1. BY,
PANARA SWATI
FROM : BHARTIMAIYA COLLEGE OF OPTOMETRY
2ndYEAR 3rd SEMESTER
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BEST FORM LENSES
2. HISTORY
(1)HUYGEN’S(1629-95)
Dutch physicist gave the wave theory of
light.
First suggested lenses should be corrected
in some manner and proposed ratio of
surface curvature 6:1.
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3. (2)WOLLASTON(1804)
An English physician first prepared
periscopic lenses.
Best forms were first went out by out
Walt(1898) the French oculist.
Later and in more detail by Percival of
new castle(1901).
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4. WHAT IS LENS?
A lens is transparent refracting medium ,
bounded by two surfaces that form part of
a sphere or a cylinder.
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5. What is best form lenses?
Ideal lens mean ,lens which correct all
aberration but this is usually not possible.
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6. AN IDEAL BEST FORM LENSES
ISI Standard
Good Material
Standardize (ANSI-American National
Standard Institue ,Z 87,Z87-2)
Easy to manufacture and Process.
Aberration free
Inexpensive
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9. ASPHERIC LENSES
A non spheric lens is called aspheric lens.
These are used to make high plus aphakics
lenses by modifying the lens curvature
peripherally to reduce aberration and
provide better peripheral vision.
E.X. our cornea is also aspheric in nature.
Aspheric lenses is depend upon the shape of
the lens.
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14. LENTICULAR LENSES
A Lenticular lens is one in which the aperture
containing prescribed power is smaller than the
frame aperture in which it is glazed.
The aperture is usually 30-40mm in diameter.
These lenses have been created particularly to
use in high power.
It is also called high powered lens.
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15. Thickness of the peripheral part poses a
difficulty while fixing the lens to the frame.
This difficulty is offset by grinding the
peripheral part which reduce the thickness by
1.2-2.0mm and improves the cosmetic
appearance as well.
Lenticular lens is depend upon the shape of the
lens.
In Lenticular lens centre has power and
periphery has no power.
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17. PERISCOPIC LENSES
Lens with base of 1.25D is called a periscopic
lenses.
This lens is depended upon the base curve.
Periscopic lenses are not much used nowdays.
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18. DEEP MENISCUS LENSES
A with a base curve of 6.00 D is called a
deep meniscus lens.
This lens is depended upon the base curve.
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20. In best form lenses the lens shape is also required
to minimize the aberration also reduce effect of
spherical and other aberration.
For positive lens a negative base curve is used and
for negative lens a positive base curve is used.
So that if one error is allowed for other is
automatically almost corrected.
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