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Options of visual correction for cataract surgery

Before proceeding with cataractA cataract forms when the natural lens in the eye is, or is starting to become, opaque. If not treated, it can lead to blindness, which in most cases can be treated. See Cataract Centre – Understanding Cataracts. surgery, it is important to determine which type of intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options. (IOL) would best suit you, as this will determine the visual outcome. The choice of lens depends on your daily visual requirements, as well as your personality. The various options, as well as the advantages and disadvantages for each correction, are discussed below:

  1. Single vision correction with the emphasis on distance vision.
  2. Single vision correction with the emphasis on near visionNear vision is the ability to clearly focus on close-up opjects and fine print. See Other Options – Options for Refractive Correction..
  3. MonovisionMonovision is a term used to describe the situation where one eye is corrected by means of contact lenses or laser for near vision, while the other is corrected for distance vision in presbyopic individuals. It enables the patient to be less dependent on spectacles or contact lenses and applies to near and distance vision. See Near Vision – Laser Blended Monovision. correction.
  4. Multifocal vision correction.
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To find out more about the different lens options that are available, click on one of the links below.

Single and Multifocal Lenses

Single and Multifocal Lenses

These intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options.es attempt to correct both distance as well as near visionNear vision is the ability to clearly focus on close-up opjects and fine print. See Other Options – Options for Refractive Correction. in each eye. The lenses are designed in such a way that a certain part of the lens is dedicated to distance vision, whilst another part of the lens focuses for near.

These lenses are therefore constructed with two 'focus zones' – one (usually central zone) to focus light from near, and a second (usually peripheral zone) which focus light from distant objects (see figure below). When one concentrates on a distant image, the light entering the eye through the peripheral part of the lens from this object is in clear focus, while light entering the eye through the central part of the lens is out of focus. Because the brain prefers images that are in focus, it 'filters' the blurred image, and the person sees the distant object in clear focus. For a near object, the reverse happens. At any given distance, there will always be a focused image as well as an unfocused image projected onto the retinaThe retina is the receptor of light at the back of the eye. It fulfils the same function as the film in a film camera or the image sensor in a digital camera. The retina translates the images into electrical signals that are sent via the optic nerve to the visual cortex in the brain, where it is interpreted as the images we see. See Info on Eyes – Anatomy. of the eye. Since the brain prefers a focused image, the unfocused portion of the image is subconsciously ignored.

Multi-focal

Advantage: The principal reason one would choose this option is to be relatively independent from glasses. Sometimes glasses are still required for intermediate vision, for example when doing work on a computer. Although this option provides some reduced dependency on glasses, glasses may still be required at times.

Disadvantages:

  • The quality of vision will never be as good as vision obtained with standard monofocal Intra-ocular lenses. This is mostly due to the fact that the image perceived will always have an overlay of the blurred image explained above. Over a period of 3 to 6 months, the brain learns to adjust and filter the unfocused image by only concentrating on the sharp focus. However, a small percentage of people never learn to adapt. This is also largely dependent on the person's personality. For example, someone who is a perfectionist might struggle to adapt, as such a personality type may always notice the blurred image. In extreme situations (if patients are not able to adapt to multifocal vision), it might be required to remove these lenses to replace them with a standard monofocal lens.
  • The quality of light in which one works and functions on a daily basis is an important factor to consider, since a well illuminated environment is essential to obtain good and comfortable reading vision with these lenses. If the illumination is poor, patients with these lenses might experience problems to perceive sharp vision. The reason for this is that a percentage of the light entering the lens is split into a near component, while the remainder is utilized for far. The most common lens designs allocate approximately 40% of the light entering the eye for near, and 60% for distance.
  • Vision under low light intensity in the presence of bright lights may be affected by starburst and halo phenomena. A typical example would be driving at night, whilst facing oncoming traffic. It is, therefore, not advisable to have these implants if you often drive at night. However, bear in mind that some level of adaptation to these visual distortions does take place over time.
  • Depending on the type of multifocal lens, it might be possible that parts of the visual field may not be in sharp focus. Certain lenses are designed to give sharp near vision (at approximately 35 cm) with less sharp focus around 2 to 3 m. Objects that are further away would then again be in sharp focus. Other types of lenses give sharper focus from 50 cm onwards. These lenses are particularly suitable for office workers who do computer work. A jeweller, for example, would not benefit since they require sharp vision nearer than 50 cm and would therefore benefit from the former type of lens.

