Cataract surgery is one of the most frequent, and often most rewarding surgeries performed by Ophthalmologists.
It involves:
- Gaining access to the eye’s natural lens, which has become cloudy forming a cataract
- Breaking up the pieces and removing them with an ultrasound machine,
- Replacing it with new, clear artificial lens.
With modern surgery, the procedure not only removes the clouding of vision caused by the cataract, but also allows for different types of functional vision. Furthermore, as our understanding of the eye has evolved, we now appreciate that taking out a cataract can help the overall health of the eye, for example to treat certain types of glaucoma.
So what are the options with cataract surgery? Ultimately, whatever you choose has no bearing on the actual surgery. Technically it is all the same. However, I believe in constant communication in making the right choice for each individual. The common options include the following:
Emmetropia
Overall, this is one of the most common choices. Furthermore, in patients with other co-morbidities (such as glaucoma) this is a very safe option. Essentially, the artificial lens chosen is usually of single power, called a monofocal intraocular lens (IOL).
This allows one to see most clearly at a certain small range of distances, with the most common choice to have vision for distance (i.e. watching television) without glasses. Vision like this that is clearest for distance viewing is called emmetropia, which is analogous to wearing simple pair of glasses for distance. However, unlike the natural lens of our eye, this type of artificial lens cannot change its focus, so it cannot allow for both near and far distance vision, which young eyes are naturally able to do. Patients with these single distance lenses will usually need a pair of reading to refine the near vision after surgery.
Conversely, if one is motivated to be spectacle free, there are now a few different ways to allow for both near and far vision following surgery.
Monovision
Monovision describes the ability of a person to unconsciously use one eye to see near objects, and the other to see far away, usually without the need for any glasses. A few people have this ability naturally. This concept can be achieved with cataract surgery done on both eyes, where one eye has a “standard” distance lens implanted, and the other has a lens of a different power that enables this eye to see most clearly for near objects and reading. Patients with post-surgery monovision usually do not need any glasses to see near and far clearly.
However, this option is most suited to people who are able tolerate the difference in vision between the two eyes. The majority of people without natural monovision are advised to trial seeing in this way for a short period of time before undergoing surgery, so that they can try seeing what the world looks like with one eye seeing for far and the other for near. This can be done with glasses or contact lenses. It should quickly become apparent to the patient if this type of vision is not suitable for them.
Multifocal intraocular lenses
Another method of being glasses-free after cataract surgery is the use of a different type of intraocular lens. These are termed multifocal intraocular lenses, which are designed to incorporate a range of power corrections. This type of lens gives the patient good vision for near, distance, and all the distances in-between. It’s like using varifocal glasses, implanted into the eye.
However, with multifocal lenses, some patients can still experience some blurring of vision with very near work such as reading, which can be corrected with reading glasses. There is also a reduction in contrast, which can make reading in dim light difficult. There is a high incidence of glare with multifocal lenses, which patients can find hard to withstand. A small number of patients report seeing haloes. Thus this type of lens is not recommended for people whose occupations depend on night driving, dim light or very near work.
Accomodative intraocular lenses
In an eye with a natural lens, we accommodate to see near objects. Accommodation enables the eye to adjust its focusing power to see clearly at all distances. This is made possible by the circular ring of muscle (ciliary muscle) that surrounds the natural lens which is housed in its capsule, called the capsular “bag”. The ciliary muscle is attached 360 degrees to the capsular bag by multiple thin fibres called the cilliary zonules. The ciliary muscle and its zonules adjust the lens power by contracting and relaxing to alter the shape and thickness of the natural lens in its capsule, allowing a large range of clear vision from near to far.
After standard cataract surgery with the removal of the natural lens, this action of accommodation is lost, which is why reading glasses are required for near vision after surgery.
Another type of cataract surgery uses accommodative intraocular lenses, which aims to mimic the action of accommodation after surgery. This lens is designed with special “legs”, or haptics, that secure the lens within the natural lens capsule. Standard monocular lenses have haptics that stabilize the lens and makes it immobile within the capsule. The special haptics on accommodative lenses are designed to be flexible, so as to move the lens forward as the ciliary muscle contracts. This motion aims to mimic natural accommodation. However it is important to bear in mind that the degree of movement is often unpredictable.
This type of lens also allows for a greater range of reading to distance vision compared to standard cataract surgery, but some patients might still find that for clearest reading vision, reading glasses are still required.