During cataract surgery the natural lens of the eye, now cloudy with cataract, is removed. The natural lens is one of the two focusing elements of the eye, the other being the cornea. This is the perfect opportunity to reconstruct the optical performance of the eye. In addition to replacing the cloudy natural lens with a transparent lens implant, imperfections in the eye’s optical performance that existed before the development of cataract may be treated. Such imperfections include short sight, long sight, astigmatism, presbyopia (reading glasses dependence) and wavefront abnormalities. These imperfections increase dependence on distance and reading glasses and reduce quality of vision, for example causing glare when driving at night or sensitivity to sunshine. You may have heard the term ’Supervision’ - this is the greatly enhanced vision resulting from successful treatment.

What is a lens implant?

Lens implants (also called intraocular lenses or ‘IOLs’) are a prosthesis, in this case a transparent plastic lens usually about 6mm in diameter. They are inserted during cataract surgery to replace the focusing power of the natural lens of the eye that has been removed.

The first ever lens implant was made by Rayner in the UK in 1949. It was designed by Sir Harold Ridley FRS FRCS a Consultant Ophthalmologist at St. Thomas’ Hospital London who also performed the surgery. Since then tens of millions of lens implants have been implanted internationally.

Lens implant technology is one of the greatest advances made by modern medicine, freeing cataract patients from the ’pebble-dash’ glasses worn previously that offered very poor optical performance and were unsightly.

Thousands of lens implant types are now available and standards have improved greatly over the years. Nevertheless lens implant quality varies greatly, from basic to extremely sophisticated.

The Alcon Acrysof family of yellow IOLs.
Toric aspheric (left); monofocal aspheric (middle); ReStor multifocal aspheric (right)

Choosing the right lens implant for you: the enhanced cataract surgery approach

The most sophisticated lens implants combine characteristics to correct all optical imperfections if necessary.

I am committed to maximising the quality of your vision and minimising your need for glasses post-operatively. This is achieved by -

Step 1) Pre-operative measurements

In-depth analysis of your eyes is performed, many of the tests requiring ultra-sophisticated equipment. Your glasses prescription is determined by an optometrist (optician). Axial length is the front-to-back length of your eyes, measured with the IOL Master, a sophisticated laser.

The IOL Master	IOL Master axial length measurement

The curvature of the cornea is assessed with a keratometer. Extremely accurate measurements of cornea curvature, the cornea’s wavefront abnormalities and the diameter of the pupil are made with the Galilei topographer, a high-tech ‘Scheimpflug’ camera system.

The total wavefront abnormalities of the eye, not only those arising from the cornea, are analysed by the Zeiss WASCA aberrometer.

Step 2) Pre-operative consultation

After the measurements, I will examine your eyes and ascertain your visual requirements, for example the extent to which you wish to be less dependent on glasses. There will then be plenty of time to discuss which lens implant is best for you.

Examples of lens implants customised for my patients' eyes:

• A patient who does not mind wearing reading glasses but has high levels of 'spherical aberration', a type of wavefront abnormality, might receive a Tecnis aspheric monofocal that will reduce dependence on distance but not reading glasses and simultaneously remove the spherical aberration.
• A patient who does not mind wearing reading glasses and who has low levels of spherical aberration might receive a Rayner aspheric monofocal that will reduce dependence on distance glasses and not increase the patient's previously satisfactory degree of spherical aberration.
• A patient who requires freedom from both distance and reading glasses and who has a moderate amount of spherical aberration might receive the ReStor aspheric multifocal which focuses both distant and near objects and corrects low levels of spherical aberration.
• A patient whose priority is spectacle independence for distance and near who has a significant amount of astigmatism might receive the Rayner multifocal toric which focuses for distance and near and also treats astigmatism.
• A patient who has signs of ‘macular degeneration’, a disease of the retina, might receive an Acrysof yellow IOL. All modern IOLs absorb ultra-violet light, but this IOL incorporates a yellow pigment that also filters excessive blue light. Ultra-violet and short wavelength blue light may damage the retina and exacerbate existing disorders such as macular degeneration: Acrysof yellow IOLs protect against this.

Step 3) Surgery

Some lens implants, for example astigmatism-correcting, require highly accurate alignment within the eye if they are to work properly. I use a method of registering the shape of the cornea before the operation begins to achieve this.

Step 4) Post-operative consultation

I will examine you and repeat many of the measurements made prior to surgery, to determine the accuracy of the outcome. I will also ask what you think of your new eyesight!

Choosing a lens implant: the ‘standard’ approach

You may be interested to learn that the standard approach is restricted to measurement of axial length (sometimes with an ultrasonic device that is often less accurate than the IOL Master) and keratometry. This will not provide a solution customised for your needs.