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Discover more about IOL’s

Allow us to explain the science of the world's most commonly used medical implant device

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What is an IOL?

An IOL is an Intra-Ocular Lens. First concept for IOL's goes all the way back to 1940's London, Where eye surgeon, Sir Harold Ridley developed and implanted the very first IOL in the world.

You would think that the IOL idea would have rocketed, but alas NO - the medical establishment at the time rejected the concept and so the story of the IOL was almost forgotten until the 1970's when a group of young eye surgeons decided to re-invent the IOL. The rest as they say is history!

Why is an IOL even required?

Your eye has two major focusing elements. First the cornea which provides around 2/3 of the focusing power of the eye. Second the natural lens which provides the rest. During cataract surgery - the clouding natural lens is removed and so with it goes the roughly 1/3 of the focusing power of your eye. Without an IOL, it is very likely that your eye would be heavily under focused. This typically means that cataract extraction without lens implantation would leave the average person very 'long sighted' or hyperopic.

You may remember people of your parents or grandparents generation wearing very heavy, thick glasses to be able to see properly after old fashioned cataract surgery - well this is the reason why IOL's became an essential part of cataract surgery. In a nutshell to provide the missing focusing power.

The safety of IOL's has now been established beyond any doubt and all around the world cataract surgery should always involves the insertion of an IOL.


  • Monofocal intraocular lenses produce a single focal point only.
  • Monofocal intra-ocular lenses are the simplest and most basic of all IOL’s. The optical design, as the name implies, is that of a lens which has just ONE focal point.
  • A single focal point means that the eyesight focus is fixed for far distance when the target prescription is set at ZERO or very close to ZERO. However if the prescription target is set at minus 2D for example, the eyesight would be sharpest at around 1/2m (50cm) from the eye. The key point to remember is that the focus can be targeted at ZERO (for far distance) all the way down to minus 2D or 3D where eyesight is in focus at closer range however these types of IOL’s will not produce a range of focus in contrast to Multifocal, Extended Focus type IOL’s..
  • Toric varieties are available to help control astigmatism .
  • All IOL’s come with a UV filter.
  • Advantages : Simple, easy to get used to, low risk if optical side effects such as night glare/haloes.
  • Disadvantages : Spectacle independence is unlikely.
  • Who is Suitable ? These implants are the most basic of all IOL’s and thus can be considered in all cases with the obvious caveat that they also have the most limited range of optical performance. .
  • Blue light filtering varieties are available. The theoretical advantage of blue light filtering IOL’s is that they may reduce blue light exposure which is thought to reduce chronic light induced damage to the retina. Reported side effects however include reduced vision performance in dim light conditions and altered colour perception. The jury is still out on whether blue light filtering IOL’s offer more benefit than risk for the majority of people. We will consider blue light filtering IOL’s in people who may be at increased risk of macular degeneration.


  • The term premium is used to describe IOL’s which although mono-focal in their underlying optical design, bring an additional optical dimension that adds further utility for the patient.
  • One example of a premium mono-focal IOL is the EYEHANCE (johnson &johnson). This is a lens implant which to the naked eye is indistinguishable to its sister lens the Tecnis monofocal IOL. The Eyehance is a monofocal lens which has a continuous change of curvature from the periphery to the centre in a way which helps to provide improved far range intermediate vision performance.
  • The net effect is an IOL which comes with little or no additional optical side effects (such as night glare/halo) but with added ‘far intermediate’ range visual performance. The difference this IOL produces over the standard monofocal lens implant is improved unaided vision at the 2-4 metre focal range. This effect is especially useful for indoor , social distance vision performance. Far vision – anything beyond around 6m is likely similar but the far intermediate range is especially helpful for improved facial recognition, TV viewing and other such activities which are often performed at the sub 6m distance range.
  • This IOL we have found also serves the purpose of monovision especially well, by setting the dominant eye to far distance focal range and the non dominant eye to a near range at say -1.50D, the overall effect of monovision can be made more comfortable and better tolerated, yielding excellent distance and close range vision in those suitable for monovision but not well suited to multifocal IOL’s.
  • Toric varieties are under development to help control astigmatism.
  • All IOL’s come with a UV filter.
  • Advantages : Simple, easy to get used to, low risk if optical side effects such as night glare/haloes.
  • Disadvantages : Near range vision is limited unless the monovision principle is applied.
  • Who is Suitable ? These IOL’s are considered to be the easiest of the premium IOL subtypes and can therefore be considered for a broad range of indications.
  • Blue light filtering varieties are available. The theoretical advantage of blue light filtering IOL’s is that they may reduce blue light exposure which is thought to reduce chronic light induced damage to the retina. Reported side effects however include reduced vision performance in dim light conditions and altered colour perception. The jury is still out on whether blue light filtering IOL’s offer more benefit than risk for the majority of people. We will consider blue light filtering IOL’s in people who may be at increased risk of macular degeneration.


