Lens Exchange

What are the reasons for IOL exchange or removal?

Intraocular lens implants (IOLs) are usually inserted in patients’ eyes as a part of cataract surgery. IOL removal involves removing the original lens implant and leaving the eye without a lens implant. Removing a lens implant is more difficult than inserting one, as the lenses are usually specially prepared to be put in to the eye by folding or rolling the lens up; the lens in the eye is already unfolded so removing it is more tricky.

IOL Exchange involves removing the previously placed IOL as above, and replacing it during the same procedure with another one.

The reasons for IOL removal or exchange may include:

• a dislocated IOL (one that has shifted out of position)
• an unstable IOL (one that isn’t properly anchored in place)
• an IOL of improper or inaccurate power
• an IOL causing undesirable visual symptoms (for instance after multifocal lens implantation)
• an IOL that has become cloudy or discoloured (this is usually an issue only with HYDROPHILIC lens types)
• as part of other operations such as corneal transplant surgery or retinal detachment surgery

If the lens is removed and not replaced other techniques to improve vision may needed, either glasses or more often contact lenses, or a secondary lens placed at a later stage. It is not possible to use only glasses to correct the vision if one eye has a lens and another doesn’t; the difference between the two eyes is too great and one eye would see things much larger than the other.

How often does this happen?

Rarely, and mostly a long time after the original cataract operation. A population study that followed every cataract operation in one American county for nearly thirty years found the risk of a lens implant becoming dislocated was about 1 in every 1,000 at ten years, rising to about 7 in every 1,000 at twenty years and about 17 in every 1,000 at twenty-five. The study counted only sixteen cases in all, so treat the exact numbers loosely – but the shape is clear enough: it is uncommon, and the risk builds slowly over decades rather than arriving early.

Two things make it more likely. The first is a weakness of the fibres that hold the lens capsule in place, which may have been apparent at the time of the original surgery or may come from a condition called pseudoexfoliation. The second is having had a vitrectomy: in one large series of these operations, 43 in every 100 of the eyes had been vitrectomised before, and the authors described this as an under-recognised risk. That is worth knowing if you have had retinal surgery in the past.

In that same series, three quarters of the operations were for a dislocated lens, about a fifth were to give an eye a lens it did not have, and about 1 in every 20 were for a lens that had gone cloudy.

What are the major risks of IOL removal or exchange surgery?

As with any surgery or medical intervention things can go wrong, and I cannot tell you about every risk: operations and procedures can result in unsuccessful results, complications, injury, or even death, from both known and unknown causes. The major risks of intraocular lens (IOL) exchange include, but are not limited to, bleeding; infection; injury to parts of the eye and nearby structures from anaesthesia, or the operation itself; retained pieces of the original IOL that cannot be removed and may require additional surgery; high eye pressure or glaucoma; a detached retina, a swollen retina, a swollen cornea, a distorted pupil, dislocation of the IOL, increased astigmatism, an uncomfortable or painful eye, a droopy eyelid, and blindness.

You may have increased night glare or halos, double vision, ghost images, impaired depth perception, blurry vision, and trouble driving at night. We might not be able to use the lens that was planned. In addition, the IOL may later need to be repositioned or replaced.

It is usually necessary to perform vitrectomy surgery as part of the IOL exchange or removal procedure. Vitrectomy involves removal of some, or all, of the vitreous jelly inside the eye, so it can better allow freeing of the IOL. Please read the information on vitrectomy surgery in conjunction with this information.

IOL Exchange surgery will not correct other causes of decreased vision, such as glaucoma, diabetes, macular degeneration, cystoid macular oedema or macular epiretinal membranes (wrinkled retina). These ocular conditions may progress or worsen after surgery.

The selection of the proper IOL, while based upon sophisticated equipment and computer formulas, is not an exact science. After your eye heals, its visual power may be different from what was predicted by preoperative testing. You may need to wear glasses or contact lenses after surgery to obtain your best vision. IOL selection after previous refractive surgery, such as RK, PRK, and LASIK is particularly difficult because of the irregular corneal shape. Additional surgeries such as IOL exchange, placement of an additional IOL, or refractive laser surgery may be needed if you are not satisfied with your vision after IOL exchange surgery.

The results of surgery cannot be guaranteed. You may still need glasses or contact lenses.

Depending upon the type of anaesthesia, other risks are possible, including cardiac and respiratory problems, and, in rare cases, death. For local anaesthesia this is an extremely rare complication.

There is no guarantee that lens exchange will improve your vision, and it is possible that the surgery or the anaesthetic could make it worse. Some complications appear weeks, months or even years later. In rare situations they can lead to poor vision, total loss of vision, or loss of the eye, and further treatment or surgery may be needed to deal with them.

What can I expect the vision to do?

It is worth being clear about what this operation is for, because it changes what counts as a good result.

A lens implant that has come loose does not usually damage the eye. What it takes away is the eye’s focusing power. An eye whose implant has dislocated out of the way behaves as though it has no lens at all: unaided it may see only hand movements, or count fingers, while that very same eye wearing a strong contact lens or a pair of aphakic glasses might read 6/9 perfectly well. The operation is not repairing a damaged eye. It is putting the focusing power back inside the eye, where it stays, instead of on the front of it.

So the question to ask is not how much the vision will improve – that depends mostly on how well the eye happened to be corrected beforehand, which tells you nothing about the surgery. The question is where the vision ends up. Two published series, one of 182 eyes using all the various ways of fixing a lens in place and one of 137 eyes using the iris-clip lens I favour, report an average final vision of about 6/16 and 6/14 respectively – a little short of the 6/12 needed to drive. Those are averages across eyes with very mixed histories, and nobody has published the figure I would most like to give you, which is the proportion of people who reach driving standard.

In practice what you end up seeing depends far more on what else is wrong with the eye than on the lens exchange itself. An eye whose only problem is a dislocated implant usually does well. An eye that has also had a retinal detachment, long-standing swelling at the macula, or a damaged cornea will be held back by those things whatever lens it is given.

How often do these things happen?

Here I have to be careful about the strength of the evidence. Cataract surgery is audited nationally and I can quote you figures drawn from half a million operations a year. Nothing of that kind exists for lens exchange, because it is a far less common operation. The best I can offer is a single published series of 182 eyes from a European retinal referral centre – a unit doing much the same work as mine, which is why I use it, but one hospital rather than a country.

In that series, within the first month after surgery:

• Bleeding into the front of the eye, which settles: about 14 in every 100
• Eye pressure too low: about 6 in every 100
• Eye pressure too high: about 2 in every 100
• The iris catching on the edge of the lens: about 2 in every 100
• Inflammation lasting longer than expected: about 1 in every 100

And by three months:

• The new lens itself shifting out of position: about 3 in every 100
• The lens sitting slightly off-centre: about 2 in every 100
• Swelling at the centre of the retina: about 1 in every 100

The lens shifting again is the one to note. It is the commonest reason for a further operation, and it is more likely with some ways of fixing a lens in place than others – which is part of why I favour the iris-clip lens, which held its position well in that series.

Two things were not seen at all in those 182 eyes: retinal detachment and infection inside the eye. That is reassuring but it is not the same as a risk of nothing. A series this size could easily miss a complication that happens around 1 in every 100 times, and both remain real risks of any operation inside the eye.

If you haven’t done so already, please read the information on vitrectomy surgery and what to expect after vitrectomy surgery.