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Intraocular Lenses: A Practical Review for Optometrists

2 CPD in Australia | 1G in New Zealand | 2 April 2018

Dr. Jay Yohendran

There are so many intraocular lenses available today for your patients undergoing cataract surgery. Understanding the unique properties of each of these lenses will help you guide your patients in deciding which intraocular lens would be most suitable for them to optimise their vision.

LEARNING OBJECTIVES

1. Appreciate the history and evolution of intraocular lenses
2. Understand the different IOL materials available, their advantages and disadvantages
3. Understand categorisation of IOLs, when each is indicated and the way they are fixated
4. Understand the properties of spherical, aspheric and presbyopiacorrecting IOLs, how to detect the type of IOL implanted in your patient’s eye and patient management for optimum vision.

 

HYPOTHETICAL SCENARIO

Mr. Jones, a 60 year old architect, is increasingly becoming frustrated with his vision. He has been a patient of yours for many years. He has previously been hyperopic, until LASIK surgery in his early 40s. He is becoming increasingly frustrated by his need for glasses. He is now mildly hyperopic again, and is of course, presbyopic. A colleague of his recently had cataract surgery, and this has prompted Mr. Jones to look into cataract surgery with interest. He has been busy researching online, and has come to ask your opinion. He would like to know your thoughts on the Tecnis Symfony IOL. Mr. Jones’ cataract is minimal, and his BCVA is R 6/6 and L 6/5. He would like to be glasses free, but his colleague had trifocal IOLs implanted, and is struggling with glare and night driving. This has steered Mr. Jones away from trifocal IOLs.
What advice would you give him?

Looking after patients with cataract is likely to be a common part of your day to-day clinical practice. However, cataract surgery is an ever-evolving procedure, with constant advancements in intraocular lens technology. Patients are becoming more knowledgeable, and demanding, especially in regards to spectacle independence. Today, there are multiple classes of intraocular lenses, and many options within each class. The following review of intraocular lenses will help bring you up to date with what options are available to your patients.

HISTORY

Casamata performed cataract operations and also implanted a glass IOL in 1795. However, the IOL dropped in the eye due to its weight, and no further IOL implants were reported until 150 years later. The true beginning of the IOL is the Second World War. Against a backdrop of the Battle of Britain, where aircraft fought for air supremacy in the skies over the south of England, Harold Ridley was a civilian ophthalmologist who operated on Royal Air Force pilots with eye injuries. It was not unusual for him to see a pilot with a fragment of a shattered cockpit inside the pilot’s eye. He realised that the immune system did not react against the plastic splinters. The material was polymethyl methacrylate (PMMA). On 29 November 1949, at St Thomas’ Hospital, London, Ridley inserted the first lens into a 42 year old woman after an extracapsular cataract excision. While history views this as a pivotal moment in the development of the field, many in the ophthalmic establishment at the time strongly disapproved of Ridley’s work. Since that time, IOL design has undergone many modifications, as researchers have developed, used, and discarded IOL designs in a continuing evolution towards a better IOL. In the 1970s, IOL implantation after cataract surgery became considered as a standard procedure.1

IOL MATERIAL

The transition from large incision extracapsular cataract surgery to small incision phacoemulsification,  propelled the development of foldable IOLs. With phacoemulsification, cataract surgery is performed through a corneal wound smaller than the diameter of the IOL.

Hence, without a foldable IOL, the small corneal wound would need to be enlarged after phacoemulsification was completed, and prior to IOL insertion. This would be a backward step in the evolution of modern cataract surgery. Silicone was the first foldable IOL material used, followed by hydrophobic acrylic and hydrophilic acrylic.

Silicone

Silicone was the first material available for foldable IOLs. Currently, silicone IOLs are not in regular use. While silicone is a very good IOL material, it cannot be used with a single-piece open loop haptic design, which is amenable to insertion through incisions smaller than 2.8mm, which is the current trend.

A problem associated exclusively with silicone IOLs is that silicone oil, used in vitreoretinal surgery, can coat the silicone IOL. Silicone oil droplets adherent to the surface of the IOL can result in the IOL needing to be explanted. Therefore, use of a silicone IOL is contraindicated in patients that have had, or are at high risk
of needing, a vitrectomy.

