State-of-the-art lens implants in cataract surgery – advantages, disadvantages, prospects

Author: Dr. Victor Derhartunian 4 January 2022

Clients of private eye clinics have a choice of state-of-the-art implants (artificial lenses). Premium lenses meet the needs of increasingly demanding patients, guaranteeing excellent quality of life and visual acuity after cataract surgery – also without the need for additional glasses. Premium implants additionally allow:

  • correction of astigmatism (toric lenses)
  • correction of presbyopia (multifocal, or multifocal lenses)
  • improvement of contrast vision (aspheric lenses)
  • prevention of age-related macular degeneration – AMD (lenses with UV filter and blue light filter)

The introduction of precise methods of calculating the power of the implantable artificial lens and new solutions in lens design have meant that today the results of toric and multifocal implants are as good as they have ever been in the history of cataract surgery, although specialists do not stop looking for new and improving existing solutions.

Let’s take a look at the most advanced implants used in cataract surgery. Like all solutions used in the ophthalmic industry, they have their advantages and disadvantages.

Toric lenses

Toric, or cylindrical, lenses are used to correct astigmatism – both in patients qualified for refractive lens replacement and in patients undergoing surgery for cataracts.

We have written more about how bothersome and how difficult astigmatism can be to treat here https://swisslaser.pl/blog/astygmatyzm/. Now we will try to answer the question of why toric lens implantation is so beneficial for the patient.

People who struggle with astigmatism often have problems with the selection of glasses and contact lenses. If astigmatism values are greater than 0.5 cylindrical diopters (according to another concept, greater than 1 diopter) they can significantly impair visual acuity. It is estimated that about 35% of patients then require correction with toric lenses – whether in glasses, contact lenses or artificial implantable lenses. However, it is important to be aware that people who have never used cylindrical correction because of difficulties in selecting lenses or poor tolerance of them may also have problems getting used to toric intraocular lenses.

On the other hand, those astigmatics whose eyes are used to cylinders should know that toric artificial lenses are used to correct regular astigmatism from 0.5 diopters to 20.0 diopters, and patients do not need time to get used to them: the effect of improving visual acuity is immediate and permanent. Toric lenses are especially recommended for patients who have been diagnosed as having varicose vision with high astigmatism in one eye, and what comes with it – the difficulty of choosing the right spectacle correction. Astigmatics operated on due to cataracts also achieve excellent visual acuity, better than at any time in the past before cataracts.

Implant toric correction can be applied to both monofocal and multifocal lenses.

Multifocal (multifocal) lenses

Implantation of a monofocal lens always results in the eye losing its ability to accommodate, which for people undergoing cataract surgery entails the need to wear nearsighted or nearsighted glasses – the choice is up to the patient.

The implantation of a multifocal lens frees the patient from the need for glasses. The possibility of obtaining a pseudoaccommodation effect with multifocal lenses did not appear until the ’80s. At that time, new technologies were applied in lens design, using the phenomena of refraction (refraction) of light known in optical physics, then – diffraction (dispersion) of light, rerfractive-diffractive (pseudoaccommodation), and finally a lens with a design that allows changing its position in the eyeball, that is, an accommodative lens. The latter type of lens, which mimics the natural lens, is not always as effective as we would like it to be. Anyway, the other two types of multifocal lenses also have their disadvantages. Which ones?

Refractive lenses

They take advantage of the phenomenon of refraction, which involves the refraction of light after it passes through an optical medium. Significant disadvantages of refractive lenses include:

  • An increase in higher-order aberrations and undesirable photo-optical phenomena of the glare and halo type, which are particularly aggravated under scotopic conditions (i.e. at night)
  • Visual acuity and contrast sensitivity in zonular lenses dependent on pupil width (this can cause difficulties when driving at night, among other things)

Diffraction lenses

They use the phenomenon of light diffraction, which involves the deflection of light rays passing through slits with a diameter comparable to the wavelength of the light wave. After the rays pass through the diffraction grating, they are deflected and then interfered with, creating an additional wavefront and thus a new image. As a result, two images are formed on the retina at the same time – for distance and near – and our eye, “in consultation” with the brain, makes a choice: betting on one sharp image and suppressing the other waves. Significant disadvantages of diffractive lenses include:

