Chord mu and chord alpha as postoperative predictors in multifocal intraocular lens implantation.

PURPOSE: With the aging population, the prevalence of presbyopia and the popularity of multifocal intraocular lenses is also growing worldwide. Unfortunately, in some cases, they are still associated with postoperative visual disturbances. Recent literature started to evaluate angle kappa- and angle alpha-derived metrics of chord mu and chord alpha as possible predictive values for visual outcomes after multifocal intraocular lens implantation but the published results are inconsistent between studies. Thus, this article aims to review the role of chord mu and chord alpha as postoperative predictors after multifocal intraocular lens implantation and lay the foundation for further research. METHODS: Relevant articles were identified using the following keywords: "presbyopia," "multifocal intraocular lens," "angle kappa," "angle alpha," "Chord mu," and "Chord alpha" up to June 2022. An attempt was made to present the majority of publications that addressed the topic. CONCLUSIONS: Chord mu and chord alpha have a predictive role on the outcomes after multifocal intraocular lens implantation but to a different extent. Cataract surgeons should take them into consideration and avoid implanting a multifocal intraocular lens for patients with speculated critical values of chord mu and alpha above 0.5-0.6 mm, depending on the device used for measurement and the multifocal intraocular lens implanted. Currently, chord alpha seems to be a more stable, more widely applicable, and reliable determinant in predicting postoperative outcomes and in patient selection prior to multifocal intraocular lens implantation when compared to chord mu. To draw conclusions on the topic, a controlled study is needed.

Influence of a multifocal intraocular lens centration and eye angles on light distortion and ocular scatter index.

PURPOSE: To assess how eye axes and multifocal intraocular lens (MIOL) centration may impact the light distortion index (LDI) and ocular scatter index (OSI). METHODS: Fifty-eight subjects implanted with the trifocal MIOL Q-Flex M 640PM or Liberty 677MY (Medicontur) were included in this retrospective analysis. The following variables were collected with the Pentacam Wave (Oculus) considering the vertex normal as the coordinates center: chord-mu to the center of the pupil, chord-alpha to the geometrical center of the cornea, and chord-MIOL to the center of the diffractive ring. These measurements were correlated with OSI (HD Analyzer, Visiometrics) and LDI (light distortion analyzer, CEORLab). RESULTS: Chord-MIOL centroid was 0.12 mm at 62°, chord-mu was 0.09 mm at 174°, and chord-alpha was 0.38 mm at 188°. A relationship was found between OSI and LDI, rho = 0.58, p < 0.0005). No relationships were found between chord-mu or chord-alpha and the LDI or OSI, neither for the total magnitude, nor the decomposition in orthogonal components (p > 0.05). The LDI was significantly correlated with the temporal centration of the MIOL versus the vertex normal (rho = 0.32, p = 0.02). CONCLUSIONS: As opposed to what has been previously described, the temporal centration of the MIOL was related to a decrease in the LDI. Future studies with extreme values of the included variables are required to establish cut-offs for considering these variables as exclusion criteria in the implantation of a MIOL.

Comparisons of biometric parameters measurements by OPD-SCAN â ¢ and Pentacam in cataract.

BACKGROUND: Comparison of OPD-Scan III and Pentacam measurements of relevant parameters guiding the selection of multifocal intraocular lenses in cataract patients. METHODS: A retrospective study included 120 patients (120 eyes) with cataract. Their chord kappa, chord alpha, corneal spherical aberration, and pupil size were measured by OPD-Scan Ⅲ and Pentacam. Pairwise t-tests, Pearson tests, and Bland-Altman analyses were used, respectively, to assess the difference, correlation, and agreement between the devices. RESULTS: There was no significant difference in photopic chord kappa and corneal spherical aberration between the two instruments (P = 0.054, P = 0.065). Chord alpha and pupil size varied significantly between the two instruments (P < 0.001). OPD-Scan III results revealed a significant association between photopic chord kappa and mesopic chord kappa (r = 0.823, P < 0.001). There was a significant positive correlation between photopic and mesopic chord kappa measured by OPD-Scan Ⅲ and chord kappa measured by Pentacam (r = 0.840, r  = 0.757, P < 0.001). The chord alpha evaluated by the two tools had a moderate correlation (r = 0.442, P < 0.001) between them. Bland-Altman analysis showed that there was excellent agreement between the two instruments in measuring chord kappa and corneal spherical aberration, while the chord alpha and pupil size were not consistent. CONCLUSIONS: The chord kappa and corneal spherical aberration measured by OPD-Scan III and Pentacam were consistent in the preoperative decision making of multifocal intraocular lens implantation in cataract patients, both of which have clinical guiding significance. In addition, OPD-Scan III provides more comprehensive day and night chord kappa and pupil diameters, which improves clinical advice for patients with complicated ocular diseases and high demands for nocturnal vision.

Chord Mu (µ) and Chord Alpha (α) Length Changes in Fuchs Endothelial Corneal Dystrophy before and after Descemet Membrane Endothelial Keratoplasty (DMEK) Surgery.

This paper will evaluate chord mu and alpha length in patients with Fuchs endothelial corneal dystrophy (FECD) and its changes following Descemet membrane endothelial keratoplasty (DMEK). Patients with FECD that underwent DMEK surgery were included in this retrospective study. Scheimpflug Tomography was carried out in order to calculate chord mu and chord alpha lengths prior to surgery and at 3 and 12 months postoperative. This study included 27 eyes from 27 patients. Significant changes in chord mu were observed within the first three months (from 0.47 ± 0.32 to 0.29 ± 0.21 mm, p < 0.01) and remained stable 12 months postoperative (0.30 ± 0.21 mm, p > 0.05). However, chord alpha remained stable throughout the 12 months post surgery (from 0.53 ± 0.19 to 0.49 ± 0.14 mm, p > 0.05). In addition to the pupillary center distance from the corneal center (from 0.35 ± 0.25 to 0.34 ± 0.20 mm, p > 0.05) also remain stable. In FECD patients undergoing DMEK surgery, chord mu length decreased, and chord alpha length remained stable after 12 months of follow-up.