When a cataract is removed it is replaced by an intra-ocular lens – this focuses the light on the retina at the back of the eye and allows you to see clearly. There are many types of lenses available and patients often ask which lens will be used and why. When choosing a lens, your surgeon will consider the following factors:
1. What it is made from. There are 3 choices when it comes to the material made to make the lens: hydrophobic acrylic, hydrophilic acrylic and silicone. Each have different physical properties which effect the way the behave when being handled (for example when injected into the eye) and when positioned within the eye. Each are used in fairly equal numbers.
2. Lens design. Lenses have 2 components – the optic (central part of lens that focuses light) and the haptic (arms that hold lens in position). If these are moulded from a single piece of material, it is considered a single piece lens. If the haptics are added to the optic and are of a different material, it is considered a 3-piece lens
3. Focal properties. Lenses can be either mono-focal or multi-focal. Mono-focal lenses have a fixed focal length – usually either for distance OR near. Multi-focal lenses attempt to provide focussed vision for more than one distance – usually distance AND near
4. Filtering. The use of a tint in the lens is sometimes used to filter out some of the UV end of the light spectrum. Whether this results in improved vision or not remains controversial.
5. Correcting Astigmatism. Astigmatism is when the eye has an irregular shape. This effects the way light is focussed onto the retina at the back of the eye and will result in blurred vision. If present, a sense tailored to neutralise the astigmatism may be used during cataract surgery.
6. Correcting Aberration. Aberration refers to any factor that interferes with the way light is focused by an optical system including your eye. There are many sources of aberration, some of which can be improved upon at the time of cataract surgery.
-Posted by Dr Colin I Clement.