Bifocal lenses meaning
Bifocal lens means the optical lense contain two power or two power segment with different designs and different manufacturing process, it for distance vision and near vision is called as bifocal lenses.
TYPES OF BIFOCAL LENSES
Depending on design, they are of different types
Kinds of bifocal lenses
Bifocal lenses has kind of design according to design it's classify in different type.
1. Kryptok bifocal lenses
2. Straight bifocal or executive bifocal lenses
3. D-bifocal lenses
4. Moon-shaped bifocal lenses
5. Round bifocal
Depending on manufacturing technique, they may be of different types:
1. Split bifocal:
It is also known as two-piece bifocal. Here two separate pieces of glass of different power are held together in a frame.
This bifocal was invented by Benjamin Franklin. It is no more used now a day.
2. Cemented bifocal:
A small plus lens is glued to the back of a distance prescription with a glue like Canada balsam which has the same refractive index as glass.
This is used today in some low vision prescriptions which require very high additions.
The modern variant of the cemented bifocal is the Fresnel lens which sticks in place with water or alcohol.
It is used sometimes as a temporary bifocal, but it is cosmetically unappealing, expensive, and optically poor, hence not fit for permanent use.
3. Fused bifocal:
This is the most commonly used variety. Here a piece of glass of higher power with higher refractive index (flint glass) is fused on the surface of crown glass.
This part acts as segment for near vision. It has good cosmetic appearance as there is no visible or palpable demarcation.
An example of this type is Kryptok which means hidden in Latin.
4. Solid bifocal:
This type of bifocal lens is made from a single material but different segments are ground with different curvatures.
The line between the two segments is visible but can be made to disappear by joining the two segments with a transition zone.
This is also known as one piece or seamless solid bifocals.
Uses of bifocal lenses
The use of bifocal lenses to correct the presbyopia (refractive error). Bifocal lenses can correct distance and near vision problem.
If patient suffering from problem with distance and near vision ophthalmologist and Ophthalmic officer given bifocal lenses for correction.
The bifocal lenses use to correct the refractive error with person have tow different Power like distance and near vision problem.
Cost of bifocal lenses
Cost of bifocal lenses is vary on depend on the design, manufacturing process, coating and type.
Cost of bifocal lens is also dependent on the Power of eye.
The approximate price of bifocal lenses may be starting from 500 to 1000 for both eyes.
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