Presbyopia / SPO - 3.2.2.1. The evolution of options

3.2.2.1. The evolution of options

Wilson Takashi Hida e Andre Lins de Medeiros

Hospital Oftalmologico de Brasilia, Brazil

Centro de Investigação Renato Ambrósio, Brazil

IMPORTANCE

It is estimated that functional presbyopia affects more than one billion people over the age of 35, including about 700 million people aged 50 years or more1,2. Thus, it is a matter of extreme importance for the refractive surgeon and more recently, with the development of calculation of intraocular lenses (IOL) and the development of their design, the cataract surgeon is more precise upon achieving emmetropia and therefore it is possible to safely perform a clear lens extraction with good results3-9. There is a growing demand for postoperative emmetropia and the independence of spectacles, as the world's population is growing older and aging healthier than in the last decades10-12. In addition, a total of about 244 million cases of uncorrected or under-corrected presbyopia among persons under 50 years of age were associated with a potential loss of productivity of $11,023 billion, and assuming that people with age <65 years are productive, this figure can be estimated at $25,367 billion. Thus, in relation to the productive population, the correction would have a significant impact on productivity2.

THERAPEUTIC OPTIONS

There are several techniques to surgically correct presbyopia: application of inlays into the cornea; in-situ laser keratomileusis (LASIK) to achieve monovision or presbyopia (presbyLASIK) and the application of cataract surgery, with monofocal lenses to achieve monovision, multifocal (diffractive and refractive) intraocular lenses and extended depth of focus (EDOF)7,13. Consequently, emmetropia is the target for all patients. However, the independence of glasses is the main objective of refractive surgery. This necessarily involves a satisfactory visual acuity (VA) without correction for distance (UDVA), near (UNVA) and, more recently, with trifocal IOLs and EDOF, for intermediate distances (UIVA)3,14-18.

Multifocal IOLs offer the convenience of correcting presbyopia after cataract surgery. However, despite optimal evolution and better technology in the manufacture of lenses, there are some unwanted side effects, including reduced contrast sensitivity (CS), halos and glare, and unsatisfactory UDVA, UIVA and UNVA19,20.

Multifocal IOLs also have been successfully applied to treat presbyopia in patients undergoing penetrating keratoplasty (PK), radial keratotomy (RK), LASIK and photorefractive keratotomy (PRK)19,21-23.

THE EVOLUTION OF MULTIFOCAL LENSES

Multifocal IOLs were introduced in the 1980s and have the advantage of simultaneously promoting satisfactory near and far vision24,25. Most of the multifocal IOLs implanted with the intention of correcting presbyopia were bifocal, since during more than a decade they were the only choice for near vision correction in patients undergoing cataract surgery, although low scores for intermediate vision were reported15,26. The first IOL ReSTOR design (Alcon Laboratories, Inc.) was well described by Davison; this is a diffractive apodised bifocal intraocular lens which is a paraphrase of the Fresnel lens, which originated in the 1820s with the improvement of the headlamp optics26. The diffractive intraocular lenses can be produced under the model of their surface in a serrated pattern, which is called kinoform. When it crosses this IOL, the wavefront undergoes a diffractive action and a fraction of this will deviate6,24. The magnitude of the deviation can be modulated by the design bythe kinoform: the width determines the near/intermediate power and the height and the amount of divided light is determined by the distance between steps6,26.

In addition, an artifact required for the refractive-diffractive optical system is to direct a portion of the light to higher-order diffractions, which is lost when the foci are too close, for example, in ReSTOR SN6AD1, which has an addition of +3.00 diopters (D), the 0 order deviation is for far, the first order deviation is +3.00 D, the second order deviation is the +6.00 D and so on. Thus, after the second-order deviation, the light is not used since these foci are located very close together26.