Silicone IOLs have also been uniquely associated with calcification in eyes with asteroid hyalosis, so this is another relative contraindication for these IOLs.2

Foldable Hydrophobic Acrylic

This is currently the most commonly used material group, due to a number of positive properties of the IOLs. Firstly, they are amenable to the generally preferred single piece open loop haptic design (Figure 4a), as the materials have very low water content, a high refractive index, and usually a high memory. This group of material unfolds in a controlled fashion, and most surgeons find the implantation process safe and reliable.

One of the drawbacks of this material group has been intralenticular changes. Small water inclusions in the optic material called glistenings can occur in hydrophobic materials (Figure 1). Over time, the glistenings can increase, but they probably do not significantly affect visual function. Either way, I avoid IOLs that are
prone to glistenings.



Figure 1: Glistenings in a hydrophobic acrylic MFIOL.

Another drawback has been dysphotopsias reported with this high refractive index material. The most common positive dysphotopsia was edge glare, which was due to internal reflections at the rectangular edge of the IOL under mesopic conditions. As a result of changes in optic geometry, these dysphotopsias
have been reduced significantly with newer hydrophobic acrylic models.

A smaller proportion of patients report negative dysphotopsias, which are perceived as a scotoma in the temporal peripheral visual field, and are also found more frequently with materials of high refractive index. This phenomenon can be quite frustrating for both patient and surgeon, as they are difficult to treat. Thankfully, over time, with neuroadaptation, these symptoms usually resolve.

The final drawback to mention here, is the issue of biocompatibility of hydrophobic acrylic IOLs. The biological impact of an implanted IOL is at the uveal and capsular levels. The uveal biocompatibility of modern, currently used foldable IOLs is generally excellent, even in eyes with higher risk of inflammation. Personally, I feel it more clinically meaningful to emphasise capsular biocompatibility. Hydrophobic acrylic IOLs generally have a low posterior capsular opacification rate, however, growth of lens epithelial cells onto the IOL can occur as a result of the proliferation of lens epithelial cells from the capsulorhexis edge towards the anterior surface of the IOL.3 I have personally seen this in many eyes with different types of hydrophobic acrylic IOLs, although not with Tecnis IOLs.

Figure 2: Lens epithelial ongrowth. Red arrow indicates rhexis edge created at time of surgery. Blue arrow indicates the extent of epithelial cell growth onto the IOL anterior surface.

Hydrophilic Acrylic

Hydrophilic acrylic IOLs have a high water content. These IOLs are cut in the dehydrated state and then hydrated and stored in solution. Hydrophilic acrylic is probably the most uveal biocompatible of all IOL materials, which may be an important consideration for cataract surgery in eyes with chronic uveitis, for example.

One major problem with some hydrophilic acrylic lenses is opacification of the optic material due to calcification. This can occur spontaneously, or after subsequent corneal or vitreoretinal surgery.4 Some cases needed subsequent explanation due to poor optical quality.

Light Filtering

All IOL materials used today include ultraviolet (UV) light blocking chromophores to filter the UV light. From in vitro and animal experiments, blue light was considered harmful due to short wavelength high energy light causing retinal damage by inducing more oxidative stress at the retinal level. Even though this has not been shown or proven in humans, some manufacturers have introduced yellow tinted IOLs to filter the short wavelength light.

The potential advantage of yellow IOLs is thought to be the reduction of chromatic aberration under photopic conditions and protection of the retina from phototoxic short wavelength light, especially in eyes at risk of age-related macular degeneration. However, there are potential disadvantages also. A yellow IOL may reduce colour contrast sensitivity, especially under mesopic conditions, and the melatonin production in the brain may be altered, causing a change in the circadian rhythms that are steered by blue light levels in the eye.5

IOL DESIGN

IOLs are often categorised according to their haptic design. Anterior chamber IOLs are fixated in front of the iris, whereas posterior chamber IOLs (PCIOLs) are fixated behind the iris, usually in the capsular bag, but potentially in the ciliary sulcus also. IOLs are optimally placed in the capsular bag, as this maximises the stability of the IOL. If there has been posterior capsular rupture, or zonular insufficiency, the IOL will be placed preferably in the ciliary sulcus, and if not possible, in the anterior chamber. Depending on their haptic design, lenses are either ‘one-piece’ or ‘three-piece’.

