How to select a lens


The surgeon can discuss with you the refractive outcome that you may want after the natural lens of the eye is removed and replaced with a plastic lens. We can replace a cataract with a lens implant of any power that is desired.


Most people prefer to have both eyes corrected so that they can see things in the distance without glasses (driving, watching TV) and are happy to have reading glasses for intermediate vision (looking at the computer, reading music) and near vision (reading very small print, needlecraft).

Individual circumstances will vary and you should take the time to discuss the desired refractive outcome with your surgeon, as it is difficult to change your mind once the lens is in your eye.


For example,

  • if you are very myopic (“short-sided”) or hyperopic (“long-sighted”) we can put a lens implant that will correct that and probably give you good distance vision without glasses but you will need reading glasses.

  • If you are younger person who needs to spend a lot of time reading or looking at computers then you may wish to be left moderately myopic in both eyes so that you can read without glasses and use distance glasses for things like driving or TV.  

  • If you have any macular problem then you may wish to be left moderately hyperopic. This means that spectacles containing “plus” lenses will be needed for both distance and near. The spectacle “plus” lens will magnify the size and area of images, so your ability to see details of the images should increase.

  • “Ocular dominance” is similar to right-hand or left-hand dominance. It simply means that your brain decided a long time ago to use one eye more than the other eye, for example when shooting a gun or taking a picture through a camera viewfinder.  For some people it may be possible to create a “blend” of distance and near vision, by using a monofocal lens implant for good distance vision in the dominant eye, and use a monofocal lens implant for near vision in the non-dominant eye. This is called “monovision”.  There will be some loss of depth perception and stereopsis. If you have found monovision acceptable with contact lenses then this is most likely to be suitable for you.


The formulae used to calculate the desired range of lens powers rely upon various measurements of the eye, including the length of the eye and the curvature of the front surface, the cornea.

These formulae predict the outcome of lens surgery and offer a range of lenses to achieve that outcome. It is not an exact science and there is the possibility that the lens implant recommended may not give the desired outcome (“refractive surprise”).  The size of the eyeball varies between individuals and the formulae used may not be very good at predicting the outcome when the eye is very short (less than 22mm) or very long (more than 28mm), or if there was any previous corneal surgery, such as LASIK, PRK or SMILE.


If you wear glasses for presbyopia (loss of accommodation because of increasing age) then you may suitable for multifocal lens implants that use diffractive rings to project more than one image on to the retina.  They require a period of neural adaptation and both eyes should have the same IOL for maximum benefit.