A choice of lenses
The human eye can change focus or accommodate by changing the shape of the human lens. In young children the ability to change focus is so good that they can see clearly from far distance to the tip of their nose!
As adults get older, the ability to change focus gets progressively weaker and weaker, so that by their mid forties most people will start to struggle to read comfortably without the help of low powered reading glasses, or, if they already wear glasses for distance, varifocals, bifocals or separate glasses for distance and for reading. As we get older still, we continue to lose the ability to change focus so that we need stronger reading glasses and may struggle even to see at intermediate distance, for example when using computers, reading music or for things like cooking and even eating.
The standard (monofocal) lenses used in cataract surgery will usually give you clear vision at a particular distance (unless you have astigmatism). I will discuss with you the distance options (near, intermediate or distance) and what will suit you best, see refractive planning. What the standard lenses can not give most people is the ability to see over a range of distances.
I was one of the first surgeons to implant the Bausch and Lomb MI60 Micro-Incision Intraocular lens when it was introduced. I have used this lens extensively in both NHS and Private Practice as my ‘single focus’ lens of choice, and am one of the UK’s most experienced users of the lens (Manufacturer supplied information).
There are a variety of special lenses or premium lenses which offer some additional ability to see over a range of distances. For those seeking the perfect solution, it is important to realise that the perfect solution does not exist; there is always a compromise to be made. The importance of the decision is to make best compromise for you as an individual.
IOL: Premium Lenses
Multifocal lenses give patients the ability to see in focus in the distance and for near all of the time (near vision may be less good in low light) Most designs do this by using a series of concentric rings of alternating near and distance focus.
They do not (with one exception) give intermediate vision
The downside of the design of these lenses is that the light coming through the “wrong” rings of focus (the near rings when you are looking in the distance and distance ring when you’re looking at something near) gets scattered and produces optical side effects or aberrations. These aberrations are most obvious at night when the pupil is large, when driving at night you may see significant haloes around car lights and street lights and get glare (where contrast between dark and light is reduced and things seem pale and it is difficult to pick out details).
If a multifocal lens is the right choice for you, I will select the lens I think best suits your needs from a range I am happy with, including the Restor by Alcon, the Technis Multifocal by AMO and a special type of multifocal lens known as an Extended-Range lens (Symfony by AMO)
IOL: Multifocal Lenses
The newest design of Intraocular lens are known as extended range or extended depth-of-focus lenses. For many patients they offer significant advantages over multifocal lenses. Rather than having a full near correction, the near-point of the lens is limited to the distance at which people tend to read newspapers and tablet devices. By limiting the strength of the near correction, optical side effects are significantly reduced and tolerance is much improved. Additionally, unlike multifocal lenses there is no out of focus region between distance and near focus as there is a range or spread of focus between the distance focus and the near focus. The Symfony extended range lens I use has an additional novel optical technology which enhances clarity by reducing chromatic aberration or colour blur.
There are lenses that change focus using the muscle inside the eye to move the lens and shift the focus. These lenses seem to have similar levels of halos and glare to standard monofocal IOLs, but give a small range of focus that covers distance to intermediate vision.
Accommodating lenses do not change focus enough to give good near vision. Reading moderate sized print in reasonable light is usually possible at arms length.
Accommodating lenses are associated with a significantly increased likelihood of developing posterior capsule opacity; a minor laser procedure, carried out as an outpatient, easily rectifies this.
Accommodating lenses can have problems with the hinge mechanism and have largely been superseded by Extended-Range lenses.
IOL: Accommodating Lenses
Monovision is a technique where your two eyes are deliberately left with a different focus, one for near and one for far, or sometimes intermediate and far. Some people have the ability to make use of this; others find it optically very confusing and will never tolerate it. To some extent this ability is hard-wired into our brains. Working out who it is suitable is not straightforward and unless you have a history of having used this either by creating it with contact lenses or because your eyes are naturally like this, there is a risk that you may discover after surgery that it is not for you. If you are interested in this option, please ask me more about it.
IOL: Monovision Lenses
Toric Intraocular Lenses
If you have astigmatism, and wear contact lenses, you may be familiar with the term “toric”, this simply means a lens with different curves, to correct an eye with different curves or astigmatism.
A toric intraocular lens can be used to correct pre-existing astigmatism and give you much better clarity of vision without glasses than you have ever had before. Toric lenses can also be multifocal, giving you the ability to see near and distant things in focus.
If you have more than a little astigmatism and choose not to have it corrected, your eye is likely to remain blurred without glasses at all distances following surgery.
Extended-range and multifocal lenses work best when astigmatism has been corrected, so lenses are often toric as well as Extended-Range or multifocal, maximising the quality of vision.