Clear Lens Exchange
(Refractive or presbyopic lens exchange)
Clear lens extraction is a surgical procedure designed to reduce or eliminate the need for distance glasses or contact lenses and it can be used to treat a wide range of far-sightedness and near-sightedness. Unlike other refractive procedures that change the shape of the cornea, clear lens extraction corrects vision by removing the crystalline lens in the eye and replacing it with a new artificial lens of a different focusing power, much like what happens in cataract surgery. State-of-the-art instruments are used to measure your eye for the correct lens power, taking your lifestyle and activities into consideration. These custom measurements are entered into sophisticated formulae to calculate your personal implant power.
Cataract surgery has been successfully performed for years and has been one of the major advancements in the restoration of sight in the last decade. The clear lens extraction procedure resembles cataract surgery. However, in cataract surgery the removed lens is cloudy whereas in clear lens extraction the removed lens is clear. Clear lens extraction has been performed extensively in Europe over the past 20 years with excellent results in correcting moderate to high far-sightedness and near-sightedness with or without astigmatism.
Cataract surgery and clear lens extraction are essentially the same operation which involves both the cornea and lens and is the commonest operation done in the UK. With more than 300,000 a year being performed.
The Surgery (The phacoemulsification procedure)
The technique was introduced by Charles Kelman in the 1960’s but required technical improvement before its widespread adoption about ten years ago. It is a quantum improvement over extra-capsular surgery and de regeur for refractive surgery. its advantages stem from the tiny (<2.8mm) incision needed. This induces very little astigmatism (termed “corneal corruption” by refractive cataract surgeons) and is much less traumatic to the eye than the comparatively giant incision it replaced.
The incision is completely filled intra-operatively by the phaco probe enabling exquisite control of the operation by the surgeon. Never before has the outcome of cataract surgery depended so much on the surgeon’s skill rather than by chance. The small incision does not generally need stitches and heals rapidly with good vision expected after a day or two (but improving over a couple of weeks).
Phacoemulsification or Phaco is the modern method for removing lenses utilising high energy ultrasound. Using this technology a cataract which measures 12mm in diameter and 4mm in thickness can be vacuumed through an incision which measures only 3mm or less! Basically, phaco uses a hollow needle which, when activated by the surgeon, vibrates at 40,000 times per second thereby emulsifying the lens. Emulsified lens material is aspirated through the hollow centre in the phaco needle and fluid is simultaneously infused into the eye in order to keep if “inflated” during surgery. Lenses CANNOT be removed by laser routinely at present (but see the FemtoSecond laser links).
With the FemtoSecond laser system, our surgeons can remove your lens in a more advanced way, using a laser. Using the FemtoSecond laser system ensures that your advanced, customized cataract or clear lens extraction procedure can be performed with laser precision. This is because of Augmented Reality, a unique imaging system that provides an advanced, 3-D view your eye to help plan and treat your cataract or lens exchange. With this advanced technology, your surgeon can offer you a better, more precise removal procedure that is customized to your eye’s own unique anatomy.
An intraocular lens or implant is routinely implanted following removal of the natural lens. The surgery takes about 30 minutes.
Finally, phacoemulsification lends itself to other ways of improving outcome such as measures to reduce pre-existing astigmatism and to reduce the dependence on reading glasses by the use of multifocal or accommodating implants.
The Choice of Implant and Reading Vision
- 1.The traditional implant is monofocal (i.e. is only perfectly focused at one particular distance) and usually chosen for distance vision but for near the patient will need reading glasses even if they did not need them before.
- 2.The multifocal lens is made of either silicone or acrylic and has optics allowing two or three separate areas in focus simultaneously. Previous versions of these lenses used to cause halos and glare but this has largely been eliminated. In one study of patients given a multifocal implant 80% did not need distance glasses and 40% did not need reading glasses at all (compared to nearly 100% needing reading glasses with monofocal implants).
These are impressive results but they demonstrate that not all can expect to be completely glasses free. The majority will enjoy reduced dependence on reading glasses but still need them for more taxing near activities. There are ways of reducing this dependence even further. Your surgeon will discuss with you whether you are suitable for these implants.
- 3. This is the third type of implant. It is designed to change position in the eye when you try to read so you can have good distance vision and also good reading vision. The ability to read with these implants varies from person to person but on average give 1.4 dioptres of accommodation equivalent to a weak pair of reading glasses. Even if this type of implant does not work very well for you the end result would be little different from having a monofocal lens; also this lens does not degrade the quality of your vision or have an effect on night driving as may occur with multifocal lenses.
Further information on the new varieties of multifocal implants that are available. You may want to have a look at
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