Zeiss’ AT-LARA 829 MP EDOF IOL’s

  • Extended depth of focus (EDOF) implants utilise a range of different optical properties to help create a single but ‘elongated’ focal point as light travels through the IOL. The aim is to provide the patient with enhanced performance compared to a monofocal IOL. EDOF IOL’s will typically produce a continuous range of vision performance extending outwards from around 2/3m (66cm) towards the far distance.
  • EDOF IOL’s therefore offer a special advantage for those patients who have a strong desire to achieve spectacle independence for computer VDU work as well as far distance vision. EDOF’s can sometimes also yield a comfortable close range viewing experience, however this is not the norm and most patients who opt for EDOF IOL’s for both eyes are likely to require off-the-shelf reading glasses for reading and other closer range visual activities.
  • What also helps to set EDOF IOL’s apart from multifocal IOL’s is the way in which the focal point is ’stretched’ tends to lead to less intense night vision disturbances such as glare/halo. We do counsel our patients that they should still expect some night vision disturbances as the ‘trade-off’ but this is often less intrusive and the vast majority of patients with EDOF IOL’s adapt quite comfortably.
  • Chromatic aberration control and aspheric optical design principles are core components of EDOF technology.
  • EDOF IOL’s come with in built UV light filters and some are also now available with additional blue light filtering chromophores. The pros and cons of blue light filtering is thought to be pretty evenly balanced and in most cases blue light filtering is not required.
  • EDOF IOL’s are generally made from an Acrylic polymer which is typically Hydrophilic. This means the implant can be implanted through a tiny 2mm incision. EDOF IOL’s are also available in TORIC variety which helps to control astigmatism and allow us to consider this type of advanced technology IOL for a wide range of situations.
  • Current EDOF IOL’s in our portfolio are .
  • Zeiss AT-LARA (inc Toric) J&J Tecnis Symfony,
  • PRO’s : High prospects of spectacle independence for distance and intermediate focus.
  • CON’s : Some night vision disturbances such as glare/halo but typically less than with Multifocal IOL’s
  • Who is Suitable? EDOF IOL’s are best suited for patients who wish to have a strong chance of achieving spectacle freedom for computer screen work but are non-plussed about needing reading glasses for any closer range vision.


BIFOCAL intraocular lenses produce TWO focal points (FAR and around 1/3m (33cm) only.

TRIFOCAL intraocular lenses produce THREE focal points. Typically FAR, INTERMEDIATE 2/3m (66cm) AND CLOSE range 1/3m (33-40cm)

