Bifocal lenses are eyeglass frames that contain two varying lens powers to aid the wearer in seeing both distance and near objects. It is usually prescribed for individuals that have lost the natural ability to change the focus of their eyes due to age. The condition is medically known as presbyopia.
Presbyopia as a condition usually starts after the age of 40 though there are recorded cases of it happening to people younger than 40 even infants. To correct this anomaly, optometrists prescribe bifocal or trifocal or progressive multifocal lenses to help the patient see better at all time and from any distance.
Multipurpose lenses in one frame
Bifocal lenses from online websites have multiple functions. The upper half of the glasses are generally used for seeing distant objects while the bottom half is used for seeing close objects. The main purpose for this segmentation of the lens functions is to help individuals with presbyopia to have better sight focus without straining the eyes or exacting undue pressure on the eyes.
Bifocal glasses are segmented, and the segmenting lines are usually visible to even a casual observer. The lenses are usually divided into the upper part and the lower part. The lower part is usually devoted to the near vision lens which is used for activities like reading and is normally shaped in a half moon or ‘D’ shaped fashion. The upper lens is usually plain and is for general vision.
The Different Types of Bifocal Lenses
There are different types of bifocal lenses, and these are:
The traditional bifocal frames are segmented into two sections for distant and close viewing. The distant section usually encompasses the entire lens while the close prescription lens is always at the bottom in a half moon shape.
Executive Trifocal Lens
Executive trifocal lenses are usually of three sections, and the segments stretch across the entire length of their section. Trifocal lenses sacrifice fashion and aesthetic for better functionality.
Blended or Progressive Multifocal Lenses
This type of bifocal lenses is perfectly blended progressively not to reveal any segmentation lines. It is usually the person with high fashion consciousness that goes for this type of bifocal lens. Though this bifocal appears more stylish, one disadvantage it has is that it takes considerable effort and practice for wearers to acquaint themselves with the multiple blended focus areas of the frame.
As we can see, bifocal lenses are prescribed to simultaneously correct long and near sightedness. Before going for a bifocal lens, it is advisable that one conducts a multiple eye test to ascertain the type of sight defect that one has.
A combination of myopia (short-sightedness) and hyperopia (long-sightedness) in one individual will result in the individual going for a bifocal prescription. If a combination of these two defects happens to be the case, then the individual would have to wear a bifocal with both plus and minus prescription.
Another form of presbyopia occurs due to rapid aging behind the retina that causes short-sightedness in relation to reading. In this instance, the person would have a poor blurry vision when it comes to long-distance objects and also experience unclear vision when it comes to close up objects. Vision is only slightly better for objects in-between. To correct this, multiple focal lenses are needed to compensate for the defect.