Designs of multifocal contact lenses

Wednesday, February 3rd, 2010 at 4:01 pm Post in Contact Lenses

People in mid-ages are more active than their counterparts several decades ago. A large number of people above 40 still participate in biking, jogging, exercising and playing sports regularly. Presbyopia is quite common among people above 40, so that multifocal lenses are needed. But for these active sports, multifocal eyeglasses are inconvenient.

A variety of multifocal contact lenses are available now, providing both convenience and best presbyopia solution. Bifocal contact lenses are the most common, which offer only distance vision and near vision. Others are just like progressive eyeglass lenses, providing a smooth power transition.

Multifocal contact lenses can be made of either soft or rigid gas permeable materials. Soft multifocal contacts are more comfortable for part-time wear, while GP multifocal contacts are capable of providing sharper vision but require some adaption. Hybrid multifocal contact lenses combine the advantages of both soft lenses and GP lenses. This type of contacts contains a GP center and a soft periphery.

For wearing schedule, multifocal contacts are available both in daily wear and extended wear. In replacement schedule, one-day disposable soft multifocal contact lenses offer the ultimate convenience.

Bifocal contact lenses are most widely used among multifocal contacts. There are mainly three types of design of bifocal contact lenses. The first design is the concentric bifocal pattern, which means different powers are arranged in different circles. Two variations are both feasible. One pattern has near correction in a small circle at the center, surrounded by a much larger circle for distance vision. The other pattern places near vision in the outer ring.

The second design is called alternating image design or translating design, which is available only in GP materials. This design is similar in power arrangement with bifocal eyeglass lenses. An alternating image multifocal GP contact lens has a top part for distance vision and a bottom zone for near vision as well a nearly invisible line for proper fitting. The wear looks through the lens for distance vision and looks down for near vision. The near zone can also be various shapes: half-moon, crescent or annular. Some alternating image multifocal GP lenses have truncated bottom edge for proper fitting. The alternating image design has only two powers and is unable to deal with intermediate vision.

The third design is simultaneous image design, meaning that distance and near vision can be provide simultaneously. Either in soft or GP materials, simultaneous image multifocal contact lenses have both distance and near vision portions in front of the pupil at the same time. This type of multifocal contacts requires adaption of the brain to choose the proper lens area.

While GP lenses are always chosen to correct astigmatism, soft multifocal lenses in a toric design have been created to treat this eye problem. A toric soft lens has unequal thickness zones and creates a prism ballast effect for proper fitting. Hybrid multifocal lenses can also be applied to astigmatism.

Another technology named monovision can be applied to contact lenses for situations that are beyond normal multifocal contacts. With monovision, your dominant eye wears a single-vision lens for distance vision and non-dominant eye has another lens for near vision. Modified versions of monovision involve fitting a near-biased or distance-biased multifocal lens in one of the eyes.

It is true that multifocal contact lenses usually can not offer the same clarity as multifocal or progressive eyeglass lenses do. Successful multifocal contacts can offer acceptable vision for 80% of the wearer’s daily activities. In some cases, multifocal contacts can never provide satisfying vision for certain people. These unsuccessful wearers can get a full or partial refund of the lenses but some parts of fitting fee is not refundable.