Intra Ocular Lens (IOL) Choices

When the natural crystalline lens is removed because of cataract or as part of refractive lens exchange an artificial lens (Intra Ocular Lens or IOL) is routinely inserted to refocus vision. The quality of vision after surgery is determined by many factors including the health and anatomy of the eye, but without an IOL vision will be very out of focus. The choice of IOL is therefore very important as it will contribute to the quality of vision and need for glasses.
Lenses have been used since 1949 and now it would be rare for an IOL not to be implanted after removal of the natural lens. Currently more than 6 million IOLs are implanted around the world every year. There are a wide range of lens designs and styles produced in a variety of different materials including PMMA (Perspex), Silicone and Acrylic. Foldable IOLs made out of silicone or acrylic can be inserted through much smaller incisions than rigid PMMA IOLs.

Features common to all lenses are :-

• 1) A central optic that is part of the lens centered behind the pupil that focuses light. Small size optics may cause halos and other unwanted aberrations while larger optics have less problems but may require larger incisions. By measuring the focusing power of your cornea (the topography) and the distance to the retina it is possible to estimate how the IOL will focus on the retina.
• 2) There is a supporting structure called the haptic which holds and centers the lens behind the pupil. There are many different haptic designs and materials.
• 3) All IOLs have an inbuilt ultra violet light blocking action to protect the retina from light damage. There is a new range of lenses that extend the filtering effect into the blue end of the visible spectrum. There is debate about whether blue light may have a damaging effect on the retina, but the trade off with this yellow tinting may be poorer vision in dim light at night and altered color perception. Perhaps the better alternative is to wear sunglasses with blue blocking effect in bright light.

The ideal lens would give perfect vision at all distances without any need for glasses, be able to be inserted through a small incision with no complications or problems, and have a long term safety record. Unfortunately this lens does not yet exist. New designs are introduced every year and time has shown some to be significant improvements, while others have higher complication rates. The difficulty is balancing proven track record and safety against better function

The quality of IOLs available in Australia is extremely high. All lenses have to be evaluated for quality of production and safety then registered for use by the Theraputics Good Association of Australia. This evaluation ensures that only the best quality IOLs are available in Australia. Unfortunatly this evaluation and registration considerably adds to the cost of lenses in Australia.
Poor finish of some lenses used overseas has been associated with intraocular complications which are potentially blinding.

Because there is such a large range of lenses it is important to select the best lens optical power and type of IOL for your visual needs. The information presented below aims to give you an overview and help you understand the choices.

Focus Zone Chart

Monofocal Implants

Overview

These IOLs have a simple optic which will focus at a single distance rather like a magnifying glass. They can be implanted to give good distance vision in each eye but then reading glasses will still be required. An alternative would be to aim for good near vision but then distance glasses will be required. If you refer to the chart zones of focus these lenses will usually provide 2 zones or in optimal conditions of light perhaps even 3 zones.Some people can manage with one eye focused for near and the other for distance (called monovision) to decrease need for glasses

Advantages

These lenses have a proven track record with rare problems
Potentially have very high quality vision with no loss of contrast sensitivity (good vision in dim light)
Low incidence of unwanted visual aberrations that usually resolve without problems

Disadvantages

Only focus for one distance so glasses will probably still be required

Types

• 1) Conventional optic which are like standard magnifying lenses
• 2) Advanced or Complex optics which have specially designed surfaces aiming to improve the quality of vision by either
  A)reducing astigmatism
  B) reducing spherical aberrations improving vision in dim light (night driving)

Multifocal Implants

Overview

These implants are designed to focus both for distance and for near. They work by having concentric rings of different power so everything is in focus. The design involves some compromise trying to minimize problems and maximize visual function and freedom from glasses. They can be made to be better for distance or for near and can have a different near focus distance.

Advantages

Reduced need for glasses (more than 90% of patients will be glasses free although some patients will still wear glasses in some situations)

Disadvantages

As the vision is different to normal there will be a period of learning and some patients have some confusion as the brain adapts to the new vision. The concentric rings will cause Halos and Glare in some lighting and it may cause problems with night driving. Vision may vary with different pupil size and lighting
Some light is focused for distance and some for near with the result that there is some light not correctly focused for any object and this will lead to reduction of vision when lighting is not perfect ( loss of contrast sensitivity)
Overall about 30% of patients have problems with these side effects but they usually decrease and become insignificant over a period of months. About 90% of patients will achieve almost complete spectacle independence, although many will need some help in poor lighting extremes.

Types

• 1) Refractive Optics have Concentric rings of different power that blend into each other. The gradual blend between zones gives a range of distance, intermediate and reading with some designs give better reading zones and more halos, other designs give less fine detail for near but also less problems with halos. These lenses tend to have good vision in zones 2-5 but not as good 1
• 2) Diffractive Optics These lenses have a sharp junction between zones and act more like a bifocal giving very good distance and near vision but may not be as good at intermediate distance (computers screens, shopping, working on a bench) These lenses have fewer problems with halos. These lenses give excellent vision in zones 1,4&5 but may have some compromise in zone 2 and3

Accomodating Lenses

Overview

In theory the muscles that focus the natural lens could affect a flexible lens changing its position in the eye and thus its focus. This would result in perfect distance vision (without halos and loss of contrast) and the ability to focus for near.

Advantages

Potentially have the ability to give perfect vision As the lens focuses on any distance, vision should be excellent without loss of contrast sensitivity and there are no rings to cause halos and glare problems

Disadvantages

New technology with limited follow up and no long term results.
Most current designs do not give a full range of focus but rather an increased range of focus (usually 4 of the focus zones rather than 5)
There seem to be a small group of patients who achieve good distance vision but do not get any assistance with their near vision. Perhaps in these patients their muscles are unable to move the new lens
. This is an area of rapid development – will there be a better lens in near future

Types

• A) Flexible lenses designed to move forward and backwards in the eye
• B)Dual optic lenses where the distance between the two lenses changes

Examples of lenses Frequently Implanted,

Softec

This acrylic lens is part of the precision series made by Lenstec in very accurate small steps to match the eye very closely. The one piece lens is aspheric to reduce aberrations and improve vision in dim lighting. It is monofocal so is only designed to give perfect vision at one distance. The attached animation shows how this lens can be folded and inserted through an incision of less than 2mm. (softec animation)

Tetraflex

This is another Lenstec precision series acrylic lens, but is designed to flex so will proved some near vision in addition to excellent distance vision without the problems of halos, loss of contrast sensitivity and poor night vision. It does not give perfect near vision but this can be boosted by making on eye slightly near dominant or by wearing weak reading glasses occasionally. The attached animation shows how this lens can be inserted though a small incision (less than 2mm) and how it flexes to help focus. (tetraflex animation)

Restor

This lens is a diffractive multifocal based on the well proven acrysof platform of acrylic lenses made by Alcon. It has two very precise focus points so gives extremely good distance vision with excellent near vision and tends to be independent of pupil size. There are some halos at night and there may be some compromise at intermediate distance for example at computer distance. (image of Restor)

Resume

This acrylic lens is a 3 piece refractive multifocal so gives a smooth blend from distance to near vision. It gives excellent distance and intermediate vision but some assistance may be needed for very fine near vision and it tends to be more dependent on pupil size. Halos are commonly noticed. (image of restor )

Technis