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Spectacle Correction of Presbyopia Bifocals Trifocals Progressive Addition Lenses (PALs)
(http://www.penrithspectacles.com.) (http://vectors.usc.edu) (http://www.eyeglasslensdirect.com)
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…
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
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.
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)
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).
PAL Design Overview
(Meister, 2008)
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)
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)
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
Progressive Addition Lens Research
Touch-screen test: Using pointing response as a metric for
measuring distortion
(http://pmxaudio.com)
w/ miracletouch
Touch-screen Test Pilot Data:
High ametropes adapt very well to the peripheral aberrations in their spectacles (ex. -10.00 D myope)