  • relatively long time needed for neuroadaptation (up to 3 months)
  • slight loss of contrast sensitivity due to beam splitting and dissipation of some of the energy

Pseudoaccommodative (refractive-diffractive) lenses

This model combines the advantages of diffractive and refractive lenses. They are built with a central diffraction zone for near and far vision, and a peripheral refractive zone with breaking power for distance. The stepped change in thickness (apodization) in the central part of the lens involves a gradual change in the properties of the diffraction zones to create a smooth transition of the diffraction zone into the refractive zone. It is apodization that makes it possible to reduce unwanted optical phenomena and improve visual comfort regardless of lighting conditions and pupil width. The latest refractive-diffractive lens designs feature an optional smaller near add to improve visual acuity to intermediate distances. The ability to additionally change the toricity of the posterior surface of the peudoacomodal lens is an additional opportunity to correct concurrent corneal astigmatism.

Accommodative lenses

In the case of an accommodative lens, the image is formed by refraction of light on the lens that changes its position in the eye or shape during the work of the ciliary muscle or with the use of electricity.

Accommodative lenses raise high hopes, but their major drawback is not only their limitation of use in the elderly – without any residual accommodative ability of the ciliary muscle – but also in patients with a theoretically efficient accommodative mechanism. After implantation, a large proportion require little additional correction for nearsightedness, especially when performing precision activities.

Accommodative lenses are a true marvel of technology. Let’s take a look at how the models developed so far work:

  • The Tetraflex (Lenstec) uses changes in the tension of the ciliary muscle (it performs a certain range of motion, but this does not allow it to provide full close-up acuity).
  • Crystalens™ (Baush&Lomb) works on the same principle as Tetraflex, plus it has been equipped with a refractive section for greater efficiency in achieving good nearsightedness.
  • Synchrony has two optical parts are connected by a spring mechanism: when the ciliary body is contracted, the optical parts remain close together, and in this position the lens is adapted to see distant objects. When the ciliary body contracts, the front optical part moves forward, changing the focus first to intermediate distances and then to near.
  • FluidVision is still in the clinical trial phase. Fluid is accumulated in the peripheral haptic portion, which is moved to the central portion during accommodative effort, changing the curvature of the front optic and adapting the optical power to see objects close by.
  • DynaCurve (NuLens Ltd., Herzliya Pituah, Israel) is a lens implanted between the iris and the lens capsule. The force of the ciliary body moves a plunger at the back of the lens, which pushes the gel through the center hole, changing the optical properties of the lens.
  • The Sapphire AutoFocal IOL (Elenza) incorporates an electro-active element in the optical part that provides automatic change of focal power. The change in focal power is designed to occur in milliseconds to provide the sensation of maintaining consistent visual acuity regardless of working distance or lighting conditions. The lens is powered by a microbattery with a lifetime of more than 50 years of cyclic charging.

Aspheric lenses

Aspheric lenses help reduce spherical aberrations experienced by the patient as a halo effect around light sources or blurring of the image. These phenomena are exacerbated by conditions of poor lighting, when the pupil dilates naturally. The level of spherical aberrations in lenses varies. In the AcrySof IQ lens, it is at -0.2 microns, which is similar to that of a natural human lens.

Lenses with UV filter and blue light filter

All the types of lenses described above can have UV and/or blue light filters. These filters eliminate the harmful part of the light beam and have a protective effect on the retinal pigment epithelium, reducing the risk of developing age-related macular degeneration. Studies show that the use of lenses with filters reduces the risk of uveal melanoma.

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Author:

Dr. Victor Derhartunian

Dr Victor Derhartunian od 2012 roku z sukcesem prowadzi własną klinikę EyeLaser we Wiedniu (Austria), zaś od 2016 roku – Centrum Chirurgii Laserowej w Zurychu (Szwajcaria). Obie te placówki należą do wysoko ocenianych przez Pacjentów klinik w tej części Europy, a wszystko to dzięki umiejętnemu wykorzystaniu innowacyjnych technologii i zastosowaniu absolutnie wysokich standardów w pracy z Pacjentami.