One-Piece PCIOLs

These lenses have thick but semi-rigid acrylic haptics moulded to the optic. One piece PCIOLs are easily injected through a small incision. Due to the risk of iris chafing by the bendable, thick haptics, however, these IOLs cannot be placed in the sulcus.

Figure 4a: J & J Tecnis: Hydrophobic acrylic, clear, 6mm optic, 13mm open loop haptics. Arrow indicates the axis markers on the toric IOL.

 

Figure 4b: Zeiss CT Asphina: Hydrophilic acrylic, 6mm optic, 11mm plate haptics

Three-Piece PCIOLs

The optic of these lenses can be made of any material. Three piece PCIOLs have thin haptics that are often made of PMMA or polypropylene. They can be placed in the capsular bag as well as in the sulcus, sutured to the iris, or sutured or glued to the sclera. These IOLs are usually reserved for cases where complications have occurred.

 

Figure 5a: Alcon Acrysof SN60WF: One-piece, hydrophobic acrylic, blue blocking tint, 6mm optic, 13mm open loop haptics.

Figure 5b: Alcon Acrysof MA60MA: Three-piece, hydrophobic acrylic, clear, 6mm optic, modified c-loop 13mm haptics.

The Optic’s Edge

The optic of traditional IOLs has a round edge, whereas newer designs have a square posterior edge. The sharp barrier of the square edge is thought to prevent lens epithelial cell migration and therefore decrease posterior capsular opacification formation.

Anterior Chamber IOLs

Placing an anterior chamber IOL (ACIOL) is indicated when capsular support for placement of the IOL posterior to the iris is deficient (capsular tear or zonular damage), the iris is normal, and the chamber is deep.

The proximity of an ACIOL to the cornea and anterior chamber angle accounts for the majority of its potential complications, which include corneal endothelium damage, glaucoma and chronic cystoid macular oedema.6

Newer ACIOL models have shown decreased complication rates compared to those of the 1970s and 1980s. The current standard ACIOL used in Australia is the MTA-UO IOL from Alcon (Figure 6b). This is a one piece PMMA IOL with a slightly smaller optic, and large haptics that are placed in the anterior chamber angle. Another option is the Artisan iris fixated IOL. The Artisan IOL is a one piece PMMA IOL also, but rather than long haptics that are placed in the anterior chamber angle, the Artisan IOL has much shorter claw-like haptics, that fixate the IOL to the iris, thereby avoiding angle damage (Figure 6a). The Artisan IOL can actually be placed in front, or behind, the pupil. To prevent pupil block, a peripheral iridectomy is required. Pharmacologically dilating a patient with an Artisan IOL is not an issue.

Figure 6a: Artisan IOL. PMMA material, 8.5mm total diameter, 5.4mm optic.

Figure 6b: Alcon MTA4UO. PMMA material, 13mm total diameter, 5.5mm optic.

Piggy-back IOL

The Rayner Sulcoflex pseudophakic supplementay IOLs are specifically designed to be placed in the ciliary sulcus as a ‘piggyback’ IOL to correct residual refractive errors following primary IOL implantation. The Sulcoflex IOL sits behind the pupil, and in front of the standard PCIOL in the capsular bag. The Sulcoflex IOL is made from hydrophilic acrylic material and has special design features to reduce complications that might develop from sulcus placement. The IOL has large 14mm undulating round edged haptics with a 10-degree angulation that reduces the risk of contact with the posterior iris pigmented epithelium and subsequent
pigment dispersion. The IOL has a round edged 6.5mm optic to prevent opticiris capture and reduce the likelihood of edge glare and dysphotopsias.

The Sulcoflex IOLs come in aspheric monofocal, toric, and multifocal versions. The multifocal is a refractive bifocal IOL with a +3.5D add that yields a +3D add at the spectacle plane. The availability of a piggyback multifocal IOL opens up this refractive option to patients who did not have a multifocal IOL with their primary cataract surgery. In addition, sulcus placement allows for easy removal if patients are unhappy with any optical aberrations from the multifocal optics. The explantation of a Sulcoflex IOL is much safer and easier than a standard PCIOL in the capsular bag.

