Cataract Surgery in 2022: Extending the Range

We can be fairly confident that the first patient who underwent phacoemulsification cataract surgery in 1967, with the ‘father of phaco’ Charles Kelman, did not utter, “Will I definitely be able to read and drive without glasses?” as they were wheeled into the operating room.

In a perfect world… most people would like to jump out of bed in the morning and have the eyes of an emmetropic 22-year-old version of themselves

 

The phaco pioneers operated with rudimentary equipment – ‘dancing on the pedal’ to keep the anterior chamber formed, often using microscopes without coaxial illumination and inserting standard +19D IOLs for everyone, as IOL calculation formulas did not yet exist. On the initial post-operative review, being able to see iris details with a pen torch was seen as a win. Best corrected 6/12 was a good final visual outcome. These days, 6/4 for distance with N4 for near is achievable – without correction.

In the last five decades, cataract surgery has evolved from a procedure to let in more light while avoiding causing serious harm and (hopefully) improving vision with glasses, to a refractive procedure which affords many people better vision than they have ever had. Today’s cataract patients are more likely to be younger, more active, more informed and more demanding of good vision at multiple distances than ever before.^1,2 Patients now expect perfection – so, how can we manage expectations and achieve the ‘perfect’ individualised outcome?

WHAT DO PATIENTS REALLY WANT?

“My neighbour Betsy doesn’t need glasses now at all, please can I have the same”, or “I would like the target pattern lens like Evelyn”, are common openers in our cataract consults. It can sound like ordering from a menu. Of course, these patients may well end up with similar outcomes to Betsy and Evelyn, but the first step in discussing cataract surgery is a gentle reminder that it should be bespoke, not off-the-shelf. We need to create an outcome that suits their own needs, and their own eyes.

In a perfect world, everyone would choose to be glasses-free (notwithstanding occasional fashion wear or eye protection); most people would like to jump out of bed in the morning and have the eyes of an emmetropic 22-year-old version of themselves. We cannot deliver that. But we do have a number of IOLs that can increase the range of vision beyond a single focus. We need to inform the patient of what is available, in a way that is easy for them to understand, and guide them to what is most likely to achieve the best result.

To create a custom outcome, we need information on the visual tasks that are important to them. Let’s put aside ocular pathology for now, and assume the patients have no relative and absolute contraindications for various IOL types. Pre-op questionnaires can help; Alcon and Johnson & Johnson provide versions which the patient can complete prior to the consult³ or while in the waiting room. We have our own modified version (Figure 1) which is shorter and leaves out the personality question, which is arguably of dubious assistance. In our practice we also ask patients to complete the Ocular Surface Disease Index (ODSI) questionnaire⁴ as missed dry eye can haunt you after surgery. The answers, rather than the raw score, can be helpful here as the blurring may be cataract, not dry eye related. Questionnaires clearly do not replace a full history and examination, but they can prompt the patient to start thinking about their own visual needs, and introduce the choices of range of vision and possible compromises. They can help the community optometrist counsel the patient prior to attending the ophthalmologist. The questions we ask our patients are listed in Table 1.

The questions can guide a decision tree for a preliminary consideration of IOL types (Figure 1).

The reason these questions are key is because any IOL choice involves some type of trade-off, and the patient needs to consider what they would be happy to compromise on. It can be useful to show patients the difference between near, intermediate and distance (Figure 2). We also explain with a schematic (Figure 3) how achieving these outcomes uses different IOLs, which are more optically complex and can introduce other visual phenomenon. Any method we use to increase the quantity of vision (range) will reduce the quality or ‘crispness’ of the vision, even if for some patients that reduction is barely perceptible. More complex IOLs can introduce positive dysphotopsias (halo, glare, or starbursts), but these tend to be most noticeable for car headlights at night so, if they do not drive at night, it is less of an issue. In the case of monovision, reduced stereopsis, poor intermediate vision and continued reliance on spectacles for both near and distance are potential issues. No one single method or IOL suits all patients’ needs.

These potential trade-offs need to be balanced with the huge benefits of having an extended range of vision which provides improved quality of life⁵ and a reduced risk of falls.⁶ We must also be careful not to project our preferences (what we would choose for ourselves) onto our patients.

HOW DO IOLS INCREASE RANGE OF VISION?

Broadly speaking, there are non-diffractive and diffractive technologies to extend the range of vision. Most of these IOLs are available in a toric platform and the rule of thumb is to correct astigmatism to <0.5D cyl for good visual outcomes. With the exception of the IC8, irregular astigmatism precludes use of presbyopia correcting IOLs (PCIOLS). Diffractive IOLs are best suited to ‘pristine’ eyes with a healthy ocular surface and no significant pathology. Nondiffractive PCIOLs can be used – cautiously – on patients with early glaucoma or macular changes, as long as the patient has realistic expectations. All of the PCIOLs rely on good centration and so should be avoided if there are zonular issues – for example due to pseudoexfoliation syndrome (PXF) or trauma. PCIOLs tend to be more sensitive to posterior capsular opacification and some surgeons plan early YAG capsulotomy to avoid degradation of image quality.⁷ 

We will refer to the IOLs based on the range of unaided vision they are designed to provide: extended depth of focus IOLs for distance and intermediate vision (e.g. dashboard and computer), and trifocal IOLs for distance, intermediate and near vision.

Diffractive Technologies 

Diffractive IOLs use diffractive rings (concentric annular zones) on the surface to split the light into distinct foci using diffraction and constructive interference. The surface areas of the zones are equal, so they appear closer together towards the edge of the lens. At the junction of each zone, an abrupt step appears. The area of each zone dictates the add power of the lens and the height of the step determines the relative amount of energy that goes into each focus. Trifocal IOLs alternate between high and low steps to create three diffraction orders, the 0th, +1st and +2nd, corresponding to distance, intermediate and near foci (Figure 4).⁸ Older multifocal IOLs corrected near and distance but with a gap for intermediate vision; new trifocal IOLs fill that gap and are sometimes referred to as quadrifocals.

Typically, the light is split into two with ~50% allocated to the distance focus and the remaining light split between the near and intermediate foci. The diffractive rings create foci within a channel of extended depth of focus. Three distinct foci are created within the EDOF channel, but away from these foci, the rays expand outside of the EDOF channel. In trifocal IOLs, approximately 10% of the light focuses outside the EDOF channel, contributing to halos, image quality loss, and visual disturbances (Figure 5).⁹

Diffractive Trifocal IOLs 

In Australia, we are fortunate to have a selection of trifocal IOLs available, including the Alcon Panoptix, Johnson & Johnson Synergy, Zeiss LISA and RayOne Trifocal (Figure 6). While they differ in material and design, these IOLs all have considerable data demonstrating their effectiveness at achieving spectacle independence.¹⁰ The Synergy is closer to a bifocal diffractive in its periphery, combined with EDOF Symfony optics in the centre. Newer trifocals are less reliant on pupil size than older designs. All of them will, by nature of their design, cause some degree of positive dysphotopsia, especially halos. These phenomena often fade with time or are only obvious in certain conditions such as night driving or when the ocular surface dries out. Additionally, as diffractive IOLs split light, there will always be some contrast loss and we need to be mindful of patients who may be at risk for quality-of-vision issues, whether because of comorbidities, such as early macular changes or glaucoma, or work-related issues (e.g. professional drivers).¹¹ Patients may notice they need brighter lights to read with due to the reduced light splitting effect.¹¹ Many patients are happy to accept these symptoms as a compromise to enable true spectacle independence, but they do need to be counselled about these potential issues. Finally, trifocal IOLs are less forgiving of residual refractive error – both sphere and cylinder – than their monofocal counterparts. As well as meticulous planning, the patient should be counselled that, in pursuit of perfect vision, an enhancement (surface treatment such as PRK, or a piggyback IOL) or even IOL exchange may be necessary.

Piggyback Trifocal IOLs 

A ‘reversible’ method for providing multifocality is to introduce two IOLs at the time of surgery – a monofocal in the capsular bag coupled with a trifocal piggyback IOL in the sulcus. The sulcus IOL can be removed or exchanged much more easily than an IOL in the capsular bag if required, due to residual refractive error or intolerance to a multifocal optic.12 Trifocal piggyback IOLs include the 1stQ Add-on trifocal and the Rayner Sulcoflex trifocal. These can also be used for patients who have had previous surgery with monofocal IOLs and are keen to pursue further spectacle independence.

