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12 December 2008

Cutting edge of cataract surgery

Cataracts are the leading cause of blindness in human beings, but with new advances in lens implants, this problem need not cloud your view.

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Cataracts are the leading cause of blindness in human beings, but with new advances in lens implants, this problem need not cloud your view.

What are cataracts?
Cataracts involve the clouding of the normally clear lens of the eye. This is a gradual process that can eventually impair vision.

The lens focuses light so that you can see objects at different distances clearly. The lens is mostly made up of water and protein, in a precise composition that keeps the lens clear and lets light pass through it.

With age, change in the chemical composition of the lens occurs: some of the protein may clump together and start to cloud a small area of the lens. This is how most cataracts are formed. Over time, the cataract may grow larger and cloud more of the lens. As the developing cataract blocks or distorts light entering the eye, patients will experience a gradual, persistent and painless blurring of vision.

The only treatment for cataracts at present is surgery. Many people with cataracts are able to use vision aids, such as spectacles, to avoid or delay surgery. People who depend greatly on their eyes for work and leisure activities may want their cataracts removed earlier than others.

Standard cataract surgery
Cataract surgery is safe, fast, almost painless and one of the most common surgeries performed. Improvement in vision after surgery depends on the initial health of the eye and the operative result.

Surgery involves replacing the clouded lens with an implanted clear plastic, acrylic or silicone intraocular lens (IOL). Vision is restored with good peripheral vision and depth perception, yet with minimal magnification and distortion. IOLs remain permanently in place, require no maintenance or handling, and are neither felt by the recipient nor noticed by others. Spectacles with thin lenses for near or distant viewing may still be required.

Mono-vision
According to Dr Mark Deist, an ophthalmic surgeon at the Sandhurst Eye Centre, the dependency on reading spectacles may be reduced by a procedure called mono-vision.

"In mono-vision the non-dominant eye is left a little shortsighted, enough to allow for reading. Consequently the patient uses one eye to read and the other for distance vision," Dr Deist said in a press release.

Dr Deist doesn’t recommend this option for all patients, as some patients find the change in visual perspective and depth perception difficult to tolerate. A three-week trial with a contact lens is mandatory to assess the suitability of this approach.

Aspherical lens surfaces
Two major advances in implant design have resulted in better quality vision and reduced dependence on reading glasses, Deist said.

The first is the use of lens surfaces that are not perfectly spherical. Such surfaces have been used to great effect in camera lenses.

This results in much improved contrast sensitivity, and greatly improves the sharpness of both day and night vision. "The return in quality vision to that of a 25-year-old is now possible," Deist said.

Multifocality
The second major advance is multifocality - the ability of the lens to provide both distance and reading vision. According to Dr Deist, more than 80 percent of patients with multifocal implants never need to use glasses again.

When multifocal lenses came onto the market about five years ago, cataract surgery was not as refined as it is today, Deist said.

Furthermore, according to Deist, these lenses weren’t optically perfect and patients experienced halos and glare at night. The majority found these side effects too troublesome, despite the fact that many were independent from their reading glasses and enjoyed their multifocal vision in good light.

Lessons learned from the laser industry resulted in multifocal implants, which deliver a much-improved quality of vision in all light conditions.

With these FDA-approved multifocal lenses, approximately 85 percent of patients are glasses-free for all visual tasks, Deist says.

How multifocals work
The brain is simultaneously presented with two images – one far, one near.

Deist explains that when focussing on the near object, the distance image will be extremely out of focus and hence ignored by the brain. And vice versa - when the patient looks into the distance at a target, they will ignore the out-of-focus image of nearby objects. The brain learns to interpret this phenomenon.

Patients who have bilateral multifocal implants experience simultaneous vision. Over the ensuing weeks to months, their near vision progressively improves as the brain learns to cope.

Patient selection
Dr Deist points out that careful patient selection is vital. Patients must have multifocal implants to both eyes, they need to accept some minor halo / glare at night, and about 20 percent of patients may require light reading spectacles for fine visual tasks, such as reading telephone-directory print in poor light or removing splinters.

The patient’s expectation levels should match what the technology can deliver. In the rare situation of intolerable side effects, the multifocal implant can, easily and safely, be removed and replaced with the standard non-multifocal implant.

Furthermore, patients must be willing and prepared to have laser enhancement if a significant refractive error is present post-operatively. About 15 to 20 percent of patients worldwide require laser touch-ups.

Lifestyle choices
It is important to evaluate a potential candidate’s lifestyle, hobbies and vocational requirements. Some multifocal implants are in reality bifocals - one focal plane for near and the other for distance vision. These lenses are probably best suited for patients who are retired and want to read books or menus.

Another group of patients may be pre-retirement and still using computers frequently – this group may require variable-focus lenses.

In some patients, a combination of different multifocal lenses may offer even more multifocality, which may benefit younger cataract patients, Deist says. – (Sandhurst Eye Centre)

Read more:
A-Z of Cataracts
Eye Centre

November 2006

Useful resources:

South African Optometric Association
Tel: 011 805 4517

South African National Council for the Blind
Tel: 012 452 3811

Retina South Africa
Tel: 011 622 4904

Ophthalmological Society of South Africa

 
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