lens form

OPTOM FASLU MUHAMMED

The total power of a lens can be achieved by combining different types of curved surfaces (concave or convex) and this is called the form of lenses.

Depending up on the from lenses could be of two types:

Flat LensesCurved Lenses

1. Both its surfaces have got same type of curvature,e.g. biconcave or biconvex

2.One surface is flat and the power is grounded on the other surface, e.g. Plano-concave and Plano-convex.

If both surfaces are convex or both concave, the lens is biconvex or biconcave.

If one surface is Plano and the other an outward curved plus surface (i.e., a convex surface), the lens is referred to as Plano convex.

If one surface is Plano and the other curved inward for minus power (i.e., a concave surface), the lens is Planoconcave.

A lens is said to be curved when there is a convex curve on one surface and a concave curve on the other surface.

Curved Lenses are of two types:MeniscusToric

These are curved lenses where both the surfaces are spherical – anterior surface is convex and posterior surface is concave.

Introduction of these lenses has made mass production of lenses easier.

These are curved lenses where one surface is spherical and the other surface is toroidal in shape.

Toric lenses are used where a cylinder is also present in the prescription..

Lenses can be made in a variety of forms, with many forms possible for a lens of the same power.

The nominal power of a lens is the sum of its front and back surface powers.

When expressed as an equation, this is

F1 + F2 = F TOTAL

For example, a biconvex lens of +4.00 D of power could have surface powers, such as the following:

F1 + F2=F T (+2.00 D) + (+2.00 D) = +4.00 D (+3.00 D) + (+1.00 D) = +4.00 D (+0.50 D) + (+3.50 D) = +4.00 D

The same +4.00 D lens power might then have any one of the following forms, which represent only a fraction of the possibilities.

F1 + F2=F T (+7.00 D) + (-3.00 D) = +4.00 D (+8.00 D) + (-4.00 D) = +4.00 D (+10.00 D) + (-6.00 D) = +4.00 D

These forms are limited only in that one meridian must have a net power of zero and the other a net power equal to the cylinder value.

+4.00 D × 90 cylinder

Q: Suppose a lens has a toric front surface. F1 at 90 is +4.00 D , F1 at 180 is +6.00 D .Back surface has a surface power of−4.00D .What is the total power of the lens?

Q: Suppose a lens has a toric front surface. F1 at 90 is +4.00 D, and F1 at 180 is +6.00 D. If the back surface has a surface power of −4.00 D, what is the total power of the lens?

When the lens obtains its cylinder power from a difference in power between two front surface meridians (i.e a toric front surface lens), the lens is said to be ground in plus cylinder form.

A lens has a cylinder component, but the cylinder power is a result of a difference in power between two back surface meridians, the lens is said to be ground in minus cylinder form.

Q: If a lens has dimensions of F1 = +6.00 D, F2 at 90 = −8.00 D, and F2 at 180 = −6.00 D, what form does the lens have and what is its total power?

Lens shape refers to outline of the lens periphery with the nasal side and the horizontal indicated.

Round Lens- Ancient lens shapes.-Not much popular- Still used for some industrial goggles and other forms of spectacle in which the fashion element does not predominate, because it simplifies glazing.

2.OVAL LENS

- Ancient lens shapes

-Elliptical in shape and not much in use.

3.Pantoscopic Round Oval (PRO)

Lower half of a circle and upper half of an ellipse with the same horizontal diameter.

It refer to the lens shape which resembles the monocular field of vision.

Round contour and the squarer contour

3.Upswept shapes

4.Rimless or angular shapes

5. Half -eye shapes.

Thank u…..