ReSTOR IOLs (SV25T0 and SN6AD1) are single-piece, collapsible bifocal IOLs that have a power addition for near of +2.5 D and +3.0 D in the IOL plane, and are entirely made of hydrophobic acrylic, which theoretically makes these lenses more resistant to late opacification, which reduces the risk of loss of overall optical quality with the years, especially in patients who may require endothelial corneal transplants or posterior vitrectomy27-30. There are two different types of diffractive bifocal intraocular lenses with an apodised design on the anterior surface, providing a satisfactory near and far visual acuity of 50 cm and 40 cm, respectively15,18,31,32. Apodization means that the IOL profile gradually decreases from the center to the periphery, resulting in a continuous change in the light energy distribution, which is directed to the 2 main foci. For example, when the pupil is in mydriasis, in mesopic/scotopic conditions, the peripheral steps are progressively exposed, with more light directed to the far vision and less to the near vision. Apodization is expected to reduce the halos that are generated by the light defocused by the high-order diffractive deviation under low light conditions. It has been shown that SV25T0 can induce less dysphotopic phenomena than SN6AD1. We have reported the association of the characteristics of both lenses with an SV25T0 implant in the dominant eye and the SN6AD1 in the contralateral eye, with satisfactory results and an increase in the range of vision for near. These lenses add a negative spherical aberration on the anterior surface to compensate for positive spherical aberration of the human cornea18,32,33.

Tecnis multifocal IOLs (Johnson & Johnson Vision, Inc.) are also single-piece, bifocal, hydrophobic acrylic IOLs, which have a posterior diffractive surface and an anterior aspheric surface which adds -0.27 μm of spherical aberration to the human eye, with additions of +4.0 D (ZMB00), +3.25 D (ZLB00) and +2.75 D (ZKB00). The advantage of these IOLs is that it is possible to customize near vision of the patients, by attaching different lenses or by adding to these other diffractive technologies, such as EDOF IOLs, such as Tecnis Symfony ZXR00. We also have a scientific article that showed the good results of this approach14.

Figure 1

The evolution of the design of diffractive bifocal lenses is the trifocal design for implantation in both eyes. This approach is considered better than the simultaneous implantation of two different bifocal IOLs, since it can solve the three-dimensional vision question for all distances^18,33. The first diffractive trifocal IOL described was the PhysIOL FineVision (PhysIOL Laboratories, Inc.), which is a hydrophilic acrylic IOL with a diffractive kinoform profile apodised on the periphery of the lens. This generates an asphericity of -0.11 μm for the human eye. The first kinoform pattern is drawn with a +3.50 D addition as first-order diffraction, and, as explained earlier, second-order diffraction occurs at a verge of 7.0 D for this addition and will be lost since this is not a very used near vision. However, the second kinoform pattern has a vertex of +1.75 D, so the second order has a vertex of 2x1.75, corresponding to +3.50 D. This second kinoform therefore contributes to the intermediate vision and improves the near vision^15,34. Another diffractive IOL that we have implanted in our patients with good results is the AT Lisa tri 839 MP (Zeiss Laboratories, Inc.), with which we were pleased to participate in a clinical trial (data not yet published). It is a diffractive IOL of hydrophilic acrylate with a hydrophobic surface^32,35,36. It has a power at about +1.66 D in the plane of the IOL in its trifocal inner area of 4.34 mm and an addition of +3.33 D in its exterior bifocal area; it is not apodised, so in theory it should be mostly independent of the pupil^32,35-37.

PanOptix IOL (Alcon Laboratories, Inc.) has a unique quadrifocal design; however, in terms of function, it acts as a trifocal IOL. It is a single-piece hydrophobic acrylic lens with a kinoform diffractive profile. It has three heights of steps, creating one of +2.17 D for the intermediate vision, one of +3.25 for the near vision, and another big step in terms of width that generates +1.085 D, which is the 2-step join of + 2.17 D with a +3.25 D in the middle, setting this third step. The light diffracted by this step is used to provide the far vision since this focus is approximately in the vertex of 120 cm^{14,16,18,34,38}. This technology is named by the manufacturer (Alcon Laboratories, Inc.) as Optical Technology Brightening and has had great acceptance and satisfaction by the patients, since the intermediate vision is very comfortable for them^16,34. We also had the pleasure of participating in the clinical trial of PanOptix FDA with satisfactory results in relation to optical performance and satisfaction of patients with this IOL (data not yet published). The diffractive zone is also located centrally and occupies 4.5 mm of the optical zone. Adds a negative spherical aberration of -0.17 μm on the anterior surface of the lens to compensate for the positive spherical aberration generated by the average human cornea⁴.

