What type of lens will be implanted in my eye/s during cataract surgery?
In cataract surgery, the cloudy, natural lens is removed from the eye. A synthetic lens has to be implanted in the eye, to allow focused vision. The implanted lenses are clear and durable and will usually last a lifetime. Intraocular lenses approved for use in Australia are of very high-quality standard but they vary in what they are meant to achieve and their optical properties. In general, replacing the cloudy lens opens an opportunity to also improve the optics of the eye so that less spectacle help will be needed after the operation. However, different patients will have different degrees of spectacle independence after surgery and no one rule applies to all.
The main types of optical designs of intraocular lenses are:
1. Monofocal spherical lenses
2. Monofocal toric (astigmatism correcting) lenses
3. Multifocal and extended range lenses
MONOFOCAL SPHERICAL LENSES are the most commonly used lenses. They focus the image at a given distance, which may be decided on by the surgeon and the patient beforehand. Options include focusing the eye in the distance (e.g. for driving, watching a movie, playing sports) or focus at the near range (reading a book or working on a computer). In the typical case, the vision will be focused in the distance, requiring reading glasses for near vision. This option is usually chosen by patients who are used to needing reading glasses prior to developing a cataract.
Alternatively, the focus may be set up close, allowing comfortable reading without glasses but requiring glasses for distance viewing. This option is usually chosen by patients who have always been short sighted and who are normally able to read without glasses and wish to preserve this ability, even though that means they will have to continue and wear glasses for distance viewing.
In some cases, each eye receives a different distance of focus. One eye is focused in the distance and the other focused up close (mono-vision). This allows for good vision over a much larger distance range, and reduced the need for glasses significantly. However, it is not suitable for every patient and needs to be carefully considered.
MONOFOCAL TORIC LENSES are similar to monofocal spherical lenses in that they are set to a particular distance of focus (distance or near). They are specifically meant for eyes with corneal astigmatism, which is a type of optical distortion requiring "cylinder correction" in the glasses. Whether or not there is significant corneal astigmatism is established by preoperative measurements of the cornea. Most patients do not require toric lenses as they have a low degree of astigmatism which is not significant for their vision.
These lenses need to be surgically positioned in a particular direction within the eyeball to achieve their purpose. In the best-case scenario, they will markedly reduce the effective astigmatism after surgery.
Upside: For eyes with significant astigmatism, better postoperative vision when not wearing glasses.
Downsides: Because toric lenses sometimes move (rotate) inside the eye after surgery, they may rarely need to be adjusted/repositioned in a second operation. They are also considerably more expensive than spherical lenses.
MULTIFOCAL AND EXTENDED RANGE LENSES are designed to allow focus over a range of distances and to minimise or eliminate the need for glasses after surgery. They may also combine a toric (astigmatism correction) component. Optically, their design is different to multifocal spectacle lenses, and the visual experience with them is different to that of multifocal glasses, although the same term is used to describe them.
Upside: A large range of focus which may allow the patient freedom from glasses or minimal need for glasses.
Downside: A small but significant percentage of patients complain of various optical aberrations and disturbances with multifocal lenses. These include halos around lights, streaks around lights, difficulty with low contrast, glare, and other optical problems. Many patients adjust to these over time, but some are sufficiently bothered by them to require removal of the intraocular lens and replacement with another, usually monofocal lens. Removal and replacement of a lens is more complex than the cataract operation itself and is riskier. These lenses are also considerably more expensive than monofocal lenses.
Dr Zamir uses all of the above intraocular lens types. The choice of lens in individual and varies between different patients, depending on their lifestyle, visual needs, habits, optical history, visual expectations and other factors. You will have a discussion about the optical plan with Dr Zamir prior to your surgery.