world
on the retina at the back of the eye. This is similar to a camera focusing
an image onto the film within it.This is a personal website of Mr Chris Heaven FRCS (Ed),
FRCOphth, FCOptom.
I am a Consultant Ophthalmologist (eye surgeon) based in the North West of
England.
The purpose of this site is:
To provide information on Lens Exchange. This is a surgical procedure
for the correction of short sight (myopia) and longsight (hyperopia). Lens Exchange
is also sometimes called:
Lens Exchange is an alternative to LASIK, epi-LASIK, LASEK and PRK laser refractive surgery. The eyes of some patients are not suitable for laser refractive surgery. The usual reason is that the degree of short or longsightedness is too large to be safely or effectively corrected using a laser procedure. Also some patients do not like the concept of laser treatment of the eye which does involve the irreversible removal of some corneal tissue. In these situations Lens Exchange may be an acceptable alternative.
Lens Exchange involves a surgical procedure on the eye that is very similar to a small incision cataract operation. It therefore uses tried and tested techniques and technologies.
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. Combining procedures in this way is called Bioptics.
For more information on any chosen aspect of Lens Exchange click onto the menu either to the left or above. This will provide an initial brief explanation.
Where appropriate a more detailed coverage is available
by clicking on the
"Want to know more" icon at the bottom of the page.
Detailed information sheets are available in the Download section.
Understanding the eye
The structure of the eye
The eye is rather like a small camera. The main function
of the eye is to produce a focused image of the visual world
on the retina at the back of the eye. This is similar to a camera focusing
an image onto the film within it.
The main parts of the eye (starting at the front of the eye and moving backwards) are:
The Cornea
This is the clear curved window at the front of the eye. It is made of regularly arranged layers of transparent collagen, and through it you can see the coloured iris. The cornea does most of the focusing of light coming into the eye and needs a smooth and healthy tear film to work well. This tear film is essential for clear vision and the health of the eyes. It has a complex composition including natural antibiotics.
The Sclera
This is the white outer wall of the eye. Its job is to provide structure and strength, and to protects the contents of the eye. It is made of the same collagen material as the cornea but the layers are irregularly arranged which is why it is white rather than transparent. Six small muscles are attached to the sclera and these move the eye around.
The Iris
The iris is the coloured part of your eye, and is like the diaphragm in a camera. The round opening within the centre of the iris is the pupil. Tiny muscles within the iris control the size of the pupil. One muscle makes the pupil smaller and another draws it more widely open. Adjusting the size of the pupil controls the amount of light allowed to pass to the back of the eye.
The Lens
The
lens of the eye sits immediately behind the pupil. It is like a lens in a
camera. It cannot be seen unless special examination instruments are used.
This natural lens, which is made almost entirely of protein, is called the
"crystalline lens" to distinguish it from the artificial lens that
is placed into the eye as part of a Lens Exchange or cataract operation.
The lens of the eye is about the same size and shape as a smartie - but transparent. It helps with the focus of the eye. In youth a small muscle inside the eye is able to change the shape of the lens and thus adjust the focus of the eye. This ability is gradually lost with age and this is one reason why reading glasses are needed from mid 40's onwards.
The Retina
This is the vital light sensitive layer that lines the back of the eye. It is like the film in a camera. In the deepest (outermost) part of the retina are light detecting cells called rods and cones. These cells sense the image focused onto them and this visual information is converted into electrical signals. These signals then pass into the optic nerve at the back of the eye and from there to the brain.
The colour sensitive cones are concentrated in the central part of your retina (called the macula) which you use for detailed vision, such as reading this. The rods are not colour sensitive, and can only detect black and white. They are found throughout the rest of the retina. They are though particularly sensitive to low levels of light and they enable us to adapt our vision to the dark. In fact our eyes can be an incredible one million times more sensitive in the dark!
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 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 from 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 standard lens implant has a fixed focus, i.e. these types of lens implants do not have focus adjustment. Lens implants with focus-ability have recently come onto the market, but their long term effectiveness is still uncertain.
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. For further information on this click here.
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
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. In excess of 250,000 cataract operations are performed in the UK annually.
Visit Mr Heaven's Cataractcare.co.uk website.
