PRELEX
Frequently Asked Questions
Who may benefit from Lens Exchange surgery?
This procedure can be used to correct both short sight (myopia) and long sight (hyperopia) that is too large to be safely and/or effectively corrected using laser surgery. It can also be used as a treatment for presbyopia.
It is best suited to those patients aged over 50 years. This is because when the natural lens of the eye is removed all ability to adjust the focus of the eye is lost. This natural focus-ability of the eye is called "accommodation". It is slowly lost with ageing. This is why, for those who have good distance vision, near spectacles are usually required after mid 40's. When "Lens Exchange" is performed on those patients aged over 50 the loss of accommodation is of little consequence as it has already been lost through the ageing process anyway. A multifocal lens implant can restore near as well as distance vision.
What does a Lens Exchange operation involve?
Lens Exchange involves removing the natural lens from the eye and replacing it with a tiny artificial plastic lens. This is called the intra-ocular lens implant, or IOL. The aim of the operation is to change the focus of the eye. The optical power of the lens implant is chosen so as to provide the desired post-operative focus for the eye.
The operation is usually performed under a local anaesthetic using a tiny incision in the eye, about 3 mms in length, and employs a technique called phacoemulsification. Lens Exchange surgery is technically very similar to modern cataract surgery and therefore involves tried and tested techniques.
Can I have both eyes treated at the same time?
Most eye surgeons will only operate on one eye at a time. This is the safest thing to do. If Lens Exchange is performed on both eyes at the same time there is a small risk that a complication could occur affecting both eyes; e.g. an infection. This could then lead to profound loss of vision in both eyes.
Can Lens Exchanged be done using a laser?
No. The natural lens of the eye must be physically removed and this can only be done surgically. The intra ocular lens implant is then inserted into the eye to replace the natural lens and to alter the focus of the eye. Sometimes following Lens Exchange (and cataract) surgery a membrane within the eye can be come opaque. This is called "posterior capsule opacification". Where necessary a laser can be used to treat this.
What anaesthetic will be needed for the operation?
Nowadays most Lens Exchange operations are done using only a local anaesthetic and without an overnight stay in hospital. This simplifies the procedure and minimises the risk to the patient's general health. There are a number of different techniques for administering the local anaesthetic. The precise technique used will depend upon surgeon and patient preference.
If I have a local anaesthetic will the operation hurt?
The surgery should be pain free. The surgeon is as keen as the patient to achieve this because a relaxed patient is the key to good operating conditions. There are though some sensations. Some eye drops sting briefly as may the local anaesthetic injection if one is used. Some patients may be aware of a stretching sensation from the clip that holds the eyelids open during the operation. There may be an awareness of a light pressure from the fluids and instruments in the eye and the touch of the surgeon's hands around the eye.
A common practice is for a member of staff to hold the patient's hand during the operation. By squeezing this hand the patient can draw attention if any pain or distress occur. Any problems can then be addressed. The patient should avoid speaking during the operation unless given the OK to do so by the surgeon. This is because when speaking, the head and the eye may move and at the wrong moment this might upset the surgery
Should I take my usual medication on the day of the operation?
It is best to check will your eye surgeon. The pre-operative assessment is a good time to do this. Most medication (e.g. regular blood pressure tablets) should be taken as usual.
Will I be able to see what is being done to the eye during the operation?
No. If a local anaesthetic injection is used this will put the sight (vision) to sleep as well as removing feeling and paralysing eye movement. Even if only anaesthetic eye drops are used the bright light of the operating microscope will tend to bleach vision and the surgical manoeuvres are so close to the eye that there is little if any visual appreciation of what is happening. The other eye will be covered.
How successful is Lens Exchange surgery?