EDOF IOLs

EDOF IOLs are a new variety of IOLs that use different technology. Currently, there are two commercially available technologies, the diffractive EDOF and the small opening EDOF. These IOLs were created to overcome the deficiency verified by the implantation of diffractive bifocal and trifocal IOLs, providing patients with continuity of vision with a good range, reducing contrast less and inducing fewer visual disturbances^14,39-43. IC-8 (Acufocus, Inc.) is a small-aperture IOL for implantation in the sac, which corrects presbyopia by widening the range of vision in the non-dominant eye. It has a built-in mask and a small opening of 1.36 mm in size. It is a hydrophobic acrylic single-piece posterior chamber IOL, which is based on Kamra inlay (Acufocus, Inc.). This IOL is suitable for monocular implantation in patients undergoing monocular cataract surgery and is willing to achieve independence of spectacles, since acceptance of a multifocal IOL may be difficult due to the image differences generated by these IOLs. Implantation of this IOL would improve UIVA and UNVA preserving UDVA^7,44-49.

The Xtrafocus pinhole (Morcher GmbH, Inc.) IOL is another EDOF designed by Claudio Trindade. It has a thin rounded haptic configuration (250 μm), instead of the square configuration of the IOLs used for implant in the bag, which adjusts it to the implantation groove. Instead of having a mask like Kamra inlay or IC-8, this IOL is all black with a small opening in the center. This small aperture is designed to achieve the maximum effect of Stiles-Crawford, since light rays reach the retina in a parallel pattern, which generates a more powerful visual response per unit of light energy, therefore, despite the reduction of light in mesopic conditions, energy luminance is better utilized, so these patients become more tolerant to low light environments^50,51. The most commonly used EDOF IOL is Tecnis Symfony (J & J Vision, Inc.), which is also a single-piece of foldable hydrophobic acrylate with a new design that promotes a wider range of focus. It also has a diffractive posterior surface (kinoform) and an aspheric anterior surface adding -0.27 μm to corneal aberration. The EDOF concept generated by this IOL can be explained by the division of light energy into an elongated focus, which could reduce the overlap of near and far images caused by traditional multifocal diffractive IOLs, generating fewer visual disturbances. This IOL also uses a patented achromatic diffractive échelette (reticulate of diffraction) design to correct chromatic aberration and improve CS^{3,5,8,14,38,52-57}.

IMPORTANCE OF ASTIGMATISM

Approximately 40% of all candidates for cataract surgery have a corneal astigmatism greater than 1 D, so it is possible that the greatest gain after the successful correction of astigmatism with IOLs is the incorporation of the technology with multifocal diffractive IOLs, that is, a merger between multifocality and toricity. Prior to the introduction of multifocal toric IOLs, the options for astigmatic correction were limbal relaxing incisions, corneal refractive procedures and the location and size of the corneal incisions, all less predictable than toric IOLs, and also generating dry eye more, foreign body sensation and low stability and predictable refractive result. Residual ametropias are the primary cause of patient dissatisfaction after multifocal lens implantation as complaints about VA reduction, halos, glare, and other visual disturbances increase. The comparison of three pseudophakic groups: monofocal, and multifocal +3.00 and +4.00, showed that high astigmatism can compromise VA at all distances, with a much smoother effect when compared to monofocals^58-60.

It is important to highlight the importance of posterior corneal curvature in the total power of corneal astigmatism. In the vast majority of patients, the posterior curvature functions as a negative lens, its axis having a larger slope in the vertical orientation, which does not change with age. On the other hand, the changes of the anterior curvature with or against the rule change over the years. Thus, if we do not consider the influence of posterior curvature in the calculation of IOL, we could expect hypercorrections for astigmatism in favor of the rule and hypo-corrections for astigmatism against the rule. There are new technologies to detect posterior astigmatism, such as the spectral-domain OCT, LED triangulation and Scheimpflug, which are currently being studied^61-65. Other important factors to be highlighted are surgically induced astigmatism and a centered capsulorrhexis, which completely covers the IOL optic zone. Currently trifocal IOLs are widely deployed since they can solve the problem of UIVA by reducing patient complaints. The femtosecond laser and the zepto brought the technology for the manipulation of capsulorrhexis, with an ideal size and centering. However, meta-analysis is inconclusive with regard to the real benefits of these technologies^66-68.

We have used the intraoperative aberrometry to confirm the biometric calculation and the perfect alignment of the IOL, with good results. Optiwave Refractive Analysis – ORA (Alcon Laboratories, Inc.) – makes captures with high reliability, rapidity and real time, providing the patient with excellent post-LASIK-like results in young patients^69-72.

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