Accommodating Intraocular Lenses

[Pseudo-accommodative intraocular lenses]

This article reviews pseudo-accommodative intraocular lenses (IOLs), providing an analysis of the terminology used in this field of ophthalmology and describing the design of modern IOLs, the technological features used to achieve pseudo-accommodation that meets the needs of patients, particularly the new extended depth of focus (EDOF) IOL technology. The article presents the main types of extended depth of focus IOLs, their description, advantages and disadvantages, as well as comparison with multifocal and monofocal IOLs based on clinical studies conducted in different countries.

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

A synthetic material of silicone rubber was used to construct an artificial lens capsule (ALC) in order to replicate the biomechanical behaviour of human lens capsule. The silicone rubber was characterised by monotonic and cyclic mechanical tests to reveal its hyper-elastic behaviour under uniaxial tension and simple shear as well as the rate independence. A hyper-elastic constitutive model was calibrated by the testing data and incorporated into finite element analysis (FEA). An experimental setup to simulate eye focusing (accommodation) of ALC was performed to validate the FEA model by evaluating the shape change and reaction force. The characterisation and modelling approach provided an insight into the intrinsic behaviour of materials, addressing the inflating pressure and effective stretch of ALC under the focusing process. The proposed methodology offers a virtual testing environment mimicking human capsules for the variability of dimension and stiffness, which will facilitate the verification of new ophthalmic prototype such as accommodating intraocular lenses (AIOLs).

An Artificial Lens Capsule with a Lens Radial Stretching System Mimicking Dynamic Eye Focusing

Presbyopia is a common eye disorder among aged people which is attributed to the loss of accommodation of the crystalline lens due to the increasing stiffness. One of the potential techniques to correct presbyopia involves removing the lens substance inside the capsule and replacing it with an artificial lens. The development of such devices, e.g., accommodating intraocular lenses (AIOLs), relies on the understanding of the biomechanical behaviour of the lens capsule and the essential design verification ex vivo. To mimic the eye’s dynamic focusing ability (accommodation), an artificial lens capsule (ALC), from silicone rubber accompanied by a lens radial stretching system (LRSS) was developed. The ALC was manufactured to offer a dimension and deforming behaviour replicating the human lens capsule. The LRSS was calibrated to provide a radial stretch simulating the change of diameter of capsules during accommodating process. The biomechanical function of the ALC was addressed by studying its evolution behaviour and reaction force under multiaxial stretch from the LRSS. The study highlighted the convenience of this application by performing preliminary tests on prototypes of ophthalmic devices (e.g., AIOLs) to restore accommodation.

Aldose reductase inhibition enhances lens regeneration in mice

After cataract surgery, epithelial cells lining the anterior lens capsule can transition to one of two divergent pathways, including fibrosis which leads to posterior capsular opacification (PCO), or lens fiber cell differentiation which leads to regeneration of lens material. We previously showed that the PCO response can be suppressed with aldose reductase (AR) inhibitors. In this present study we show that AR inhibition, both genetic and pharmacologic with Sorbinil, can augment the process of lens regeneration. Extracapsular lens extraction (ECLE) was carried out in C57BL/6 (WT), AR overexpression (AR-Tg), and AR knockout (ARKO) mice, and in some cases in mice treated with the AR inhibitor sorbinil. Whole eyes were harvested approximately 8 weeks after ECLE and evaluated by histological analysis and immunostaining for the fiber cell marker γ-crystallin. All eyes examined for lens regeneration were paraffin embedded for serial sectioning to produce three-dimensional reconstructed models of lens morphology and size. We observed that AR-null mice respond to ECLE by regenerating a lens-like structure with a circular shape and array of cell nuclei reminiscent of the lens bow region typical of the native mammalian lens. Although WT and AR-Tg eyes also produced some regenerated lens material after ECLE, their structures were consistently smaller than ARKO regenerated lenses. WT mice treated with sorbinil showed higher levels of lens regeneration after ECLE compared to WT mice, as assessed by size and three-dimensional morphology. Altogether, this study adds evidence for a critical role for AR in the response of lens epithelial cells to cataract extraction and lens regeneration.

Intraocular lens correction of presbyopia

The continued development of intraocular lens (IOL) technology has led to a dramatic improvement in refractive outcomes. New and innovative ways of achieving the desired postoperative refractive goals continue to be developed. This article aims to review the currently available IOL modalities for correction of presbyopia at the time of cataract surgery, including reference to high-quality comparative studies, where available, and discussion of strengths as well as limitations of the currently available IOL technologies. It has been shown that multifocal compared to monofocal IOL was associated with higher rates of spectacle independence, but higher rates and severity of symptomatic glare as well as reduced contrast sensitivity. Within multifocal IOLs, diffractive compared to refractive IOLs tended to have better near vision and a lower rate of symptomatic glare. Extended depth-of-focus IOLs compared to diffractive multifocal IOL demonstrated equal or superior intermediate visual acuity, with less than or equal rates of glare. Accommodative IOLs represent a broad range of technologies that continue to develop, and new technologies offering opportunities for postoperative adjustment of refractive outcome are emerging.

Premium intraocular lenses: The past, present and future

Purpose

To present potential benefits as well as limitations of premium intraocular lens (IOL) use, and provide insight in future of premium cataract surgery.

Methods

Bibliographic research was performed in PubMed/Medline database, and the most recently updated papers were evaluated. Keywords used were: premium intraocular lens, multifocal intraocular lens, toric intraocular lens, toric multifocal intraocular lens, accommodative intraocular lens, and the respective brand names.

Results

Multifocal IOLs provide uncorrected distance visual acuity (UDVA) of 0.03 logMAR in 82.3%–95.7% of patients and overall spectacle independence in 81%–85% of patients. Toric IOLs provide UDVA of 0.3 logMAR in 70%–95% of patients, residual astigmatism of 1 D or less is noted in 67%–88% of patients, and spectacle independence is reported in 60%–85% of patients. Toric multifocal IOLs provide UDVA of 0.3 logMAR in 92%–97% of patients, and spectacle independence is reported in 79%–90% of patients. Accommodative IOLs represent intensively developing field in ophthalmology, and the results are still variable depending on the IOL model.

Conclusions

Premium IOL technology and advanced surgical techniques have significantly improved postoperative visual outcomes. Future developments will potentiate development of new premium IOL designs that will provide spectacle independence and excellent visual outcomes after cataract surgery.