The aim of Lens Exchange surgery is to alter the focus of the eye. Special measurements of the eye are taken before the operation. Formulae are then used to calculate what power of intra-ocular lens implant to use in order to achieve the desired focus for the eye. In the large majority of patients the achieved new focus for the eye is close to that intended. The current consensus amongst eye specialists in the UK is that at least 85% of eyes should be within 1 dioptre of the intended focus. This does mean that for a minority of patients the focus of the eye after surgery is not quite as intended (though still usually much improved). For these patients spectacles, contact lenses or some additional surgical procedure such as laser surgery may be required to get the focus "spot on".
One reason for missing the intended focus in some cases is that although the formulae used to calculate the intra-ocular lens power are well tried they are not perfect. This is because of biological variability. For example two eyes may appear the same and give identical measurements. However even if the same implant power is used the two eyes may not achieve the same focus after the operation.
What are the risks of having a Lens Exchange operation?
There is a small risk in having any operation including Lens Exchange surgery. In the hands of an experienced surgeon, the risk of ending up with worse vision as a result of the surgery is very small; perhaps of the order of 1% or less. The risk of losing all vision or of requiring removal of the eye after the operation (e.g. because of an infection) is extremely remote; but it is not zero. The types of risk involved in having Lens Exchange surgery include:
Infection within the eye: Bleeding within the eye: Disturbance to the retina, e.g. a retinal detachment or a swelling of the centre of the retina called cystoid macular oedema.
Permanent clouding of the cornea: A long term increased pressure within the eye: A drooping of the upper eyelid.
These complications are rare. If they occur further surgery to the eye may be required. It should be emphasised that in the vast majority of cases Lens Exchange surgery is uneventful with excellent results. However this cannot be guaranteed.
Can the operation go wrong?
In a small minority of cases technical difficulties can occur during Lens Exchange surgery. The delicate structures around the natural lens within the eye sometimes break. This can make it more difficult to remove the natural lens and/or safely insert the lens implant. For example the very thin membrane behind the natural lens may rip. This is called "posterior capsule rupture". This membrane separates the natural lens from the vitreous jelly which fills the main cavity of the eye. If this membrane breaks the vitreous jelly can move forward into the front part of the eye. Additional surgical steps are then necessary to remove this misplaced vitreous.
If these events are correctly dealt with the visual outcome is still favourable in most cases. Occasionally it is safer not to insert a lens implant when these complications occur, although this may be possible at a later date. Very rarely the natural lens may fall to the back of the eye during surgery. Referral to a vitreoretinal surgeon in order to remove it will then be necessary. Again it should be emphasised that in the vast majority of Lens Exchange surgery is uneventful with excellent results. However this cannot be guaranteed.
What is the intra ocular lens implant?
The intra ocular lens implant (referred to as the IOL by eye surgeons) is a clear plastic artificial lens inserted into the eye once the natural lens has been removed. The intra ocular lens implant replaces the natural lens of the eye; hence the term "Lens Exchange". Without a lens the eye would remain wildly out of focus and thick very strong spectacles or a contact lens would be needed to refocus the eye. Once inserted the intra ocular lens implant can be forgotten about by the patient. There are different types of lens implants and they can be made from a range of plastic materials.
How long will the lens implant last?
A lifetime. The plastics from which the lenses are made have been subject to accelerated ageing tests. It is estimated that in the eye the lens materials will last in excess of 150 years before showing signs of significant degradation.
Will the lens implant move?
If the surgery was routine and without complications it is extremely unlikely that the lens implant will move out of position.
Will I need an over night stay in hospital?
In most cases no. The vast majority of Lens Exchange surgery is done on a day case basis. Occasionally it may be necessary to stay in hospital overnight following surgery, for example if a general anaesthetic is given towards the end of the day.
Do I need to get a referal letter from my GP about Lens Exchange?
This is not essential but it can be helpful. If you wish to you may make arrangements for a consultation by contacting my secetary directly. However your GP may be able to provide important background and medical information.
Questions about what happens after a Lens Exchange operation
What restrictions are there after the operation?
