Cataract Surgery

Although this is done in some places around the world, in Australia this is generally not done due to a number of reasons, including the very low but serious risk of sight-threatening complications.

An intraocular lens implant (IOL) is an artificial lens made of plastic (typically acrylic) inserted into the eye during cataract surgery after removal of the natural (crystalline) lens of the eye.

An IOL is almost always inserted during cataract surgery. If there are technical reasons that make insertion of the IOL difficult at the time of surgery, then the IOL can be inserted during a second operation.

An IOL is usually implanted in the “capsule” or “capsular bag” which is the thin envelope that is left behind after removing the natural crystalline lens. If there is a weakness or tear in the rear part of the capsule then a different type of IOL may have to be implanted between the iris and the capsule (sulcus-fixated IOL) or in front of the iris (anterior chamber IOL).

The vision in this case will likely be very blurred and thick lenses in your glasses or a contact lens will be required to achieve visual clarity.

An IOL focuses the light entering the eye onto the retina. In the same way that lenses in glasses have a specific “power” or “number” expressed in Dioptres (D), the intraocular lens (IOL) inserted into your eye will also have a specific power tailored to the size of your eye.

Measurements of the eye (known as “biometry”) are taken before cataract surgery to allow your surgeon to choose an IOL that is appropriate for the size and shape of your eye.

These measurements are then inserted into various mathematical formulae to estimate the correct IOL “power” for your eye. The “power” of a lens is expressed in Dioptres (D).

Modern optical biometry machines are very accurate but not perfect:

• Dense cataracts can make measurement of the length of the eye less accurate
• The measurements of the cornea can be affected by dry eye and other external eye conditions.

Large studies have shown that in 70-80% of cases the estimated refraction (power) differs from the actual refraction (power) after surgery by up to 0.5D. In 20-30% of cases the degree of error can exceed 0.5D. For this reason, please note that glasses may be required after cataract surgery for near vision or distance vision or both.

Assuming the second eye has a significant cataract, surgery is usually performed a few weeks to months later allowing the first eye to heal and achieve a stable refraction (power). In some cases, it may be appropriate to perform surgery for the second eye sooner.

• The natural crystalline lens of the eye can alter its shape allowing focussing of objects in the far distance, in the intermediate distance or up close. This is called accommodation.
• Most people find that their accommodation gets weak around the age of 40 to 45 leading to a need for reading glasses (or bifocal/multifocal glasses).
• An intraocular lens (IOL) implant, unlike the natural crystalline lens of the eye, cannot accommodate.

There are many types and brands of intraocular lenses (IOLs) available and they are typically made of acrylic. Each type and brand has their own advantages and disadvantages and some may be more suitable for you than others.

The main types of IOLs are:

• Monofocal, Multifocal and EDOF (extended depth of focus)
• Toric vs Non-Toric

A monofocal lens implant is a standard IOL with a single focal point. Glasses are required to focus objects at other distances.

Examples:

• If a monofocal IOL is implanted to give clear distance vision, objects up close will be blurred, and reading glasses will be needed to read or use your phone.
• If monofocal IOL is implanted to give clear reading vision, objects in the distance will be blurred and glasses will be needed for distance vision.

A multifocal lens implant allows the patient focus at multiple points and thus see both near and distance objects out of the operated eye simultaneously using diffraction optics (these lenses do not accommodate). As a result, there can be a compromise in visual clarity and contrast. Many patients also report glare and haloes with these lenses. The visual quality can be significantly degraded if problems develop in the macula (central part of the retina) in the future, such as age-related macular degeneration. These lenses are used for patients who are highly motivated to be free of all glasses after cataract surgery and are willing to accept the associated compromises in visual quality.

An Extended Depth of Focus (EDOF) lens is a relatively new concept where the IOL still has a single focal point but it is enlarged, allowing improved intermediate vision with little or no compromise for distance. Most patients still require reading glasses for very near tasks but intermediate vision can be improved.

A “toric” IOL may be used if an eye has significant astigmatism. Astigmatism is where the cornea (the front window the eye) has a cylindrical shape (like a rugby ball) rather than a spherical shape (like a soccer ball). It is common for some astigmatism to remain even with the use of a toric IOL. Low degrees of astigmatism are easily incorporated into glasses. Toric monofocal and multifocal/EDOF IOLs are available.

Toric IOLs are specially ordered for the patient for routine placement in the “capsular bag”. If an IOL needs to be placed in an alternative location (sulcus-fixated or anterior chamber) it may not be possible to neutralise the astigmatism with an IOL.

Monovision or blended vision is a strategy used in some cases to reduce dependence on glasses by using an IOL in one eye to achieve clearer focus for distance vision while in the other eye an IOL is used to achieve clearer focus for intermediate or near vision.

• It can take 6 or more weeks for the refraction (power) of the eye to stabilise after cataract surgery.
• In some cases, the refraction (power) of the eye may change further down the track.

An intraocular lens (IOL) is usually implanted for life. Only in rare circumstances does it need to be removed.

Not uncommonly, a thin layer of lens material can slowly grow between the back of the intraocular lens implant (IOL) and the posterior (rear) capsule of the lens, after successful cataract surgery. This, in association with wrinkling and thickening of the posterior capsule, causes blurring of vision and is called Posterior Capsular Opacification (PCO). It can be treated with a painless procedure called YAG Laser Capsulotomy which is performed in the clinic. It occurs more commonly in younger patients.