Positional accommodative intraocular lens power error induced by the estimation of the corneal power and the effective lens position

Influencing factors of effective lens position in patients with Marfan syndrome and ectopia lentis

AIMS

The aim of this study was to analyse the effective lens position (ELP) in patients with Marfan syndrome (MFS) and ectopia lentis (EL).

METHODS

Patients with MFS undergoing lens removal and primary intraocular lens (IOL) implantation were enrolled in the study. The back-calculated ELP was obtained with the vergence formula and compared with the theoretical ELPs. The back-calculated ELP and ELP error were evaluated among demographic and biometric parameters, including axial length (AL), corneal curvature radius (CCR) and white-to-white (WTW).

RESULTS

A total of 292 eyes from 200 patients were included. The back-calculated ELP was lower in patients undergoing scleral-fixated IOL than those receiving in-the-bag IOL implantation (4.54 (IQR 3.65-5.20) mm vs 4.98 (IQR 4.56-5.67) mm, p<0.001). The theoretical ELP of the SRK/T formula exhibited the highest accuracy, with no difference from the back-calculated ELP in patients undergoing in-the-bag IOL implantation (5.11 (IQR 4.83-5.65) mm vs 4.98 (IQR 4.56-5.67) mm, p=0.209). The ELP errors demonstrated significant correlations with refraction prediction error (PE): a 1 mm ELP error led to PE of 2.42D (AL<22 mm), 1.47D (22 mm≤AL<26 mm) and 0.54D (AL≥26 mm). Multivariate analysis revealed significant correlations of ELP with AL (b=0.43, p<0.001), CCR (b=-0.85, p<0.001) and WTW (b=0.41, p=0.004).

CONCLUSION

This study provides novel insights into the origin of PE in patients with MFS and EL and potentially refines existing formulas.

Correlation of Intraoperative Optical Coherence Tomography of Crystalline Lens Diameter, Thickness, and Volume with Biometry and Age

PURPOSE

To characterize crystalline lens dimensions derived from in vivo spectral-domain optical coherence tomography (SD-OCT) and identify associations among these parameters, ocular biometry, and age.

METHODS

In this retrospective study, lens thickness (LT), lens diameter (LD), and lens volume (LV) were measured intraoperatively using SD-OCT in 293 eyes undergoing lens surgery. Correlations among LT, LD, LV, age, axial length (AL), and anterior chamber depth (ACD) were analyzed. Multiple regression analysis was performed to determine whether a combination of biometric data could predict LD and LV.

RESULTS

Wide variations were observed in LT (3.6-5.7 mm), LD (7.5-11.9 mm), and LV (119.9-312.4 mm³) of aging eyes. Correlations among the 3 lens dimensions were statistically significant (LV-LT: r = 0.785; P < .001; LV-LD: r = 0.696; P < .001; and LT-LD: r = 0.121; P = .039). With age, the correlation coefficients of LT, LD, and LV were 0.526, 0.326, and 0.573, respectively (P < .001). Although there was significant correlation of AL with LT (r = -0.137; P = .002) and LD (r = 0.268; P < .001), it was not significant with LV (r = 0.084; P = .15). Subgroup analysis revealed that 19.8% of long eyes had LD >1 standard deviation (SD) above and that 5.2% had LD <1 SD below the mean LD.

CONCLUSIONS

Dimensions of the aging lens vary considerably and are most accurately characterized by direct measurement of LT, LD, and LV, rather than making assumptions based on AL. These findings challenge historically proposed relationships between LD and AL and represent a normative dataset of contemporary geometric features of the aging lens, possibly aiding in surgical decision making and future developments in lens surgery.

Could anatomical changes occurring with cataract surgery have a clinically significant effect on effective intraocular lens position?

PURPOSE

To assess if the calculation of the effective lens position (ELP) of two different monofocal intraocular lenses (IOLs) could be optimized by considering the potential anatomical changes occurring after cataract surgery.

METHODS

Prospective, descriptive, single-center study involving 472 eyes of 280 subjects (mean age 73.5 years) undergoing cataract surgery that were divided into two groups according to the IOL implanted: group 1330 eyes with AcrySof IQ SN60WF (Alcon), and group 2142 eyes with Akreos MI60L (Bausch + Lomb). Refractive and biometric changes were evaluated during a period of 6-month follow-up with an optical biometer (considering potential measurement artifacts). Comparison of ELP estimated with the SRK-T formula (ELP_SRK-T) and ELP calculated considering clinical real data was made (ELP_{AXL-corrected clinical}).

RESULTS

Besides significant changes in refraction (p ≤ 0.020), a significant increase in anterior chamber depth (ACD) (p < 0.001) and a significant reduction in the axial length (AXL) (p < 0.001) were detected at 1 month after surgery. Mean 1-month postoperative AXL change was - 0.08 ± 0.06 and - 0.10 ± 0.11 mm in groups 1 and 2, respectively (p = 0.001), with no significant changes afterward. Mean difference between ELP_SRK-T and ELP_{AXL-corrected clinical} was 0.17 ± 0.39 and - 0.23 ± 0.43 mm in groups 1 and 2, respectively (p < 0.001). A strong and statistically significant correlation of these differences with the prediction refractive error was found in both groups (group 1, r =  - 0.723; group 2, r =  - 0.819; p < 0.001).

CONCLUSIONS

The estimation of ELP using the SRK-T formula for the two IOLs evaluated may be optimized considering biometric changes with surgery, helping to understand better some problems of refractive unpredictability.

Intraocular lens alignment methods

PURPOSE OF REVIEW

This article reviews current concepts in intraocular lens alignment strategies to maximize intraocular lens (IOL) positioning.

RECENT FINDINGS

A variety of strategies has been developed to maximize toric IOL position, including preoperative calculators to determine the appropriate IOL power and orientation, intraoperative alignment devices, and postoperative software to determine if IOL rotation would be beneficial for refractive outcomes.

SUMMARY

The combination of using multiple toric IOL calculators and intraoperative alignment devices has improved toric IOL outcomes. The relationship of the posterior corneal power and its effect on outcomes remains to be fully elucidated. Postoperative IOL rotation may be necessary even when the IOL is aligned as planned because of surgically induced astigmatism.