The eye’s lens has the ability to change shape.  This allows it to focus light on the retina whether the light is coming from far away (the lens becomes thin), from a near object (the lens becomes thick) or from anywhere in between.

This process is called accommodation, and is strongest in early life.  However, the lens’s ability to accommodate declines with time because of a natural loss of its elasticity.  Presbyopia is the result of these changes and is noticed when we reach our 40’s and 50’s. This is why reading glasses become necessary – they provide the extra focusing power required to see near objects.

When the natural lens becomes cloudy with the passage of time, this is called cataract.  During cataract surgery, the natural lens is removed and replaced with a clear plastic lens.  This new lens is monofocal, and is best able to focus light on the retina from one distance.  Spectacles are then required to see clearly at other distances.  Usually, patients like to see clearly in the distance and use spectacles for intermediate (computers, painting, sheet music) and near (reading) work.  However, there are some exceptions.

"I am considering cataract surgery or refractive lens exchange, but I don’t want to rely on glasses to read afterwards".
Instead of a standard lens implant, you may consider choosing a ‘premium’ lens to reduce your reliance on glasses for reading and other ‘near vision’ activities.  Such lens implants include multifocal and accommodating lenses.

Multifocal Intraocular Lenses (mIOL’s) employ new technology to mimic the process of accommodation – they are sometimes called pseudoaccommodative IOL’s. 
The main mIOL’s I currently use in my practice are illustrated below.  They create focal points for light coming from far, intermediate and near objects – but the patient only sees the object of interest.

The Acri.LISA lens:  Provides excellent distance and near vision.  Intermediate vision (computer screens, etc.) is fairly good, but not quite as good as the near vision.

The ReZoom lens:  Provides excellent distance and intermediate vision, and fairly good near vision. 

The Rayner MFlex lens:  This comes in two strengths.  One of these provides excellent distance and near vision (like the Acri.LISA lens), whilst the other provides excellent distance and intermediate vision (like the ReZoom lens).

It is not usual to implant a monofocal IOL in one eye and a multifocal IOL in the other.  The eyes most commonly receive the same kind of lens, although each case is treated individually and each patient is advised with their best interests in mind.
Depending on an individual patient’s requirements, the same mIOL may be used for both eyes or a “mix-and-match” approach to mIOL implantation may be advised.  This may involve, for example, placing the Acri.LISA lens in one eye to achieve good distance and near vision and a Rayner MFlex lens in the other eye to give better intermediate vision.  Different surgeons use other combinations. 

With most multifocal lenses, astigmatism needs to be accurately corrected before or after the lens has been implanted and there are several ways of doing this.  However, the Acri.LISA and MFlex multifocal lenses are available in a ‘Toric’ form.  This means that the lens implant corrects astigmatism in addition to giving good distance and reading vision.  This is all done in one operation and avoids multiple surgeries with higher expenses.

The lines on the lens mark the axis of astigmatism correction.  This allows the surgeon to place the lens in exactly the correct orientation in the eye that allows patients to enjoy their full visual potential without glasses:  Far and Near.

No, but the chances are significantly increased compared to a standard lens.
The vast majority of patients are able to see satisfactorily at all distances without using glasses.  However, some people may need to wear spectacles for some tasks, such as using a computer, reading for prolonged periods of time or driving at night. 
It is important to understand that there is a difference between “satisfactory” vision and “crystal clear” vision.  For example, a patient may have vision that is “crystal clear” (or 20/20 vision) for distance and near tasks and “satisfactory” (or 20/40 vision) for intermediate distance.
When analysing reports about these lenses, it is also important to be aware that some studies give the proportion of patients who “never wear spectacles” whereas others give the proportion who “either never or only occasionally wear spectacles” – these are different measures and should not be compared as though they are the same thing.

Glare, halos and reduced contrast sensitivity.

Glare and halos may occur after implantation of regular monofocal IOL’s as a result of lens design.  They are more likely with mIOL’s because, in addition to lens design effects, mIOL’s create in-focus images for distance and near objects simultaneously and this overlay of images can cause symptoms.
Contrast sensitivity is the ability to differentiate between an object and its background.  A reduction is inevitable following implantation of mIOL’s, and the tolerability of this depends on the patient’s expectations.  Unrealistic expectations often lead to disappointment in the visual outcome. The following table is provided as a brief summary of outcomes.  Please note that a great number of studies have been performed to look at the outcomes of lens surgery and implantation of monofocal as well as multifocal IOL’s.  You should ask any questions you have before you make a decision regarding your desire to have mIOL implantation.

A small proportion of patients (between 0 and 2% in different studies) have experienced symptoms of such severity that they have requested the mIOL be removed.

No.

People who are long-sighted (hyperopic) or emmetropic (no spectacle correction required) tend to have favourable outcomes more often than those who are short-sighted  (myopic).  Astigmatism may need to be corrected before mIOL implantation, depending on the examination findings.

Most surgeons would advise against mIOL implantation for the following categories of patients:

Patients that are hypercritical with unrealistic expectations

Patients with excessive complaints about their prescription

Patients who drive at night for a living or whose occupation or hobbies require night vision

Patients who are amateur or commercial airline pilots

Patients who have life long complaints about glare

Patients who are happy wearing glasses

Patients who want guarantees on surgical outcomes

Those with co-existing eye problems e.g. corneal problems, glaucoma, and macular degeneration, amongst others

Caution should be exercised in patients that have had laser refractive surgery in the past

The natural process of changing the eye’s focus from far to near is called accommodation.  When the natural lens is removed, a type of lens that is flexible and can make very small movements in the eye may replace it.  Because this mimics the natural process of accommodations, these lenses are known as accommodative lens implants.  There are a few types on the market and several others under development.
Accommodating lenses have the advantage of being monofocal lenses and so do not produce the halos that are associated with multifocal lenses.  On the other hand, the chance of achieving spectacles independence for reading is lower with accommodating lenses (around 70-80%) than with multifocal lenses.
Accommodating lenses are suitable for patients that would prefer to read without glasses but:

• Are not suitable for a multifocal lens because of the reasons given in the previous section
• Do not feel able to accept the risk of halos associated with multifocal lenses

Mr Muhtaseb implants the TetraFlex accommodating intraocular lens for suitable patients

Patients choosing the TetraFlex lens should perform daily focusing exercises, such as:

• Performing usual daily focusing activities such as reading newspapers, magazines or books, computer use, watching television, writing, drawing etc for 10-30 minutes
• Doing word searches for 10-30 minutes
  Alternate every 15 seconds between reading or puzzle solving and focusing on an object in the distance (i.e., across the room)
   

To achieve optimal post-operative results, patients selecting the TetraFlex lens should avoid use of reading glasses after surgery, except for essential near vision tasks.
Typically, the best intermediate and near vision is achieved after approximately 4-8 weeks from the time of surgery, if the exercises are performed regularly.

Visual exercises can be downloaded by clicking below:
Workbook 1 ( PDF.256kb). You will need Adobe Acrobat Reader to view this file.

Workbook 2 ( PDF.228kb). You will need Adobe Acrobat Reader to view this file.

The following animation of the TetraFlex lens explains how it is implanted and how it has its effect after surgery: