Bifocal Contact Lenses

Developments in the field of contact lens technology are producing ever better contact lenses that are increasingly convenient to wear throughout the whole gamut of vision conditions and lifestyles. Bifocal contact lenses are today available to correct presbyopia, a common problem in the over-40 age group.

Presbyopia is a vision condition in which they eyes are not able to focus clearly on near objects. It usually begins after the age of about forty when the lenses in the eye start reducing in flexibility. Presbyopia affects around 90 million adults in the USA alone and about one in four patients passing through an optometrist’s door will suffer from it.

Symptoms of presbyopia include difficulty in reading, difficulty in seeing in low lighting conditions and, occasionally, headaches.

Traditionally these vision problems were addressed with the old-fashioned reading glasses. Or existing eyeglass wearers could opt for bifocal eyeglasses. However the use of modern contact lenses for use with presbyopia has some distinct advantages beyond their cosmetic appeal. For example they can be well suited to other aspects of a wearer’s lifestyle such as sporting activities, exercising or using a computer.

Recently, contact lenses for correcting presbyopia have become available in more convenient types such as disposable or frequent replacement varieties. Today these are very popular lens types providing obvious benefits for the wearer.

HOW CONTACT LENSES CORRECT PRESBYOPIA

From a technical perspective, there are three distinct ways by which contact lenses can be used to correct presbyopia, each with advantages and disadvantages for particular types of patient. But the important thing here is that there is a choice and each wearer is likely to find one method best suited to their unique situation. The different contact lens methods are as follows:

MONOVISION

The monovision technique involves using in one eye a lens for seeing near objects and in the other eye a lens for seeing distant objects. Many people find that monovision works very well for them. It relies on the brain’s ability to selectively process and combine information from the best available sources in order to provide the clearest possible vision. In some instances, the optometrist might employ a bifocal lens in one eye and a normal distance lens in the other. The main problem associated with monovision is the apparent loss of depth of vision for some patients.

BIFOCAL CONTACT LENSES

As with traditional bifocal eyeglasses, each lens in bifocal contact lenses possesses two powers – one for seeing near objects, the other for distant objects. Some types of bifocal lenses when magnified look a little like a bull’s eye with an central inner zone surrounded by the outer zone. The drawback to this type of lens is that in certain conditions of reduced lighting, the vision might not always be as sharp in certain areas.

MULTIFOCAL CONTACT LENSES

Multifocal contact lenses work very much like the progressive lenses for eyeglasses. These lenses possess several zones of differing power in order to assist the eye gradually as it changes its focus on different objects at different distances. Therefore these lenses are designed to function well for seeing near, intermediate and distant objects. Their drawbacks are typically the same as for bifocal contact lenses, with occasional loss of visual acuity.

Bifocal lenses are available in two basic design types, 'Translating' and 'Simultaneous', the essential characteristics of which are as follows:

TRANSLATING BIFOCAL LENSES

Another name for the translating lens type is an 'alternating lens'. Gas Permeable bifocal lenses are regularly of this type. Their usage is very much like that of traditional bifocal eyeglasses. The wearer will look through one zone for distance vision then ‘translate’ to look through the other zone for near vision. Both zones aren’t looked through at the same time.

SIMULTANEOUS BIFOCAL LENSES

The majority of soft bifocal contact lenses on the market are of the 'simultaneous' type. As the name implies, with simultaneous lenses the wearer actually looks through the various powers of the lenses at the same time. What happens is that the brain steps in and ‘suppresses’ the power or powers, which aren’t needed at that particular time in order to see clearly. There exist further subdivisions of this lens type, but we won’t go into the details in this brief overview.

As with all contact lens selection and wear, choosing the right type of bifocal lens depends equally as much upon the wearer’s unique lifestyle as his unique vision characteristics. For example a patient who regularly undertakes sporting activities will have different needs from one who only needs to wear them socially or for use at work.

However, the success of adopting bifocal contact lenses relies very much on the expectations of the wearer who should realize that, almost by definition, bifocal lenses are very much a compromise and that he or she is never going to regain the acuity of vision in all environments that they had when younger. In most cases this is perfectly acceptable and bifocal lenses have now earned their place in the optometrist’s ever-expanding repertoire.

BY DR. BIANCA TAVARES
Dr. Tavares is a medical consultant with wide-ranging experience and interests in both traditional and complementary medicine and health care.