New intraocular lenses
There is a huge range of IOLs available to the surgeon of today
Fig: A: Segmented bifocal; B: EDOF IOL; C: Small-aperture IOLs; D: FluidVision in-the-bag accommodative IOL; E: Dynacurve sulcus implanted accommodative IOL; F: Scharioth macula lens
In today’s increasingly demanding world, the perfect cataract surgery needs to be complemented by a suitable IOL. Surgeons can choose from an ever-increasing array of monofocal, multifocal and accommodative IOL options to meet their patients’ needs.
Multifocal IOLs have two distinct foci with blurry vision in between. Focusing on one, may cause glare and haloes from the other. The Mplus, Mplus X (Oculentis) and SBL-3 (Lenstec) are rotationally asymmetric segmented bifocal IOLs with sector-shaped near vision segment giving two focus zones for better depth of focus.
AT Lisa (Zeiss), FineVision (PhysIOL), PanOptix (Alcon), Alsafit (Alsanza) and Acriva Reviol (VSY Biotech) are available trifocals and most have toric versions. Trifocals provide better intermediate vision with fewer side-effects by using second-order light diffraction and asymmetric light distribution. These are popular in Europe.
“I prefer the AT Lisa Trifocal and the PanOptix IOL for correcting presbyopia. Both of these gave us good visual acuity for all distances and high patient satisfaction,” notes Thomas Kohnen MD, Professor and Chair, Department of Ophthalmology, Goethe University Frankfurt, Germany.
Extended depth of focus (EDOF) IOLs are the latest variation in multifocal lens solutions. An elongated area of focus extends depth. Peak resolution is only minimally affected, thereby giving reasonably clear vision at all distances with lesser glare and haloes or loss of contrast as compared to multifocals. They are preferable over conventional multifocal IOLs in eyes with maculopathy, irregular corneas or glaucoma.
An AAO Task Force consensus statement requires EDOF IOLs to be within one line of BCVA of monofocal IOLs; to have 0.5D more of defocus than a monofocal at 20/30 level (therefore, approximately 1.25D defocus), and 50% patients to be better than 20/30.
In my experience, EDOF IOLs have generally given good uncorrected distance and intermediate vision: however, near vision from standard multifocals may be better. Therefore, it may be implanted in the dominant eye first followed by a micromonovision strategy with EDOF IOL or a multifocal in the non-dominant eye.
EDOFs like the Tecnis Symfony IOL (AMO) use a biconvex design, anterior aspheric surface, posterior achromatic diffractive surface with an echelette design to give better intermediate vision with less haloes and light scatter.
The AT LARA 829MP (Zeiss) is the latest EDOF lens to appear. It has a diffractive aspheric design, chromatic correction and smoother phase zones that optimise contrast sensitivity and minimise light scattering and visual side-effects. In pre-clinical studies, it has shown higher visual acuity over wider range of focus than the Symfony.
“Concerning monofocal IOLs, I see many IOLs at a very high standard. I still prefer open-loop IOLs and hydrophobic acrylic that are fully transparent (not blue blocking) and that do not have any reports of significant glistenings. In the arena of presbyopic correcting IOLs, I prefer trifocal IOLs for patients that are hoping for spectacle independence. For myopes and less risk-taking patients I prefer classical mini-monovision of 1.25D or EDOF IOLs with micro-monovision of 0.5D,” said Oliver Findl MD, of the Vienna Institute for Research in Ocular Surgery.
Small-aperture IOLs also extend depth of focus. These are especially effective in post LASIK, post RK eyes and in irregular corneal astigmatism.
The IC-8 IOL (AcuFocus) is a single-piece hydrophobic monofocal IOL that works similar to Kamra corneal inlay and uses the pinhole principle to increase depth of focus to about 3D. It has a non-diffractive 3.23mm diameter opaque PVDF mask with 1.36mm central aperture. Results show good distance, intermediate and near vision (especially when targeting -0.75 D myopia) and improvement of up to -1.5D of astigmatism. It is also more forgiving of missing the target refraction.
The XtraFocus Pinhole implant (Morcher) designed by Trinidade et al. is another small-aperture sulcus IOL made of black acrylic with a central pinhole. Fundus imaging is possible and vitreo-retinal surgery can be performed when required through both these IOLs.
