Lecture 3: Spectacle Lens Tilt

Question 1

Effect of Lens Tilt: When you tilt the lens, what happens?

Answer 1

The SPHERE POWER WILL ALWAYS INCREASE. And CYLINDER POWER will be INDUCED!! (Aberration Radial Astigmatism is the Cyl)

Tilt a Plus lens: Increase in Plus sphere power and Increase with Plus Cylinder and Axis will be 180 (panto tilt)

Question 2

Effect of Lens Tilt

1. The Following effects will occur ONLY if the Optical AXIS of the Lens FAILS to do what?
   a. What happens to SPHERE POWER?
   b. INDUCED CYLINDER POWER has what sign?
   c. Axis of INDUCED CYLINDER is the SAME as what?
   i. This is NOT the Same as what?

Answer 2

1. To Pass through the Eye’s Center of Rotation
   a. it INCREASES
   b. Has the SAME SIGN as the SPHERE
   c. as the AXIS OF ROTATION
   i. as Lens Effectivity

Question 3

1. Pantoscopic Tilt: Increase PANTO in AXIS of ROTATION of 180 degrees, Power will be INDUCED where?
2. INCREASE FACEFORM, axis of ROTATION is 90 degrees, and Power is INDUCED where?

Answer 3

1. At the 090 Meridian

2. At the 180 Meridian

Question 4

Calculating the Resultant Spherocylinder

1. New Sphere power?
2. Induced Cylinder power?
3. Axis of Induced Cylinder for PANTOSCOPIC TILT is what?
4. And for Wrap-Around Tilt?

Answer 4

1. S’ = So [1 + (sin^2a)/2n)
2. C = S’(tan^2a)
3. 180 degrees
4. 90 degrees
   * Some people can only handle 1/8 Diopter change in power; Most can handle 1/4 of a diopter. (is this true…)

Question 5

What if you Tilt a Spherocylinder Lens?

1. Only the TOTAL POWER in what MERIDIAN is affected by PANTOSCOPIC TILT?
2. The power in the VERTICAL MERIDIAN is used to calculate the newly induced what?
3. If the Axis if 090, does the cylinder AFFECT the Vertical Meridian?

Answer 5

1. In the VERTICAL MERIDIAN
2. Newly Induced SPHERE and CYLINDER POWER
3. NO! so no need to Transpose.

Only if Axis is 180 do you need to transpose to determine the Power in the Vertical Meridian!

Question 6

Tilting A Cylinder Lens

1. So, the ORIGINAL CYLINDER POWER MUST Be where?

Answer 6

1. In the MERIDIAN of ROTATION!

(Pantoscopic: Transpose to 090)

Faceform: Transpose to 180

Question 7

Rule of Thumb

1. How do we avoid inducing unwanted Power due to Normal Pantoscopic Tilt?
   * When is this done?

Answer 7

For EVERY 2 DEGREES of PANTOSCOPIC TILT, drop the VERTICAL OC 1 mm from PUPIL LEVEL

*Only for HIGH POWERED SV or MULTIFOCAL LENSES, but NOT PALS

Question 8

How do I avoid Inducing unwanted power due to Faceform Tilt?

Answer 8

Order lenses that compensate for the wrap from your lab?

Question 9

Old Rx Limitations for Wrapped frames

1. Sphere range?
2. No more than what of cyl?

Answer 9

1. +2 to -4.00

2. No more than -2.00 D of cyl

Question 10

Why do we adjust the OC for Panto?

1. Due to Oblique Astigmatism from unwanted sphere and cyl power errors.
   a. When is Oblique Astigmatism Introduced? (2)

Answer 10

1. a. Wearer views an object thru the PERIPHERY of the LENS and the LENS IS TILTED IN THE POSITION OF WEAR.

Question 11

1. Oblique Astigmatism can be reduced or eliminated by what 2 things?

Answer 11

1. a. Lower OC of the lens relative to the line of sight in PRIMARY GAZE to maintain the intersection of the Optical Axis of the lens with the CENTER OF ROTATION OF THE EYE
   b. Modify the SPHERE and CYL POWERS of the ORIGINAL Rx to NEUTRALIZE the OBlIQUE ASTIGMATISM that’s created (COMPENSATED Rx)

Question 12

Caveats About OC Adjustment

1. In order for this to work, Oblique Astigmatism through the PERIPHERY must be corrected by what?
2. This cannot be applied to FACE FORM TILT. Why?
3. TOO MUCH Vertical Decentration will cause what?

Answer 12

1. by Best form Lens Design or an Aspheric or Atoric Lens Design
2. Because HORIZONTAL PRISM will be INDUCED
3. Significant TRANSVERSE CHROMATIC ABERRATION!