In Lens Exchange the natural lens of the eye is removed using a surgical procedure called "Phacoemulsification". Precisely the same technique is used for modern small incision cataract surgery.
It is therefore a tried, tested and frequently used procedure.
Phaco or Phako means lens.
Emulsification means to turn a solid into an emulsion, i.e. break a solid into a fluid suspension.
Phacoemulsification offers the advantages of a small incision in the eye and a relatively rapid visual recovery following surgery. In routine cases the eye is usually fully recovered and the vision and focus stable after 2 to 3 weeks.
Once the natural lens is removed the artificial lens (The Intra Ocular Lens Implant) is placed into the eye. This is usually made of a pliable plastic so that it may be folded and inserted through the small incision without having to enlarge the wound significantly. Once within the eye, the Lens Implant unfolds and manoeuvred into its correct position.
In most cases the operation is performed using only a local anaesthetic and is a day case procedure, i.e. no overnight stay in hospital is required. The surgery itself usually only takes about 15 minutes to perform but it can be longer than this.
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The Lens Implant
Lens Exchange alters the focus of the eye by removing the natural lens of the eye and replacing it with an artificial lens. This artificial lens is known as the Intra-Ocular Lens Implant. Eye surgeons call it the IOL.
The desired change in the focus of the eye is achieved by choosing a Lens Implant of the appropriate power. Measurements are performed on the eye before the operation and from these the optical power of the Lens Implant needed can be calculated. This process is called Biometry. For more information click here.
Intra Ocular Lens Implants are made from clinical grade plastics. The most popular Lens Implants currently used are made from pliable plastics. This enables the lens to be folded and inserted into the eye through a tiny incision, usually around 3 mms in length. Once within the eye the Lens Implant unfolds and can then be manoeuvred into position.
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In order to achieve the desired focus for an eye it is sometimes necessary to use more than one type of procedure. This may be necessary if the focus error of the eye is too large or complex to be fully corrected by one procedure alone. Combining procedures in this way is called Bioptics.
Different procedures may be used at the same time during a single operation, or used in a sequence of two or more surgeries over time.
An example:
An eye may have too large a degree of short or longsighted-ness to correct with laser (e.g. LASIK or LASEK). Lens Exchange surgery may be performed to correct the majority of the focus error, i.e. to debulk it. Once the eye has recovered from this surgery the eye can be assessed to see what degree of focus error remains. If necessary a laser procedure can then be used to refine the focus of the eye. The relatively small focus error left after the Lens Exchange being within the range for laser treatment.
Combining procedures means a specific (bespoke) treatment plan can be devised for individual eyes and focus corrections can be achieved that would otherwise be beyond the boundaries of any single procedure used alone.
Lens Exchange is often used to correct large refractive (focus) errors. For example relatively high degrees of short-sightedness where laser (LASIK or LASEK) cannot be used because they would thin the cornea too much. These cases are more difficult to fully correct than smaller simpler errors in "one hit", i.e. with a single procedure type performed once. One reason for this is that one is "shooting at the target from a long way off". There is therefore an increased chance that the desired focus result will not be fully achieved after the initial procedure. A further procedure(s) may be needed in order to reach the refractive goal.
Theoretical combinations of procedures involving Lens Exchange include:
* Lens Exchange followed by LASIK, epi-LASIK or LASEK
* Lens Exchange combined with or followed by Limbal Relaxing Incisions (the latter for correction of astigmatism)
* Lens Exchange followed by CK (Conductive Keratoplasty). The latter for correction of residual longsight or astigmatism
Pre-operative measurement
Before Lens Exchange surgery can go ahead pre-operative measurements must be performed.
In Lens Exchange the natural lens of the eye is removed and replaced by a plastic lens (called "the intra ocular lens implant"). Before the operation the eye needs to be measured in order to calculate the optical power of the intra ocular lens implant that is needed to achieve the desired change in focus of the eye. Taking these measurements is called "biometry". The measurements are simple, quick and painless.
These are the measurement of the eye from which the power of the Intra Ocular Lens Implant is calculated. These measurements are simple and painless and usually take just a few minutes to perform.
There are two main measurements:
a. The curvature of the cornea (the window of the eye).
b. The overall length of the eye; called the axial length.
Sometimes the depth of the front chamber of the eye is also measured.
Once these measurements are known formulae are used to calculate (by computer) the Lens Implant power needed in order to obtain the desired focus of the eye after the operation. In other words the Lens Implant power is calculated and chosen for each individual eye.
The formulae used are well tried and the best available but they are not perfect. In the large majority of cases they will predict with reasonable accuracy the power of Lens Implant that should be used. However in a minority of cases the focus of the eye after surgery may not be quite as expected. In the UK at present there is a consensus amongst eye specialists that about 85% of eyes should be within one dioptre of the desired focus following surgery. The reason that the formulae, and therefore the focus results of surgery, are not perfect is "biological variability". For example two eyes may appear to be identical. They may give identical biometry measurements. However when implanted with the same power of lens they may not achieve identical focus after the operation. One reason may be that the Lens Implants sit in a very slightly different position within the eye. There may also be minor variability in the taking of the measurements and in the surgery itself which can also have an effect on the resulting focus of the eye.
After Lens Exchange surgery
Do's and Don'ts after a Lens Exchange operation
These apply whilst the eye is healing and are particularly important in the first few days after the operation.
Do
Don't
Recovery after surgery
The exact post-operative experience will vary from patient to patient. The following though may give some idea of what to expect. Specific instructions and advice on what to do during the recovery period should be provided by the patient's own ophthalmic team.
There may be some discomfort in and around the eye in the initial hours after the operation. This should not be distressing. If it is the eye should be checked by the surgical team.
The morning after surgery the lids may be slightly crusted. This is the dried residue from the watering of the previous day and night. This crusting may be wiped away by simple bathing of the eyelids with cotton wool wetted with sterile saline. No undue pressure should be put on the eye. Once the lids have been cleaned the post-operative eye drops should be commenced. These drops are usually needed for several weeks.
The eye may initially be a little red and light sensitive. This is normal. Sometimes there is a bruise overlying the white of the eye. Like a bruise elsewhere it will clear over a week or two.
The speed of improvement in vision varies. Many patients obtain good vision within a few days. For others the vision may require longer to settle even when the surgery has been entirely straight forward. In most cases, where a small suture-less incision has be used, the eye will be recovered from surgery in about 3 weeks. As the eye heals the focus of the eye may change a little. Usually by about 3 weeks this has stabilised and the focus result of the Lens Exchange can be assessed. If a relatively large incision was needed, requiring stitches, then full recovery may take 2 to 3 months.
During the recovery period the eye should become progressively less red, more comfortable and have improving vision. If the opposite happens and the eye becomes more red, more painful or the vision becomes worse then the patient should seek urgent review by their surgical team.
Risks
There are risks involved in any surgical procedure. This is also true for Lens Exchange. The risks are essentially the same as those for cataract surgery. The risk of ending up with worse best corrected vision after the operation than before is small but not zero. It is probably of the order of 1% or less. There is an extremely remote chance of losing all vision in the eye, e.g. from a severe intra ocular infection.
The main risks are: Infection within the eye (called endophthalmitis), a disturbance to the retina (e.g. cystoid macula oedema or retinal detachment), permanent clouding of the cornea, intra ocular bleeding, unacceptable position of the intra ocular lens implant, technical problems during surgery, and a need for re-operation. This is not an exhaustive list but these are what eye surgeons consider are the main risk factors.