Zeiss AT-LISA Trifocal Toric (top) and Non toric IOL’s

  • Any IOL which produces more than ONE focal point is technically classified as a ‘MULTIFOCAL’ IOL. However our view is that since the arrival of TRIFOCAL IOL’s in 2013 I would prefer to use the correct term to describe the specific type of multifocal IOL.
  • In my clinics bifocal IOL’s have been completely superseded by Trifocal IOL’s since their advent in 2013.
  • Trifocal IOL’s are designed to help provide the very best prospects for full spectacle independence after cataract or RLE surgery. They produce strong far and close range vision with the majority of patients being able to achieve 20/20 for distance AND close range vision. The third focal point is the ‘intermediate’ focal point which is designed to provide a focal point around 2/3m (66cm) from the eye – an area typically where a computer VDU screen may be placed.
  • Trifocal IOL’s are an excellent choice for the majority of patients who desire a high level of spectacle independence.
  • Multifocal IOL’s are generally made from an Acrylic polymer which is typically Hydrophilic. This means the implant can be implanted through a tiny 2mm incision. Multifocal IOL’s are also available in TORIC variety which helps to control astigmatism and broadens the utility of these advanced lens implants.
  • All IOL’s come with a UV filter.
  • Blue light filtering varieties are available. The theoretical advantage of blue light filtering IOL’s is that they may reduce blue light exposure which is thought to reduce chronic light induced damage to the retina. Reported side effects however include reduced vision performance in dim light conditions and altered colour perception. The jury is still out on whether blue light filtering IOL’s offer more benefit than risk for the majority of people. We can consider blue light filtering IOL’s in people who may be at increased risk of macular degeneration. .
  • Multifocal IOL’s in our portfolio include: Zeiss AT-LISA Trifocal (inc toric), J&J Synergy (inc blue filter), Physiol Fine-vision (inc toric and blue filter)
  • PRO’s: Excellent prospects of high level vision for far close and often intermediate range as well.
  • CON’s: Night vision glare, haloes around car headlights are common but the majority of patients report a high degree of tolerance and also adaptation of this side effect over 3-6 months. Close range vision is optimum in good natural light and in well lit conditions. Some patients notice some decline in contrast perception – which is the ability to perceive subtly different shades of grey. Reduced contrast can mean patients will require good lighting conditions for optimum performance.
  • Who is Suitable? Multifocal IOL’s are best considered in patients who have a strong motivation for being able to read without having to resort to reading glasses on a constant basis. Not all eyes are suitable for Multifocal IOL’s – contra indications can include conditions such as: Very high pre operative eye prescriptions, high astigmatism, corneal scarring, abnormally large pupils, Vitreous degeneration, Retinal degeneration (e.g. from myopia), Epi-retinal membrane and disorders such as significant diabetic eye disease and macular degeneration. Its also worth noting that we would caution against the siren call of unrealistic expectations – PERFECT vision with total crystal clarity is unlikely with any type of lens implant !


Two different designs of monofocal toric IOL’s. Top is ‘C loop’ haptic and bottom is plate haptic design. The line marks on the optic area denote the axis of the astigmatic power.

Effect on vision of even mild degrees of astigmatism

  • Non toric IOL’s whether monofocal, multifocal or EDOF have 1 primary power called the base power. In contrast Toric IOL’s have two powers arranged at a 90 degree axis to each other. This arrangement is designed to help correct astigmatism. To clarify, astigmatism can have more than one component, but in practice the important determinant of astigmatism in relation to cataract and RLE surgery is what’s termed corneal astigmatism.
  • Your spectacle astigmatism is a combination of the corneal astigmatism plus the astigmatism of your natural lens. Of course in cataract and RLE surgery the natural lens – also called the crystalline lens- is removed to be replaced by an IOL. You can therefore see that the key remaining astigmatic measure is what's left behind which is the corneal astigmatism. Its possible for us to quantify this very precisely with modern keratometry (corneal measuring device) and topography (a device which allows us to visualise the type of astigmatic pattern we are dealing with).
  • Armed with these two main measures, it is very often possible to reliably correct or reduce the expected astigmatism which would arise from the cornea.
  • Toric IOL’s are always ‘special order’ IOL’s as they are much more customised to your precise eye measurements than non toric IOL’s. Toric IOL’s do require careful and precise placement and orientation at the time of implantation, unlike non toric IOL’ which can be oriented in any direction, toric IOL’s work best if aligned to within a few degrees of the desired and planned orientation.
  • Great news … Most varieties of Multifocal and EDOF IOL’s come with special Toric varieties as well so we can take care of your astigmatism AND help provide a wider range of vision performance.
  • What does this mean for your vision? – put simply ignoring astigmatism in my view is not acceptable if we are to maximise vision improvement. In my practice I always take these measures into account and whilst not every patient will require a toric IOL, we find in our hands around 30-40% of patients would be able to benefit from the advantages afforded by toric IOL technology.
  • PRO’s : Where pre op corneal astigmatism is 1.0 D or greater, toric IOL’s offer the best chance of an excellent vision outcome .
  • CON’s : Inaccurate alignment or post op rotation of IOL could reduce the positive impact, the IOL will often have to be ordered from the manufacturer and thus a 1-2 weeks delay in scheduling your treatment is possible.
  • Who is suitable? Up-to 35% of patients having cataract surgery could be eligible for toric IOL’s to be considered for them. All the advanced IOL’s (e.g. Multifocal, extended depth of focus) nowadays will also come with a TORIC variety.


