Premium
Sensitivity of off‐axis performance of aspheric spectacle lenses to tilt and decentration
Author(s) -
Atchison David A.,
Tame Simon A.
Publication year - 1993
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.1993.tb00502.x
Subject(s) - tilt (camera) , optics , astigmatism , spherical aberration , physics , square (algebra) , lens (geology) , mathematics , geometry
Apparatus was modified lo measure, and theoretical raytracing was used to predict, off‐axis powers of spectacle lenses in the presence of till or decentration. In response lo poor fitting in the form of lilt or decentration, lenses with aspheric from surfaces were found to have greater off‐axis power errors than best‐form lenses with spherical surfaces. This is attributable to the aspheric lenses having flatter surfaces than the spherical lenses. The errors are up to twice those occurring for the spherical lenses, and can be quite high. e.g. 0.9 D astigmatism for + 6D power with 10° tilt in 20° upgaze. Negative lenses are more sensitive to poor fitting than are positive lenses of the same power. The errors for straight ahead vision associated with tilt are approximately proportional to the square of the angle of tilt, and the errors for straight ahead vision associated with decentration are approximately proportional to the square of decentration. It is most important that aspheric lenses be correctly fitted, which means that each 2° of pantascopic tilt should be accompanied by approximately 1 mm decentration.