Choosing the right implant for cataract surgery is sometimes not an easy decision. I will try to explain it in as simple words as possible to help you making your decision.
Please, read my cataract leaflet first for better understanding of terminology like short-sightedness, ling-sightedness, astigmatism, cataract surgery, capsular bag and the anatomy of the eye.
Monofocal implants
- If you do not mind wearing reading glasses, then it makes sense to choose the monofocal implant that allows you to see as best as possible for distance without glasses (TV, driving). You will need to wear reading glasses for reading books, or working on the computer.
If you have a pre-existing astigmatism in the cornea (the shape of the cornea is not ideally spherical but close to elliptical like a rugby ball), then you will need glasses for distance as well as for reading, unless you go for the toric monofocal implant that will correct your astigmatism and will allow you to see well for distance without glasses. You will wear reading glasses for computer work and reading books.
Some people who read many hours a day, ask to make them read without glasses for near vision and they prefer to wear glasses for distance vision. This can be done with monofocal implant. Usually, those people lived all their life with mild to moderate degree of short-sightedness and could read without glasses before they developed cataract.
- Full Monovision is also an option with monofocal implants in patients who want to reduce their dependence on glasses for reading. In this case, the dominant eye gets the best possible vision (without glasses) for distance (TV and driving) and the non-dominant eye gets the best possible (without glasses) near vision (reading books and working on the computer). If you choose this option, you will use each eye separately, one for distance and the other for reading vision. If you change your mind later and you want to use both eyes together for distance or reading vision, then you need to wear distance and reading glasses.
- Mini–monovision is a compromise for people who do not want to wear glasses all the time especially when driving and shopping, who do not want to use each eye separately for distance and reading vision like in the full monovision version and who don’t mind wearing reading glasses books and mobile phone reading. In that case, the none-dominant eye will be left minimally short sighted to see the dashboard of the car and possibly the computer screen without glasses while the dominant eye will focus for distance. With this option, the patient would need to wear reading glasses for books reading and long mobile phone work.
Multifocal implants
Multifocal implants have multiple foci for distance vision (watching TV, driving), intermediate vision (computer desktop work) and near vision (Books, mobile phone work) at the same time.
- As mentioned in my cataract leaflet, the decision of having a multifocal implant is not an easy decision. If you do not like wearing glasses and you would like after surgery to become as much as possible glasses free then, multifocal implants are an option to be considered.
Nowadays, the ophthalmic industry is producing high quality multifocal implants with a very high satisfaction rate. This option is a compromise or a trade-off, where the patient sacrifices a small proportion of the quality of vision she/he gets from monofocal implants for the sake of being glasses free for distance and reading (as much as possible).
The most common side effect of multifocal implants is mild glare or dazzle from coming cars when driving at night or seeing the rings of the lens in sunny days. Those are becoming very mild symptoms with the new generation of lenses and the brain gets used to them and learns to ignores them within the next few months after surgery, the same as it ignores seeing floaters in the eye once people have them for some time.
Some patients report they still need reading glasses when they read in dim light at night.
Very rarely, a multifocal implant ends up being exchanged to a monofocal implant as with the best efforts of the surgeon, it does not centre well in the bag of the natural lens of the eye.
- Not all eyes are suitable for multifocal implants, for example if the patient has macular diseases like age-related macular degeneration or diabetic macular disease (macula is the central part of the retina) then, I do not recommend having this implant due to the high rate of dissatisfaction of this category of patients.
- The anatomical centre of the cornea is the central point of the cornea while the optical centre is the central focus point through which the light enters the cornea. The optical centre is very close to the anatomical centre but it does not fall on it.Some patients have slightly unusual structure of the cornea where the distance between the anatomical centre and the optical centre of the cornea is too large.
Then, multifocal implants are not advised, again due to higher rate of dissatisfactionAnother point to take into consideration is the centre of the pupil which is usually slightly displaced from the above two centres and this also should not be too far from them.
- Your suitability for multifocal implant will be explained by the surgeon.
- Sometimes I do not recommend multifocal implants to certain people whose profession might be affected by the multifocal implants like lorry drivers or other drivers who drive a lot at night. The glare from the lights coming from opposite cars might affect the quality of their driving night vision. This can be discussed in details during your clinical visit.
Discussing your needs is crucial to know what is the best implant to put in your eye.
Extended depth of focus implants without rings built-in: PureSee implants
This is a new technology where the implant gives excellent distance and intermediate vision (computer desktop, car’s dashboard…) without glasses but you might still need reading glasses for closer objects like reading books or working on your mobile phone. The advantage of this implant is that it does not have ring built-in, hence its side effects are the same as the standard monofocal implant. Any patient can have this implant including patients who have macular degeneration or who were denied multifocal implants due to their non-suitability.
This is an ideal implant for patients who do not want to risk having side effect of the multifocal implants, but keen on having good quality distance and intermediate vision without glasses.
There are different refractive outcomes available within this category of implants, like aiming the dominant eye for excellent distance vision, and the non-dominant eye for minimal short-sightedness. That would still give good-quality distance vision in the non-dominant eye, probably not as good as with the dominant eye, however with the gain of seeing better for closer distances with minimal dependence on glasses, if any.
Toric monofocal or multifocal implants
- If you are told by the doctor that you have astigmatism in your cornea and you do not mind wearing reading glasses but you would like to be glasses free for distance vision, then toric monofocal implant is the best option for you. In this case, the implant must sit in a specific position inside the eye to compensate for the astigmatism in the cornea.
- Monofocal toric implants can focus the light either for the best distance or the best reading vision, depending on the patient’s visual requirements.
- Occasionally these implants rotate inside the eye, usually within the first 24 hours after surgery. Then, they need to be repositioned to the original place with another small surgery. Having said that, this happens in less than 5% of patients.
- Corneal astigmatism will be automatically corrected with the multifocal implants and extended depth of focus implants (PureSee) to provide the best possible vision for distance and reading. It does not make sense to leave the astigmatism uncorrected, as the patients would need to wear distance and reading glasses after surgery and loose the purpose of having a multifocal implant in the eye, which is glasses free vision for distance and near.