Figure 7: Sulcoflex IOL

SPHERICAL ABERRATION

Spherical aberration in the human eye is a combination of the positive spherical aberration of the cornea, and the negative spherical aberration of the crystalline lens. In young eyes, the positive spherical aberration of the cornea is compensated by the negative spherical aberration of the lens; as a result, overall spherical aberration in the young eye is low. As the eye ages, the optical properties of the crystalline lens change, resulting in overall positive spherical aberration and decreased optical performance. Spherical aberrations generally reduce the contrast of the retinal image and affect visual performance, especially under mesopic conditions.7

Conventional spherical IOLs add approximately 0.08μm (over a 4mm pupil) positive spherical aberration to the preexisting aberrations caused by the cornea, increasing the total spherical aberration of the eye. In 2002, an aspheric IOL design was introduced to compensate for the positive spherical aberration of the cornea. Aspheric IOLs generate negative spherical aberration, leading to a smaller amount of postoperative spherical aberration as compared to spherical IOLs. Currently, the vast majority of IOLs used in Australia are aspheric, as studies consistently show that post-operative contrast sensitivity is significantly better with aspheric IOLs, when compared to spherical IOLs. Monofocal aspheric IOLs are more forgiving of centration errors also.

Various modern aspheric IOLs available in Australia generate different amounts of negative spherical aberration (SA). For example, Tecnis ZCBOO generates -0.27μm SA due to its prolate anterior surface and Alcon SN60WF generates -0.2μm SA due to its prolate posterior surface. There has been some interest in optimising patients’ post-operative outcome by tailoring the IOL chosen to their pre-operative corneal spherical aberration. Using devices such as the Pentacam corneal topographer, the pre-operative corneal spherical aberration can be measured. In a recent study, eyes with >0.27μm SA were treated with a Tecnis IOL (SA = -0.27), eyes with 0.2 – 0.27μm SA an Alcon IOL (SA = -0.2), and eyes with < 0.2μm SA a Rayner IOL (SA = 0).8

Unfortunately, this study found that customising the IOL to the pre-operative corneal SA did not lead to better visual outcomes. This has been my personal experience also. In reality, the difference made by addressing spherical aberration is usually very small compared to correcting spherical error and astigmatism. The only occasion that I change my IOL choice based on corneal SA is in a patient who has previously had hyperopic corneal laser refractive surgery. In such patients I use an IOL with zero SA, as these patients will have a cornea with negative, rather than positive SA (for example, Bausch + Lomb Envista IOL).

PRESBYOPIA-CORRECTING IOLS

I categorise presbyopia correcting IOLs into three categories: multifocal, extended-depth-of-focus (EDOF)  and accommodating IOLs. The multifocal category encompasses refractive and diffractive optic lenses,  classified according the physical mechanism causing the bundling of light. Diffractive IOLs can be bifocal, or more recently, trifocal. EDOF IOLs have an extended far focus area which reaches to the intermediate distance.

Unfortunately, to date, accommodating IOLs have had modest and short-lived success, and there are no accommodating IOLs available in Australia.9

Diffractive IOLs

Classic multifocal IOLs are diffractive bifocal (Alcon ReStor, Tecnis Multifocal). They are dependent on two focal points, representing far and near working distances, at which they produce a sharp image on the retina. However, because the intermediate viewing distance falls between these two focal points, patients fitted with these IOLs typically require spectacles for purposes such as computer use. In the last few years, diffractive trifocal IOLs have been developed, and there are now three available in Australia (Zeiss AT LISA Tri, FineVision Trifocal, Alcon Panoptix).

Figure 8: Finevision diffractive trifocal hydrophilic IOL

The main drawbacks with all diffractive multifocal IOLs, is that they split light between distance, intermediate and near and hence compromise visual quality, with halo, glare and starburst. This is a real problem currently, although may be slightly less of an issue with the modern tri-focal designs. Only about 7 per cent
of Australian cataract surgery patients at present will have multifocal IOL implanted. Patient selection is paramount, though this can me more of an art than science. Demanding patients, and those needing perfect visual performance in low light conditions, should not have these lenses implanted. Equally, those with
coexisting ocular disease, such as dry eyes and macular degeneration, should not have these lenses. Post-operative residual refractive error and posterior capsular opacification must be treated more aggressively, to ensure a satisfied patient.

