Lens form

Lens form

1. OPTOM FASLU MUHAMMED

2. 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 Lenses
Curved Lenses

3. 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.

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

6. 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.

8. 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:
Meniscus
Toric

9. 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.

11. 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..

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

13. 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

14. 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

15. 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

16. 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.

17. +4.00 D × 90 cylinder

19. 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?

21. 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?

22. 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.

23.  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.

24. 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?

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

28. 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.

29. 2.OVAL LENS
- Ancient lens shapes
-Elliptical in shape and not much in
use.

30. 3.Pantoscopic Round Oval (PRO)
Lower half of a circle and upper half of
an ellipse with the same horizontal
diameter.

31. It refer to the lens shape which resembles
the monocular field of vision.
Round contour and the squarer contour

32. 3.Upswept shapes
4.Rimless or angular shapes
5.Half -eye shapes.

33. Thank u…..