What is Lens Exchange?

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.

Intra-ocular Surgery

Because the natural lens of the eye is located within the eye the procedure does involve intra-ocular surgery. In other words it is an operation that involves entering the eye with surgery performed within the eye. In this sense it is different to laser refractive surgery (LASIK, LASEK or PRK). These involve surgery to reshape the cornea that is done on the outside of the eye. Lens Exchange is very similar to a cataract operation.

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 and/or effectively 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.

In some cases in order to achieve the best or desired focus for the eye it is necessary to combine Lens Exchange with other techniques. For example in eyes with large refractive errors (e.g. high myopia) Lens Exchange may be used to correct the bulk of the error and some laser treatment (e.g. LASEK) may be used to correct or refine any residual defocus. This approach is called Bioptics.

Why 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.

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. Approximately 300,000 cataract operations are performed in the UK annually.