Diffractive EDOF IOLs 

The AT Lara 829MP (Carl Zeiss Meditec) and the Tecnis Symfony (Johnson & Johnson) are two commonly implanted IOLs in Australia. The Lara 829 features two additional focus planes at farintermediate and intermediate distances to provide continuous visual acuity over a range of distances from far to intermediatenear. The Tecnis Symfony has a biconvex, wavefront-designed anterior aspheric surface, and a posterior achromatic diffractive surface with echelettes, to extend depth of focus.¹³ Both IOLs perform similarly in increasing functional intermediate vision.¹⁴

The EDOF IOLs that use diffractive rings often seem to be perceived as trifocal-lite – that is, they have a bigger landing zone in terms of refractive error, and fewer dysphotopsias. This is not entirely true – due to the diffractive design, halo and glare are still an issue.¹⁵ Also, they are less likely to achieve near vision.¹⁵ Generally, if a patient is happy to tolerate haloes then they may be happier with trifocals or a trifocal/ non-diffractive EDOF combination (with the trifocal in the non-dominant eye) both of which would provide more near vision; if not then a non-diffractive EDOF may be more suitable.

Non-diffractive EDOF and Multifocal IOLs 

With patients who are more concerned about the possibility of dysphotopsias, avoiding diffractive IOLs is sensible. Although any IOL (including monofocal IOLs) can cause some degree of dysphotopsia, particularly if there is residual refractive error, non-diffractive EDOF IOLs are less likely to cause glare and halos. Often these IOLs can be a better choice than trifocals if there is ocular pathology.

Currently, there are a few different ways to extend the range of vision – playing with spherical aberration, a wavefront stretching IOL design, employing the pinhole effect and refractive IOL segments. For maximum range, a degree of micro (+0.5D) to mini (+0.75-1.25D) monovision is employed, so it’s important that the patient knows the distance and near vision may be slightly different between the eyes. It’s about the binocular result.

Using Spherical Aberration to Increase Depth of Focus 

Spherical aberration (SA) describes how much light is bent as it passes through a refracting surface, such as the cornea, and compares the relative position of the focal points for the peripheral and central light beams. Positive SA occurs when the peripheral rays are focused in front of the central rays (Figure 7). Leaving SA (positive or negative) in the optical system improves depth of focus but will reduce contrast sensitivity.

The average cornea has +0.27 SD +/- 0.1 positive SA.¹⁶ This can be measured, for instance, by using iTRACE (Tracey Technologies, Corp.). Eyes that have undergone corneal refractive surgery vary widely in corneal spherical aberrations, as do eyes with corneal pathologies.

Spherical Aberration IOL Designs 

Different monofocal IOL designs have differing degrees of SA correction – the Tecnis platform (-0.27) corrects all of the average 0.27um, resulting in a very sharply focussed image but with reduced depth of focus and a smaller landing zone of refractive outcome. Alcon Acrysof IOLs correct some, but not all (-0.19) (i.e. average residual of 8um), and the Bausch & Lomb IOLs are SA neutral – neither adding nor subtracting, potentially allowing more depth of focus. CT Asphina (Carl Zeiss Meditec) has both neutral and SA correcting versions. Other than in unusual or post refractive eyes, corneal SA is not frequently an important part of the decision tree in the selection of monofocal IOLs.

The recently released Rayner EMV, developed by Professor Graham Barrett with Rayner, is an extended range of vision IOL that takes it a step further by purposefully increasing SA to achieve more depth of focus. The EMV design, with an aspheric anterior surface and a two-zone design, reduces pupil size dependence and aberrations in mesopic conditions. The inner optic zone increases SA, the outer reduces SA. It provides the equivalent of +1.25 add; or +2.25 add when used as mini-monovision with the non-dominant eye targeting -1.¹⁷

The toric version has not yet been released in Australia, restricting its current use to those with no or low astigmatism (< 0.5D). The Tecnis Eyhance uses negative SA in a non-zonal design to achieve a small but measurable improvement in intermediate vision, with very little drop-off in distance vision and no increase in dysphotopsias when compared to standard monofocal control IOLs.¹⁸ It is referred to as a ‘monofocal plus’, as with +0.4D add it does not meet Food and Drug Administration (FDA) criteria for EDOF IOLs,¹⁹ although it has been reported by some to provide intermediate vision comparable to diffractive EDOFs.^20,21

