How bifocal contact lenses work?
Bifocal contact lenses work in different ways, depending on the design of the lenses. The design of the lenses can be categories into three basic groups:
1. Alternating or translating vision:
These bifocal contact lenses are called so because the wearer’s pupil moves alternately between two powers, as their gaze shifts upward or downward. These lenses work like bifocal eyeglasses. They have two power segments with a line separating the distance and the near power.
The distance corrections are place on the top portion, and the near corrections are place at below portion. The eyes of the wearer adjust where to look depending on whether they are watching a distance or near. Alternating bifocal contact lenses are gas permeable lenses and provide better vision. They are smaller than soft lenses in their diameter. They move along with the movement of the eye.
Thus, allowing the wearer to see the distance vision when looking up and near vision while looking down through the lens. These lenses are best suitable for driving and reading task but may pose a challenge while using computers and other immediate vision range task.
2. Simultaneous vision:
These bifocal contact lenses require the wearer to look through both distances and near vision at the same time. It comes in both soft and gas permeable materials. In this type of lens, both the near and distance vision portion lies right in front of the pupil. Hence, the wearer has to adjust accordingly as to which part of the lens they are using and ignore the part that is not in use immediately. This may seem like a daunting task for the brain, but a little practice will make the eyes adjust and achieve almost natural vision experience. Simultaneous vision lenses come in two types:
a. Concentric ring design: This is the most commonly used lens for bifocal contact lenses. In a concentric pattern lens, the near vision is in the center of the lens and is surrounded by rings or circles which contain the distance vision correction. This arrangement can be the other way round where the distance is in the center and the near vision correction on the outer ring of the lens. Concentric bifocal contact lenses are made of the following materials:
i. Gas permeable lenses: They usually have the distance power in the center. They are also known as centre-distance. It give the best vision, though wearers may require some adaptation. They should regularly be worn to adjust to the eye condition.
ii. Soft bifocal lenses: They usually have the near vision in the center. They are also known as centre-near. These types of lenses require a little adjustment. The best results can be obtained by wearing them on a part-time basis.
b. Aspheric multifocal lens design: Aspheric multifocal lenses work more like progressive eyeglass lenses. The prescription powers blends across the lens, but unlike eyeglasses, the aspheric lenses are designed in concentric rings. The rings of distance and near prescriptions simultaneously placed in the central visual area, on or close to the pupil.
3. Monovision lenses:
These are the latest addition to the list of bifocal contact lenses. Monovision lenses are a good choice for those not comfortable with the other types of bifocal contact lenses mention above.
To wear monovision lenses, one needs to identify which eye is dominant. This means identifying which eye is more dominant than the others in viewing the object.
For example; right-handed people tend to have right-eye as dominant and left handed people have left-eye as dominant. For a clear result, a thorough examination by an eye care professional will be able to determine the dominant eye.
Single vision contact lenses for distance is fit in the dominant eye and bifocals on the non-dominant eye. Though the term might be a little misleading both the eyes works together to provide better vision.
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