How to choose appropriate IOL
Once in a lifetime decision
“Planning cataract surgery for yourself or family? Learn how to choose an appropriate IOL”
Treatment for cataract has changed drastically during the last three to four decades. Most people will realise it when they or their family member have been diagnosed with cataract and are perplexed by the choice of IOLs (Intraocular lenses) offered.
Gone are the days when cataract surgery was primarily done in temporary eye camps with hundreds of surgeries being done in a day with absolutely no surety of visual gain. The need to wear thick glasses was a foregon conclusion. Choosing the appropriate IOL will allow a significant independence from glasses after surgery.
I’ve discussed the details of cataract surgery in another article. But just to summarize – cataract surgery is replacement of an opacified natural lens with a clean artificial lens. This implantation of a new artificial lens (Intraocular lens or IOL) gives us an opportunity to also reduce dependence on glasses after surgery. And this is where your choice of IOL makes a big difference.
To simplify things I’m excluding older variants of IOLs such as non-foldable and silicon lenses from the discussion as they are obsolete. ‘Foldable’ IOL of ‘single piece’ design made of ‘hydrophobic acrylic’ is by current consensus the IOL of choice. Let’s learn about variations in this design which can help you get most of out of this procedure
Aspheric IOL
Asphericity in lenses in an old concept most photographers are familiar with. Introduction of the same concept into IOLs has allowed a sharper focus created with aspheric lenses compared to older designs
Practically what difference does it make for the patient?
- In strong lighting – no difference compared to spherical lenses. When the pupils are small only the central part of IOL is involved. Thus there is no difference in quality of vision.
- In dim lighting – Aspheric lenses gives a crisper vision with better contrast. The light from the peripheral part of the lens also focuses on retina thus giving a better quality of vision. This is especially important in activities like night driving.
Almost all the major IOL companies use this aspheric design in their top-end lenses reserving the older design only for their cheaper models.
Toric IOL
Toric IOLs are those which also have a cylindrical power to correct astigmatism in the patient’s eye…..Confusing? Then let’s first understand astigmatism.
Spectacle prescription frequently consists of 2 components powers- the spherical and the cylindrical. The cylindrical part corrects for any astigmatic error in the eye. This error happens when the cornea (the transparent part of the eye in front) has different curvature in 2 axis. This is similar to a rubgy ball which has much flatter curve in one axis but is more curved in the other. It’s not that the patient’s eye start looking like a rubgy ball since the difference in curvature is very mild. But this mild difference is enough to generate astigmatism requiring cylindrical powered glasses for optimum vision.
If the patient has signficant astigmatism and we use a normal IOL during cataract surgery, the astigmatism remains uncorrected increasing dependance on glasses after surgery. Toric IOLs tackle this problem by including this cylindrical power in the IOL itself. This reduces the dependance on glasses after surgery. These IOLs are used when a cylindrical power > 1 D is noted during preoperative checkup.
These IOLs are usually more expensive and the extra cost is usually not covered by insurance companies.
Monofocal vs Multifocal IOl
This is the most important decision patient has to take while choosing an IOL. Whether to go for monofocal IOL and use near glasses after surgery. Or use multifocal IOL to reduce the need for reading glasses.
Monofocal IOLs
These lenses are the most common type used during cataract surgery. They give good vision and has no negatives except for one – “need for near glasses after cataract surgery”. As the name suggest, these lenses have one focus or one power. This allows them to create a good focussed image only for one distance – either far or near. To create a good focus for other distances, the patient has to use external glasses – usually reading glasses.
Multifocal IOLs – The elusive holy grail in IOL design.
As the name suggest, these lenses have more than one power, thus giving good focus for both near and far (Bifocal) or near, intermediate and far (Trifocal).
These lenses have rings over the lens optics which allow light to be divided into 2 or 3 points of focus. The patient can thus see with good focus at multiple distances without glasses. But if these IOLs can give significant independence from glasses, why are they not the IOL of choice in all surgeries? Let’s understand the limitations of multifocal IOLs
- Cost – The major limitation of multifocal IOL is cost. They are more expensive than the routine monofocal lenses – usually many times the price of a monofocal IOL. And most of the insurance companies do not cover for the extra cost putting a significant financial burden on patient.
- Glare and Haloes – The rings on the IOL while creating the multiple points of focus also create haloes around light. This is perceived by patients during night driving causing glare. This used to be significant problem with older multifocals. With advancement in design, this issue has been significantly curtailed though not eliminated. Its rarely perceived by people not driving at night. And amongst people who do, its noticed but not perceived as a problem by most. However there is a small minority who do perceive significant glare, enough to prevent them from driving at night.
- Decreased contrast or crispness of vision – Since the light gets divided to create more than one points of focus, the contrast or crispness of vision is reduced. This is not perceived by the patient unless there are different kinds of lenses in the 2 eyes. And that’s why only the same kind of IOLs should be used in both eyes.
- Unrealistic expectations – This is not a deficiency of the lens but of human psychology. It is occasionally a cause of dissatisfaction of the patient after surgery. The purpose of multifocal IOLs is to “reduce dependence on spectacles”. But if the patient approaches surgery with an expectation of “complete independence from glasses all the time”, the chances of dissatisfaction are high. Yes complete independance can be achieved in a signficant majority, but not all. A more realistic expectation should be “signficantly reduced dependance on glasses compared to monofocal IOLs”
Which IOl is best for me?
With this background knowledge in mind, let’s go through a pragamtic decision making process to choose an appropriate IOL for the patient.
- If cost is a strong consideration, then just choose any “Foldable IOL” of “Single Piece Design” made of “Hydrophobic Acrylic”. All such lenses give good vision and last whole life of the patient. If option is available then choose an “aspheric IOL”
- For patients with more than 1 D of corneal astigmatism, consider “Toric IOL”.
- Choose “Multifocal IOL” only if
- The higher cost is acceptable
- Patient has a motivation to reduce dependence on spectacles
- Patient is ready to understand the potential negatives of a multifocal IOL.
- Apart from cataract, the eye is otherwise healthy. Do not use multifocal in the presence of significant other eye diseases like retinal diseases, corneal opacities, advanced glaucoma etc.
- The other eye is also a candidate for multifocal or already has a multifocal IOL. Always use similar IOL in both eyes. Do NOT use multifocal if the other eye already has a monofocal IOL from previous surgery.
- For all other patients, monofocal IOL becomes the default option. and that’s why these are the most commonly used. lenses.