Refractive IOLs

Instead of having symmetrical rings like other multifocal IOLs, the Oculentis Mplus takes its design cues from Benjamin Franklin’s bifocals. It is a one-piece zonal refractive lens with plate haptics and two refractive segments: a large aspheric distance vision zone and a sector shaped zone with a near add, embedded on the posterior surface. The add sector is the only area of the lens that directs light to a near focal point; the remainder of the optic acts as a monofocal IOL for distance vision.

Figure 9a: Oculentis MPlus.

Figure 9b: Acufocus IC-8

 

Extended-depth-of-focus IOLs

In 2014, the first EDOF IOL was introduced into the Australian market. The Tecnis Symfony IOL has an elongated focus rather than splitting the light and creating a second focal point. This helps provide intermediate and some near vision with a lower incidence of glare and halo, with less of a compromise to distance vision. This lens uses diffractive optics in two complementary ways. First, the Symfony makes use of diffractive echelettes, a type of diffraction grating, to slightly elongate the focus. Secondly, it corrects chromatic aberration to enhance contrast. So, the Symfony IOL may provide a middle ground option for presbyopia correction. The patient’s near vision will not be as good as with currently available diffractive trifocal IOLs, however, the symptoms of glare and haloes will likely be less of an issue.

Figure 10: The Tecnis Symfony creates an elongated focus, rather than one or two distinct foci.


In late 2017, Zeiss released its EDOF IOL, the AT LARA 829MP. This is likely to be an expanding field, as more EDOF IOLs are currently being developed. The IC-8 IOL is a novel EDOF IOL that uses the pin-hole principal. The IC-8 is a one piece hydrophobic acrylic IOL with an embedded black circular mask. The mask
blocks unfocused rays of light, extending depth of focus and providing patients with unaided vision across a range of distances. The lens is implanted in the non dominant eye, with a standard monofocal IOL in the fellow eye. Early experience with this IOL has shown that this IOL is ‘forgiving’, in that patients with moderate residual spherical and astigmatic error post-operatively, still have good vision.10 As such, apart from being a presbyopia correcting IOL, it could also play a role in eyes with less predictable refractive outcomes with cataract surgery, such as patients with previous LASIK or ectatic corneas.

Accommodative IOLs

A truly accommodative IOL would be capable of undergoing a progressive change in its power in relation with the active contraction of the ciliary body. The ideal accommodative IOL would fully resolve the inconvenience of presbyopia, without the side effects of current surgical options, including glare and halos, and the compromised quality of vision of a multifocal IOL. Obviously, this ideal accommodative IOL would have a huge impact in cataract and refractive surgery, which explains the interest from many different companies in developing such lenses. Unfortunately, to date, results with these lenses, such as the Crystalens (Bausch + Lomb) have been modest in relation to the restoration of the accommodative power of the eye, and these modest benefits are usually lost with time due to the long-term changes in the capsular bag.

The dual optic Synchrony IOL (AMO) had much promise. The Synchrony dual optic IOL appeared to offer great potential, because it required less movement of the optic to achieve an accommodative effect. Yet despite having completed a phase III FDA trial with the IOL, AMO has withdrawn the lens from the approval process. As such, no accommodating IOLs are available for use in Australia. However, there remains much hope and ongoing research in this area.

HYPOTHETICAL SCENARIO REVISITED

Summary: Mr. Jones, a 60 year old architect, previous hyperopic LASIK, now hyperopic again with  presbyopia. Considering cataract surgery with a Symfony IOL.

Discussion
  • Given Mr. Jones has previously had LASIK, the refractive predictability with cataract surgery is sub-optimal. As such, a sulcoflex piggy-back IOL may be required to correct any postoperative refractive error.
  • It may be best to avoid an EDOF IOL or multifocal IOL (MFIOL) in a patient who has previously had LASIK, as these eyes will have more aberrations than eyes with a virgin cornea. • Mr. Jones will have a cornea withnegative spherical aberration, so it may be best to avoid an IOL with negative spherical aberration, such as the Symfony IOL.
  • Mr. Jones is visually demanding, and requires crisp near vision. An EDOF IOL is unlikely to provide the near vision he needs. He should be appropriately counselled, so that his expectations are realistic.
  • EDOF IOLs may have less glare and haloes than MFIOLs, though patients should be told to expect them.