Partially accommodating IOLs rely on changes in axial position of the IOL. Single-optic IOLs such as Crystalens (B&L), 1CU IOL (HumanOptics), Tetraflex (Lenstec) as well as dual-optic IOLs such as Synchrony (AMO) give antero-posterior movement said to give some degree of both near and distant vision. Synchrony Vu has a central blended aspheric zone to extend depth of focus.
Accommodative IOLs remain the holy grail of ophthalmic surgery. Several options now available are getting closer to the goal of restoring accommodative vision. Some of these act by various mechanisms, including changing optic shape, curvature or thickness to change focus.
In-the-bag accommodative IOLs are an interesting innovation. The FluidVision (PowerVision) changes accommodative power by increasing and decreasing the quantity of fluid within the optic.
The Sapphire IOL (Elenza) is electronically controlled, remotely programmable, customisable and utilises nanotechnology, artificial intelligence and advanced electronics to auto-adjust focus in response to pupillary changes. Speed and amplitude of pupillary responses are used to differentiate between light and accommodation. The power-cell requires recharging every three-to-four days, has hibernation mode and a fail-safe mechanism that converts it to monofocal status till recharged.
Juvene (LensGen) is a two-lens modular IOL made of a monofocal base lens into which a fluid-optic accommodating component that changes curvature is placed. The WIOL-CF (Medicem) accommodative polyfocal IOL has a 9mm optic made of proprietary hydrogel (WIGEL). The hyperbolic posterior optic gives polyfocality, and ciliary body contraction causes lens deformation, pseudoaccommodation and accommodation. Capsular fibrosis and IOL tilt can lead to loss of effect of in-the-bag accommodative IOLs.
Sulcus-implanted accommodative IOLs are also making an appearance. These are not affected by capsular bag fibrosis. The Dynacurve IOL (NuLens) changes curvature in response to accommodation by using the collapsed bag-zonular complex as a mobile diaphragm, which activates a piston that modifies a flexible membrane to provide spherical or aspherical dynamic surface, thus giving accommodation. The Lumina lens (Akkolens/Oculentis) has two optical elements shifting in a plane perpendicular to the optical axis producing accommodation.
SPECIAL FUNCTION IOLS
Tecnis toric, Symfony toric, Trulign, Lentis toric, enVista, Acrysof IQ and Acrysof IQ ReSTOR multifocal toric are some of the choices available for astigmatism correction.
Adjustable IOLS allow postoperative adjustments. Light Adjustable Lens (LAL – Calhoun Vision) is a silicone IOL containing light-sensitive macromers that are modified post-operatively using a digital light delivery device to attain desired refraction. UV-protective glasses are worn till changes are finally locked in by re-irradiation.
Refractive indexing utilises the femtosecond laser to create patterns in the IOL, thereby correcting myopia, hyperopia, astigmatism and higher-order aberrations. It also gives the ability to create specific focal patterns in the IOL.
Multi-component IOLs allow adjustability by changing the optic component alone while the base component remains fixed, e.g. Precisight (IVO) and Harmoni (ClarVista Medical).
Piggyback IOLs are available for primary or secondary implantation. Piggyback aspheric, multifocals, torics, negative dysphotopsia (ND) and Age related Macular Degeneration (AMD) IOLs are available. Some examples are Clariflex (AMO), Sulcoflex (Rayner) and AQ5010 (Staar).
The Scharioth macula lens for AMD has central 1.5mm diameter with +10D add giving magnification of about 2X. The EyeMax mono, also for AMD, extends usable macula by 10 degrees in all directions. However, progression of AMD can negate the effect. The Masket ND 90S IOL (Morcher) for negative dysphotopsia has a peri-optic groove to capture the rhexis.
All of the preceding options notwithstanding, monofocal IOLs remain the most commonly implanted IOLs. The field of monofocal intraocular lenses also continues to evolve. For example, Alcon recently released the Clareon IOL with higher water content, glistening free material and modified anti-glare edge. It comes with an automated lever-based disposable pre-loaded injector (AutonoMe).
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India, and can be reached at email@example.com.