Toric Lenses

Toric Lenses

Patients with nearsightedness and farsightedness often also have astigmatismAstigmatism is a condition caused by a cornea that has more than one curvature, similar to a rugby ball. The same image, therefore, focuses on multiple points in front of, on and/or behind the cornea, creating multiple and ghost images. Astigmatism may also be found in association with either myopia or hyperopia, which complicates the condition substantially. See Info on Eyes, Optics and Refractive Errors - Astigmatism.. Astigmatism is caused by an irregularly shaped corneaThe cornea is the clear, transparent 'front window' of the eye through which light enters the eye. It handles about two-thirds of the focusing power of the eye and is critical for good vision. See Info on Eyes – Anatomy. - instead of being round like a soccer ball, the cornea has multiple curvatures like a rugby ball. These multiple curvatures cause blurry vision.

If you have astigmatism and require cataractA cataract forms when the natural lens in the eye is, or is starting to become, opaque. If not treated, it can lead to blindness, which in most cases can be treated. See Cataract Centre – Understanding Cataracts. surgery, it can be corrected by placing a toric IOL (intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options.) in the eye. The alternative is to have a standard IOL placement and continue to wear glasses or contact lenses afterwards to correct the astigmatism.

Advantage: It is a safe and predictable option to reduce or eliminate refractive astigmatism of more than 1.25 dioptres.

Disadvantages:

  • The lens can be costly if it has to be manufactured specifically to your prescription.
  • If the toric lens is misaligned in the eye, it could affect vision.
  • You will still require to use either reading or distance glasses after the surgery, depending on whether the focus is set for near or distance.

Accommodating Lenses

Accommodating Lenses

One of the inconveniences experienced by those who reached the presbyopic stage in their vision (age 40 years and more), is having to cope with reading glasses. For this reason many people go about their daily routine with glasses around their neck, have multiple pairs of readers all around the house, or wear a bifocal or multifocal pair of spectacles on a permanent basis.

A new and novel intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options. is currently under development, which will enable patients to regain a certain degree of focusing ability or 'accommodationAccommodation is the physiological process by which the eye changes focus. A ring of muscle around the lens, called the ciliary body, changes the shape of the lens, which allows the eye to focus at different distances.'. Such an accommodating intra-ocular lens will help patients see at various distances, adjusting the focus like you used to do during your earlier days. This means that the patient will be less dependent on glasses for daily tasks such as driving, using a cell phone, looking at price tags, receipts and menus.

With the current progress in the study of this lens, we anticipate that it will be commercially available in the near future.


1. Single vision correction with emphasis on distance vision

This is the most common type of refractive correction after cataract surgery and involves a lens implant that fully corrects both eyes for distance vision.

Advantage: The visual results are excellent for good distance vision and depth perception. This type of correction is suitable if you prefer good vision without glasses at distance (for example: driving and sport).

Disadvantage: The implantation of lenses that correct distance vision, immediately results in presbyopiaPresbyopia is an age-related condition. As we age, the natural lenses in our eyes gradually become inelastic and lose their ability to focus on nearby objects and fine print. From the age of 40 it becomes increasingly noticeable and people often jokingly complain that their 'arms are getting too short'. See Info on Eyes – Optics and Refractive Errors - Presbyopia. (dependence on reading glasses). This means that you will need reading glasses to enable reading or other close-up activities. The combined effect, however, of reading glasses and a distance correction gives good and comfortable reading vision in most circumstances as well as in all conditions of illumination. Bear in mind that presbyopia is inevitable after the age of 45 in the normal population, in the absence of any surgery.

2. Single vision correction with emphasis on near vision

If you prefer to see clearly close-up without glasses, this is the type of correction you should choose. This is mostly considered by patients who have been short-sighted for most of their lives, since they are accustomed to being able to see well at near without glasses, and do not mind the distance vision being blurred. Here, both eyes are set for near (usually at a comfortable reading distance), with the result that one has to wear glasses to see far.

Advantage: This type of correction is ideal if you mostly do close-up work e.g. knitting, reading, etc.

Disadvantage: As distance vision is not in sharp focus, you will need glasses for distance vision, for example when driving or for sport.

3. Monovision correction

Monovision refers to a situation in which one eye is corrected for distance (usually the dominant eye) and the other eye for near (usually the non-dominant eye). Patients who are able to adjust to this situation are very happy, as they benefit from vision both for near and distance. Before this method of correction is attempted, a compulsory contact lens trial period is usually completed to determine whether this type of correction will work according to your specific needs. During this trial period, contact lenses are placed into your eyes for approximately 3 days to simulate the Monovision correction, after which they are removed. It gives us a good indication of whether you are a suitable candidate for this type of correction. This contact lens trial period is advisable, since about 70% of patients are able to adapt to this type of visual experience, while 30% would prefer balanced vision either for near or for distance.

Advantage: The main benefit of such a correction is that it enables you to function without glasses for most tasks, since the brain automatically selects the 'near eye' for close-up work like reading, while the other eye is used for distance tasks. Such patients often become minimally dependent on glasses.

