With more than six million IOLs implanted yearly, there is tremendous research directed at improving visual quality and at decreasing complications
Intraocular lenses (IOLs) have come a long way since Sir Harold Ridley’s first implantation in 1949 after noticing inert acrylic plastic splinters from aircraft canopies in eyes of pilots during World War II. The first IOL, made from polymethylmethacrylate (PMMA), was manufactured by Rayner.
With more than 6 million IOLs implanted yearly, there is tremendous research directed at improving visual quantity and quality and at decreasing complications. As the new decade begins, I’d like to share some trends, some of what I have learnt, the type of IOLs that I prefer and what I would like to see in the future.
One of the most important things that we have learned with time is that it is important to identify what the patient expects from surgery and in what way as well as how much of what he/ she wants, we would be able to deliver. Once cataract extraction has been decided on, one of the things I discuss most importantly is their lifestyle – whether they have a preference for distance-dominated, intermediate or near-dominated work. Other things that matter are their occupation, how much they are willing to wear spectacles, whether they would accept some trade-off in terms of photic phenomena as well as some loss of contrast sensitivity, checking what their expectations are from the surgery and setting right these expectations, the terms of their insurance as well as willingness for co-payment etc.
Other important issues to be looked at are factors such as dry eye, macular pathology, irregular corneal astigmatism, large angle kappa, history of previous refractive surgery etc. as well as to explain to the patient the effect of these on choosing the right IOL and the expected outcomes.
One of the categories of lenses I now like, post its evolution over the years is the pseudoaccommodative IOL. These include multifocal IOLs and EDOF IOLs. Until recently, the term, “Multifocal” referred to bifocals with only two distinct foci, one for near and another for far. Though we earlier sometimes used a modified monovision strategy by combining the expanded range of vision offered by different multifocals, eg., a low add +2.75 or +3.25D in one eye and a high add +4.00D in the other depending on visual needs, disadvantages were still present. Blurry intermediate vision, presence of significant photic phenomena, decreased contrast sensitivity etc. were some of the reasons of dissatisfaction with these bifocal lenses resulting in multifocal explantation becoming a major indication for IOL explantation the world over. Missing the target refraction would compound problems and patient unhappiness further.
However, recent advances have made me enthusiastic about this class of IOLs again. Traditional trifocals such as the AT LISA (ZEISS), FineVision (PhysIOL), Alsafit (Alsanza) and Acriva Reviol (VSY Biotech) have two add powers at 40 and 80cm in addition to distance. The PanOptix (Alcon), which is a quadrifocal IOL, has add powers at 40, 60 and 120cm. Trifocals provide better intermediate vision with fewer side-effects by using second-order light diffraction and asymmetric light distribution. PanOptix™ is manipulated to act as a trifocal by redistributing the intermediate focal point (120 cm) to distance resulting in higher transmission of light (88%) with 3mm pupils unlike other trifocals. This improves contrast sensitivity and quality of distance vision.
Currently, I find that trifocals are a good solution for spectacle independence as they give clear vision over all distances. Defocus curves of both bifocals and trifocals have shown better vision for distance with larger pupils (4.5mm) and for other focal points with smaller pupils (3mm).
Another group of IOLs I like using are the EDOF IOLs such as the Tecnis Symfony (Johnson & Johnson Vision) and the AT LARA 829MP (ZEISS), which provide an elongated area of focus that extends depth. Minimally affected peak resolution allows reasonably clear vision at all distances with lesser glare, haloes and loss of contrast as compared to multifocals. However, as near vision with these IOLs is not as great as with multifocals, I implant it in the dominant eye first followed by a micromonovision strategy with EDOF IOL or a multifocal in the non-dominant eye. I also prefer these IOLs over multifocals in eyes with maculopathy, irregular corneas, glaucoma and in those patients with greater night driving needs. They have been variably reported to have better contrast to no difference in contrast as compared to trifocals. Trifocals, however, do show more pupil independence than bifocals and EDOFs with EDOFs, showing best visual acuity at 2mm pupil size.
While I haven’t used any of the rotationally asymmetric segmented bifocal IOLs (Mplus, Mplus X [Oculentis] and SBL-2 and 3 [Lenstec]), I have been encouraged reading reports about these. The sector-shaped near-vision segment results in two focus zones for better depth of focus while reducing photic phenomena. Other interesting IOLs are the Precizon Presbyopic IOL (Ophtec), with a butterfly-shaped geometry that makes it more tolerant of decentration and limits dependence on angle kappa, and the Mini WELL (SIFI), a progressive aspheric EDOF IOL with two concentric central zones with spherical aberrations of opposite sign and an external monofocal zone.
Two small-aperture IOLs using pin-hole principle – the IC-8™ IOL (AcuFocus) and the XtraFocus Pinhole Implant (Morcher) – extend depth of focus and may also be effective in post-LASIK, post-RK eyes and irregular corneal astigmatism. For irregular corneas, however, I use a technique described by myself – CAIRS (Corneal Allogenic Intrastromal Ring Segments) – to implant allogenic tissue segments (similar to Intacs™) into femtosecond laser-dissected intra-corneal channels before proceeding with cataract surgery.