If Harold Ridley were alive today, he would be amazed at the vast array of IOL options available to the cataract patient in 2018. Each IOL has its own unique qualities and drawbacks, and like everything in medicine, there is a balance of risks and benefits that must be taken into account. The optometrist and cataract surgeon must keep abreast of the technology, and help their patient make an informed decision. It is exciting to think of what advancements will be made in the coming years.

Practical Tips

  • Use retroillumination to help assess what type of IOL has been implanted in your patient’s eye. The rings or segments of a MFIOL will become obvious, and if not seen, then a monofocal or toric IOL has been used. At the periphery of the optic of a toric IOL, there will be axis markers (usually dots or lines).
    • With the availability of toric IOLs to correct small increments of astigmatism, they are becoming more  frequently used. Personally, 85 per cent of my cataract cases had toric IOLs implanted in 2017.
    • Patients with MFIOLs should be referred for a YAG capsulotomy early, as even small amounts of PCO can be visually debilitating.
    • Three-piece IOLs are generally only used currently in cases where there have been complications. Hence, if you see thin blue haptics attached to the PCIOL, there has likely been a posterior capsular rupture, or zonular weakness.
    • Sulcoflex piggy-back IOLs are a useful tool in correcting residual refractive error after uncomplicated cataract surgery.
    • Dysphotopsias (positive and negative) are not uncommon after routine cataract surgery, and are generally not a sign of sub-optimal surgery. They usually settle with time.
    • Personally, even though I use MFIOLs in appropriate patients, I generally prefer monovision or mini-monovision.



         


Dr. Jay Yohendran is a Sydney-based ophthalmologist who specialises in refractive cataract surgery. Dr. Yohendran is a member of the Royal Australian and New Zealand College of Ophthalmologists, as well as the Australasian Society of Cataract and Refractive Surgeons. He is locally trained, and is one of few ophthalmologists who have completed the Graduate Diploma of Cataract and Refractive Surgery at Sydney University.

Dr. Yohendran is the Founder and Medical Director of Northern Sydney Cataract on Sydney’s Lower North Shore, and also consults at Northern Beaches Cataract. He performs cataract surgery at Chatswood Private Hospital and is a Visiting Medical Officer at Royal Prince Alfred Hospital, where he helps train the next generation of ophthalmologists.

    

 

 References:
1. Apple AJ, Sims J. Harold Ridley and the Invention of the Intraocular Lens. Survey of Ophthalmology. 1996;2001-2002.
2. Stringham J, Werner L, Monson B, Theodosis R, Mamalis N. Calcification of different designs of silicone intraocular lenses in eyes with asteroid hyalosis. Ophthalmology. 2010 Aug;117(8):1486-92.
3. Özyol P, Özyol E, Karel F. Biocompatibility of Intraocular Lenses. Turk J Ophthalmol. 2017;47(4): 221–225.
4. Morgan-Warren PJ, Andreatta W, Patel AK. Opacification of hydrophilic intraocular lenses after Descemet stripping automated endothelial keratoplasty. Clin Ophthalmol. 2015;9:277–283.
5. Mainster MA. Violet and blue light blocking intraocular lenses: photoprotection versus photoreception. Br J Ophthalmol. 2006;90(6):784-792
6. Donaldson KE, Gorscak JJ, Budenz DL, et al. Anterior chamber and sutured posterior chamber intraocular lenses in eyes with poor capsular support. J Cataract Refract Surg 2005;31:903–9.
7. Majid Moshirfar, MD. Spherical Aberration of Intraocular Lenses. J Ophthalmic Vis Res.2010;5(4):215–216.
8. Al-Sayyari TM, Fawzy SM, Al-Saleh AA. Corneal spherical aberration and its impact on choosing an intraocular lens for cataract surgery. Saudi J Ophthalmol. 2014;28(4):274–280.
9. Breyer D et al. Multifocal Intraocular Lenses and Extended Depth of Focus Intraocular Lenses. Asia-Pac J Ophthalmol 2017;6:339–349.
10. B. Dick. How is the IC-8 small-aperture IOL performing in the real world? Ophthalmol. 2016; 0116:402

' Spherical aberration in the human eye is a combination of the positive spherical aberration of the cornea, and the negative spherical aberration of the crystalline lens '