Disadvantages:

  • Patients need time to adapt, since the brain must learn how to differentiate between the images from the two eyes to see both at distance and at near. Some individuals adapt quickly, while others never learn to use the two eyes together. This is usually determined prior to the surgery by the contact lens trial.
  • Depth perception is affected to a certain degree, so Monovision is not recommended for patients who require binocularity in their daily activities. For example, people who play sport, such as gholf, tennis, cricket or squash, would probably not be suitable for this type of correction. Those who have to function in environments where there is uneven terrain will also not be ideal candidates for a Monovision correction.
  • Patients with a latent (dormant / hidden) squint may have a manifestation of this squint when having a Monovision correction.
  • During the pre-operative evaluation, all the above factors are considered by the attending physician to ensure that the patient will not experience these potential problems afterwards. For this reason, it is crucial that the contact lens simulation is done before proceeding with the actual surgery.

    4. Multifocal correction

    These Intra-ocular lenses attempt to correct both distance as well as near vision in each eye. The lenses are designed in such a way that a certain part of the lens is dedicated to distance vision, whilst another part of the lens focuses for near.

    These lenses are therefore constructed with two 'focus zones' – one (usually central zone) to focus light from near, and a second (usually peripheral zone) which focus light from distant objects (see figure below). When one concentrates on a distant image, the light entering the eye through the peripheral part of the lens from this object is in clear focus, while light entering the eye through the central part of the lens is out of focus. Because the brain prefers images that are in focus, it 'filters' the blurred image, and the person sees the distant object in clear focus. For a near object, the reverse happens. At any given distance, there will always be a focused image as well as an unfocused image projected onto the retinaThe retina is the receptor of light at the back of the eye. It fulfils the same function as the film in a film camera or the image sensor in a digital camera. The retina translates the images into electrical signals that are sent via the optic nerve to the visual cortex in the brain, where it is interpreted as the images we see. See Info on Eyes – Anatomy. of the eye. As the brain prefers a focussed image, the unfocussed portion of the image is therefore subconsciously ignored.

    Lens

    Advantage: The principal reason why one would choose this option is to be relatively independent from glasses. Sometimes glasses are still required for intermediate vision, for example when doing work on a computer. Although this option provides some reduced dependency on glasses, glasses may still be required at times.

    Disadvantages:

  • The quality of vision will never be as good as vision obtained with standard Intra-ocular lenses. This is mostly due to the fact that the image perceived will always have an overlay of the blurred image explained above. Over a period of 3 to 6 months, the brain learns to adjust and filter the unfocused image by only concentrating on the sharp focus. However, a small percentage of people never learn to adapt. This is also largely dependent on the person's personality. For example, someone who is a perfectionist might struggle to adapt, as such a personality type may always notice the blurred image. In extreme situations (if patients are not able to adapt to multifocal vision), it might be required to remove these lenses to replace them with a standard monofocal lens.
  • The quality of light in which one works and functions on a daily basis is an important factor to consider, since a well illuminated environment is essential to obtain good and comfortable reading vision with these lenses. If the illumination is poor, patients with these lenses might experience problems to perceive sharp vision. The reason for this is that a percentage of the light entering the lens is split into the near component, while the remainder is utilized for far. The most common lens designs allocate approximately 40% of the light entering the eye for near, and 60% for distance.
  • Vision under low light intensity in the presence of bright lights may be affected by starburst and halo phenomena. A typical example would be driving at night, whilst facing oncoming traffic. It is, therefore, not advisable to have these implants if you often drive at night. However, bear in mind that some level of adaptation to these visual distortions does take place over time.
  • Depending on the type of multifocal lens, it might be possible that parts of the visual field may not be in sharp focus. Certain lenses are designed to give sharp near vision (at approximately 35 cm) with less sharp focus around 2 to 3 m. Objects that are further away would then again be in sharp focus. Other types of lenses give sharper focus from 50 cm onwards. These lenses are particularly suitable for office workers who do computer work. A jeweller, for example, would not benefit since they require sharp vision nearer than 50 cm and would therefore benefit from the former type of lens.
  • There are a number of types of multifocal lenses available. Below are some examples:

    1. ReStor and Tecnis lenses
      These lenses are most suitable to patients who mostly work at near i.e. reading and embroidery. They use so-called 'apodised optics'.
    2. ReZOOM lens
      This lens is most suitable for office workers who mostly do intermediate work i.e. on a computer. This lens utilizes the principle of so-called 'refractive optics'.
    3. Lentis lens
      This lens is constructed very similar to the bifocal lens which one often see in normal spectacles. It is said to cause less optical distortions compared to the other types of lenses.

    The current trend in ophthalmology is to make patients less dependent on a spectacle correction. Current technology is, however, not at a level where the patient will never need glasses or contact lenses again. Depending on the option selected above, a pair of spectacles or contact lenses may still be needed under specific circumstances.