As ours is a very high-volume practice, we still implant many monofocal IOLs and often employ a monovision strategy. We also frequently implant toric IOLs, advising them for patients with astigmatism more than 1D. Lesser amounts can be managed by making the incision on the steep axis, limbal-relaxing incisions or opposite clear corneal incisions. Multifocal and EDOF torics are good for patients desiring freedom from glasses for all distances. Customised torics can be made to order for very high cylinders. We do pay a lot of importance to the type of astigmatism, amount of posterior corneal astigmatism, accurate biometry, appropriate IOL formulae, reference marking etc.
We also commonly utilise aspheric IOLs, especially in patients with larger pupils, preferring zero spherical aberration IOLs (Akreos AO®, Bausch + Lomb) to improve depth of field and in some patients, to decrease the impact of IOL decentration/ pupil eccentricity. We advise negative spherical aberration IOLs in post-myopic LASIK, those with large mesopic pupils or with night-time driving requirements. The Tecnis® (Johnson & Johnson Vision), with -0.27microns of spherical aberration, compensates corneal positive aberrations completely whereas the AcrySof IQ Aspheric® (Alcon ), with -0.20microns of spherical aberration, compensates partially. Both mono- and multifocal IOLs are available in aspheric design. For post-hyperopic LASIK patients, we prefer traditional spherical IOLs with positive spherical aberration. The TECNIS Eyhance® IOL (Johnson & Johnson Vision) is a new monofocal that I would like to try as it is claimed to give some amount of intermediate vision as well. Of course, most newer IOLs are micro-incision lenses allowing sub-2mm cataract surgery.
WHAT IS THE FUTURE?
With the flurry of technological advancements, surgeons as well as patients would justifiably love to have more and more of better and better. Youthful vision at all distances completely free of glare, haloes and decreased contrast; regained accommodation; refractive outcomes not so crucially dependent on IOL calculation formulae and biometry; the ability to easily adjust and readjust refractive errors at any point postoperatively; predictability, repeatability etc would all be highly desirable. The future does promise to be very exciting with much in the pipeline.
The SmartIOL (Medennium) uses a solid rod of thermodynamic hydrophobic acrylic material that softens at body temperature to transform in about 30 seconds into a biconvex, soft gel-like material, 9.5mm wide and from 2-to-4mm thick that completely fills the capsule and has precise dioptric power and dimensions.
In-the-bag accommodative IOLs are another very exciting prospect with many new technologies: antero-posterior movement giving near and distant vision with single-optic IOLs such as Crystalens (Bausch + Lomb), 1CU IOL (HumanOptics), Tetraflex (Lenstec); changing accommodation by increasing and decreasing fluid within the optic (FluidVision [PowerVision]); modular IOLs with monofocal base lens and fluid-optic accommodating component (Juvene [LensGen]) etc.
I particularly look forward to the futuristic Sapphire IOL (Elenza), which is electronically controlled, remotely programmable, customisable and utilises artificial intelligence to auto-adjust focus in response to pupillary changes.
Accomodative IOLs placed within the bag, however, are susceptible to capsular fibrosis and IOL tilt. To solve this, sulcus-implanted accommodative IOLs that are not affected by capsular bag fibrosis have been developed. IOLs here are the Dynacurve IOL (NuLens), which changes curvature in response to accommodation by using the collapsed bag-zonular complex as a mobile diaphragm, activating a piston that modifies a flexible membrane to provide spherical or aspherical dynamic surface, thus giving accommodation; and the Lumina lens (AkkoLens), which has two optical elements shifting in a plane perpendicular to the optical axis, producing accommodation.
In addition to these IOLs, the other big thing that I look forward to is postoperative refractive adjustment. Though this can be via adjustable IOLs such as the Light Adjustable Lens (LAL – Calhoun Vision), containing light-sensitive macromers that are modified postoperatively using digital light delivery to attain desired refraction, and multicomponent IOLs that allow adjustability through changeable optic component and fixed base component (Precisight [IVO] and Harmoni [ClarVista Medical]).
What I can’t wait to incorporate into my practice is the concept of refractive postoperative adjustment using the Perfect lens (Perfect Lens LLC). This technique (Laser Induced Refractive Index Change – LIRIC) allows postoperative refractive index adjustment of the IOL using femtosecond laser-created patterns in the IOL, thereby correcting myopia, hyperopia, astigmatism and higher-order aberrations. Precision up to 0.01D, ability to change and even reverse multiple times, ability to use on almost any implanted lens from any manufacturer are huge advantages. What could be better?
Two other interesting developments that I look forward to utilising are the ability to preoperatively offer simulation of the type of vision expected with different kinds of IOLs (SimVis [Spanish National Research Council]) and the ability to assess preoperatively the patient’s objective behavioural data, allowing better understanding of specific visual needs (Vivior Monitor [Vivior AG]). I also like the Gemini Refractive Capsule (Omega), an intra-capsular device that holds the capsular bag open and has ridges allowing precise effective lens position, accurate refractive prediction, ability to shift IOL between ridges to achieve refractive changes and ability to place other IOLs, drug delivery systems, sensors etc within it.
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.