A cataract occurs when the eye’s lens, which is normally clear, become opaque. This lens is located inside the eye behind the pupil where it sits in a lens bag. Cataract causes blurred vision by blocking light as it travels through the eye. It can also change the focal point of the eye, further blurring the vision.
The only proven treatment for cataract is surgery. Through micro incisions, a circular opening is made in the lens bag and the lens is broken into small fragments with ultrasound and removed from the eye. With the natural lens (and thus the cataract) now removed, a transparent folded artificial lens (intra-ocular lens: IOL) is inserted into the lens bag where it then unfolds. The focusing power of each lens implant is specific to each eye and highly precise measurements are taken of the eye before surgery to determine the exact lens strength for your eye.
This depends on 2 main factors, the type of intraocular lens (IOL) used and the focal point of the IOL. You can choose 4 options.
The traditional approach has been to insert lens implants with a single focal point (monofocal IOL) focused for distance in both eyes. This usually results in excellent quality distance vision without spectacles. After cataract surgery, spectacles are required for near (eg reading) and intermediate distance (eg using computers, reading the dashboard of a car).
Blended vision or monovision reduces spectacle dependence after cataract surgery. At the time of cataract surgery, a lens implant focused for distance is inserted into the dominant eye. In the non-dominant eye, a lens implant focused for near is inserted. With both eyes open, one is able to see clearly for distance and near. Depending on your individual case, a trial with contact lenses may be required to ensure that the brain will be able to adapt to a different point of focus in each eye.
Extended depth of focus IOL’s work by having a greater focal range and thus provides for distance and intermediate vision. With extended depth of focus IOLs, spectacles are usually required for fine near vision.
Multifocal/trifocal intraocular lenses work by splitting the light that travels through the eye into 3 different focal points: distance, intermediate and near. The result is very good vision for objects at all distances and significantly reduced spectacles dependence or even spectacles independence. However, spectacles may still be required for fine near work in low light conditions.
Multifocal/trifocal IOL’s have some potential downsides which are unique to these lenses which don’t occur with monofocal IOL’s. Because these lenses work by splitting the light travelling through the eye into 3, the quality of vision for distance, for example, is not quite as sharp is it would be if the lens focused all light for distance vision. However, the great benefit with these lenses is that they give vision at all distances.
The second issue is that glare and haloes around lights are more commonly experienced by patients than in monofocal lenses. This usually does not cause any significant problem and, after several months, these are much less noticeable. However, in around 1 in 200 cases, glare and haloes can be very troubling to the point where these lenses need to be removed.
The third is that multifocal/trifocal lenses require that the distance focal point be very precise. Highly sophisticated scans are taken of your eye before cataract surgery to determine the correct strength of lens required to achieve the correct focus. These scans are not perfect, however, and the focal point for distance after surgery may not be exactly what the scans predict. In monofocal lenses, this is rarely an issue. In eyes with multifocal IOLs, further surgery to “fine tune” the focus of the eyes with either laser or a second intraocular lens may be required.
This is a very individual decision and depends on several factors. The first is your visual requirements. If having excellent distance vision is your main priority and you are happy to wear spectacles for near work then having monofocal lens implants is an excellent option. If you require excellent distance and intermediate vision, then monovision or an extended depth of focus lens implant are excellent options, though spectacles are likely to be required for fine near work. If you are seeking very good vision for all distances without spectacles then a multifocal lens implant or monovision are the options most likely to achieve this.