BY,

PANARA SWATI

FROM : BHARTIMAIYA COLLEGE OF OPTOMETRY

2nd YEAR 3rd SEMESTER

1

BEST FORM LENSES

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.

2

(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).

3

WHAT IS LENS?

A lens is transparent refracting medium ,

bounded by two surfaces that form part of

a sphere or a cylinder.

4

What is best form lenses?

Ideal lens mean ,lens which correct all

aberration but this is usually not possible.

5

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

6

TYPES

(1)ASPHERIC LENSES

(2)DEEP MENISCUS LENSES

(3)LENTICULAR LENSES

(4)PERISCOPIC LENSES

7

TYPES

8

Aspheric lens

Deep meniscus

lens

Lenticularlens

Periscopic lens

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.

9

10

11

12

13

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.

14

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.

15

16

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.

17

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.

18

19

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.

20

21