You should avoid any situation where you might be hit in the eye and you should not rub the eye. Usually the surgery is performed through a very small incision, often only 3mms in length. This means that the eye is very robust after the operation. The wound is extremely unlikely to give way.
It is OK to bend and do light physical activities almost immediately after the operation. If such activities cause the eye to throb then it is wise to stop and rest. Normal activities and past times can usually be fully resumed after about one or two weeks; always check with your surgeon if you are in doubt.
How soon after a Lens Exchange operation will I be able to drive?
This depends. If you have driving standard vision and a normal field of vision in the fellow (non operated) eye then you may legally drive a private car on the day following the operation (applies to UK). However if you have been used to driving using two eyes it is wise not to drive until you have regained good and balanced vision in both eyes, or you have adapted and are confident to drive with only one eye.
The time taken for the eye to regain driving standard vision after the operation varies from one patient to another. Sometimes driving standard vision may be regained within days of the surgery but this cannot be guaranteed in advance. Sometimes new spectacles will be required in order to obtain driving standard vision. It is best to ask your surgeon and not to drive until he has stated that your vision has reached the required standard. Do not drive until the effects of the anaesthetic or any sedation have worn off.
How soon after the operation can I go back to work?
This will vary from patient to patient. It depends on the nature of your work and the speed of recovery of the eye.
There are though some general principles. Usually the surgery is performed through a very small incision without the need for sutures. With this surgery the eye usually takes about three weeks to fully settle. For sedentary occupations it may be acceptable to return to work within about a week. For work involving physical exertions 2 weeks may be preferable.
When returning to work (and at other times too) avoid situations where you might be hit in the eye. Dry or dusty atmospheres may cause some irritation to the eye but are not directly harmful.
How soon after the operation will I be able to play sport or swim again?
This will vary from patient to patient. The type of surgery will affect how soon these activities can be resumed. Usually the surgery is performed using a small incision without the need for sutures. With this form of surgery the eye usually takes about three to four weeks to fully settle. It may be wise to wait until the eye has fully healed before returning to swimming and sports. Contact sports and small ball games (e.g. tennis, squash, badminton) represent the greatest threat to the eye as they carry a risk of a direct blow to the eye. The chlorine in swimming pools and the salt in the sea may irritate the eye a little more than normal in the first weeks after surgery but are unlikely to be directly harmful.
For how long will I need eye drops after the operation?
In most cases for 3 to 4 weeks, though occasionally it may need to be for longer than this.
How soon after the operation can I fly?
There are no restrictions on flying after Lens Exchange surgery. It is quite safe to do so. The air conditioning within an aircraft may make the eye feel a little dry and irritable but this is not harmful. However do not fly away from post-operative supervision until your surgeon is happy that the eye has sufficiently recovered from surgery.
Will I need to wear an eye patch afterwards?
No, but you should wear a plastic shield over the eye to sleep with for three nights after lens exchange surgery. This is for added protection to the eye in this period while the eye is vulnerable.
Will I still need glasses after the operation?
The usual aim with Lens Exchange is to alter the focus of the eye and reduce dependence on spectacles or contact lenses. However, depending on the type of implant used, these may still be required after the operation for some tasks in order to put the eye into optimal focus.
What is "posterior capsule opacification"?
After a Lens Exchange operation a thin membrane remains within the eye that separates the fluid filled space at the front of the eye from the jelly filled main cavity towards the back of the eye. This membrane is called the "posterior capsule". It is in fact the back layer of the natural lens of the eye which is purposely preserved (whenever possible) during surgery. It helps preserve the compartmentalisation of the eye and provides some support for the intra ocular lens implant. At the end of surgery this membrane is transparent. In some patients it may become hazy or opaque during the following months and years. This is called "posterior capsular opacification".
If this happens and it will impairs vision.This can be treated by making a gap in the capusle using a laser, a quick simple painless outpatient procedure taking just a few minutes to perform. This treatment is called a "YAG laser posterior capsulotomy".