How accomodation works

A double optic accomodative IOL design (withdrawn)

  • Nothing would please us more than the arrival of a fully accomodative IOL. However as of Late 2020- the world still waits for an IOL that can reliably, consistently and persistently provide true accomodation.
  • The search for an accomodative IOL is something of a holy grail in the world of cataract and RLE surgery. Despite many £100’s of millions worth of research over forty years plus, we have not yet been able to produce an IOL that can provide you with a full range of accomodation with natural reading effort.
  • The natural human lens, called the crystalline lens is a real biological marvel, it can flex on demand to provide extra focusing power for close range viewing. This is achieved with contraction of a ring shaped muscle called the ciliary muscle. Contraction of the ciliary muscle causes a release of the tension on suspensory ligaments called the zonular fibres which attach onto the equator of the crystalline lens. Ciliary muscle contraction therefore leads to LESS stretch on the crystalline lens which thus shortens and thickens to produce the extra focusing power that your eye needs to see things like newspapers and print in focus.
  • As we age the crystalline lens becomes less flexible and whilst its thought that the ciliary muscle is still active well into old age, contraction of this muscle no longer leads to the desired enhanced near range focusing power. This age related decline is what we call PRESBYOPIA.
  • I very much hope one day, perhaps far into the future we will have a truly accomodative IOL which really can provide sustained accomodative effect in a safe, effective and reliable way.
  • Designs that have been trialled in my practice include Human Optics’ Tetraflex, AMO Synchrony dual optic IOL and the Crystalens. None of these IOL’s produced results that were anywhere near good enough for me to continue using them.
  • Thankfully ‘Pseudo-accomodative’ IOL’s (Multifocal and EDOF) have progressed incredibly over the last twenty years and it is wonderful to have access to IOL’s that CAN effectively, reliably and sustainably produce the treasured FAR and CLOSER RANGE vision which was always the desire with true accomodating IOL’s.

How can Mr Rehman help you choose your IOL?

  • All the technology in the world cannot replace one of the simplest and most effective means of selecting an IOL for your treatment.
  • The conversation - a dialogue, between you and your surgeon is still the best way to figure out which IOL is going to deliver what you want.
  • This involves a careful and detailed conversation, as a surgeon I am always conscious of the importance of the decision and it's one that I want us to get right.
  • Once I understand what your major goals are, I can start whittling down the IOL choices that are available to us. It is also important for you to not only what can be achieved but for you also to understand the limitations of current technology and the potential optical side effects that can occur. Combining this, personal goal setting information, with the high tech scans that you will undergo at my clinics, I can help you make the choice of IOL that's most likely to give you the result you're looking for.
  • In my conversations with patients, I have come to understand how skilled communcation is just as important as a skilled pair of hands when it comes to delivering the ultimate goal - a satisfied patient, happy with the outcome that we have acheived for them.
  • You will be pleased to know that my extensive experience of working with many of the most advanced technology lens implants available anywhere in the world, is probably your best assurance of success.

See the video below to hear Mr Rehman explaining Refractive Cataract Surgery to Sky News in October 2018.


Frequently Asked Questions

It’s certainly true that IOL designs have proliferated over the last 25 years or so – that is a good thing! But of course, it does make it all the more important that as a prospective patient who may be considering Refractive Lens Exchange or Cataract Surgery, you do your own research and consult a surgeon who has peerless experience of using many different types of lens implants. Mr Rehman is passionate about giving his patients as much choice as possible when it comes to selecting their IOL and he is exceptionally well positioned to help navigate you through the decision-making process so that you have the very best chance of meeting the goals you wish to achieve.

In my conversations with many hundreds of patients every year, I get asked this question quite often! There is no such thing as the ‘best IOL’ - in other words different types of IOL’s are designed to achieve different things. Very few independent head to head clinical trials exist comparing similar types of IOL’s. As an experienced surgeon, I like to workwith IOL companies with a long and established track record of design andinnovation – such as Zeiss, Rayner, Alcon, Johnson & Johnson. The key issue is for you and your surgeon to agree on your major objectives and priorities and then to be guided by your surgeons’ personal experience on which IOL’s to select.

