Biomechanical Stability of Three Intraocular Lenses With Different Haptic Designs: In Silico and In Vivo Evaluation

Rotational stability of toric intraocular lenses by lens model and haptic design: systematic review and single-arm meta-analysis

Rotational stability is key for optimizing postoperative visual outcomes because even a small degree of rotation of a toric intraocular lens (IOL) from its target axis can result in a significant reduction in astigmatic correction. This systematic review and meta-analysis evaluated the rotational stability of toric IOLs of different lens models and haptic designs. All published studies and clinical trials that investigate postoperative rotation of toric IOLs were searched and evaluated. Quality of studies was assessed using the Methodological Index for Nonrandomized Studies scale. A single-arm meta-analysis was performed in R4.3.1 software with subgroup analysis performed based on lens model and haptic design. 51 published studies of 4863 eyes were included in the meta-analysis. The pooled mean absolute rotation of all toric IOLs was 2.36 degrees (95% CI, 2.08-2.64). Postoperative rotation is dependent on many aspects of lens material and design. Modern commercially available toric IOLs exhibit exceptional rotational stability.

Optical quality in vitro and in vivo of an extended depth-of-focus intraocular lens with isofocal design

PURPOSE

The aim of this study is to compare optical quality results obtained in laboratory analysis (in vitro) versus clinical data (in vivo).

METHODS

The optical quality of ISOPure intraocular lens was assessed both in vitro and in vivo using the modulation transfer function (MTF) for 3.0 and 4.5 mm pupil diameters. In vitro measurements were obtained using deflectometer NIMO TRF1504, while in vivo measurements were taken with OPD-Scan III in a set of patients implanted with this lens. Ray tracing techniques were used to determine the MTF and area under MTF curve (MTFa) from the measured wavefront for the isolated lens and for the whole eye.

RESULTS

The MTF of the isolated lens obtained under both in vitro and in vivo conditions showed comparable results for both pupil sizes. However, differences were found when comparing the MTF of the whole eye with the lens implanted versus the MTF measured in vitro for 4.5 mm pupil size. Also, the MTFa defocus curve was compared with the defocus curve measured in vivo.

CONCLUSION

The defocus curve from the in vivo study aligns closely with the MTFa of the in vitro model, with a useful defocus range of 0.40D. Thus, it is possible to anticipate the visual results of the implanted isofocal lens by using measurements on an optical bench and conducting optical simulations.

Visual and Refractive Outcomes After Bilateral Implantation of a Biconvex Aspheric Toric Monofocal Intraocular with a Double C-Loop Haptic Design

Purpose

To show the visual and refractive outcomes in cataract patients with corneal astigmatism when bilaterally implanted with a biconvex aspheric toric monofocal intraocular lens (IOL) with a double C-loop haptic-design.

Methods

Forty-seven cataract patients (94 eyes) with corneal astigmatism (≥0.75D) were implanted with the monofocal PODEYE toric IOL and assessed for 4-6 months post-surgery. Measurements included monocular and binocular uncorrected-distance visual acuity (UDVA) and corrected-distance visual acuity (CDVA), under both photopic and mesopic lighting conditions. Refraction, photopic and mesopic contrast sensitivity (with and without glare), and rotational stability were also recorded at the last postoperative visit.

Results

At 4-6 months, 78.2% and 98.9% of eyes were within ±0.50D and ±1.00D of the target refraction, respectively. The mean spherical equivalent and refractive cylinder values were 0.09±0.35D and -0.36±0.35D, respectively. 76.5% and 98.8% of eyes presented a postoperative refractive cylinder of ≤0.50D and ≤1.00D, respectively. 91.5% and 100% of patients had a binocular UDVA and CDVA of ≥20/25, respectively. The mean binocular UDVA and CDVA were 0.02±0.08 and -0.02±0.07 logMAR, respectively. Under mesopic conditions, 78.7% and 83.0% of patients presented a binocular UDVA and CDVA ≥20/32, respectively. The mean binocular UDVA and CDVA were 0.15±0.11 and 0.12±0.11 logMAR, respectively. The patients showed good contrast sensitivity under photopic and mesopic conditions. The mean absolute IOL rotation was 1.22±2.21 degrees with 97.87% of eyes having a rotation of <10 degrees.

Conclusion

This study shows good visual and refractive outcomes for the PODEYE toric IOL when implanted bilaterally in cataract patients with corneal astigmatism.

Evaluation of the mechanical stability of intraocular lenses using digital image correlation

This study aimed to evaluate the mechanical stability of seven different intraocular lens (IOL) haptic designs by using digital image correlation to measure their mechanical biomarkers (axial displacement, tilt, and rotation) under quasi-static compression. The IOLs were compressed between two clamps from 11.00 up to 9.50 mm whilst a 3D deformation dataset was acquired every 0.04 mm. Results revealed that flexible and mixed IOL designs exhibited better mechanical response for smaller compression diameters compared to stiff designs. Conversely, stiff designs performed better for larger compression diameters. These findings may aid in the selection and development of more mechanically stable IOL designs.

