LENS EXCHANGE

Also known as:

CLEAR LENS EXTRACTION

Purpose

The aim of this procedure is to alter the refraction (or focus) of the eye by removing the natural lens of the eye and replacing it with a plastic artificial lens. This plastic lens is called a “lens implant”. The natural lens is being exchanged for an artificial lens.

Who May Benefit

This procedure can be used to correct both short sight (myopia) and long sight (hyperopia) that is too large to be safely corrected using laser surgery.

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. The procedure may still be performed on younger persons but near vision spectacles will be a new requirement for such patients.

Unlike the natural lens of the eye in a young patient the lens implant has a fixed focus, i.e. proven designs do not have focus adjustment. Lens implants with focus-ability are currently under evaluation.

How does Lens Exchange work?

The eye is like a camera. Inside the eye there is a lens, as there is a lens inside a camera. The natural lens of the eye sits behind the pupil but it cannot be seen without special examination instruments. It is similar in size and shape to a “smartie”, i.e. like a little discus.

The focus of the eye depends on three main factors. These are: the cornea (the window of the eye), the lens inside the eye, and the length of the eye. Ideally the cornea and the lens should work together to create a focused image on the retina at the back of the eye. In short sight (myopia) the clear image falls in front of the retina and in longsight (hyperopia) it would come into focus behind the retina.

To adjust the focus of the eye either the curvature of the cornea may be changed or the optical power of the lens of the eye altered. The length of the eye cannot be changed. The curvature of the cornea is altered during laser refractive surgery. “Lens Exchange” is the procedure that permits the power of the lens to be changed.

What is involved in Lens Exchange?

This is a surgical procedure that involves placing tiny instruments inside the eye. In other words, in medical parlance, it is intra ocular surgery. In this way it differs from laser refractive surgery. With laser surgery tissue is removed from the cornea in order to alter its curvature. This is all done on the outside of the eye. There is no need to go inside the eye. Lens Exchange should therefore only be performed in a fully equipped eye operating theatre. Such facilities may not be available within a high street laser clinic.

The procedure is usually performed using a local anaesthetic and as a day case; i.e. no over night stay is required. The lens of the eye is broken up and removed using a technique called “phacoemulsification”. The tip of the instrument is inserted into the eye through a tiny incision, usually only about 3 mms long. This tiny cut is made in the periphery (edge) of the cornea (the window of the eye). In most cases the replacement artificial lens is also inserted through this tiny incision. To make this possible the lens is made from pliable plastic and is folded, posted through the incision, unfolds within the eye and is then nudged into position. In most cases no suture is needed.

In a few patients there are special factors that may require the use of a non-folding rigid artificial lens. In this situation the incision will need to be enlarged a little to allow the insertion of the lens and a few very fine sutures may be required to ensure that the wound is secure. The entire operation usually takes only 10 to 15 minutes to perform.

After the surgery eye drops need to be used for about 3 weeks. Vision is often good within days but the focus of the eye may take several weeks to finally settle.

These comments give a general guide to the nature of the procedure but the specific details and experience will vary from one patient to another.

Like a cataract operation.

Lens Exchange is technically very similar to modern small incision cataract surgery.
A cataract is an opacity or clouding of the natural lens of the eye that reduces and compromises vision. The treatment of a cataract is to remove the cloudy lens and replace it with a clear artificial lens. This restores vision. With Lens Exchange the same thing is done. The only difference is that the natural lens of the eye is not cloudy. . . it is clear. This is why the procedure is sometimes called Clear Lens Extraction. The operation is not being done to restore vision dimmed by cataract but to alter the focus of the eye.

Because the technology used in Lens Exchange is exactly the same as that used in every day cataract surgery it is well tried and tested.

Pre-operative Assessment

Before the operation a number of measurements need to be done on the eye. This is called “Biometry”. These measurements allow a calculation (using complicated formulae) to be made of the strength of the artificial lens required for a chosen post-operative focus. In this way the power of the lens used is tailored for the individual eye. The measurements are simple and painless. They involve assessing the curvature of the cornea and the length of the eye. The instruments that measures the corneal curvature do so by analyzing the reflection from it. The length of the eye is determined by instruments that either bounce an ultra sound or infra red signal from the back of the eye. Some of these instruments need to touch the cornea at the front of the eye and an anaesthetic eye drop is then used to make this possible.

The formulae used to calculate the lens power are well tried but not perfect. Because of a natural biological variability between eyes and the possible small errors in measurements sometimes the predicted focus result is a little out. If this occurs and the unaided vision (i.e. the vision without spectacles or contact lenses) is not acceptable to the patient some further surgery may be required; this might be laser refractive surgery or conventional surgery.

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 loosing 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.

Combining Refractive Procedures

One refractive procedure alone may not achieve the desired improvement in the focus of the eye. For example Lens Exchange may not correct astigmatism. In order to achieve the optimal outcome two or more procedures may be combined. This approach is called “Bioptics”. The procedures may be done at the same time, or more commonly in a staged manner over time.

A patient with a very high degree of myopia may undergo Lens Exchange to debulk the myopia, i.e. to correct most of it. Once the eye has recovered from this surgery some laser refractive surgery (LASEK or LASIK) may be performed to “touch up” the focus of the eye. Indeed the higher the initial focus error the harder it is to achieve the desired result in “one hit” because one is shooting along way from the target.

Posterior Capsule Opacity

During Lens Exchange (and cataract surgery) a very thin membrane is preserved within the eye. This is called the Posterior Capsule. It separates the jelly (vitreous) that fills the main cavity at the back of the eye from the fluid within the front of the eye. It also helps to support the artificial lens implant. At the end of the operation this membrane is usually crystal clear. In some patients as the months and years pass this membrane can become hazy. This is called Posterior Capsule Opacity. This may dim or blur vision. If it does so a simple laser treatment called a Yag Laser Capsulotomy may be performed to create a small opening within the centre of the membrane thus clearing the line of sight and restoring vision. This laser procedure is a simple painless outpatient treatment taking just a few minutes to do.

Any More Questions?

Visit our Lens Exchange frequently asked questions section.