FOR OPTOMETRIC OPTICS

1. TILT INDUCED POWER IN
SPECTACLES
OPTOM ASKAR.PK

2. TILT INDUCED POWER OF ASTIGMATIC LENS
TILT
When (a home center) pencil of light incident normally along the optical axis of a
spherical lens,the refracted pencil of light to be astigmatic.

3. • If the lens is pantascopically tilted so that the pencil of light is obliquely incident
upon the optical axis of the lens at its front pole,the refracted pencil will be
astigmatic.
• The astigmatism occurs as a result of the obliquely of the incident light.Not only
is a cylindrical component introduced,but the spherical power also changes.

4. • The spherical refraction produced by the lens increases in power & the cylinder
that is generated has the same sign as that of the original sphere.
• The axis of the resulting cylinder is parallel to the axis of rotation of the lens

5. • For Eg:if A Plus Lens Is Pantoscopically Tilted(tilted Inwards Towards The
Cheekbone).So That The Wearer Looks Through The Pole Of The Lens
Obliquely,plus Cylinder Is Induced & Since The Axis Of Rotation Is Horizonatl,the
Axis Of Induced Plus Cylinder Is Horizontal.
• Likewise If A Minus Lens To Panstoscopically Tilted,a Minus Cylider Is Induced
With Is Axis Horizontal.

6. • Fig a:homocenter pencil of light incident normally to the optic axis of a spherical
lens.

7. • Fig B:lens Is Tilted In The Vertical Meridian Woith Respect To Homocenter Bundle
O0f Incident Light.The Refracted Rays In Thr Vertical Meridian Form A Horizonatal
Focal Line ‘H’.
• The Refracted Rays In The Horizontal Meridian Form A Vertical Focal Line ‘V’.
• For Small Value Of Angle Α ,The Power Of The New Sphere Is Given By The
Expression,,

8. • S’= So[1+ Sin ^ 2 α /2 n ]
• S’=power of new sphere
• So=power of old sphere
• α= angle of obliquely/tilt

9. • If the index of refraction of glass or plastic is assumed to be 1.50 ,equation then
becomes
• S’= So[1+ Sin ^ 2 α /3]
• THE INDUCED CYLINDER IS GIVEN BY THE EXPRESSION
C=S’tan ^ 2 α

10. USES
• In Aphakic Patients Who Frequently Have A Cylinder In Horizontal Axis Which
Must Be Decreased In Strength After Some Weeks,a Change Which Can Be
Affected By Straightening The Spectacle.
• Another Advantage Of Method Is That Lenses Are Lighter Without
The Cylindrical Addition.

11. THANK YOU