Other Non-diffractive Tricks of Light to Increase Range of Vision 

Stretching the Wavefront 

The AcrySof IQ Vivity extended vision IOL (Alcon) X-Wave technology delivers extended range of vision while maintaining a monofocal-like visual disturbance profile. Alcon reports the wavefront shaping anterior surface of the IOL ‘stretches and shifts light without splitting it’.²² The Vivity has two features that affect the wavefront differently: elevation and a curvature change. The elevation slows down the central wavefront, while peripheral light rays continue to enter the eye and proceed to the retina at the same speed, effectively stretching out the wavefront. Distance visual acuity exceeded the comparative monofocal in the US trials; at six months, 98%, 97% and 58% of Vivity patients reached 20/32 or better for binocular distance, intermediate and near (near point 40cm), respectively with plano as the target.²³ Adopting minimonovision with -0.5 in the non-dominant eye can increase the functional near;²⁴ one study reported 87% spectacle independence and a low (6.7%) incidence of haloes.²⁵ We have found a combination of Vivity in the dominant eye and Panoptix in the non-dominant to be a powerful method to achieve full spectacle independence with minimal dysphotopsia while maintaining excellent distance vision.²⁶ 

Small Aperture IOLs 

The IC8 IOL is a pinhole IOL with an opaque 3.2mm annular mask, which blocks scattered, defocused and aberrated peripheral light, but allows the passage of paraxial, central light rays through the 1.36mm aperture. This enables it to provide up to 3.00D of extended depth of focus with functional near vision of 6/12.²⁷ The design can tolerate up to 1.00D deviation from the target manifest refraction spherical equivalent and accommodate as much as 1.50D of corneal astigmatism, including an irregular cornea, but not with central corneal scarring that overlaps the centre aperture. Eyes with mesopic pupil sizes (>6mm) risk dysphotopsias, especially glare. Small aperture IOLs increase the depth of focus of the eye, but they do reduce the amount of light entering the eye, and consequently are typically only implanted monocularly.

Refractive EDOF and Multifocal IOLs: Segmented Design 

Refractive multifocal designs use multiple segments for near and distance instead of diffractive rings. There are a number of different designs. Most are rotationally symmetric (i.e. can work regardless of orientation) and generate multiple focal points by providing annular zones of differing refractive power. The Teleon family of IOLs28 are used by many surgeons in Australia; these are rotationally asymmetric where the upper segment is for distance vision and the inferior sector-shaped segment for near or intermediate vision. The Lentis are plate haptic hydrophilic IOLs with an add of 1.5, 2 or 3D whereas the Teleon Acunex are hydrophobic c-loop IOLs with an add of +1.5 or 3D. The Femtis is a similar refractive design but requires fixation to the anterior capsule and hence a perfect (laser assisted) capsulorhexis. Also in this family are piggyback refractive IOLs with a double c-loop design in +1.5D or +3D – providing the get-out clause of reversibility if the patient should not tolerate the optics.

The idea is that by avoiding the diffractive rings, refractive EDOF and multifocal IOLs can reduce dysphotopsias while providing an extended range of vision.²⁸ They are not entirely free of dysphotopsias; ghosting can be an issue so are generally best used in the non-dominant eye. In comparative studies, refractive and diffractive PCIOLs have achieved similar degrees of spectacle independence,^29,30 however, for complete spectacle independence trifocal diffractive IOLs are the go-to for most Australian surgeons.

CONCLUSION

When it comes to IOL availability for our patients, Australia is a lucky country with many designs from several manufacturers across a wide range of powers and toricity correction. Given the array of options available to extend the range of vision, even for those with co-morbidities, arguably now the bilateral monofocal IOL option should be the exception rather than the rule. If patients come in and ask for “the best” IOL, the truth is all modern IOLs are excellent, and the key is finding the best fit for the individual.

Dr Madeleine Adams MB ChB BSc Hons PhD FRANZCO is an ophthalmologist specialising in cataract and lens surgery, providing custom vision corrections to best suit patients’ eyes and lifestyles. 

Dr Adams trained in Queensland and undertook fellowships in Australia and overseas. She was awarded a PhD by the University of Melbourne for her research into age related macular degeneration. Dr Adams has published widely and has presented at numerous national and international conferences. She is the founding director of Insight Eye Surgery with practices in Brisbane and Noosa, Queensland. 

To earn your CPD hours from this article visit mieducation.com/cataract-surgery-in-2022- extending-the-range. 

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