1. Progressive Addition Lenses: Distortion & Directionalization

2. Spectacle Correction of Presbyopia
Bifocals
Trifocals
Progressive Addition Lenses (PALs) ( ( (

3. Progressive Addition Lenses
Spectacle correction of choice for Presbyopes:
Bifocal or PALs?
PALs were preferred by 92 percent of the participants. (Boroyan, 1995)
Other studies provide similarly high preference scores. (Hitzeman, 1985) (Borish, 1983)
PAL designs continue to improve…

4. Progressive Addition Lenses
Despite high preference scores, some report adaptation problems (10-15%)
(Pope, 2000; Cho, 1991; Gresset 1991)
Possible Causes
Frequent head movements
Higher order aberrations
Excessive unwanted astigmatism
Distortion

5. Distortion

6. What is Distortion?
As it applies to optics, distortion is the result of changes in magnification in a lens system--causing objects to appear different in size and orientation.

7. PAL Design Overview Eliminating the multifocal segment line Achieve:
blending between the surfaces
steepening in the inferior portion of the lens
Add:
obliquely oriented cylinder
(Meister, 2008)

8. PAL Design Overview
Distortion applies to progressive addition spectacle lenses
Increasing amounts of obliquely oriented cylindrical power creates changes in spectacle magnification; these changes in magnification cause straight edges to appear tilted or curved (non-uniform).
(Meister, 2008)

9. Previous Studies
Effect of visual distortion on postural balance in a full immersion stereoscopic environment.
(Faubert, 2004)
Background:
The effect of refractive blur on postural stability (Anand, 2002)
Simple visual defocus = increase postural instability (other senses disrupted)

10. Previous Studies Procedure: 8x8x8’ CAVE immersion virtual environment
Stimuli = sinewaves moving in a checkerboard pattern (varying amplitude and viewing distance)
Non-linear visual distortions (similar ro PALs)

11. Previous Studies

12. Previous Studies

13. Previous Studies

14. Previous Studies
Effect of visual distortion on postural balance in a full immersion stereoscopic environment
(Faubert, 2004)
Conclusions:
When viewing at a distance, postural instability is less affected by non-linear, progressive-like distortions.
When viewing at near, progressive-like distortions create significant posture instability.
Lateral movement shows the most postural instability as a function of wave amplitude

15. Progressive Addition Lens Research
Touch-screen test:
Using pointing response as a metric for measuring distortion
w/ miracletouch (

16. Touch-screen Test

17. Touch-screen Test Pilot Data:
High ametropes adapt very well to the peripheral aberrations in their spectacles (ex D myope)

18. Touch-screen Test No correction Plano +2.00 D add progressives
(PAL trial set)

19. Touch-screen Test Hypothesis:
We expect increased pointing error with non-linear distortion

20. Progressive Addition Lens Research
Other interests/potential projects:
Measurements of surface optics for current designs (Using Rotlex Class Plus Lens Analyzer)
Individualized vs. Traditional Progressives