Intraocular Lenses (IOLs): Monofocal, Bifocal and Trifocal

• There are various types of intraocular lenses, depending mainly on their focusing capabilities.
• The implantation of intraocular lenses is very common for problems such as presbyopia or cataracts, with excellent results.
• Recovery after intraocular lens implantation is simple, but it must be done well.

Before intraocular lenses (IOLs) were invented, people had to wear glasses with very thick lenses to see after cataract surgery. The intraocular lens (IOL) focuses light entering the eye through the cornea and pupil onto the retina. Its function is to act as a synthetic artificial lens that replaces the natural lens that is usually removed in cataract surgery.

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Intraocular lenses (IOLs) are made of a flexible, bendable material and contain filters that protect the retina from light radiation, such as UV rays.

The vast majority of intraocular lenses (IOLs) have a yellow filter, which protects the retina from developing AMD (a degenerative disease that occurs in the area of the retina). Its function is to reduce the absorption of blue light.

Intraocular lenses (IOL) are usually implanted in the case of: having a healthy (clear) crystalline lens, but with a refractive or graduation problem, for which phakic lenses are used, which correct it without replacing the crystalline lens; or having a crystalline lens that does not work properly, either because it has many dioptres, or because it suffers from presbyopia or cataracts.

• Presbyopia: also known as eyestrain. In this case, the crystalline lens does not fit properly due to loss of mobility as a result of age, it becomes rigid and cannot focus correctly on objects at close range.
• Cataracts: occur when the crystalline lens becomes opaque, there is no longer any transparency and therefore no longer any vision. When cataract surgery is performed, it is often used to correct myopia, hyperopia and astigmatism.

Intraocular lenses (IOLs) can be classified according to materials and focusing ability:

According to the type of material of the intraocular lenses

Depending on the type of material they are made of, intraocular lenses (IOLs) can be rigid or flexible:

• Rigid lenses are made of polymethacrylate and are rarely used today, as stitches are sometimes required to close the eye after implantation.
• The flexible ones are currently the most commonly used. They are usually inserted into the eye rolled up, so that the incision that needs to be made in the eye is smaller, once inside, they are unrolled and correctly positioned. As a very small incision is made, no stitches are necessary, as the incision closes on its own. If the surgeon believes that it will not close on its own, a stitch is placed to ensure that the wound is sealed.

Depending on the focusing ability of the intraocular lens 

A healthy crystalline lens should be able to focus objects at different distances. In many cases, when a certain age is reached, the elasticity of the crystalline lens decreases and focusing ability is lost.

Depending on their ability to focus at different distances, IOLs can be monofocal: they focus at a single distance, or multifocal: they focus at several distances.

The monofocal intraocular lens

These are those with only one focus and are indicated for distance vision (more than 1m), making it necessary to use glasses for near and intermediate vision.

It is the type of intraocular lens (IOL) that has been the most widely used for decades.

With age, presbyopia appears, as the lens of the eye loses flexibility, making near vision more difficult.

Multifocal intraocular lenses

These lenses have concentric circles on their surface, making it possible to see at different distances. Depending on where the incoming light is concentrated, you will be able to see objects that are close and those that are far away, as they allow different points of focus.

With this type of intraocular lens (IOL), spectacles may be needed occasionally for highly focused work, or for a prolonged period of time or in low light.

• Bifocal lenses: These are lenses with two focal points in the optical zone, one for distance vision and the other for near vision. The result is good near and far vision.
• Trifocal lens: This type of IOL has three foci in its optical zone, one for distance vision, one for near vision and one for intermediate vision. It provides the ability to focus at three different distances.

Toric intraocular lenses

Whether monofocal or multifocal lenses, there are toric versions of each of them. This type of intraocular lens (IOL), in addition to solving the above problems, also corrects astigmatism (oval cornea instead of being round and smooth).

The brain must adapt to the change in vision and the improvement in vision must be progressive until it is complete, which is why, with any type of intervention for the placement of an IOL, one eye is operated on first, and the other eye cannot be operated on until 6 to 12 weeks have passed since the first intervention. 

The time difference between the operation on one eye and the operation on the other eye depends on each individual case and must be determined by the doctor.

It is necessary to inform the doctor of all medications you are taking, known illnesses and allergies. You will be prescribed a pre-treatment for eyelid hygiene, eye drops to prevent infection and a relaxant.

Before the surgery, a complete ophthalmological examination is also necessary. The operation is performed on an outpatient basis, so local anaesthesia is applied. 

The operation usually lasts 15 to 20 minutes.

On the day of the operation, you should clean your eyelids as instructed and apply eye drops. It is very important to come to the operation without make-up.

Characteristics of the surgery

Before the surgery, you will be asked to sign a consent form indicating that you agree to undergo the operation and that you have been informed of the characteristics of the operation.

As in any surgical procedure, your vital signs, such as pulse and respiration among others, will be monitored.

Local anaesthesia is usually used for this type of procedure, except in very specific and extreme cases of phobias or small children, in which case general anaesthesia is used.

After anaesthetising the area, the lens is injected between the crystalline lens and the iris through one or more micro-incisions. It does not require stitches, it seals itself. 

You can follow the step-by-step of intraocular lens implantation surgery in any of the following links:

• Cataract surgery with trifocal lens
• Cataract surgery with monofocal lens
• Cataract surgery with multifocal lens

Immediate postoperative period

It is normal to feel a stinging in the eye, as long as it is not a very strong stinging.

At first your vision will be blurred, but this is normal, and you will gradually recover your vision over the course of the day. Visual recovery is very quick.

Your doctor will probably prescribe medication to combat pain. He or she will also prescribe antibiotics to prevent and fight possible infections and will probably prescribe steroids, in the form of drops, to reduce inflammation.

What to expect the day after intraocular lens implantation?

One day after the operation, it is estimated that about 90% of your vision will have recovered, the rest will gradually recover over the next month.

At some times of the day your vision will be better than others, this is normal.

You should see your doctor the day after surgery and then a week later.

You can return to work one day after the operation, but it is advisable to rest for a week after the operation.

There is a risk of intraocular infection or post-surgical inflammation, due to the delicacy of the surgical site, but this is very rare (only 1 case in every 1000 operations).

Regular check-ups should be carried out every one and a half to two years to check that everything is still in place and to detect any anomalies, if there are any, so that they can be corrected in time.

When should I see a doctor?

As this is an operation in a very delicate area, it is necessary to see a doctor as soon as the slightest complication is noticed, in order to prevent further complications.

The main cases in which you should see your doctor are:

• If you are in a lot of pain.
• If you suddenly lose your vision.
• If your eye produces a lot of discharge.
• If you feel a lot of stinging after the first day.

Complete healing of the operation will take place approximately one month after surgery. Recovery will be gradual.

After the surgery, it is necessary to follow a series of specific care measures to ensure that recovery is favourable and is completed as soon as possible. 

The main recommendations are:

• Wear sunglasses as soon as you leave the clinic.
• Wear protective goggles for sports for the first 2 weeks.
• Do not wear make-up for the first 2 weeks.
• Clean eye secretions with gauze with serum, rubbing the eyelid area extremely gently.
• Do not rub your eyes.
• Avoid getting the sun in your eyes for the first 15 days.
• Avoid being in dusty, smoky or smoky environments to avoid infections.
• Avoid strenuous physical exercise.
• It may be necessary to use artificial tears for 3 months after the operation.
• Application of the drops prescribed by the doctor. The application of these drops is essential for the healing of the operation. Before applying them, the hands must be thoroughly washed with neutral soap. As with all eye drop applications, the drop dispenser must never touch any part of the eye or eyelid.

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