Yes it is! Given that different IOL’s provide different optical properties, it is indeed possible to select IOL’s with complimentary properties in order to deliver a particular type of visual outcome. One example is a scenario where we sometimes select a TRIFOCAL IOL for one eye and an Extended depth of focus IOL for the fellow eye. These two types of IOL often work very well together in a supportive, complimentary way to provide an even greater prospect of spectacle independence for close range, intermediate (VDU work) and far distance. That said – our default position is to use the same type of IOL in both eyes – e.g Trifocal / Trifocal or EDOF / EDOF as this tends to work very well for the majority of patients that we treat.

Unfortunately, with the best will in the world and even with ‘perfect surgery’ not everyone treated with IOL surgery will achevie the results that they hoped for. This is not by any means common – and in my experience significant dissatisfaction is very uncommon – with around 98% of patients reporting satisfaction in surveys. For those who do not meet their goals, occasionally there is a clear path towards achieving theirgoal – this may be with some additional vision correction treatment – typically Laser vision enhancement with LASEK/PRK or LASIK can be considered in many situations. Make sure you ask your surgeon or clinic whether there would be an additional charge for this and also that they will be able to offer this service for you – many do not or will not. Rest assured, in my practice most of our patients opt for the ‘Refractive package’ and thus we are easily able to offer this service where its required. A secondary option is even less commonly utilised, which is IOL exchange – something I outline below.

Yes – but it is not something that we undertake very often at all – in fact in my practice, IOL exchange is something we consider in less than 0.3% of our patients – this is a strong reflection of the overall success of our treatments as many clinics report significantly higher rates of IOL exchange. IOL exchange surgery is a little more complex than primary implantation but is something that can be considered in the following circumstances:

  • The Implanted IOL is in some way damaged and is thus compromising vision.
  • The implanted IOL is failing to deliver the outcome which you had wished for
  • The implanted IOL has resulted in a large optical prescription and where this prescription cannot be corrected by Laser enhancement

IOL exchange is thus perfectly feasible but is not an option that should be undertaken lightly due to additional risks. Equally please ensure that your surgeon is capable of IOL exchange as a surgical procedure – not all

Technically it may be – but we would strongly advise against changing an IOL just to upgrade to a ‘better’ IOL in the future. IOL exchange as indicated above is a more complex procedure and is something that we utilise in highly specific circumstances only. We would like to think of your primary IOL as the first and only IOL you will need

Forever! IOL’s are designed to stay inside your eye permanently and with a extremely low risk of significant problems arising with the IOL itself (such as lens implant clouding) we fully expect the IOL to last a full lifetime

Essentially NO. IOL’s are made out of materials which are highly biocompatible with the eye, this means ‘rejection’ in the true sense of the word Is extremely unlikely

No! The key parameters that lead to an eyesight prescription are the following:

Focusing power of the cornea

Focusing power of the natural lens (or IOL)

Length of eye from front to back

Its assumed that the focusing power of the cornea is largely stable after middle age as is the length of the eye, this means that once an IOL (with a fixed power) is positioned inside the eye to replace the natural lens (which often changes a lot from middle age onwards) – we have a theoretically very stable situation with respect to your post-surgery eye prescription outcome. This is the reason why we expect your eye prescription (which should be close to zero post op) remains stable on a long-term prospectus

The commonest treatment required in patients who have had IOL implantation surgery is YAG Laser Capsulotomy. This is required in around 10-20% of patients within a 2-5 year time frame post op. This treatment is required if the capsule membrane within which your IOL is positioned starts becoming a little cloudy (called PCO – posterior capsular opacification). PCO occurs as a result of cell ingrowth onto the capsule behind the central area of the IOL. When this occurs, your vision may start going a little cloudy once again. The good news is that YAG laser capsulotomy is a simple, routine outpatient procedure – taking just a few minutes. It is painless and highly effective in creating an opening in the capsule behind the IOL. Once the capsulotomy is created, it is extremely unlikely to recur meaning that this is generally a once only procedure. One point I would suggest patients seek clarity on is the funding position of YAG laser treatment. In my practice, the refractive package covers for the possibility of YAG laser being performed if it arises within a period of twelve months post op. Many clinics do not have such cover, so please be aware of this possibility in the future.


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