BIFOCALS /
TRIFOCALS / MULTIFOCALS
How will bifocals work
For the average grocery clerk?
Do you fear to recommend
Trifocals to a life long-friend?
Is it worth a few more bucks
To go into varilux? (Progressive)
No doubt you will known just how to cope
By the time that you are presbyope |
A multifocal is one that contains 2 or more
prescriptions for correcting vision at different distances.
WHY ARE MULTIFOCAL LENSES
PRESCRIBED?
As people reach the age of early to mid forties, their eyes gradually lose the ability to
focus on objects that are close. They are no longer able to read small print at the
distance they used to.
Multifocal lenses are prescribed to compensate for these changes. Bifocals are prescribed
to aid in both close and distant vision in one pair of glasses. Trifocals are prescribed
to aid in distance, near and intermediate distance vision.
DON’T BIFOCALS /
TRIFOCALS INDICATE A SEVERE VISION PROBLEM?
Not really. The gradual inability of the eyes to focus is a natural part of the aging
process.
WHAT IS THE USUAL PERIOD OF
ADAPTATION?
It will take about a week or two to adjust to your new multifocals. You will have to
develop new pattern and habits of viewing.
WHAT IS THE MOST COMMON TYPE
OF MULTIFOCAL?
The bifocals are the most widely used type of multifocals. There are several types of
bifocals. The popular ones are:-
- Kryptok or Fused Bifocal
- Executive Bifocal
- Univis-D Bifocal
The Kryptok (or Fused) Bifocals have a circular arc
for dividing line which is least visible compared to the other bifocals, this being its
advantage. But these have the disadvantages of (a) Jump
effect where there is a shift in the apparent position of object when the
wearer looks from distance to near and (b) Chromatic aberration (color fringes)
due to the use of different materials for main lens and segment.
The Executive Bifocals
are made of single piece of glass in which two different curvatures are ground. For
this reason the dividing line is very prominent and the change in curvature can be felt at
the dividing line by running the fingers across the lens surface. There can also be
accumulation of dirt at the dividing line. There is minimal or no jump
effect and this also offers a wider field of view for reading. These are averagely priced.
The Univis ‘D’
Bifocals are also of the fused type but with a barely visible straight
dividing line. They are also called Flat-Top bifocals.
They have very minimal Jump effect, but are priced higher. The ‘D’
Bifocals are very popular aboard and are fast gaining popularity in India.
All these are available either in Glass or Plastic (CR39).
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