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 new 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