- and post-surgery. Note that the spread of the points before the surgery (white circles) changes to a more concentrated distri- bution (black circles) post-toric IOL implantation, indicating a reduction of both components and there- fore the astigmatism. These outcomes agree with those reported by Thomas et al. [20], using the same vector analysis. Other studies [18, 19, 21, 22] analyzing the surgical- and target-induced astigmatism and angle of error also support the good findings reported. It is expected that good refractive findings should be correlated with good visual acuity outcomes. Figure 5 shows that UDVA and CDVA increased after the surgery, with 77% and 100% of eyes with UDVA and CDVA, respectively, of 20/25 or better. Mean values for UDVA and CDVA were 0.88 ± 0.17 and 0.96 ± 0.07, respectively. Mean values reported in other studies (see Table 3) are quite similar. Specifically, Vale et al. [18] reported that 100% of eyes achieved a UDVA of 20/30 or better, and Ferreira et al. [19] and Jung et al. [22] indicated that 82% and 91% of eyes achieved a UDVA of 20/25 or better, respectively. Bandeira et al. [21], in the emmetropia target group, reported 72% and 95% of eyes with UDVA and CDVA of 20/25 or better, and 84% and 98% when it was 20/32 or better. All these values agree with those found in our sample: 77% and 100%, and 94% and 100%, respectively. Toric rotation can be analyzed both directly, using the slit-lamp, and checking the postoperative residual refraction through vector analysis or wavefront aber- rometry. We analyzed the rotation of the lens by measuring the IOL marks with mydriasis, showing a mean toric axis rotation of 1.10° ± 1.71° (range from 0° to 5°). It has been estimated than 1° of rotation can result in a loss up to 3.3% of the IOL cylindrical power [26]. Considering our mean values of rotation (about 1°) and cylindrical power (about 3D), this gives a mean loss of power of about 0.10D, which is clinically negligible. We should consider that 10° or more of rotation, generally, requires surgical repositioning.   We have introduced that deviation might occur intraoperatively or after the surgery. In the first case, the use of intraoperative aberrometry reduces this possibility, because the postoperative rotation of the lens is the source of the deviation. Immediate rotation of the lens may be caused by an incomplete removal of an ophthalmic viscosurgical device [9], and late rotation may occur due to capsule shrinkage and compression of the IOL haptics (in certain IOL designs and materials). It has been suggested that closed-loop haptics (used in this study) are longer than plate haptics, which should give good initial friction, and the loops have a second insertion on the IOL that might resist later capsular compression and subse- quent rotation [18, 27–29]. Our mean value is very good because it is similar to those values found by previous studies on small samples and short follow- ups (from 1.50° to 3°; see Table 3 for detailed mean values and ranges). It has been indicated that IOL rotation may be greater in eyes with long axial lengths up to about 3° [30]. Our sample includes eyes with axial length up to 30.11 mm, but if this happened, it was not clinically relevant. Note that the accuracy of the measurement using the slit-lamp is 5°. Other methods, using digital photography, for example, increased the accuracy of measurement. In our case, no eye showed a larger value than the step of 5°. Clinical evaluation of the lens shows good rotational stability, but despite this, it has been reported in vitro that this lens is robust to rotation. In an optical bench analysis [17], the Precizon lens showed maximum rotation tolerance compared with other toric IOL models (bitoric, posterior toric surface, or with an anterior toric surface), providing superior image quality despite pupil size changes in the presence of decentration. This comes from its transitional conic toric surface (consistent power from the center to the periphery), and an aberration-free IOL tolerates decentration better than a negatively aspheric IOL [31]. This surface blends into the aspheric surface of all meridians, leading to a broader toric surface that could be more tolerant to rotation, misalignment, tilt, and decentration. In addition to the robustness in image quality that the lens provides with decentration, we have to consider the excellent rotational stability of the lens when implanted. The mean values reported previously, confirmed by our results at one year, indicate that the haptic design also offers good stability of the lens, providing a valuable platform that allows correcting a large amount of astigmatism with high-powered toric IOLs. Factors, such as the size and the asymmetry of the capsulorhexis, may affect the rotational stability of the IOL implanted. We consider that the ideal diameter for the capsulorhexis should be adjusted to the IOL optic diameter to maintain an overlap of the anterior edge of the IOL by the capsulorhexis. (In our series, we considered 5 mm.) It has been shown that FLACS produces a more predictable capsulorhexis, allowing a more stable position of the IOL within the capsular bag [14, 32]. Espaillat et al. [14] were the first to analyze exclusively toric IOL with FLACS in a sample of 63 eyes using standard phacoemulsification and 53 eyes with FLACS. They reported that there were no significant differences in UDVA and CDVA between FLACS and standard phacoemulsification. However, Chee et al. [33] found, in 794 surgeries with FLACS and 420 with standard phacoemulsification, that 12% more patients in the FLACS group had UDVA C 20/ 25, although there was no difference between the groups in terms of the percentage of eyes with UDVA C 20/32. The study by Espaillat et al. [14] indicated that FLACS may be associated with a lower absolute SE, but the differences relative to standard phacoemulsification may not always be clinically significant. These authors also found that the residual refractive astigmatism (B 0.50D) was higher in FLACS at both one month and one year (although significant only at one month). Kanellopoulos and Asimellis [16], in 66 eyes with standard phacoemul- sification and 67 with FLACS, also found a higher percentage of eyes with postoperative cylin- der \ 0.50D after FLACS (82.1%) than after standard phacoemulsification (67.7%). Several authors [14, 15] have reported that lower internal vertical coma was statistically significant in FLACS. Miha ́ltz et al. [15] suggested that visual quality may be improved by lower IOL tilt, related to lower magnitudes of coma in FLACS when compared to the standard surgery. Our results with FLACS were good but also comparable with previous studies indicated in Table 2, which used standard phacoemulsification. Matched groups (pre- operative cylinder, SE, and age); using both tech- niques would be needed to confirm this hypothesis. In any case, we consider that better sizing of the capsulorhexis carried out by FLACS is related to better IOL position and consequently a decrease of internal aberrations.