Rotational stability and clinical outcomes after implantation of a new monofocal toric intraocular lens with double C-loop design

PURPOSE

To investigate rotational stability and visual outcomes of patients unilaterally or bilaterally implanted with a new monofocal toric intraocular lens (IOL).

SETTING

Ophthalmology service, clinique Beausoleil, avenue de Lodève, Montpellier.

DESIGN

Single-center retrospective study.

METHODS

This study included patients who underwent routine cataract surgery with the PODEYE toric (BVI/PhysIOL SA, Liège, Belgium) IOL using the ZEISS CALLISTO eye®. Biometry and keratometry data, refractive outcomes, rotational stability, and astigmatism correction were recorded. IOL rotation was evaluated using an image analysis technique. Postoperative assessments were performed at 1 week, 1 month, and 4 to 6 months after surgery.

RESULTS

Clinical outcomes of 102 patients (136 eyes) were analyzed. Patients had a mean age of 74 years. Of the included eyes, 25% had an axial length greater than 24.5mm. Median postoperative IOL rotation from baseline (surgery) was 2̊. With the exception of one outlier (15̊ rotation), IOL rotation was ≤ 6̊ (1 month) and ≤ 10̊ (4-6 months) in 100% of the eyes. No surgical IOL re-positioning was required. Median postoperative corrected distance visual acuity was -0.08 logMAR, and median postoperative subjective cylinder was between 0.25 and 0.50 D.

CONCLUSION

The PODEYE toric IOL showed high rotational stability, allowing for correction of corneal astigmatism during cataract surgery.

Predicting the biomechanical stability of IOLs inside the postcataract capsular bag with a finite element model

BACKGROUND AND OBJECTIVES

Although cataract surgery is a safe operation in developed countries, there is still room for improvement in terms of patient satisfaction. One of the key issues is assessing the biomechanical stability of the IOL within the capsular bag to avoid refractive errors that lead to a second surgery. For that purpose, a numerical model was developed to predict IOL position inside the capsular bag in the short- and long-term.

METHODS

A finite element model containing the implanted IOL, the postcataract capsular bag, the zonules, and a portion of the ciliary body was designed. The C-loop hydrophobic LUCIA IOL was used to validate the numerical model and two more worldwide IOL designs were tested: the double C-loop hydrophobic POD FT IOL and the plate hydrophilic AT LISA IOL. To analyze the biomechanical stability in the long-term, the effect of the fusion footprint, which occurs days following cataract surgery, was simulated. Moreover, several scenarios were analyzed: the size and location of the capsulorexhis, the capsular bag diameter, the initial geometry of the capsular bag, and the material properties of the bag.

RESULTS

The biomechanical stability of the LUCIA IOL was simulated and successfully compared with the in vitro results. The plate AT LISA design deformed the capsular bag diameter up to 11.0 mm against 10.5 mm for the other designs. This design presented higher axial displacement and lower rotation, 0.19 mm and 0.2^∘, than the C-loop design, 0.09 mm and 0.9^∘.

CONCLUSIONS

All optomechanical biomarkers were optimal, assuring good optical performance of the three IOLs under investigation. Our findings showed that the capsulorexhis size influences the stiffness of the capsular bag; however, the shape in the anterior and posterior curvature surfaces of the bag barely affect. The results also suggested that the IOL is prone to mechanical perturbations with the fusion footprint, but they were not high enough to produce a significant refractive error. The proposed model could be a breakthrough in the selection of haptic design according to patient criteria.

Experimental evaluation of the injection force exerted in intraocular lens delivery with syringe-type injectors

The process of intraocular lens (IOL) delivery within the capsular bag during cataract surgery is crucial, as the integrity of the IOL, the injector and the ocular structures should be preserved at all times. This study aims to obtain the main parameters that affect the injection force exerted in the ejection of an intraocular lens (IOL) through syringe-type injectors. For that purpose, ejection tests were carried out in vitro, measuring the resistance force throughout the entire delivery process. The effect of IOL material, haptic design, IOL thickest area and ophthalmic viscosurgical device (OVD) was studied by ejecting seven IOLs with four syringe-type injectors of different sizes, 3.0, 2.2 and 1.8 mm. In all injectors, plate hydrophilic IOLs present the lowest resistance forces; hydrated C-loop hydrophobic IOLs present higher forces and the C-loop hydrophobic IOL in dry conditions presents the highest resistance forces. All IOLs could be properly delivered with an injector size of 2.2 mm, making injector sizes of 3.0 mm outdated. The injector size of 1.8 mm damaged several IOLs. IOL material and cartridge nozzle size were the most influential parameters in IOL delivery. IOL thickest area was also relevant but in a lesser extent whereas IOL haptic design was not as relevant.